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!