-30 short term fuel trims need help
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From: Hurley, VA
-30 short term fuel trims need help I'm getting -30 to -35 stft on both banks on my 02 trans am. I had a injector o ring sucking air and did find another vacuum leak between the upper and lower shell of my FAST 102 but since fuel trims are negative wouldn't that be a rich condition. What could the problem be. No exhaust leaks around the 02s and both banks are high so I doubt it's the sensors themselves. What could it be?
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-30 short term fuel trims need help Negative trims indicates the opposite of an airleak, i.e. indicates too much fuel... possibly due to multiple leaky injectors or a leaky FPR (check reference hose if so equiped).
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From: Hurley, VA
It's in a 02 Trans Am so no hose. Fuel pressure gauge reads a steady 64psi idling. I'm running a racetronix pump and hotwire kit and 42lb racetronix injectors. With the engine off and key on I'm getting 51 ish and it appears to be climbing a pound or two the 3 or 4 minutes it's sat with the key on not running. I just don't understand how both banks would be basically dead even at -30 to -35 percent. I can watch trims and spray starting fluid on the passenger side and trims will climb to the -39 area and then drop back to -30 when I stop spraying. Would the 64psi vs 58 I think cause it.
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From: Hurley, VA
Just noticed something else. When the car does it's won't idle non sense the pressure will fluctuate between 68 and 62 ish really erratically. And with steady throttle trims go back down to lower teens sometimes close to zero. Does the regulator on these allow for constant fuel pressure or does something command higher lower fuel pressure. I would think if I had an injector problem pressure would bleed down instead of spiking up and down. I don't actually see a regulator on these Fast fuel rails like the stock ones. Pressure is twitching up towards the 70psi range and with the engine not running the needle stays at a steady 51.
You have a vacume leak. The ecm is adding fuel due to low vacuum ie it thinks the throttle is open and is adding fuel accordingly. The fact that you state you can spray with staring fluid and trims go down signify an air leak
Last edited by watman02; Jul 12, 2015 at 10:23 AM.
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From: Hurley, VA
Strangest thing happened. I turned ltft back on and fuel trims dropped into the mid teens. I held the car at 2500 Rpm for a few seconds and all the sudden fuel trims dropped to -6 or closer to zero. Is it possible where the car has sat for so long the plugs were trying to foul so the ECM was pulling fuel the car ran the same with not idling well even in open loop. Just all of the sudden fuel trims fell to normal and the car runs fine. Next step is burning the stupid thing.
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From: Hurley, VA
What I mean by sitting is started moved 20 feet and turned off over a 6 month period of putting the cage and everything in the car. It's seen a lot of 10 minute idle sessions or less. And the trims are going higher into the negative rather than closer to zero. It actually idled for a good 20 minutes at -6 or better but after driving it I stopped all at once and the car went back into the -20s. Cruising around trims stay pretty normal
OP. Have you TUNED your car? If i read right, you added a bigger pump and have 42 lb injectors? your FP is too high at idle as well. More so if its vacuum referenced. Your o2's are both agreeing that there is 30 percent excess fuel. if you multiply stoich by .7 (.30 rich) you would get 14.7*.7= 10 afr pretty much. You are running pig rich and have probably fouled plugs and your oil. Your STFT get closer to 0 when you turn on your LTFT because that's the whole point of LTFTs. Get a tune if everything in your fuel system is mechanically good.
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From: Hurley, VA
The car was professionally tuned but it's a hack job. My Pe table from 4800 up is set to 1.30 but I'm getting mid 12s and at say 2000-3000 rpm heavy throttle gets me 10.0 afr. It's a mess but I worry my injectors are an issue. I'm running a racetronix pump and Hotwire kit with 42lb racetronix injectors. It's been tuned for all this but they had fuel trim issues and I'm not confident they knew what they were doing at all. I'm running the stock regulator with fast ls2 rails. Would my regulator need replaced since I'm getting 64psi and it will occasionally jump to 68 and bobble between 60-68 possibly need a aftermarket regulator.
if he had a vacuum leak his trims would be positive unless theres so much excess fuel that it even a vacuum leak cant lean out the rich condition
The car was professionally tuned but it's a hack job. My Pe table from 4800 up is set to 1.30 but I'm getting mid 12s and at say 2000-3000 rpm heavy throttle gets me 10.0 afr. It's a mess but I worry my injectors are an issue. I'm running a racetronix pump and Hotwire kit with 42lb racetronix injectors. It's been tuned for all this but they had fuel trim issues and I'm not confident they knew what they were doing at all. I'm running the stock regulator with fast ls2 rails. Would my regulator need replaced since I'm getting 64psi and it will occasionally jump to 68 and bobble between 60-68 possibly need a aftermarket regulator.
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From: Portland OR
Why the big injectors and elevated fuel pressure?
42# injectors are good for 512hp (@43#) plus you raised the pressure (which adds more).
You might be good for as much as 600hp (yep @ 64# with those injectors you are good for 615hp).
Not that you will make that much power, but the injectors are capable of supporting that much. (more if you max out duty cycle!)
Fuel pump wont affect your tune, except at the top if it falls short.
Regulator only affects the tune by changing the fuel pressure.
42# injectors are good for 512hp (@43#) plus you raised the pressure (which adds more).
You might be good for as much as 600hp (yep @ 64# with those injectors you are good for 615hp).
Not that you will make that much power, but the injectors are capable of supporting that much. (more if you max out duty cycle!)
Fuel pump wont affect your tune, except at the top if it falls short.
Regulator only affects the tune by changing the fuel pressure.
Last edited by RixTrix; Jul 14, 2015 at 08:00 AM.
Call me crazy but... If there is a vacuum leak, the engine is ingesting unmetered air, which would lead the O2's to report a leaner than normal condition, which would force the PCM to add fuel resulting is a positive fuel trim.
What has been fail to be metioned it if the car is a maf only or a SD car or combination of both (ie factory) if you have a maf car the vacume leak (post maf) would result in less air being read by the maf and the o2's would show a lean condion and positive fuel trims. In a SD only system the leak/ loss of vacume would be interpreted as more air and more fuel would be added. The o2's however would see this as a rich condition and be taking fuel away resulting in a negative fuel trim.
Therefore as and outside fuel being added (spraying with carb cleaner or something flammable) if there was a vacuum leak in both cases fuel trims would drop due to the o2's seeing less un consumed oxygen (richer afr).
Therefore as and outside fuel being added (spraying with carb cleaner or something flammable) if there was a vacuum leak in both cases fuel trims would drop due to the o2's seeing less un consumed oxygen (richer afr).
What has been fail to be metioned it if the car is a maf only or a SD car or combination of both (ie factory) if you have a maf car the vacume leak (post maf) would result in less air being read by the maf and the o2's would show a lean condion and positive fuel trims. In a SD only system the leak/ loss of vacume would be interpreted as more air and more fuel would be added. The o2's however would see this as a rich condition and be taking fuel away resulting in a negative fuel trim.
Therefore as and outside fuel being added (spraying with carb cleaner or something flammable) if there was a vacuum leak in both cases fuel trims would drop due to the o2's seeing less un consumed oxygen (richer afr).
Therefore as and outside fuel being added (spraying with carb cleaner or something flammable) if there was a vacuum leak in both cases fuel trims would drop due to the o2's seeing less un consumed oxygen (richer afr).
