I had something similar to mine happen with boost and the BOV not working correctly.
There was a tear in the rubber diaphragm in the BOV..
Check that!

 

I checked the BOV. It seems to be ok. Now I am reading about how important the grounds are and also found this video on youtube.


The guy's car has similar problems with mine and the main ECU ground was the cause. I think that I checked the ECU ground when I removed the UIM and it was properly screwed in place. I don't know though if it was corroded.
You can see it at post #60. Does it look corroded to you?

 

Just an update...
I try to eliminate any obvious cause for my boost problem. So I will try to check again for vacuum leaks as FurherTuner suggested in another thread. Also I will try to readjust all the throttle body screws as Pyroman suggested.
I bought a brand new water thermosensor (the one beside the coolant pump)...some symptoms that are described in the FSM are similar to mine so I thought to replace it...after all it hasn't been replaced for almost 30 years.
I also bought an endoscopic camera and I will use it to adjust the cam roller position. I checked it last week and found out that the idle cam does not separate from the roller when the car is warmed up. The first photo is taken right after 20 minutes driving and the second one when the car is colder.

 

Hmm does the thermosensor work outside the car and is in spec? That would only increase idle and not make a boost issue.
I have removed mine.

 

Well I don't think that I will test it since I have bought a new one.
It does not correlate directly with boost issues but it might send wrong signal to the ECU about engine temperature.

 

I will copy paste this info here that might help anyone who wants to read more about it.

The problem started to be really bad after the injectors replacement but now I believe that a certain strange startup procedure that occurred before the replacement could be an early sign of the same problem.
So, in the past the car could not cold start without some throttle right after the turning of the key. BUT...it could cold start just fine every time that I pressed the clutch and had engaged a gear in the gearbox, lets say 1st gear.
So...I used to start it with a gear and the clutch pressed and then drove it with no boost until the engine was warmed up. If I tried to boost it while it was cold, the car behaved like it does now. Also during warm up my idle was a little high, 1500 rpm just after start and then slowly settled to 900 rpm. Back then I had the AWS and the BAC valve on the engine but the BAC was unplugged.

So after the injector replacement the start up procedure changed and the car starts fine without the clutch and gear trick. My hypothesis is that something is wrong with the throttle body screws adjustment.
Another fact also supports this hypothesis. One year ago I replaced the AFM, adjusted the TPS and the thermowax idle screw. After that the car was fine for 2 months or so and that's why I think that the problem is probably not related with the injectors.

I will try and check for vacuum leaks again with the device that FuhrerTuner suggested in the another thread and try to understand the correct procedure to tune all the throttle body screws.
Also a friend has an APEXi POWER FC ecu that he can send it to me, in order to monitor how the car behaves while on the road. Do you think that this might help?
Thanks in advance.

 

Another symptom that occurred recently is that idle stays above 1000 rpm for a few seconds if I engage the neutral gear before 1000rpm let's say at 1200 rpm. If I engage neutral at 1000rpm then it dives a little to 600-700 and then idles at 800rpm.

 

I think that nobody reads this long thread anymore but I will update it just for my own reference.
I had access to a mazda self diagnosis error checker and I got these errors:

8, 11, 18, 26, 27, 33, 34, 37, 38

8 is AFM. I replaced the old one few months ago as I said previously with a used one from ebay. I measure the resistance according to the FSM and the values are within range.
11 is air intake temp sensor. I installed a brand new one few months ago. How can this be broken?
18 is TPS. Also I installed a new one few months ago. Can it be damaged in such a short time?
26, 27 and 37 are the OMP errors. I think that this might causing my problems. Maybe what I am trying to describe for so long in here is a limp mode. I also read in another thread that the OMP could also fry the ECU.
33 are the rats nest solenoids. I tried to check them and realized that my car although that is an S5 has 4 rats nest solenoids! I read in the FSM that S5s have 3 and S4s have 4. I am really confused about it...12 years ago I installed a new motor core. Probably the guy who installed it changed my rats nest...I really don't know what is going on.
34 is the BAC. I have removed it.
38 is the AWS (removed) and the ASV. I have ordered a brand new ASV from the mazda dealer.

I also cleaned and checked the OEM injectors and I will reinstall them soon.

Any help or opinions would be highly apreciated.

 

I still read your thread as my fc3s is in the same boat. I'm trying to figure why at start I can Rev to red but then I can never get to 2500. I started my own thread but I never caught traction.

 

I was the last person to comment on your thread and I recommended making a boost leak checker. Did you ever do that?

 

did you check for codes?

 

Erevos,

all of those codes are for devices on the engine wiring harness. They share electrical grounds to the engine block, or the ground at the ECU to the car. Check your electrical grounds, clean them, shine them up. That's the simplest thing to check. If that fixes your electrical issue, then go back and do the checks that we keep insisting on so we can help you get going.

 

Almost...I have made the leak check device that you told me and I hope that I will find time this week or the other to go to the mazda repair shop and check for leaks.
In the meantime I spend hours reading many threads in here and as I told you last weak I had the opportunity to check for errors with the diagnosis test checker.
I am almost certain that the problem is the MOP and that's why the ECU enters limp mode. The symptoms are exactly the same with these:

"Originally Posted by lastphaseofthis
Limp MODE
1. can only be activated by the failure of the OMP(oil metering pump), or it's cirucits within the ecu, usually when the OMP fries, it takes out the omp control within the ecu. NO other sensors will activate LIMP MODE.

2. after you start the vehical it takes about 4 seconds for the check engine light to come on, and limp mode to be active.

3. you cannot exceed 3500 rpm, or fuel will be cut to the REAR rotor.

4. You cannot exceed ~30 percent throttle, or fuel will be cut to the FRONT rotor.
you can down shift(to get above 3500 rpm) and floor the pedal and get no fuel at ALL."

Yesterday I checked the MOP for leaks and there are no any visible leaks. And the oil lines that go to the nozzles seem empty from oil. I also checked the harnesses of the MOP and they look fine. I spayed some electrical contact spray.
I have bought an APEXi POWER FC and I was thinking to delete the MOP and start premixing. In fact I premixed today for the first time with this engine. The car starts ok so I guess that the damage is not big yet. A new MOP is really expensive here in Greece. Do you think that I can rebuild the MOP and make it work again?

Today I checked the TPS with a multimeter when the engine was cold and it was way off range. The narrow range was 1.8! I adjusted it, drove the car until the engine was warm and checked again. It was not within limits so then I adjusted it again and noticed that the close throttle values of both narrow and full range were within limits but the WOT values are a little bit lower than the proper ones (0.2-0.4). I also used the two LED lights method and finally adjusted the TPS based on the lights. The car starts fine but I have idle hunting when hot and sometimes the engine cant idle when I try to park. But I found out that the power steering pressure switch cable is broken and I must fix it somehow. Also I have ordered a new ASV and a new water thermosensor that I think also cause idle problems.

I have two more question than I still try to answer. As I told you I bought a POWER FC (AP engineering, plug n play for S5), a FD air intake sensor and a map sensor. I can't find any info about how to install the map sensor to the stock harness. I went to the mazda junkyard and found two harnesses that fit but I dont know how to connect the cables. The map sensor has 3 cables black, red and white and I dont know which one goes where. The stock harness has one brown/white, one brown/black and a green/black cable. You can see that in the photos.
Does anyone know to install the map sensor?



Question two is about the water thermo valve that is located near the dashpot on the UIM. The FSM shows that the A line goes to the vacuum port of the UIM and the B line goes to the throttle diaphragm on the front of the throttle body. Is this correct? As you can see in the photo mine is the other way around. Can this cause problems? Should I replace the one way white/green valve? I tried to blow in it and it seems that the air does not flow with enough speed in the one way and the other way that is supposed to not allow the air to pass, a little bit or air is leaking.






That's my update guys. I really thank you for all the help, the advises and the ideas. Any help is always appreciated.

 

Hello friend! I thought about the grounds and spayed all the visible ones with electrical contact spray. I think that I have to go to proper electrician and let him check them properly.

 

well, yes...the error codes are posted two posts above .

 

Check your MOP mate...LIMP mode might be the problem....

 

I forgot to mention that I also suspect the ACV as another possible problem. I think that it is stuck somehow because when I put my finger in the round hole that the air gets out, I can feel the spring. Does anyone know if this is normal? When I did the smoke test, there was smoke coming out of the ACV hole. I guess that the vacuum leak test will show if this leaking, right?

 

My comment was directed towards Reidnoah

 

oh you are right, sorry. Do you happen to know how the thermovalve vacuum lines should go? Are they are properly installed in the photo above? I cant find anything related to that and the FSM sketch seem obscure.

 

I dont have an engine to look at right now but heres the vacuum diagram.

 

Yes, that's one of the obscure diagrams that I was looking at.
I think that I found it out...but I asked for a friend to send me a photo in order to confirm my hypothesis. Thanks.

 

Hi all! So...almost one year after I started this thread I finally managed to fix my car! As I wrote before the problem was the LIMP mode that was caused by a faulty OMP. I would like to thank again everyone who helped me to troubleshoot the problem and especially the guys that spent their time to answer my questions again and again (you know who you are ). ROTARIES RULE!!!

 

Glad you got it running. You should still consider swapping in your old injectors before you have a catastrophic event.

 

Everything seems to work fine right now. The wide band sensor shows a good A/F ratio during acceleration and all other readings in the PowerFC commander are within the proper limits. The friend who helped me to install the PowerFC runs the same injectors in his car for a long time with no problems at all.

 

Mkay