10psi + boost... studdering and braking up
 

I'm having some problems recently. Well one of the problems is i can't go over 9psi, but I'm working on that. However, sometimes when i hit 10psi it won't accelerate. It studders and brakes up and it's so hard to get it to redline.

I changed new spark plugs, new spark plug wires.
It started happening recently when i took the midpipe off and put the hi-flo cat on.

Anybody have any idea what would cause this? I used to have ignition break up (at least that's what i though) when i went around 14psi, but never below 14. Now it's happening anywhere over 10.

My mods are: Dp, hi-flo, catback, intake, PFS IC, PFS ECU, and some other goodies. Ignition is stock other then Magnacore 10mm race wires.

Thanks for all your help guys.

When I had the stock ECU I used to have to reset it when i had issues that were kinda the same.

I rested mine already, nothing changed.

Any other input?

Amel

The cat might be clogged. The symptoms seem similar. Put the midpipe back on and see if you still have the problem. If you don't, then the cat is the source of the problem.

I can understand the cat being the problem for me not getting anything over 9psi. But i dont' see why would it studder and break up as soon as i wot it.

Amel

My car did car did something similar before I ended up popping the engine. It would seemingly hit fuel cut at 9-10.4psi in any gear 3rd or up at around 5500 rpm. I could never figure out why except for that it would go away if I shut the car off and restarted then tried again. It could be an ECU problem or an O2 sensor problem as I think mine was because it never started until I replaced it.

Replacing the cat with the midpipe seems like the easiest possible fix at this point so I would try that and see what happens. I can see it studdering if the cat is clogged well enough to prohibit exhaust flow considerably.

I'm very curious to see what the problem is and how you fix it though. Good luck!

I replaced o2 sensor a month ago. I also disconnected the battery yesterday, so it would reset itself over night. However I don't think it will help anything. I don't really want to put the midpipe back on because it smells too much, and since my 2nd turbo is going away slowly it smokes :(

Amel

Is it possible the injectors are giving out? May not be the case, but they DO have some mileage on them correct Amel?

I never changed injectors. I wanted to change fuel filter today, but Nobody has it in stock. So I had to order it. Fuel filter has 19k miles since the last time i changed it.

I don't know what else could be, As soon as i go up to 10psi or just a tad over it, it's like huge hesitation, that won't go nowhere.

Amel

I get similar simptoms when I try to go over 12psi. But I have old plug wires. Other than that, I have a 2"1/5 restrictor after downpipe. I have this feeling that my car is faster running 10psi as the studdering doesnt happen.

I have no idea what it could be. I'll try resetting my ECU also and will change my plug wires soon. At the same time I hope I will get my injectors cleaned.

Also I haven't yet changed the grounds. Do you have new grounds ?

Oh... mods in sig.

I have a lot of grounds, Everywhere. My car is running messed up at 10 psi as well, not just 12. As I said, I have changed wires and spark plugs, but still the same problem.

I reseted the ecu, Only thing left for me to do is put my old cat, and see then.

Amel

Also, You have a different ecu, and you are getting same problem as I am, So I doubt it's the ecu then.

Amel

If it is injectors, then shouldn't i get same problem at 9psi as well? If i'm correct, 550's work all the time and 850's open at 3k. So at 9psi i can go to redline easy and no problems whatsoever. 10 and up, start the problems :(

You boost gauge is reading correctly ?

yup

Interesting you mentioned your 2nd turbo is "going away". I have a similar problem. Engine breaks up above 4500 rpm. Was at KD yesterday and Dave diagnosed it as my 2nd turbo not spinning freely. I also have a 10-5-10 boost pattern, which he attributes to the 2nd turbo problem as well.

My engine breaks up as soon as i floor it. I can't go past 9psi or it's like getting a lot of fuel cuts but also picking up some fuel, or whatever that feels like.

Amel

BoOsTin FD,

Do you still have the knock sensor in the first housing?

I've heard of PFS/EMI ECU users needing to relocate the knock sensor because of similar problems.

I never touched knock sensor. To tell you the truth, I don't know what it looks like either. But what i don't get, why would it happen now, after i switched from midpipe to hi-flo and then now back to stock cat.

I tried midpipe back again, doing the same damn thing.

Amel

There is always a line from when something is working, to when it's not working any more. ;)

The housing each have a hole for a knock sensor but in stock form there is only one sensor. The knock sensor holes are located above the spark plug holes. You might try relocating it into the rear housing and see if the problem still exist.

You also might want to get a fuel pressure gauge and see what's going on as you approach those upper boost numbers. I would start with relocating the knock sensor and see if that helps.

I have the FP gauge. If i remember correctly it shows 32 or something like that at idle. and when i ground fp and gnd it gets something like 44+ or something similar.

so if i understand you correctly, the stock knock sensor is in the front housing above spark plug wires. Could i have maybe knocked the wiring to it or something?

Why do they have 2 holes for the knock sensor if we are only using one?

thanks Mahjik

Amel

https://www.rx7club.com/attachment.p...postid=2407881

There's a picture of it above. It's just a housing, so both of them are the same (I believe). Why Mazda choose to use the front housing (or just one sensor), I'm not sure. I'm sure they have their reasoning.

I'm not saying this is your problem, but since it's a common problem with the PFS/EFI ECU, it's a good place to start.

so what you are saying, that if I disconnected the PFS ecu and ran on the stock ecu, i wouldn't have this problem? I know I can run 10psi with stock ecu without blowing my engine. I can't run 10psi with pfs because of the bucking and hesitating and what not.

I'll try to move knock sensor first, if nothing happens i'll disconnect the pfs see what happens then.

I just have one last question, at what psi is the stock ecu's fuel cut?

Amel

Fuel cut depends on PSI as well as RPM:

http://www.scuderiaciriani.com/rx7/fuel_cut_info.html

Keep us updated on what happens!

UPDATE:

I moved knock sensor to rear housing, still same problem.

I disconnected the pfs ecu completely, ran on my stock ecu, and here is what's happening now.

If I get 9psi, everything is perfect, just like it used to be. If i get 10psi, as soon as i reach 10psi it's like a fuel cut or some kind of cut. A/f gauge goes to lean and I loose power.

I know it's not the ecu now because with ecu, i didn't have total fuel cut, it was just hesitation a lot.

Maybe it could be my injectors, but I don't see why would it run perfect at 9psi then.

Also, I can't raise the boost on profec to 10psi, i can't raise it to any setting, All i get is 9 and then when it hit's 10 it's bad.

Amel

anybody have any suggestions on what to check next?

Amel

I don't have the FSM with me here at work (or remember the values) but I would start first by checking and making sure you get getting the right fuel pressure.

After that, I would test the coils and make sure they are ok.

on the diagnostic box which ones do you short out to get the reading? and how much am i suppose to get?

Also, how do you test coils?

Amel

I'm sorry but I don't have my FSM right now (I'm at work) or I would direct you do the exact pages. Take a look in the FSM, the test procedures are listed in there (in the respective sections) as well as the tolerance values.

Ground and TEN.

I changed the Fuel Filter, Checked the FP pressure and everything by the manual. Everything turns ok with Fuel pressure.

It stopped happening at low rpm, it's only happening now at the transition and then at around 5-6k.

I guess my next step would be to replace turbos and see what's gonna happen then.

Anybody have a link or phone number for those guys where I send my injectors to get cleaned and balanced?
Also, how much is it per injector?

Amel

Sure: http://www.rceng.com/

I think it's about $26 per injector. Most people have have new o-rings returned back with the injectors. You might also look at replacing a few other items:

https://www.rx7club.com/showthread.p...hreadid=232603

Thanks Mahjik.

Hey boostinfd did your problem get solved.. I am having the same problem..

Was on the twins when it started happening in the first boost that i gave the car after a rebuild run-in...5-6 psi it was fine but if i floored it same hesitation.. so i changed my turbos and got a single turbo.. Had lots of problems with controling boost first but now everything is all set.. but still when i floor the car i get hesitation at around 5000rpms .. even if i run 9psi or 12psi.. whats strange is that it became ok a few days back and for two days it ran great... but then i replaced the midpipe and put a resonated midpipe in and the problem came back so i put the midpipe back in.. But the problem is still there...What could it be??

I'm still waiting to purchase a nice set of twins. Then i'll see if it's not the twins, i swear i'll sell that car.

Amel

I said the saqme when i did the second rebuilt.. and guess what.. have spent like another $5000 on the car after the rebuild and say to myself everyday that i'll sell the car ....

What's your FP under WOT reading? How old is your pump?

I never changed pump and the reading at idle is around 35 i think wot is around 40.. something.

see this

https://www.rx7club.com/showthread.p...l+and+pressure

I checked it out, but there isn't much he knows either. I got plenty of grounds, and they don't do squat on my fd.

Amel

plenty of gounds ? what do you mean by that ?

I mean i have 11 grounds on my engine, exhaust, etc. Doesn't make a difference.

There`s always a thin line between love and hate...don`t you hate it when you buy one of the most respected cars and when you drive it on the road and it doesn`t run right?

I`ve had the same problem...even with my mods being a supra tt pump, 9`s and 10`s cold plugs, pms, DP, cat back. I`ve notice while running 15 psi boost in the pri/sec turbo`s as i easy into the throttle it runs to 9,00o rpm`s with ease and no problems. but when i punch it, as it climbs to a higher rpm 6-6800 rpm there is a shutter like a lack of fuel...so i change the map sensor and wire in a 5 bar with a inline filter. The ones that comes in the profect-B and problem solve

different map sensor, doesn't make a difference with PMS unless you have a PFC, then yes.

Amel

Anyone else find out a cure for this ?

Tom

I haven't found it yet. :(

I have a 93 with a street port. Its always misfired over 45k when there is boost over 5psi. I found it was running too rich and the plugs would not be able to handle the A/F mixture. I have a map sensor fuel computer and set back the fuel curve 20 percent. runs great now.

I think my problem is fixed, after i replaced twins. I don't have that problem any more and i can boost 15psi till redline with no problems.

Amel

I also replaced a map sensor from my buddies 93 fd so that might have helped too.

Amel