P0171/P0174 Help!
in [Technical]
|
From: Pete C. on 15 Jul 2008 00:02 aarcuda69062 wrote: > > 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?) 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.
From: mr158912 on 15 Jul 2008 20:01 intake gasket leak maybe "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!
From: Pete C. on 15 Jul 2008 20:07 mr158912 wrote: > > intake gasket leak maybe Well, the upper IM was just off and now has new gaskets. > > "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!
From: ben91932 on 16 Jul 2008 00:55 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!
From: mr158912 on 19 Jul 2008 17:16
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! |