Okay, This is a LONG story so here goes...

Rundown of setup:

2.0L GSR bottom end, Fully sleeved/built, 9:1 CR
ITR head, stock, supertech valve train. GE cam gears
Top mount, GT30R, 38mm wastegate, 3" exhaust
880 Injectors, walbro 255lph hp pump, AEM FPR, Aeromotive fuel filter.


Ive been running 20psi for a long time, then one night, I started to get this slight, miss at high rpm, redlining at 9000, it would randomly happen anywhere between 8000-9000. But ONLY under high boost(20psi), low boost(14psi) it was fine right to redline. I had races to attend so I just kind of put up with it because it was only happening every once in a while. Till it slowly started to get worse and worse. The hesitation/miss felt like a soft touch rev limiter, very feint, I could hold my foot tot he floor while it was doing it and it'd hold my RPMS and limit me wherever it wanted. While it would hesitate, my A/F never moved, 11:1. It wasn't hesitating because of going lean. I started to replace things, first obvious things were spark plug gaps. I tried heat ranges 7-9's, all with gaps from .020 - .032. No change what so ever. Same problem. I figured it was spark related because of the soft touch style limiter it felt like. So I started replacing, alot. I d/c my MSD stuff, no change, I CHANGED distributors with a known good one, no change. Changed main fuel relay, grounds, spark plug wires, spark plugs again. I had basically replaced everything next to the ECU. I even thought maybe the ECU was seeing a false RPM signal from a messed up tach by chance? so I D/C everything that tied into the RPM line, and no change, Changed to different AEM FPR's no change. Now it's been 2 months changing things left and right, and the problem has progressively got worse, from what started from a soft touch limiter, now became a more harsh buck and every time it would re-engage, a cloud of black smoke would shoot out my exhaust telling me it's being flooded with fuel because either A: spark is going out, or b: fuel injectors sticking? So I changed my 750's out for 880's... No change.... Now I'm getting mad, thinking it's the ECU being finicky so I have on order a OBD1 ECU which I will run a new EMS on, I'm OBD0 running ZDYNE. So the other night, we hook up a FPR gauge onto my car off my existing FPR gauge, but this one has a hose where we can mount the gauge by the window so we can see. and we noticed something interesting. At 45psi idle, we pull the vacuum hose off, and the PSI stays at 45psi. Put hose back on, and blip throttle. No change. We take it for a drive and redline the motor, and pressures STAY 45 base pressure whole way up. wtf? It should at least go up by 10psi for WOT< and then 1 psi per pound of boost if I'm not mistaken. So we think it may be pump related? So we pinched the return line and primed the pump to see it build over 100psi without any problem. We forget the pump and figure it's FPR. Tonight I changed the FPR back to my old AEM from 2 months ago when the problems started to occur. Set pressures at idle to 45 psi, pull hose off, it goes to 55psi, AH HA! Like it should. So whatever, I take it for a drive, I know it'll still have the same problems considering this is the same regulator as before when the problems started. I rev it up, and whenever VTEC engages, the car pegs out full lean and the car bucks. Running out of fuel. I wonder wtf, only thing changed is FPR. So I'm thinking VTEC sol is bad? So I move VTEC higher up but keep the vtec maps the same so it still adds a lot of fuel at 5300rpm. And every time more then 25% throttle in boost at that area the car runs full out lean now. At 15% throttle I can rev it a bit higher, but still does it around 5700. Now I'm really starting to think it's fuel pump, because I'm thinking that 2 months ago the pump wasn't that bad, but now, its'; gotten so bad now that as boost and pressures build, anything over 60ish psi under load, the pump cannot keep up and falls on its face. And it may have not done this on the 2nd regulator because that regulator was stuck at 45psi only and never moved even at WOT so it was on the edge of running out of steam. Tomorrow night I will hook the FPR gauge back onto it to see what it actually does. The only thing that bothers me though is, when it hesitated at top end at 45 psi on the bad regulator, why did the A/F not move at all? Where now at 5000rpm I can actually see it go full lean. I'm wondering if there is more to it then I think? I'm running the PLX wideband.


Any questions or comments let me know... I'm willing to take any advice right now. I'm gonna order a enw fuel pump and obd1/ems anyways jsut incase... I've already ran 12.1's witht his setup with a clean 20psi run, I'd like to be able to hit 11's in street trim.

 

It's probably your fuel pump. You may have been starving other cylinders like 1 or 2 under high load as the fuel pump couldn't keep up with the power. Make sure you check out your fuel filter to make sure it isn't clogged (they are cheap enough anyways).

When it was hestitating was the rpm able to go up? If not the ecu may have just been stuck in one load cell, and the fuel pump was able to barely keep up to that load cell. Also, your wideband may not be reporting rapid changes in a/f depending on the resolution of the unit itself. (The innovative lm1 that I use has a setting for that in its menu that can be altered depending on application).

 

jeremydde: I'm gonna replace my fuel filter just in case, but it's only got the same miles as the engine, 4000kms. But i'll do so just in case. When it would hesitate, the RPMS would not go up, it would stay there like a rev soft touch rev limiter, very smooth and faint, 2 months pass and it's alot more aggressive and bucks when I hit it now, but still doesn't rev up. I see what you are saying about the wideband, I was also thinking that maybe at high rpm/high load etc, the wideband doesn't show the a/f change like it does at my problem of 5000rpm now. Just seems odd to me. I've logged my A/F when it does it at high rpm, and there is no change at all when it's doing it, you'd expect some kind of hiccup? Thx for the input!

 

I know this doesn't really help, but try datalogging it!

When it hesitates just shut the car right off and check the plugs.

 

raene: When I datalog it when it did it at high rpms, the A/F did not change. I cannot datalog timing. But it definantly show the RPMS hesitatig. last tiek checkni plugs, they were a tad rich, no detonation.

 

Sounds more and more like the fuel pump. I had a similar issue with a mazda before. Would buck like crazy at 12 lbs of boost even though it was running at 12:1 A/f, but was fine up to 5lbs. Then I changed the fuel pump and the bucking went away, and the car was fine again.

Have you noticed if it is better accelerating when the fuel tank is full, or when the car has had a little time to cool down? Both are indicators of a poor fuel pump. The more fuel in the tank the cooler the pump runs, and usually the lower temp results in more flow as well.

 

Also, keep in mind that just because the pump is able to keep pressure up, doesn't necessarily mean it can keep up volume wise.

 

There is no difference weather it's full or empty, or hot or cold. I took it for a drive again with teh FPR guage hooked up and at 5400ish whenever it woudl start bucking, it would be at about 70psi(1:1 FPR) and the pressures didn't change when it bucked. But you're right it could just not be supplying the volme, and maknig the pump work alot harder to keep the pressures up with little volume. my A/F still go full lean when id did it, but now I'm wodnering if it's gongi lean AFTER it starts bucking... I hooked my old regulator back on which I had no problems with(the one taht only held 45-50psi the entire time) and I'll take it for a drive again tonight and see if I can rev past 5000 now like I sued to be able to before putting old regulator back on. if I can, then it's definantly tellnig me the pump, if I still limits, I'm chalking down to the ECU sicne I did ahve to retune it a bit for the rising rate regulator so I did ahve to reupload a new tune.. I'll keep you guys in tune... I have a new walbro pump now to put incase I have to

 

Okay, so I took the car for a drive tonight, and with the bad ragulator that would hold 45-50psi all the time even wot in boost, the car revved past 5000 no problem and kept climbing, I didn't continue tor ev it uot because I know it'd hit it's weird hesitation again at top end like before. So I think this is telling me the fuel pump can't provide the volume... Either way, I'm gonna throw a new pump in sunday.

 

Well, it wasn't the fuel pump.. Changed it alst night and no dice.. Gonna throw my 750's back in and see what's up, cause I never had this 5000rpm bog until playing around with thigns after isntallnig the 880;s

 

I put the old 750's back in and took it for a drive with the rising rate good regulator and it revved past 5000 no problem. Something musta been wrong with those Precision 880's after 70psi they jsut shut down.... So atleast I sovled one of the problems. Now gotta solve the top end hesitation problem. I haven't had a chance to rev it out yet so we'll see later tonight... If it still hesitates, then Nothing left but change ECU's. Which invovles me covnerting to OBD1 and what not... :S

 

So I took the car out tonight. and back to the same old song. hesitating at top end. On the flip side, atleast with this proper rising rate ragulator my injector pulsewiidths are under 17ms where as before it was near 20 to makeup for the lack of pressure. So We're back to 2 motnhs ago now. Hesitating at top end. I can throw timngi at it or take away, doesn't make a difference. I can't control indiviodual cylidner trims with ZDYNE. It's too old school for anything fancy. It again, feels like an ignition related thing now, which I've replaced everything now next to ECU. I'll just have to bite the bullet and get S300 and retune it all on OBD1 base and hope it fixes it...

 

Hmmm, if you ever head out towards vancouver (or abbotsford) we can test the ecu with one of mine. I have a modded p28 with the ostrich and datalogging, etc. that I use to tune friends cars with and we could eliminate the ecu possibility without you having to go out and purchase an s300 on a whim.

 

AHh I think I'm gonna do it anwayys.. I always wanted to covnert to OBD1 anyyyyyyways...... :S lol. Worse coems to worse, I can just socket the P72 I have comnig and just sue crome with my ostrich that I seu to tune other peopels cars.

 

Could a weak alternator be a cause of weak ignition? I have a volt gauge and when it hesitates, the voltage stays above 14 volts charging.. but I don't know if it's providing enoghu amperage under load. Could taht be a possibility?

 

Lol OMG after struggling with this problem for months, I finally found it. A few months back I had rewired the fan switch ground to the thermostat housing which shared the same grounding as the ECU, and that's about when problems started occurring at top end. Turns out, although the grounds were GOOD, there wasn't an adequate amount of grounds so that's why it was cutting out under heavy load. So I added a ground wire from T-stat housing to battery and it's perfect now!!!


9000+ revs at over 22psi

 

**** it's always something simple hey? Good job on finding it, happy boosting

 

Yep!! THanks for all the help guys.