Re: P0171/P0174 Help! *update*

Mike Romain wrote:
>
> Pete C. 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!
> >
> > After erasing the previous codes and logging another 140 miles or so, I
> > have yet another set of P0171/P0174 set and another pending set. New
> > freeze data is as follows:
> >
> > Closed loop / closed loop
> > Calc. load 10.1%
> > Coolant temp 172F
> > ST1 17.9%
> > LT1 24.9%
> > ST2 21.0%
> > LT2 24.9%
> > MAP 17.1 in/hg
> > RPM 1489
> > MPH 28
> > MAF 3.875 lb/min
> > TPS 12.9%
>
> In my opinion, the folks that sold you the scanner are laughing all the
> way to the bank along with the mechanics that live in your area.
>
> I think those things are sucker tools.....
>
> Does the vehicle run OK or not?
>
> I mean it's over ten years old and the mini pins on all the sensors only
> pass computer signals which means tons of intermittent failures 'show'
> on these foolish tools without meaning squat as far as running goes.
>
> A good spray with an electronic contact cleaner on all the plugs and
> sockets for the sensors on an old vehicle can do wonders for them.
>
> They 'really' are a 'sucker tool' you know....
>
> Just my $0.02,
>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 'New' frame in the works for '08. Some Canadian Bush Trip and Build
> Photos: http://mikeromainjeeptrips.shutterfly.com

Well, the scanner was very cheap and does quite well within it's limits.
It displays and clears codes and displays associated freeze frame data,
which I think is worth the $60 or so I paid for it.

As for mechanics in my area, after several years of searching for a good
one, I concluded they all work for race teams, so I DIY everything.

I could see an intermittent connection causing a stray code, but this is
a consistent issue and clearly shown in both the short and long term
fuel trim values.

As for how the truck is running, generally ok, but I haven't pulled a
heavy load in the past couple months, so I'm not sure how it would do at
more than 20% load.

As for age, I'm no longer in the rust belt, I have much better shop
space and it's a 3500 dually, so it doesn't wear all that fast in the
mostly light service it gets. I have no plans to replace it any time
soon. The gas savings calculator on edmunds.com says trading it for a
hybrid would save me money in 54 years, my calculation was more like 25
years, but clearly there is no good reason to replace it.

Sounds like a big vacuum leak common to both banks.
Can you do a propane test?
HTH,
Ben
>
> No trouble codes other than the P0171/P0174 have ever been set.
>
> Any ideas where else to look?
>
> Thanks!

it seems to me you have a vacumm leak of some sort either intake
plenium/manifold gsaket or egr valve and maybe evan a pcv system leak
but looking at your posted data even without o2 data i must ask if you have
a cold air intake kit with a k&n filter the oil from them plays hell with
the maf sensors
i would expect to see a little more maf signal at 1400rpms
mike the days of your kind of repairs and troubleshooting are going away
fast
"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!