Low throttle fuel trim problems

[jimh]

I have recently installed 550's in my car and ever since I have been unable to get the low throttle fuel trims correct. On the stock injectors I had the fuel trims zeroed out and the S-AFC settings were +2 across the board. I started tuning the 550's by setting the low to -10 across the board and watching the datalogger. The car is asking for a lot less than -10, it will zero out around -25 or -30 which causes severe drivability issues. The idle is terribly rough and the car feels like it's choking so I have left the settings at -10 until I can get some help. At idle, the O2's aren't cycling properly, they are up in the .8-.9 range. Only when I take more air out with the AFC will they cycle properly. The O2 has 10k miles on it, could it be going bad already? Any help is appreciated.

 

[98autogstspyder]

have you found out what has been going on with your car?

Tyler

 

[talon1979]

After you set your low fuel trims and you drive around for a while do they change? If so you may have some type of boost leak.

 

[jimh]

I was not able to determine what the problem was. I checked for leaks, changed O2, and resistance checked the ignition system. The trims were bad enough that the car started throwing error codes (PO170 and PO301 I believe). So I resorted to putting the stock injectors back in the car and as soon as I did that and reset the S-AFC, the car idled perfectly.

 

[EuroGSTSpyder]

something wrong with the injectors maybe? If one isnt working properly so the car sees an uneven supply of fuel..? Just a thought...

 

[jimh]

Originally posted by EuroGSTSpyder
something wrong with the injectors maybe? If one isnt working properly so the car sees an uneven supply of fuel..? Just a thought...

I thought that might be the problem as well. However, I'm not sure what could go wrong with injectors or how to tell. I resitance tested each injector as per the manual's instructions but they all fell in the range. Although when I pulled the plugs, #2-#4 were black and #1 was normal. Any ideas/thoughts are welcome.

 

[EuroGSTSpyder]

if you test them individually as when you test for flowrates you should be able to see if it functions properly.
On the cylinder part I hae no direct clue..but I am sure someone else has ;-)