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1998 pontiac grand prix 3.8 code p0171

03-25-2011, 09:06 PM
this code keeps coming up. (p0171) any ideas or help to find out whats going on or what to look for to resolve this problem. 1998 pontiac grand prix. 3.8 non super charged

03-25-2011, 09:27 PM
P0171 System too lean bank 1

That means the fuel mixture is not within the proper values.

Possible causes can be:

Bad dirty MAF sensor
Low fuel pressure
Clogged fuel filter
Dirty injectors
Vacuum leaks.

Since you only have p0171 I would think your problem is either with injectors or a bad gasket causing a vacuum leak.


03-25-2011, 09:37 PM
here is a link for all the other threads relating to the p0171 codes. there is useful information here.

03-27-2011, 11:43 AM
so i ran a fuel pressure test and it was 42 with the key on, 41 while it was running, and stayed at 41 while it was in gear. not sure about the stuff i gathered fro live stream but here it is.
bank 1 fuel trim. started at 9.36-11.7 and after it was warmed up went to 16.0
o2s,b1,s1 stf 14.97
rich to lean test 0.39
lean to rich 0.51
st fuel trim b1 -71.09
o2s b1 si stf -86.72

any suggestions or other tests i should try? i thought the pressure had to be between 48-55 according to alldata

03-27-2011, 01:25 PM
ok so far today i took apart the air intake and cleaned all the grime out of everything. cleaned the mass air flow sensor with mass air flow sensor cleaner. checked for vacuum leaks. didn't find any. took out the fuel rail and cleaned and changed the injector o rings.

03-27-2011, 02:55 PM
i also have changed the fuel filter.
new stats
fuel sys sta b1: cl closed using ho2s
calculated load 1.56
st fuel trim b1 16.39%
o2s b1 s1 stf 16.39

03-27-2011, 04:21 PM
did you recheck fuel pressure after changing filter??

any suggestions or other tests i should try? i thought the pressure had to be between 48-55 according to alldata

your right f/press 48-55 you have 42 may not be your issue here
just remember espec. if its original

03-27-2011, 07:28 PM
fuel pressure stayed exactly the same

03-28-2011, 03:17 PM
If the fuel pressure stayed the same after you changed the fuel filter that would indicate you either have a leak somewhere or your fuel pump is on it's way out and since the value is not within specified values, that can be the cause of the P0171 DTC.

You don't mention there is any fuel smell so it's unlikely you have problems with the leaky fuel lines, the remaining things to do are:

Inspect the Fuel Pressure Regulator (FPR) remove the vacuum line on top of it and see if any fuel drips from it, in that case replace it. NOTE: When the engine is running the Fuel pressure should go about 10PSI higher when you remove the vacuum line from the FPR. Check that too! ;)
Check for damaged/collapsed fuel lines from the fuel tank to the engine compartment.
If everything is correct, then the last thing would be to replace the Fuel pump...


03-30-2011, 05:38 PM
well i pulled the vacuum line off the fuel pressure regulator and it does go up ten psi. should i be leaning towards the fuel pump?

03-30-2011, 08:28 PM
I would say yes, you have a bad pump the good news is that you don't need to drop the fuel tank.

There is an access cover in the trunk right at the back of the rear seat, remove the carpeting and you should see it.

You don't need to buy the whole pump assembly, it is enough to buy the replacement kit: motor, both filters and in some cases the fuel pump gasket, even if it doesn't comes with it it would be a good idea to buy a new one to avoid any vacuum leaks causing an EVAP system DTC.


04-02-2011, 06:52 PM
i changed out the sending unit/fuel pump today and the fuel pressure went up to 44 psi from 40

04-03-2011, 07:11 PM
44 is better than 40, but it's still a bit low...

Have you looked for any bent/pinched lines?. I'm assuming you replaced both small filters in the tank right?

04-07-2011, 10:49 PM
Check the intake plenum. Actually, take it off as the design is poor and a fault occurs with the plastic between the coolant flowing through. Replaced that once myself. Also had the replacement fail a few years later as a hose on the inside fell apart and both times the 171 code came up.
Mine is a 97 Pontiac Grand Prix, 3.8

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