check engine light

I'd start with a set of factory manuals ... then see if it looks like I could handle the trouble-shooting / repairs.

This could be anything that makes bank 1 look lean to computer. The way that computer knows bank 1 is lean is from oxygen sensor input. Best way to troubleshoot this problem is with a scanner. With a scanner you look at fuel trims (is computer adding or subtracting fuel over a baseline amount). Baseline is in factory with a engine hooked up to monitoring equipment they determine the amount of fuel an engine needs at every rpm and load imaginable to run stoichometrically, and create a table in computer memory. So with a scanner and car running you can see when bank 1 is running too lean, at idle, or cruise, or under load. If an intake air leak fuel trims are too positive at only idle for instance. The way a computer normally works is if oxygen sensor is telling it lean the computer adds fuel (increasing injector on time), which is positive fuel trims, it keeps increasing trims till it sees oxygen sensor swing rich, then it lessens fuel trims , subtracts fuel over the table till it sees oxygen sensor swing lean, then it repeats this cycle over and over again. This results in a rich lean cycle close to stoichometric, this is to help catalytic converter work. So in your case based on bank1 oxygen sensor it tells computer lean so computer tries to add fuel (up to programmed limit) but it never sees bank1 oxygen sensor swing rich. So it sets code and defaults to table value for fuel delivery. So it could be oxygen sensor bank 1 is biaised lean so it never tells computer rich, so it needs to be replaced , or intake air leak only affecting bank1, or clogged injectors on bank1 (long shot), or exhaust leak on bank 1 before or near oxygen sensor. I think this is also associated with a bad MAF sensor sometimes, but usually code PO174 bank 2 lean is also present.

Hi, Ed - while you're on this topic could I ask you what the difference between long and short term trim is?

Thanks!

Reply to message from "edmechanic" (Sun, 24 Apr

e> This could be anything that makes bank 1 look lean to computer. The way e> that computer knows bank 1 is lean is from oxygen sensor input. Best e> way to troubleshoot this problem is with a scanner. With a scanner you e> look at fuel trims (is computer adding or subtracting fuel over a e> baseline amount). Baseline is in factory with a engine hooked up to e> monitoring equipment they determine the amount of fuel an engine needs e> at every rpm and load imaginable to run stoichometrically, and create a e> table in computer memory. So with a scanner and car running you can see e> when bank 1 is running too lean, at idle, or cruise, or under load. If e> an intake air leak fuel trims are too positive at only idle for e> instance. The way a computer normally works is if oxygen sensor is e> telling it lean the computer adds fuel (increasing injector on time), e> which is positive fuel trims, it keeps increasing trims till it sees e> oxygen sensor swing rich, then it lessens fuel trims , subtracts fuel e> over the table till it sees oxygen sensor swing lean, then it repeats e> this cycle over and over again. This results in a rich lean cycle close e> to stoichometric, this is to help catalytic converter work. So in your e> case based on bank1 oxygen sensor it tells computer lean so computer e> tries to add fuel (up to programmed limit) but it never sees bank1 e> oxygen sensor swing rich. So it sets code and defaults to table value e> for fuel delivery. So it could be oxygen sensor bank 1 is biaised lean e> so it never tells computer rich, so it needs to be replaced , or intake e> air leak only affecting bank1, or clogged injectors on bank1 (long e> shot), or exhaust leak on bank 1 before or near oxygen sensor. I think e> this is also associated with a bad MAF sensor sometimes, but usually e> code PO174 bank 2 lean is also present.

- robert -

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