Big Fuel Trim Issues, Help!!!!!!!!!

[92_75i]

I have a 91 GSX with a maft 660cc injectors and an evo 8 fmic w/ a evoIII 16g keeping it at 15psi... i keep playing around w the maft but can never get my fuel trims to 100 and KNOCK keeps comming up even at around 3000 rpm's im hitting 29 knock.....which then goes up to like 40-50 on WOT??????? that cant be right

i just did some runs and logged it and its as follows?

LOW - 139.8%
MED - 95.3%
HIGH - 88.2%

as far as the o2-R im usually in the .50-.60V not making sense at all...

i tried richening it up a bit w. the maft and car just starts sutterting and bogging so i dont know where to go from here

anything helps..

thanks,

-az-

 

[jott5555]

Maybe we need to kill the lower fuel a bit.. set idle in the Neg range and try to richen up mid a lil and WOT a lil... im outta idea's dude..

also on a side note he is runnin a 255 hp fuel pump w/ a stock fuel pressure regulator.. another afpr is in the work's, which i have a feeling is causeing the improper fuel issue's

 

[95blackGsTurbo]

FPR is going to be your big problem. Without an aftermarket one you are just overrunning the one you have and that is killing you right there. Not being able to maintain a constant fuel pressure is most likely what is giving you your issue's. Especially on 650cc injectors. At 15psi on an EVO III you can still use 450cc injectors and it will run fine. Try trimming your fuel way down to compensate for the larger injectors.

 

[Skunked tsi]

FPR is going to be your big problem. Without an aftermarket one you are just overrunning the one you have and that is killing you right there. Not being able to maintain a constant fuel pressure is most likely what is giving you your issue's. Especially on 650cc injectors. At 15psi on an EVO III you can still use 450cc injectors and it will run fine. Try trimming your fuel way down to compensate for the larger injectors.

Yes, the regulator is an issue that should be taken care of, but I doubt his issues are caused from that. As he stated he was getting .50-.60 volts which means he is lean, an over running regulator cause's a rich condition not a lean one.

I would try to fatten up the mid-wot area and see if that gets your 02's up where they are supposed to be. Also have you made sure that the maft isnt set to run say a 3.5 instead of a 3 or something, just a thought and something to check.
Tyler

 

[steve]

LOW - 139.8%
MED - 95.3%
HIGH - 88.2%

If nothing else were going on these would be a big red flag for boost leaks.

How old are the O2 and knock sensors?

Steve

 

[92_75i]

^^ dont know how old they are, but as far as boost leaks go, i think im pretty good at that, we've checked everything and it looks fine.... might be the sensors....

afpr is on the way just got one from ebay

-az-

 

[Spooling99]

Did you actually do a boost leak test and used soapy water? Or did you just visually look? There a many places that could leak. Good luck.
-ADAM-

 

[jott5555]

Were going to do one tomrrow just to verify .. but its all pretty good... things's welded up well.. question is should we lean out the idle and richen up the mid & wot?? we seem to Really fowl plugs and get a heck of a bucking when we do...

 

[alex99gst]

This may sound stupid, but are you sure it is not in RPM mode? I have heard of people overlooking that and getting crazy numbers.

 

[steve]

Were going to do one tomrrow just to verify.
Question is should we lean out the idle and richen up the mid & wot??

So in other words you haven't pressure tested.

Based on the trims given the car is already lean at idle and rich in the mid and high.
Remember <100% ECU is taking fuel out because the feedback is rich.
> 100% ECU is adding fuel because the feedback is lean.

Please, pressure test the intake, install the AFPR and set the base fuel pressyre. Check to make sure the AFPR tracks manifold pressure, reset the MAFT and start from the beginning.

Steve

 

[jott5555]

ya but running a MAFT setup that would have an effect on the fuel trim's seein as the engine see's no air before the maft includeing boost leaks that would be in the intake track.

 

[92awddsm]

This may sound stupid, but are you sure it is not in RPM mode? I have heard of people overlooking that and getting crazy numbers.

I also agree with this and the boost leak theory. First, if you have the rpm wire hooked up, verify that the switch is set to rpm mode. If you dont have the rpm signal wire hooked up, verify that the switch inside the maft is set to airflow mode. And do a boost leak pressure tes. A leaking injector seal, im gasket, tb gasket, or pcv will pull unmetered air after the maf which can result in some of the same problems you are having.

 

[alex99gst]

Either way a huge leak can cause fuel cut because of the turbo having to work so hard. I had a nice 2x1" size hole in one of my couplers that I didn't know existed. I turned the boost way down after I put the new one on and it spiked to 30 psi for a second, so you know the turbo was cranking out some killer pressure just to be able to fill the piping with 11 psi. After the simple coupler swap I stopped hitting fuel cut.

 

[Nautica985]

I have the MAFT and 650's. It took me forever to get it tuned right, my fuel trims were about where yours are. The MAFT manual said to set the base knobs to AUX=1, BASE=7 for 650's. My car ran like shit like that and knocked like a mofo. I was playing around with the base settings one day and i finally got it to run good with AUX=0, BASE=some where around 6, and i had to richen up the idle 3 or 4 clicks. My fuel trims now are HIGH=100 MID=100 and LOW=109