Help! Car Leans Out Gradually After 5000Rpm..

[rondofj]

Hi SAU, I need your help / suggestions...

Took my car to my tuner today to get my ignition timing advanced a few degrees, (road tune only) we found that my R34GTT leans out gradually after 5000rpms, sometimes around 4500 onwards, no matter how much fuel my tuner is adding, it still does this.. I have also noticed previously that it dosen't have any top end (its constant and smooth but not 'weld-me-to-my-seat'). That was with our previous tune. We then loaded the stock R34 maps and started from scratch and it still does this even with the stock maps.

As a matter of fact, we backed off and will be taking it to the dyno next week to check if the fuel pump, fuel reg is playing up? Now the pump is a new Walbro GS3442 that was installed and re-wired not more than a couple of months ago, it has a factory sock which has a bit of play where it meets the pump. The car has the usual FMIC, exhaust, 12psi (which holds constant from 2800 onwards), cold airbox, Nistune. So I will be driving in low rpms for now hehe..

Someone please throw in your suggestions as to what could be the cause of this?? ECU retarding timing in high rpms?? We detected no knock thank god, never did, even with previous tunes.. Fuel pump?? I hope not, its the newest item on my car, and it gave me a lot of noticeable power gain after the install, more than anything else.. Fuel reg?? what what..

[R.3.2.G.T.R]

walbro genuine? i think its fuel pump

[rondofj]

Genuine mate, bought from GAS Motorsport, walbro stamp in metal, and STEEL gears not plastic..

[rondofj]

Could it be my AFM is dirty? - its the stock one.. BTW just wanted to add that before the Nistune and fuel pump, my car was hesitating and had the flat spot at this SAME 5000rpm band - something like 4700-5700rpm - a flat spot zone, Nistune has fixed that, the flat spots gone, acceleration is smooth but theres just no power in this zone - ie I dont feel the turbo pushing me hard in my seat..stock turbo 12psi... before I could feel it, from 6000-7000rpm it felt the strongest then.. And now this leaning out from 5000rpm onwards..

[SiR_RB]

Changed ur fuel filter lately??

[rondofj]

yep fuel filter, oil filter, engine oil done 2-3months ago..

[rondofj]

Having a read here:

http://www.evoxforums.com/forums/archive/index.php/t-35897.html

one guy says:

"Don't rule out a bad sensor for your AFR guage. The last two I had fail both started reading lean by almost 3 full points. Funny thing is, they would read okay in closed loop, just not when you got on it."

another says:

"Try ur fp relay first. I seen another post with a guy using blue fpr, same problem, switched to syock, problem solved"

and the answer is:

"found the culprit it is a missing fuel freaking pump relay in my fuse box in the engine bay ! i took the horn relay and put it in the fuel pump relay and my afr was PIG RICH.

really weird and i dunno why evo x over here does not have a fuel pump relay.

been busy @ work but will load up a map and see what happens from there on.

but nevertheless i will double check all hoses again but afaik everything's tight and will do another full boost leak test.

will keep everyone posted soon."

How good to have internet and good people!.. But I still havent found my answer yet.. duh

[rondofj]

But in my case I have a brand new relay and it was re-wired as well..

[rondofj]

Please pour your suggestions fellows

[SiR_RB]

injectors could be dirty?

[rondofj]

Shud try an injector cleaner in my fuel tank maybe and clean my afm too

[femno]

Connect a fuel pressure and flow guage and monitor pressure and flow while its playing up.

Will save you a fuel pump if theres plenty of pressure and flow.

Also monitor response of the fuel reg - could have a hole in it and not increasing rail pressure with boost.

If he knows what hes doing, your tuner should know to do all these things without you having to find out for yourself on the internet.

[rondofj]

Hey sir rb, jez is tryin to organise a dyno session this sat up north and mentioned u mite be there? I will be goin, he will be tuning a 300zx too

[rondofj]

Sure he knows that femno, he mentioned that to me before, thats why we wil be goin to the dyno shop where all the equipment is ie the fuel pressure tester

[rondofj]

Thanks for the idea on the hole in fuel reg, worth checkin that one one, the r34 has THREE regs, will u belive it!

[DVS JEZ]

One is a dampner Ron.

Need to get it on the dyno with the fuel flow/pressure tester as discussed with u. Its extremely unsafe to do this on the road.

I need to check ur install on the fuel pump. Last time this issue went after filling the tank full.

Have even loaded the fully stock factory map and the issue is still there

Ur car had the same or similar issue with ur old tuner and old fuel pump.

Wiill get it sorted for u. Just harder because u cant leave the car with me

[DVS JEZ]

Want to try cleaning ur air flow flow meter an check all ur piping etc

[rondofj]

Have heard pple sayin to check the afm, but if that was dirty, we would get less clean air into engine per unit of fuel which means its running rich, but its not, its the opp ie, running lean, dont understand this one

[rondofj]

anyone else's opinions??

[Dose Pipe Sutututu]

I might have a stock R34 fuel reg sitting at home. If I do, you can have it since you're just at Parra. Try that....