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From: Pete C. on 13 Jul 2008 20:58

'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!
From: boxing on 14 Jul 2008 05:28
does it run ok? did you do a fuel pressure check? It is possible to
have a bad fuel pump right off the shelf. I came across these things
on the web. This info is for Ford but I don't think GM would be much
different.
P0171 - System Too Lean (Bank 1) P0174 - System Too Lean (Bank 2)
The Adaptive Fuel Strategy continuously monitors fuel delivery
hardware. The code is set when the adaptive fuel tables reach a rich
calibrated limit.
Fuel System:
· Contaminated fuel injectors
· Low fuel pressure or running out of fuel (fuel pump, filter, fuel
supply line restrictions)
· Vapor recovery system (VMV)
Induction System:
· MAF contamination
· Air leaks between the MAF and throttle body
· Vacuum leaks
· PCV system concern
· Improperly seated engine oil dipstick
EGR System:
· Leaking gasket
· Stuck EGR valve
· Leaking diaphragm or EVR
Base Engine:
· Exhaust leaks before or near the HO2S
· Secondary air concern
Powertrain Control System:
· PCM concern
From: Steve W. on 14 Jul 2008 09:01
Pete C. 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!

Any common items when the code is set? Something like the codes set when
your driving uphill, or only after you fill up at a particular gas
station? Only when the A/C is on while going uphill?

I take it the codes have set after you replaced the FPR? What is the
running fuel pressure and how is the flow rate from the new pump?

--
Steve W.
Near Cooperstown, New York
From: Pete C. on 14 Jul 2008 10:32

"Steve W." wrote:
>
> Pete C. 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!
>
> Any common items when the code is set? Something like the codes set when
> your driving uphill, or only after you fill up at a particular gas
> station? Only when the A/C is on while going uphill?

No hills in this part of TX. I've not noticed and correlation to a
particular situation, most driving here is level 70 mph or so with A/C
on.

>
> I take it the codes have set after you replaced the FPR? What is the
> running fuel pressure and how is the flow rate from the new pump?

They've set and pending set in the ~40 miles since the FPR change. I've
not tested the flow rate. The pressure runs about 55psi at idle and will
peak up to around 65psi when you blip the throttle and the change in
vacuum boosts the pressure.

Thanks
From: aarcuda69062 on 14 Jul 2008 21:51
In article <fxxek.12414$cW3.4359(a)nlpi064.nbdc.sbc.com>,
"Pete C." <aux3.DOH.4(a)snet.net> 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?)
Have you tried cleaning the mass airflow sensor?
Fuel filter?
Disconnected and plugged the PCV and vent and checked for vacuum leaks
between the intake manifold and crankcase?
Any coolant loss?
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