Okay so I have been workin on this issue for a month now and can't seem to fogure it out. I have a 1991 Jdm turbo swapped FC that is all stock besides injectors fuel pump. I have all emissions removed besides the bac. The car ran perfect before the oil seals went in the engine. I rebuilt the engine and have since put it all back together. Ad have put 3k miles on it...ever since the rebuild I have had a leaning issue that started with just higher rpm (5-8k) leaning (around 12psi) I have 750 secondaries and a walbro 255 fuel pump so 12 psi on stock turbo should be fine. I rewored my fuel pump with the relay relocated in back with no luck the issue actually has gotten worse. Now the car runs lean whenever on the throttle (10 vacuum+) but sometimes will not lean out if I hit the throttle a little harder. Also it seems to run better cold. Idle is absolutely fine and is around 13:1. I replaced the AFM, fuel pump wiring, injectors, fuel line, and wiring to the tps. Any help would be appreciated greately, thank you all.
I've done much searching on this topic and next step is to test the tps.
-Justin

 

You running a stock computer?

 

Yes

 

That would be the likely issue. The stock computer does not like running anything past stock boost levels. Its doable but not really suggested as its not all that safe. Your best bet would be to get an aftermarket computer. I personally run a microtech and you can get them for around $500 used and is pretty much plug and play if you get one with a harness. If you wanna save some money you can get an rtek or pfc.

 

I have been running the car on the stock computer for 3 years this issue is something new...I plan to purchase rtek 2.1 soon but I do not believe it will fix my issue. Any other tips?

 

Its possible that your loosing fuel pressure in the high rpms

 

Just made a fuel pressure gauge...everything looks good. The fuel pump is brand new because I thought my old one was the issue also all the wiring is. So today I took it on a ride let it warm up first went out hit boost 5-9 psi two times then it started to lean out shut the car off turned it back on back to normal? Until I hit boost again weird...my ecu had a built in fcd and I ran 14 psi on it maybe its failing? Back to more testing! Thanks for the tips

 

Having no way to check my fuel pressure while driving is killing me. Is there a way to check to see if my car is in limp mode?

 

Bump really need assistance

 

So I tried a fuel cut defender today just out of interest and nothing next step ecu?

 

Back at work today tried a new ecu Jdm eu made it run on one rotor my Jdm ecu is chipped so it works idk getting rtek soon if anyone has an n370 ill pay big for it. Also noticed when I plugged in the fcd I hit boost cut. When I don't have it plugged it I don't hit the typical 8.6 boost cut I lean out towards 10 psi also noticed I seem to lean out the higher rpm I'm at

 

Also tested tps and swapped maf sensors with no results

 

picked up an air intake temp sensor today ill give it a shot

 

I have same problem, been dealing with it for awhile

 

I'm gonna check my grounds tomorrow because I've tried everything else

 

Took the car for a ride today and at around 3k in 4th I hit 14 psi then some hesitation stopped at the next red light took off in first WOT and had some bad hesitation after getting into boost. Havnt had a chance to take the intake mani off after the ecu ground
Help! :p

 

To me it definitely sounds like you aren't getting adequate fuel pressure at high rpm. This can be because of the regulator, fuel filter, or fuel pump. But I would bet my money on it being the fuel pump. I've had bad brand new Walbro's on a number of occasions, it's definitely nothing new, but a pain-in-the-*** regardless.

Definitely don't hook up an additional FCD when you already have one built in the ECU tho.

My next suggestion would be to check for positive resistance in your ground system. Check the negative terminals in your MAF, ECU, etc. Grounds losing their contact surface due to corrosion, rust, or anything like that is fairly possible. My friends car was actually just diagnosed a couple weeks ago for stumbling and leaning out. It was 100% a grounding issue with the engine wiring harness, when it use to run just fine.

 

I'm thinking a ground I've gone through 3 fuel pumps the fuel filter is fresh and I'm getting good fuel pressure. I still havnt got a chance to check my grounds and I will for sure...because it started happening after my engine rebuild I think I may have messed up the ecu ground...checking that when Ivey a free moment. Thanks a bunch for your input!

 

No problem, sounds it's definitely possible for a ground then. I know I always mess at least one ground up every swap that I have to go back and find.

 

backprobe the pump 12v wire and take it for a drive and see if the voltage is dropping off at higher RPMs.

 

Will do I tried regrounding today no luck...when I rewired the fuel pump I kept the resistor relay in place because when I tried running without it I went into limp mode

 

the 2 step relay shouldn't put the car into limp mode.

 

If the fuel resistor relay was bypassed then it would run a continous 12 volts to the fuel pump which maybe could cause some running issues.

 

I was hitting limp mode with the resistor not wired in. Atleast that what it felt like. Any boost and it would feel like I was hitting a rev limiter and lean out also couldn't go over 3500 rpm

 

If anything I would be running rich