check engine light

My check engine light has come on - '96 T100, V6.

The auto parts store ran a diagnostic check, and the machine says
the problem is a "P017" (P0171?). The diagnostic machine complains about
"bank 1 running too lean".

The auto parts guy thinks it could be oxygen sensors or maybe EGR. What
would be a good way to troubleshoot this -- or is this best left to the
full-time mechanics?

Any advice really appreciated.....

On Sat, 23 Apr 2005 13:52:35 -0500, Don Carpenter
<DonCarpenter@sailone.org> wrote:
[color=blue]
>My check engine light has come on - '96 T100, V6.
>
>The auto parts store ran a diagnostic check, and the machine says
>the problem is a "P017" (P0171?). The diagnostic machine complains about
>"bank 1 running too lean".
>
>The auto parts guy thinks it could be oxygen sensors or maybe EGR. What
>would be a good way to troubleshoot this -- or is this best left to the
>full-time mechanics?
>
>Any advice really appreciated.....
>
>[/color]

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" <edokamoto@earthlink.net> (Sun, 24 Apr
2005 23:37:33) about "Re: check engine light":

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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