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Kind of running out of options here. My Celica has a p0171 code.
What I've replaced: Intake manifold gasket, spark plugs, coilpacks, MAF
I got tired of just replacing stuff randomly with no results and then I found scannerdanner's youtube videos which became very helpful. I used the live data off my OBD2 scanner to identify some vacuum leaks I had (high STFT on idle - Dropped to -10/+10 from 25% min most of the time).
I'm not sure what else to test but I've been reading up forums and what not on long term fuel trims since mine is always at a minimum of 30% all the time. I was hoping someone here could enlighten on a diagnosis of what the 30+ % on the long term fuel trim means. Even if I can't fix the problem I'd still like to learn for the future.
How does the car run? Any idling, misfiring, or drive-ability issues? Or, is the only indication the P0171?
Long Term Fuel Trim of +30 is a lot. If it is a vacuum leak, it should be, fairly, easy to find. Can you hear any sucking/whistling sounds. What is you Short Term Fuel Trim? Is it maxed out, too? Or, is there some up-and-down fluctuation?
Have you looked at your O2 Sensors?
"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer." I have learned more by being wrong, than I have by being right.
When I reset the ecu, the car misfires a lot in cylinders 1, 3 and 4. I get the codes relating to the misfires but after 20 minutes of driving around the misfires stop (I'm assuming because I don't hear popping sounds anymore). And I'm only left with a p0171 code. I'm now assuming the misfires are the main cause of the p0171 code.
I have been monitoring my o2 sensors as well and the numbers for the upstream seem to fluctuate faster from .1 to .9 versus the downstream which only fluctuates from .1 to .75 (very slow increases and decreases).
Also after resetting the ecu, the short term fuel trim is high at 25% then drops down to normal operating conditions because the long term balances it out I'm assuming after watching the video I posted earlier more thoroughly again. Long term is now at 30 min and max 40 ish.
I'm beginning to think it's injector related. That or its the fuel pump or my engine is just flat out dying on me. I've already purchased used injectors because I'm assuming 1 3 4 are bad. I tried the screwdriver to the ear test but couldn't verify if it was bad or not.
Question: when doing the resistance test can I leave the Injectors on the car still (battery unplugged of course) or will the engine skew results?
When revving the engine manually by hand I can hear a hiss noise indicating an obviously vacuum leak. But I don't think that's causing the misfires?
johnv466267 wrote: When I reset the ecu, the car misfires a lot in cylinders 1, 3 and 4. I get the codes relating to the misfires but after 20 minutes of driving around the misfires stop (I'm assuming because I don't hear popping sounds anymore). And I'm only left with a p0171 code. I'm now assuming the misfires are the main cause of the p0171 code.
I suspect the opposite. I suspect the P0171 (LEAN condition) is the cause of the misfires. When you reset the ECU, you reset Fuel Trim. Do to the vacuum leak that you have,
When revving the engine manually by hand I can hear a hiss noise indicating an obviously vacuum leak. But I don't think that's causing the misfires?
, the Air/Fuel mixture is very LEAN. The short term fuel trim immediately goes MAX POSITIVE, adding MORE fuel to compensate for the extra air. But, it's STILL LEAN. The Long Term "catches up" and the Air/Fuel ratio becomes closer to the "ideal" 14.7:1 ratio. The misfires go away.
Correct the "hiss noise"/vacuum leak, and I suspect you will have fixed the problem.
"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer." I have learned more by being wrong, than I have by being right.
johnv466267 wrote: Question: when doing the resistance test can I leave the Injectors on the car still (battery unplugged of course) or will the engine skew results?
You can l leave them in the car, but disconnect the connector.
"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer." I have learned more by being wrong, than I have by being right.
Is this the 1.8L engine? I think you're right to suspect injectors, especially after the parts that have been changed previously. Paul has run across this a couple different times - the injector balance test always shows the issue.
How the trims behave driving down the road will be a clue. If the trims stay high while cruising, then you're onto something. If the improve significantly, then keep chasing a vacuum leak.
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