Fuel Trims jacked....

[FutureDSMer2007]

Hello Tuners,

I’m having problems trying to figure out why my fuel trims went south. When I initially installed my 550 injectors and rewire fuel pump, I was golden! My trims stayed at 0 on closed cycle and WOT pulls showed no knock and trims holding 0. a couple of weeks later, my idle shows STFT @ 17 and LTFT @ 12. As I accelerate to about 3000rpms, STFT cycles between -1 and 3 while the LTFT stays at zero. My SAFC settings are 1K: -21 2K: -25 3K: -29 and so on. I'm planning on boost leak testing soon as I get the materials to test it with. Anyone experienced similar symptoms with 550s and 190 fuel pump re-wire? Oh yea, I have searched this issue.

 

[donmagicjuan]

Definitely start with a boost leak test. A major boost leak will cause extra unmetered air to enter under vacuum, creating a lean condition (ECU corrects with positive fuel trims), and less than the metered value to enter under boost (rich conditions seen at WOT). If your test comes out ok, come back and we can go from there.

 

[FutureDSMer2007]

Definitely start with a boost leak test. A major boost leak will cause extra unmetered air to enter under vacuum, creating a lean condition (ECU corrects with positive fuel trims), and less than the metered value to enter under boost (rich conditions seen at WOT). If your test comes out ok, come back and we can go from there.

Boost leak test done. No leaks, but still running lean as hell. Checking my datlogger, my 02v sits steady at 0.03 with no cycling during idle. Could I have a faulty O2 sensor? I noticed when it did cycle, I wasn't running lean. Any thoughts or similar experiences?

 

[98gst14b]

My o2 has always read like .02 - .04. I dunno if the logger isnt reading right or if the sensor is bad or what, I would think the ecu would throw out a cel if the sensor was bad though. At this point I dont even try n log o2 nemore and just tune to timing.....

 

[95FlamingTalon]

Boost leak test done. No leaks, but still running lean as hell. Checking my datlogger, my 02v sits steady at 0.03 with no cycling during idle. Could I have a faulty O2 sensor? I noticed when it did cycle, I wasn't running lean. Any thoughts or similar experiences?

It doesn't sound like you have a faulty 02 sensor, because it most likely wouldn't be cycling at all. I had a similar experience with my ltft low jumping up to 12.5 shortly after installing injectors. The 02 voltage read low at idle only. It was caused by a leak around an injector insulator.
Like previously stated, a boost leak will cause you to run leaner where you you have the most vacuum(idle). I find it hard to believe that if you just did your first boost leak test on the car, there wouldn't be a leak somewhere. When you did your boost leak test, did you just listen for leaks or did you also spray soapy water on everything? I would do another test spraying soapy water on everything and feeling around the injector insulators for leaks.

 

[95FlamingTalon]

My o2 has always read like .02 - .04. I dunno if the logger isnt reading right or if the sensor is bad or what, I would think the ecu would throw out a cel if the sensor was bad though

It sounds like the o2 sensor may be bad on your car though. It is common for the ecu not to store a code for a faulty o2 sensor because it takes a couple trips of at least 20 minutes of driving.

 

[FutureDSMer2007]

It doesn't sound like you have a faulty 02 sensor, because it most likely wouldn't be cycling at all. I had a similar experience with my ltft low jumping up to 12.5 shortly after installing injectors. The 02 voltage read low at idle only. It was caused by a leak around an injector insulator.
Like previously stated, a boost leak will cause you to run leaner where you you have the most vacuum(idle). I find it hard to believe that if you just did your first boost leak test on the car, there wouldn't be a leak somewhere. When you did your boost leak test, did you just listen for leaks or did you also spray soapy water on everything? I would do another test spraying soapy water on everything and feeling around the injector insulators for leaks.

I did do numerous boost leak tests, flowed through all areas and used soapy water. I truly believe my front 02 sensor is bad because when I wiggle the wire to the sensor, my fuel trims are perfect and the voltage is cycling. I stated earlier(without the wiggle) that my sensor voltage reading stayed at 0.03 during idle causing the lean condition.

 

[donmagicjuan]

I did do numerous boost leak tests, flowed through all areas and used soapy water. I truly believe my front 02 sensor is bad because when I wiggle the wire to the sensor, my fuel trims are perfect and the voltage is cycling. I stated earlier(without the wiggle) that my sensor voltage reading stayed at 0.03 during idle causing the lean condition.

If you wiggle the wire to the sensor and the problem goes away, it's either your sensor or the wiring itself. If you have an extra sensor lying around, you can swap it to see if it fixes the problem, but I would check the continuity of the wires before splurging on a new one.

 

[mnexcited]

Something is not right, you shound not have to pull that much fuel with 550's. You aren't venting right, also I know it's only a 190lph but you could have a small overrun problem.

 

[spyderturbo007]

When O2 sensors die, they start showing the ECU a false lean condition. This causes your FT's to move in the positive direction as yours are. My last O2 sensor seemed to have a mind of it's own when it started to go. Sometimes it would work, other times it wouldn't.

But like Don said, check the continuity before you go dropping money on parts.

 

[adrian2627]

for 550's your trim settings are kinda lean. Im using evo 560's and im only at -18 +/- 3 at the high settings.

 

[FutureDSMer2007]

for 550's your trim settings are kinda lean. Im using evo 560's and im only at -18 +/- 3 at the high settings.

I suspect I may have a over-run prob because I've been -23 for a while. My fuel trims are some what ok. STFT is at 0 while the LTFT cycles from +4-+7 during closed. I want to make certain I tuning right: During closed, I should shoot for zeros on both STFT/LTFT? Or should it be for example: STFT -12 + LTFT 12= 0? And how do I get my LTFT to go down? (Sorry for the machine gun questions, though I do appreciate everyones help.)