Really strange boost problem. FC3S S5 91' (video inside)
 

Greetings. My car jerks/bucks and backfires when I try to boost it but this happens after two or three runs with no problem at all. I boost the car with no problem at all and then something happens and the A/F ratio goes nuts when I try to boost it.
The problem started when I changed the injector with new ones. I also replaced the TPS with a new one and adjusted it at 1 Kohm. Also the fuel pump and fuel filters are new.

The problems disappears when I turn the engine off and on again. You can see this happening in this video.
Problem and reset problem

The next video shows the how the car runs when the problem happens.
Problem with no reset

Could this be caused by a faulty AFM? Recently I changed it with an old one that I had and the problem disappeared for a month or so. Now the problem occurs again and I am thinking to buy another AFM but I want to be sure.
Could it be something else?
Any help would be appreciated.

Assuming you're still on the stock ECU(AFM mentioned) then running a BOV isn't helping anything. Is the BOV a recent install?

Are the new injectors OEM? Has the TPS been set to 1.00V?
Do the sputters happen in a particular RPM range?
How much boost are you running?
When did this problem arise?

There are 3 things I would check.
1. Boost or vacuum leaks. Seal the front of the turbo, and use about 8 or 10psi compressed air to identify boost leaks
2. Make sure you have good grounded electrical connections
3. If you are running the factory ECU, have a look at the electrolytic capacitors inside it. I replaced the ones in my ECU and it made the TPS and other sensors much more consistent

Yes I am on the stock ECU right not but I have also installed an HKS FCON that is set to 0 so there is no change in the fuel map.
The BOV is a Blitz (the classic blitz with the trumpet...DD i think) and I have it for 10 years.
The injectors are DENSO and bought from the ebay: ebay injectors
The TPS is set to 1 Kohm with the method descibed in the FSM for the narrow range, close and full throttle, key on. No back probing. Just measuring the ohm with the multimeter on the pins A and B of the harness. The full range is within limits for close throttle but shows 3.2Kohms for full throttle position. According to FSM this is a bit low and I don't know if that matters on not.
The sputter happens everytime that I try to boost the car but I also feel a little hesitation at 2300-2500 rpm. If I raise rpm slowly without boost or little boost, I can reach 3800 rpm and then its difficult not to boost so it sputters if I don't change gear.
The boost is not high. The stock boost meter goes up to half the reading full throttle and the aftermarket one shows something like 0.25 bar which is low. I know that there might be a small pressure leak from my wastegate but the car's boost was like that for 10 years or more. I have also installed a FMIC, 10 years ago.
The problem appeared after I installed the injectors. A mazda certified mechanic installed them but he is not a rotary expert.
I also installed a used but in very good condition, oil radiator.

I searched for vacuum leaks and could not find any obvious ones. I sprayed all over the engine, the revs are steady. The mechanic who installed the new injectors is also certain that they fitted well on the intake. I will try to do what you suggest.
I checked also all the obvious grounds of the intake. I have also grounds on the battery and the firewall. Are there any extra grounds that I could add just to be sure?
Yes as I said the ECU is stock but there is also a HKS FCON that is set to 0. Is it easy to open up the ECU and look inside?

I'm working up an answer on your other post. It will include the ECU stuff

Isn't it strange that the problem disappears for a short time when I turn off and on the engine? Are there any sensors that can be related to that?

ok thanks mate.

Do you still have the old oem ones?

You mean the injectors? Yes, but they are not usable. They are the OEM injectors that had been on the car since 91 and although that I have proffesionally cleaned them two times they are not in usable condition. The rubber seals are worn etc.

I will try to do what a fellow forum member suggests in another topic that I have started about my idle. Seems like the two different problems might have the same solution which is throttle adjustment.

I will update in here when I have news.

All other suggestions are welcome.

Just an update. Yesterday I measured the ohms of my Duty Solenoid Valve - turbo boost pressure control (FSM Fuel and emissions 91' turbo, page F2-41).
Its a little bit higher (36-36.5 ohms, fluctuates a little bit), than the normal value (30-34 ohms). Is this an acceptable value? Do I have to get a new one?
Also I would like to ask how to check my boost sensor. The FSM says that I have to check the D pin with the key to on position but I don't understand how to do that since I have to unplug the harness.

Here is another video that shows how the car behaves when I try to boost it even a little bit. When I press the gas pedal even a little bit more than 5-10% the fuel/air ratio goes nuts and the car bogs and jerks.

Still running those ebay injectors? Did you ever change the 30 year old fuel filter?

You need to get some stock injectors and rule out those ebay injectors. You cant trust them. Also, they are rated at 550cc @ 3 bar (roughly 45psi). Stock TII fuel pressure is under 40, meaning you're probably running lean even if the injectors are working. You're playing with fire my friend.

Here's the old thread if anyone wants to get caught up.

https://www.rx7club.com/2nd-generati...issue-1138165/

Can your old injectors be rebuilt?

Mr Injector - located in WA

You can mail your injectors to him and he will rebuild and flow test and replace all seals and internal filter screens.

Thanks for your reply.
Yes I changed both the fuel filters, the spark plugs and also I installed another fuel pump that a friend gave me. It was from an RX8. I also bought another AFM and installed it.
I understand that the injectors might be bad but if that was the case then why the did the car boosted perfectly for over a month? If you read my last post in the other thread I replaced the AFM with another one and adjusted the TPS and then the car was ok. I thought that I had fixed it. But now the problem is back. Also the problem is gone if I turn the engine off and on again but only for two or three pulls. You can see that in the video. Also the problem appears when the car is about to boost. That's why i checked the Duty Solenoid Valve (turbo boost pressure control) and found out that it gives low values. Can this valve be related to my problem? I also noticed that this valve was making a fast tick-tick sound when I shut off the engine and It stopped when I pushed the front cap and the harness that plugs to the cable.One last thing. Today I noticed that I can hear a whistling sound at 2500 rpm for 1-2 seconds just before the rpm (~2500rpm) that the problem appears. Can this sound coming from the solenoid valve?

Any ideas are welcome...I am desperate again...

Unfortunately not. There are damaged beyond repair. I am willing to buy new ones but I want to eliminate all other factors before that. As I said the car was boosting nice for a month with these injectors and then the problem appeared again.
I am living in Greece and there are not any rotary mechanics in my area. That's why I try to troubleshoot this problem on my own.

There is something about your car that you should know.

It it VERY VERY picky about which injector it is using. Another thing you have to consider is that your cheap eBay injector might say it can run in a rotary but it really can't. The fuel requirements of a rotary are double the requirements of a piston engine. This is due to the fact that the rotary engine inherently has half the time to inject the fuel needed for an event. This is the reason you need a SPECIAL injector that is robust enough to be operating at a much higher frequency.

Pairing an aftermarket injector with an Rx-7 stock ECU is simply a bad decision. If there are any discrepancies you cannot tune them out. The sh!tty thing is now your stock ECU knows something's not right and will try to make it right. This can cascade into an unsolvable problem. You would've been much better off to buy used OEM ones. I'm still trying to figure out why yours were unsalvageable. Did you drop and bend them? It's just hard to believe.

Another note: If you're running stock everything then why not just bypass the stock turbo control? Keep it plugged in but unplug vacs and plug the lines. I found it to have a bit more spirit. It definitely comes on a bit sharper but stock pressures leave something to be desired anyway right? Try it out, this will hurt nothing and it's a 10 second mod.

You say you want to eliminate all UKNOWN factors before you change the KNOWN factor which is your crappy eBay injectors. I hope after reading that sentence you'll start looking for new ones haha. The ONLY reason you would every change your injector is if: You have a standalone and you have HIGHER THAN STOCK fuel requirements.

EDIT: At stock pressures it blows my mind that you're running a BOV. Run that f#$ker straight man. You will be glad you did.

Erevos,

can you please take some pictures for us?
Pictures I would like are of your vacuum line setup. Theres a chance that we might get a visual clue to help. A picture is worth a thousand words, so try to cover as many details as you can. I believe Alkymist would like to see pictures of your stock injectors from multiple angles. Also, can you measure the resistance (ohms) of your old and new injectors?

I will try to take some pictures this evening of my ECU and show you what ECU things to check with that reply. In the meantime, let's examine those injectors and make sure we can rule them out.

Alkymist, any thoughts?

The reality is it might not even be the injectors. The problem with running non-OEM injectors is we can't be certain of anything. Is it the injectors? Or is it something else?

Another problem is that no one on here is running this setup. If you do research you will realize that many people have had issues with eBay/aftermarket injectors -enough threads to convince you to avoid them at all cost. You also will find that many of these threads end in the OP putting OEM injectors in and bob's your uncle.

If you could get some OEM injectors and the problem still persisted at least you know that. That is a victory in itself. The goal here is to eliminate the items on the list. The injectors are on that list -at least from here. We only know as much as we're told here. It's hard to inspect wires over the net.

That ECU is just so particular about so many things. It's best to keep her happy and give her exactly what she's looking for lol.

Bet he pulled those "crappy" rusty Mazda injectors out and threw them in the trash because he has these new shiny awesome injectors.

Im in for injectors or vacuum leak (probably leaking around the new awesome injectors), that is if he actually did any of the troubleshooting from the other thread like set the brand new TPS, change the fuel filters, etc..

I'm also thinking injectors or vac leak/improper vac setup. Also in the video on the other thread, it sounds to me like there is a squealing sound like a bearing going out.

If all those check out, was gonna have him check out the capacitors in the ECU. I replaced mine a few years ago and it made worlds of difference in how the sensors behaved, TPS especially. I'd put it further down the list, but not discount it. The electrolytic caps in these things are 30ish years old, at least 150% beyond their designed life. Sometimes they leak and eat the boards too.

First of all I want to thank all of you for your answers.
Dear FurherTuner (scary nickname mate :) ) I am not a lazy, arrogant ricer who buys crappy things from ebay. And I did not threw away the old ones...I will post a photo of them later. In fact, for the last 19 years, I have managed to maintain my turbo S5 FC3C in good working condition, although that I live in an area with no rotary experts at all. . This might not be something important for all of you who probably have mechanical knowledge and repairing experience and you live in areas with proper rotary mechanics. I am an academic researcher and I have to spend more than 300euros for fuel in order to visit a rotary expert in Athens. That's why I like to repair my car as much as I can. Rotaries are my passion, I was one of the founder members of rx7 club in Greece and my FC is my one and only car, daily drive for almost 19 years.
In Greece there are less than 20-25 properly working RX7s nowadays...

With that being said, I want to mention that these injectors have been used by 2 friends of mine for their RX8's with no problem at all. I don't say that the problem might not be related with the injectors. I just say that I bought them because they work with no problems in other cars and that I had no boost problems for over a month with these injectors, when I replaced the AFM and adjusted the TPS. You can read about this in this thread:
https://www.rx7club.com/2nd-generati...1138165/page3/

Also, as I have mentioned many times, the problem disappears for a while when I turn off the engine and on again. Could a faulty injector work like that? If the answer is yes, then could you please explain how?

Rotary Alkymist and FurherTuner mention that our cars are very picky with the injectors and I accept that...that's why I will try to refurbish the old ones or buy another pair of OEM injectors. But in order to check the resistance or replace the injectors I have to remove the UIM. This is something that I have never done and I have to go to the local Mazda repair shop. This means extra money for me. That's why I check other factors before that.

Also I want to mention that the car is not stock. I have installed a FMIC, a TID mod with the classic HKS "mushroom" filter, a turbo back Motoria exhaust with 80mm downpipe and a HKS FCON parallel ECU that is not currently changes any fuel map since it is set to 0.
The air pump has been removed and the AWS system is supposed to be removed, but I dont know if this is done properly. The aws valve is still on the UIM. My BAC valve is not working properly (probably...) and I have removed the plug but the valve is also on the UIM. All these mods were done 12 years ago and the car had no problem at all for all these years. The only problem was that the maximum boost pressure was a little bit low and I though that this was cauced by boost losses from my slighty ported wastegate. The BOV is also on the car for many years with no problems.

As I mentioned before, I found out that the Duty Solenoid Valve - turbo boost pressure control (FSM Fuel and emissions 91' turbo, page F2-41) gives wrong values. Its a little bit higher (36-36.5 ohms, fluctuates a little bit), than the normal value (30-34 ohms). Is this an acceptable value? Do I have to get a new one? I read that this valve is related to maximum boost pressure so it can be the cause for my low maximum boost.

I have also found out that there is a broken hanging wire that goes to the main cables next to the battery. You can see that in the photo. Does anyone know what this cable is?

https://cimg7.ibsrv.net/gimg/www.rx7...94759acc21.jpg
Broken cable, goes to the main cables next to the battery


I will also post some photos of the vaccuum lines later.

19 years running is quite an accomplishment. Congratulations! I know you're getting frustrated with this process, but we are trying to get as much info as we can from you from halfway across the world. If we were there, we'd already have it apart in your driveway. The stuff we are asking about is based on our experiences, and we are trying to eliminate the common issues associated, so we can narrow it down. Keep in mind that for some of the stuff like the injectors, we are asking about to ensure there are not compatibility differences (more on that later). Your car is Euro spec most likely, and from what I have found, there was some mixing and matching of systems at Mazda. We are trying to establish commonality between versions. Since you're a fellow academic, think of it this way. You have stated a problem, and right now, we are still trying to gather evidence to fully describe the problem. We are not quite to the literature search (or interview) stage yet. Let's go through this last post and see what we can eliminate.

-First point of order: You will most likely have to take off the UIM at some point. This is really easy, and takes about 10 minutes. We're not to this point yet, but to prepare yourself for this, you will need a screwdriver set, a pair of pliers, and a 12mm socket. Thats it. There are some additional tools that are beneficial that you can easily make for yourself if needed. If you need to

-Injectors: What we are wanting to know on the injectors is the flow rate, physical dimensions, and impedance of the coil inside. Flow rate is a big deal because too much or too little fuel will result in combustion conditions outside the designed operating envelope. The physical dimensions of the injectors matter too. Look at this picture with my injectors.

https://cimg6.ibsrv.net/gimg/www.rx7...679596f991.jpg
RC aftermarket injector (left) and Stock S5 Turbo injector (right)

I use 2 stock injectors as the primaries, and 2 aftermarket injectors for the secondaries. The aftermarket injectors are slightly shorter (about 1/16") than the stock ones, as well as about .010" smaller in diameter where they meet with the fuel rails, and rubber grommets. These were supposed to fit well, and with brand new grommets and o-rings they did. As the rubber grommets and o-rings settled in, these injectors started to leak fuel from the top, and boost/vacuum from the bottom due to the size differences. Impedance is also an issue with injectors. We are wanting to eliminate the possibility of electronics problems by making sure your new injectors have approximately the same resistance as your old ones. This matters to the ECU drivers, because mismatched injectors can damage those circuits (not likely the problem but possible).

-AWS: If this is still attached and not leaking, it will not cause you to lose boost. It raises idle during cold starts to warm up engine faster. Perhaps the system that was disabled was the cold idle cam that you had pictured earlier. That is a separate system meant to keep your idle up during cold starts as well. There are a couple other cold start systems as well, but none of these will cost you boost when working or disabled, unless they are leaking boost/vacuum.

-BAC: If this is still attached and not leaking, it will not cause you to lose boost. This only controls idle using closed circuit air.

-Boost control solenoid: As long as the solenoid is not stuck open, this cannot cause you to lose boost. The function of this solenoid is to drain boost from the wastegate actuator back into the turbo inlet piping, and should maintain a closed air circuit (closed meaning extra air does not enter or exit the system except through the MAF and the exhaust).

-Blitz BOV
This is the Blitz BOV I am using. Yours is probably similar. Examine the BOV and make sure it opens and closes smoothly and is properly adjusted, or return to the stock BOV. I have removed the trumpet, and had an adapter made so I can plumb the BOV back to the turbo inlet piping, as the stock one was. This ensures that any erroneous operation or improper adjustment of this valve will still keep the air in a closed circuit state. I made friends with a machinist and he was able to whip one up in a few minutes. I am sure your University has a machinist associated with the engineering schools. Making friends with those guys helps out a lot and you usually learn something.

https://cimg7.ibsrv.net/gimg/www.rx7...e7f5201684.jpg

At this point I am going to say let's start simple and try to do a boost leak test. This is easily done by removing the turbo inlet plumbing and covering the turbo inlet as shown here. I got all the pieces to do it in the plumbing section of my local hardware store.

https://cimg8.ibsrv.net/gimg/www.rx7...0c7dba862d.jpg

Next, disconnect the vacuum hose to your MAP sensor. This way we wont damage the sensor, and can do the next step. Take an air compressor, and blow air into the vacuum port on the manifold that you just disconnected. You will only want to use 10-15psi (.69-1.03bar) of pressure to pressurize your intake (similar to larger boost conditions). If there are any leaks, you will hear a hissing sound from the source of the leak, or if you have hooked up a cheap mechanical pressure gauge to the manifold, you will notice a problem holding pressure. If there are no leaks, your intake should be able to hold pressure for half a minute or so. Try this step and then get back to us please. Keep in mind that boost/vacuum leaks in your system will behave differently depending on location in the system.

What's your field of research? Do you teach classes, or are you strictly on the research side? I mostly just do teaching and contract work anymore. The research I do anymore is pretty much on my own time.

NA engines run 440cc injectors from the factory. It makes sense that these 550cc (@45psi) injectors work fine in your buddies RX8s considering the 38psi fuel pressure probably puts them around 440cc. Also NA engines are completely different beasts than turbo engines.

As I explained to you in your previous thread, and this is only a theory, but if there is something off about the resistance in the injectors, it can cause the drivers (IDMs) or the injectors themselves to heat up and fail. The injectors could also be failing themselves after long drives because of high duty cycles. Turning the car off and on could essentially reset everything. We dont know, because we dont know anything about these injectors. What we do know is this:

That's why I say you either have a vacuum leak, from doing the install, or a problem with the injectors, or both.

I'm sorry if I'm coming off as rude, but you come off a bit arrogant. You're here asking for help, and many members here have given you great advice, and you choose to not accept it because you do not understand.

When we asked you what happened to the OEM injectors, you reply "They are no longer usable"; a super vague response that doesnt make a lot of sense unless you dropped them or threw them away. Injectors dont really go bad, they get dirty, unless the inside has been rusted out somehow.

I'm also not sure how you're running an atmospheric BOV with a air flow meter. Once that metered air leaves the system you're going to be running extremely rich, as the ECU wont compensate fuel for the loss of that metered air. This may or may not be a contributing factor, but it's definitely not making your engine run any better. As recommended by others you should revert back to a circulating system. You dont need that atmospheric BOV anyway since you're not a ricer :).

Dear Pyroman I will definitely check everything that you suggest!
My research field right now is VR/AR but I have also studied civil/geotechnical engineering (Phd), geology (bachelor degree), computer engineering (but...never got a degree) and Architecture (post-doctoral research).
I am also a Senior Lecturer and I teach video game design and game engines. That's why I don't have much time to spend on my car!!! :) :) :)

I know that you all trying to help and I really, really appreciate that. I believe a lot in the power of the people and the rotary community! After all this forum is something that I visit and support for all these years and I am really sad that the Greek Club is no more due to lack of members and support. As I told you there are very few RX7s left in Greece. In my city, when I drive around in the FC, I get thumbs up all the time and the cops usually stop me to ask me about my car.

As for the BOV...well....I might be a little ricer after all because I really like the sound of it!!! :) :) :)
I took some photos and videos from the injectors and the vacuum lines. I ll post them...

Here are the injectors. The mazda certified mechanic said that they cannot be used anymore.

https://cimg0.ibsrv.net/gimg/www.rx7...9691833e20.jpg
.

Here is the back of the UIM, you can see that the fast idle assembly is not aligned with the roller when the car is cold, and I have a video in the other thread that shows that it is not aligned even when the car is hot. Is this normal?
https://cimg6.ibsrv.net/gimg/www.rx7...0baee795bd.jpg

This is the video.

Another video of the engine bay and the vacuum lines.

This is the video that shows that the TPS is adjusted. I use the led light method that Pyroman suggested,

Those injectors look like 19550-2020s, which should be high impedance 550cc. Double check resistance on those injectors. If you get ~15ohms they're probably fine. If they're clogged you can send them out to get them cleaned. They'll put new pintle caps, grommets, and orings. its around 25usd per injector plus shipping. But since it was running before how could they be bad? That doesn't make sense. Did your mechanic say what was wrong with them? Maybe try running them and see what happens.

Also double check the resistance on the injectors you bought. They should be around 15ohms as well. You can access the secondaries without removing the intake manifolds.

Also, since the engine idles, spray carburetor or starter fluid around the engine while its idling and listen to the rpm. If the rpm speed changes then you have a vacuum leak.

Thanks for posting the videos.

Commentary:
Video 1: Fast Idle Assembly will not affect boost levels. It will change idle, and can be adjusted in a later step. Priority 1 is your big boost problem because if there is a boost/vac leak, it will alter your idle settings. Idle adjustments can't be made until the system is determined to be airtight (or close to it).
Video 2: Your AWS solenoid sitting on top must be addressed. It is in frame on top of your intake manifold in the second video at 1:36. It is attached to your intake and is intended to bypass intercooled air around your throttle body and into the intake to allow the computer to raise idle during cold operation to compliment that provided by the Fast Idle Assembly. In the video, there is no hose connecting the AWS solenoid to your post-intercooler piping. This solenoid is not made to hold a large pressure differential, such as manifold boost to atmosphere. It is meant to handle the pressure differential between intercooler pressure at idle and the manifold vacuum at idle. This could be a potential source for your problems as it is a sizable diameter orifice. The two solutions to this are a) run a hose from the AWS solenoid to the post-intercooler piping, closing the air circuit and retaining function of the AWS system, or b) remove and disconnect the AWS solenoid and cap the manifold port, eliminating the AWS function. This might not be the solution to your problems, but it is a significant problem to address.

Do the compressed air vacuum/boost leak test after performing the repair for the AWS. This should let you determine if the system is airtight or has a major leak. Beware of doing the vacuum leak check with combustibles as listed by FuhrerTuner. You would be spraying flammables in an engine bay that could be ignited from hot exhaust, or loose electrical connections. This type of test is better suited (still not a great idea) to natually aspirated engines as opposed to turbo engines because the entirety of a naturally aspirated intake is under vacuum. On turbo vehicles, any leaks in between the turbo compressor and the throttle plates are at near atmospheric pressure under idle conditions and can go undetected with a combustibles test.

If after conducting the leak test, the system holds air adequately, then we can get you through the process of setting hot idle, and the fast idle assembly. Let us know how it goes.

Cancel.

Hi all and thanks for your replies guys.
I have read your posts and I just wanna say that your help is really precious to me. I will check everything that you suggest and try to find that stupid monkey on my motor...

Right now, the whole Greece is under strict quarantine and we are not allowed to go out...just in case for food supply , short exercise or emergency situation. I am super busy trying to teach by teleconferences etc. The e-class platforms were not prepared for heavy use and we are trying to manage all this from our houses. The good thing is that the pandemic is going well here in Greece because of the really strict measures that had to be taken. Our public health care system would have collapsed if we had not taken these measures.

FuhrerTuner, my injectors were refurbished two times in the past and the engine had a hot start problem. Not a severe problem but sometimes the engine flooded and I thought that my injectors were leaking. That's why I thought to buy new ones.

Pyroman, I will do everything that you suggest and post an update.

Guys I do not know how the things are going in your area but try to stay at home and avoid contact with others as much as you can. Try to protect yourselves and your families.

Best wishes and just remember that we will ride again our 7s soon...

Good to hear you're still around. Hopefully you can get outside and get some fresh air soon. Not too bad here, just boredom. I've torn apart and refurbished all the small electronics projects I've had around the house, and am waiting for parts to finish.

Had a thought, also check your engine compression while you're at it. It would be good to know that the compression is still good. If you see your oil pressure rising with boost, that issue will take priority over whatever we have suggested here.

Hi guys! The strict quarantine measures are almost over and I will try to continue the troubleshooting by checking the injector's resistance as FurerTunner suggests. I just want to ask if the 15ohms value is right? Is it 15 ohms indeed (seems low...), or 15 Kohms?
And I will spray all over again with some carb cleaner to check for vacuum leaks. Can I safely spray near the injectors to check if there is a leak in there? I mean, is it safe to spray directly to the injectors with the engine running?

Yes you are right Pyro, I have thought to check that too but I have to go to the mazda service shop in order to do that.
Previously you proposed to remove the UIM myself. Is it that easy indeed? Do you just follow the FSM instructions?

Forgot to tell you that there is still a wire hanging near the PS pump...this the thread that I made about this:
https://www.rx7club.com/2nd-generati...ttery-1142949/

Most people suggest that it is related to the power steering pump but I thought to mention this too.

I forgot to mention that I have also bought a complete block off plate kit. I will try to tap the AWS as soon as possible! Should I also block anything else...just in case? Any suggestions?

I think looking into the injectors is definitely a worth while expedition, as a trained aircraft mechanic we are constantly tracing back to work that has previously been performed while troubleshooting, you should never assume a job was done correctly. I have recently undergone a S4 TII swap on my FC, so there may be some differences in electronics, however some of the principles will still apply. I had only recently gotten my Greddy Type-S BOV to function (was using the wrong vacuum source), and shortly after I had a weird part throttle issue, where only lightly feathering the throttle would cause the car to run very rich, 9.5-10.5 AFR, with a lot of backfiring, missing, hesitation, etc. If you increased the throttle a tiny bit more, it would run normally in the 11-13.0's AFR's under boost, 14's while cruising. I spent hours researching, did a boost leak check described above with no results, cleaned grounds, checked out most of my sensors, the coolant thermo switch behind the water pump (richens for cold starts, often causes hard starts, rich mixtures when bad), the TPS (causes bucking & hesitations under decel, more important on S5's with the full range capability), the MAP (very critical for turbo cars), the AFM (also very critical for any RX-7 not using stand alone ecu), IAT (richens mixture cold/retards timing hot), and O2 sensor (only affects the car during cruise to lean the mixture for fuel economy), and I didn't even consider the last thing I had worked on (the BOV) could be the cause. I finally decided to stiffen the spring pre-load on my BOV so it would not open anymore, and just like that, problem went away.

I believe my issue was actually under that specific condition, of near atmospheric pressures (not vacuum, not boost) created while feathering the throttle, paired with maybe too soft a spring pre-load, the BOV was actually slightly opening, causing a intake leak, the AFM was metering a set quantity of air, the ECU was delivering a preset amount of fuel for that quantity, but not all of the air was actually going into the engine, and a rich condition would occur. Now if I had recirculated the BOV and not vented it like a ricer, I wouldn't have had that issue. And maybe I need to revisit my spring pre-load and see if I can run it vented without that issue. BUT it still doesn't fix the fact that a vented BOV in a stock ECU will not account for the missing air that gets vented, so richness, and backfiring can be expected, especially during gear changes.

Now this may or may not be your issue, I'm just explaining what I had, and how I went about troubleshooting, and alot of the time, issues that follow shortly after new work was carried out, are usually connected to that work, I ignored it, and it took me hours chasing ghosts.

I would honestly look at the impedance as previously stated, the stock ECU's are very old, and cannot learn, they only respond to what they were pre-programmed to work in conjunction with, so if a injector is out slightly in resistance, the solenoid might take longer to react with the voltages provided, and not deliver the correct fuel amount. Also, another angle to consider, is the injector seals themselves, there are 4 seals on each injector. the top o-ring to seal in the fuel rail, the rubber spacer in between the fuel rail and the injector body to provide the clamping force, a rubber sealing grommet between the injector body, and the intake manifold (secondary)/rotor housing (primary), and a o-ring in the air-bleed diffuser that sits inside of the intake manifold.

The injector grommets that sit between the injector in the intake have been known to be the culprit of many weird issues, they may seal while the engine is cold, and not while hot, or vise versa, as well, there are 2 different styles. S4 grommets are cut square on the corners, S5 grommets have a slight chamfer (rounded edges) where it sits in the injector boss in the intake manifold. I old thread I found in my research for my BOV problem had a fellow, who had S4 grommets in a S5 intake manifold, and would get richness, bucking, hesitations, etc, while running hot. He was convinced it had to be the coolant thermo switch or IAT sensor. That thread was 3 or 4 pages long full of attempts at checking sensors, flow checking injectors (and re-using the old seals, bleh), cleaning grounds, checking ecu pins, replacing parts, etc. Finally he got it hot, and did the old-carb cleaner check around the injectors, and he found it.

So any time you do injectors, use new seals on everything, the rubber gets hard and brittle as it ages, and make sure you get the correct parts!

Thanks for your reply P_Lav.
Your comments are very informative. I have suspected that my BOV could be leaking and I removed it to check but could not find anything wrong with it. I will try to stiffen the valve by turning the screw that has on top of it.
I have used this greddy BOV that vents to the atmosphere with no problem for 10 years.

The specs of the injectors that I used are these:
- Genuine Part (fit Denso) - Direct fitment to top feed fuel rail.
- 550cc flow rate at 3 bar.
- Flow matched 4 piece set.
- 12 Month Warranty.
- High Impedance.

I am planning to buy an air compressor and check for vacuum leaks with the method that Pyroman suggested. I tried to do that with the carb cleaner method but I think that I messed that up...Pyroman knows... ;)

I hate to jump back on the injector train but....

You should also measure the distance from the bottom of the fuel injector grommet to the center of the oring. OEM is ~63.5mm. IIRC Bosch EV14 long style injectors are 60mm, which could potentially cause an air leak.

Also again about the 550cc at 3 bar; Stock FCs run around 2.5 bar putting you at around 475cc.

I really want to remove the upper intake and check the injectors but I still don't know how to do that. For now I will buy a small air compressor and try to check for vaccuum leaks by using the method that Pyroman suggested. I will also try to remove the BAC and the AWS valves.
Also I contacted the ebay shop that sells them and he insist that the injectors are proper for S5 turbos. He also send me this...

https://cimg2.ibsrv.net/gimg/www.rx7...ddd18c3d01.jpg

Just an update.
I used Pyroman's method and checked for vacuum leaks by pumping air in the vacuum line that the boost sensor goes which is this one.

https://cimg4.ibsrv.net/gimg/www.rx7...e42b3b682e.jpg

I found out that there is a vacuum leak for sure since the system could not hold any pressure at all. I can hear a sshhhh sound under the UIM and now I want to remove it and check there.

Also I removed the BAC and AWS valves and covered the holes with a block off plate (BAC valve) and a tapped silicon hose (AWS valve). Here is a photo.


https://cimg9.ibsrv.net/gimg/www.rx7...fde30ef06e.jpg
https://cimg1.ibsrv.net/gimg/www.rx7...ee6df7aad1.jpg

I could hear the hissing sound before I removed the valves and also after that so I guess the UIM leak is certain, right?
I drove the car around the block and realized that now it has some hot start problems, the idle is weak and often dies.
While I drove I started to hear a rattling/knocking sound coming from the catalyst converter. \
I went to a local exhaust service shop and found out that the catalyst was broken. I had a spare catalyst and replaced it. Here is a photo of the broken piece of the old one.

https://cimg4.ibsrv.net/gimg/www.rx7...4af1888e22.jpg

While the car was lifted I noticed that there is a small oil leak on the turbo. Is this normal?

https://cimg4.ibsrv.net/gimg/www.rx7...0e62e8d561.jpg

There you go, the vacuum leak from the lines or injectors is most likely the problem, but its also possible you could have blew a line off while testing. Make sure you throw some small zip ties on those vacuum lines to keep them on.

Yeah I will certainly do that when I remove the UIM. Do you think that the turbo oil leak is serious? Any idea what it might leaks down there?

Assuming the injectors are properly sealed to the intake/fuel rails (which I am not.)

Injectors aside, I wonder if there is a vacuum/boost leak somewhere on the lower intake manifold. It may be smart to replace the LIM to engine gasket "while you're in there."

The only problem with this is replacing the LIM gasket assumes it can be:
1. Done properly with an MLS gasket and clean sealing surfaces.
2. Done without creating any new issues.

The above can be tedious, time consuming, and potentially expensive. LIM gasket replacement WILL be more expensive though if the injectors were not the issue this whole time and this gasket is overlooked.

I am not saying ignore the injectors as a possible issue; the above arguments are very valid to that end. However, do not rule out the LIM gasket until you've removed it and verified it's servicable. I've been guilty of this error in the past with a similar problem and thats my only reason for this post.

Thank you for your reply. When I replaced the injectors I had also bought the UIM gasket and the LIM gasket but the mechanic did not bother to remove or check the LIM gasket. He also did not change the UIM gasket and he used the old one because he said that it was ok. I was not present when he replaced the injectors. I just went there when he had finished the job. When I told him about the problem he said that if there was a vacuum leak from the gaskets the car would had the problem all the time.