Re: P0171/P0174 Help!

aarcuda69062 wrote:
>
> In article <fxxek.12414$cW3.4359@nlpi064.nbdc.sbc.com>,
> "Pete C." <[email protected]> wrote:
>
> > '97 Chev K3500 7.4L
> >
> > Been chasing after the source of intermittent P0171/P0174 (always both
> > set) for some time without success. I'm running out of ideas on what to
> > check now, I don't have a full feature scan tool so I can't perform all
> > the possible checks. Some of the possible items seem to not be
> > applicable due to it always setting both codes, i.e. exhaust or HO2S
> > issues not likely since it's dual exhaust with dual cats.
> >
> > I've replaced the fuel pump recently and the tank interior was spotless,
> > so clogging / contamination is not likely. I just replaced the FPR and
> > it's filter screen was clean as well. The FPR did fix pressure leak down
> > on pump shutoff, but that seems to not have been a significant issue.
> >
> > I did plugs/wires/cap/rotor while I was at it this last service
> > Saturday, and the removed plugs all had moderate tan deposits that seem
> > consistent with the 130k or so on them. I also cleaned the IM passages
> > and ports while things were apart.
> >
> > I do have freeze frame data from the trouble codes as noted below:
> >
> > Closed loop / closed loop
> > Calc. load 19.2%
> > Coolant temp 167F
> > ST1 0.7%
> > LT1 24.9%
> > ST2 1.5%
> > LT2 24.9%
> > MAP 17.4 in/hg
> > RPM 2521
> > MPH 65
> > MAF 7.152 lb/min
> > TPS 20.7%
> >
> > No trouble codes other than the P0171/P0174 have ever been set.
> >
> > Any ideas where else to look?
> >
> > Thanks!
>
> Are you certain that the fuel trims for -both- banks are positive?
> (not one positive and one negative?)

Yes, that freeze data is correct, and consistent with the freeze data
from other times the codes have set (always both P0171 and P0174).

> Have you tried cleaning the mass airflow sensor?

Yes.

> Fuel filter?

Replaced last pump replacement. Tank spotless, pump screen near spotless
(and replaced), FPR screen spotless, pretty unlikely anything is
clogged.

> Disconnected and plugged the PCV and vent and checked for vacuum leaks
> between the intake manifold and crankcase?

No, but the upper IM has new gaskets now.

> Any coolant loss?

No.

~199,500 miles BTW, all on M1 synthetic.