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.
.

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