Lean codes mystery - O2s replaced, no vac leak, MAF okay

mlnnc

mlnnc

Well-known member
Mar 23, 2008
267
31
Charlotte
A friend I've been trying to help has been chasing codes on his '04 DII for a long time with no luck (P0171 and P0174, system too lean banks 1 and 2).

He's changed O2s a few times. We did a cigar smoke test but could not ID any vac leak. This weekend I installed the MAF from my truck in his and the codes persisted.

The only thing we haven't tested or changed is the fuel pump, but the truck drives just fine, including hard acceleration. I would expect that if it was the fuel pump causing the lean codes the engine would not perform well under hard acceleration.

A local mechanic who is known for his expertise with DIIs is scratching his head too. He suggested it could be a bad ECM. Have any of you encountered this situation and found the problem to be a bad ECM? And if so, would an ECM from another 4.6 SAI truck be swappable without reprogramming? Thanks.
 
KyleT

KyleT

Well-known member
Mar 28, 2007
6,059
8
39
Fort Worth, TEXAS
O2 won't fix those codes alone normally. Check for vacuum leaks, do a fuel injection cleaning with b&g or some other one that hooks up to the fuel rail. Can also try to take the O2 plug apart and clean it. They do funky stuff once oil gets in the connector.
 
crown14

crown14

Well-known member
May 11, 2006
6,288
4
Clayton, NC
I agree oil in the harness near the O2 connectors is quite common

Also, pull the sensors, wire brush the bungholes, and reinstall with COPPER anti seize on the threads.
 
J

juramico

Well-known member
Mar 6, 2005
175
0
LONG ISLAND NY
Make sure the O2s are Bosch. From my experience, the aftermarket ones from AB never took care of those codes. I had 3 sets ent to me before the lights went away.
 
mlnnc

mlnnc

Well-known member
Mar 23, 2008
267
31
Charlotte
P.T. asked about miles and state of tune. The truck is at ~150,000 miles. The owner's son installed new plugs and Magnacores a few years and maybe 35K miles ago. No misfire codes, and the truck seems to run well and strong otherwise. The O2s he's used are all Bosch 15175s from Advance. And yes, the connectors are clean.

Injector-related solutions are an interesting idea, but would there not likely be other discernible drivability issues if it were a fueling problem?

Again, please, have any of you seen situations where the ECM was the problem, and can any DII 4.6 SAI ECM be installed and work fine w/o Testbook or other programming?

Thanks.
 
seventyfive

seventyfive

Well-known member
Jan 3, 2010
4,280
100
over there
you need to smoke test the intake manifold with a smoke machine not a cigar. Without knowing 100% that you don't have a vacuum leak you are wasting your time.

Do you have a scanner so you can watch the O2's? If so have you injected some propane to see if the front O2's go flat?

It's not the ecu.
 
jymmiejamz

jymmiejamz

Well-known member
Dec 5, 2004
6,008
361
35
Los Angeles, Ca
I've seen a couple of DII's that have cracked injectors in the past year or so. If you pull the injectors it would be easy to spot. When you say the connectors are clean, did you remove the white piece inside of the connector and clean it thoroughly with brake clean? If you didn't you need to do that. I've fixed a bunch of O2 sensor faults on DII's by just cleaning the connectors out.
 
mlnnc

mlnnc

Well-known member
Mar 23, 2008
267
31
Charlotte
Seventyfive (and others), thanks for your input. My friend is out of patience and not willing to spend much more chasing diagnoses. He REALLY wants to sell the truck and be rid of it.

I watched the O2 activity with my UltraGauge only, and the fronts come and go intermittently. Please elaborate on your inject some propane suggestion. Where? And how?

And jymmiejamz, I'll suggest that my friend clean the O2 connectors again carefully. He's actually become pretty adept at dealing with the connectors after changing the O2s so many times. Not sure if he'll want to go so far as pulling the upper intake to check out the injectors.
 
pdxrovermech

pdxrovermech

Well-known member
Jul 3, 2009
1,807
57
Portland, OR
start by spraying carb/brake cleaner around the plenum, injectors, and intake manifold. I've seen 2 warped plenums from over tightening in the past year.
 
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