Cool weather brings on P0171 bank one lean

[ChrsLytn]

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98 k1500 5.7 321k miles
I don't know if this screen shot is cooperating.

LTFT 1 is 19.6% LTFT 2 is 15.2%
These mean extra fuel is being added to trying to correct the lean condition.
Is that right? And it could be a half dozen or more possibles? From an exhaust leak to an intake leak. I bought a hand vacuum/pressure pump. Is it good for finding a vacuum leak? How would I go about hooking it up? Thanks

 

[skylark]

You need a can of any spray fluid. It will suck in the vacuum leak and cause a change in how it runs. I like using flammable brake cleaner because it is clean and picks up rpm. A spray bottle of water will do it too though, it will suck the water in and cause a stumble.

 

[ChrsLytn]

Yeah,I've done that. Never hit on anything. Sometimes it sounds like I hear a quiet, kinda high pitched whirring going down the road. Not a whistle though. Is there anything that would do that going down the road more so than at idle? And cooler weather definitely makes the SES get active. It turned itself off yesterday. But it runs rich. Good but rich. No bogging, no skips. Tends to be 171 and 174.

 

[RawbDidIt]

You need a vacuum guage. They're about $20 at the parts store. You hook it up to any vacuum port in the intake to read it. With it reading lean on both sides you can eliminate most causes. Exhaust leak is not likely to be on both sides, two O2 sensors are not likely to go out simultaneously. Not likely to be fuel injectors, but if you're still on the stock mechanical injectors, can't rule it out entirely. It's likely a vacuum leak as discussed. Could also be low fuel pressure, so a fuel pressure guage for fuel injected engines as they operate at higher pressures.

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[stutaeng]

BOTH banks being lean is mostly always going to be a fuel delivery issue. The one with 15% is right on the line where the SES light comes one, the other one being a tad higher...

What's the fuel pressure? Check at key ON/engine off, at idle and at high RPM...report those numbers.

Also, if your scanner has live data, check the fuel trims at idle and under load. If they stay lean as RPM increases, you can most likely rule out vacuum leak...

 

[ChrsLytn]

KOEO 55
Idle 50
Idle 650 rpm slowly to 2k rpm stayed 50
Rev it up it goes to 60

At idle
LTFT1 4.7
LTFT 2 -1.6

RPM up to 2k B1 10.2
B2 5.5

Back to idle
B1 3.9
B2 -3.1

I'm about to hook up my vacuum gauge and see what it does.
Thanks for your help.

BOTH banks being lean is mostly always going to be a fuel delivery issue. The one with 15% is right on the line where the SES light comes one, the other one being a tad higher...

What's the fuel pressure? Check at key ON/engine off, at idle and at high RPM...report those numbers.

Also, if your scanner has live data, check the fuel trims at idle and under load. If they stay lean as RPM increases, you can most likely rule out vacuum leak...

 

[stutaeng]

KOEO 55
Idle 50
Idle 650 rpm slowly to 2k rpm stayed 50
Rev it up it goes to 60

At idle
LTFT1 4.7
LTFT 2 -1.6

RPM up to 2k B1 10.2
B2 5.5

Back to idle
B1 3.9
B2 -3.1

I'm about to hook up my vacuum gauge and see what it does.
Thanks for your help.

Not sure what some of those values are, but the LTFT don't actually look out of the ordinary. What is KOEO? What is the first 50 number at idle?

 

[RawbDidIt]

Sounds like his fuel pressure at idle vs key on engine off

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[ChrsLytn]

Not sure what some of those values are, but the LTFT don't actually look out of the ordinary. What is KOEO? What is the first 50 number at idle?

Fuel pressure
Key on eng off is 55
Idling 50
Goose it and pressure goes up to 60

The other morning it got down to about 37'. SES came on and I got the 171 code and it said 174 pending. Couple of hours later it had warmed up and SES light was off . When it does that I tend to think it's something to do with the intake/plenum. Plastic contracting in the cold temperature or something. **** if I know. It did this crap last winter off and on. Come spring and summer it'd be ok, other than running rich. It has new style spider injector assy. that's about two years old.

 

[stutaeng]

50 psi idling sounds a tad too low.

Those SES lights come and go on these codes. Sometimes the SES light goes off, but code is always stored or pending.

Is the fuel pump original?

I've got a basic fuel guage with a short hose. It's good, but wish it had a long hose. The professional fuel guages like MAC have long hoses. Hook it up and give her the beans on a uphill. Maybe it doesn't supply enough fuel under those conditions, which would definitely be intermittent. That would be consistent with the codes getting activated only sometimes. I think they sell extensions for those fuel guages?