P30 454 TBI - Code 44

[thesameguy]

I've got a '93 P30 motorhome that has started lighting the CEL periodically while cruising at freeways speeds. There didn't seem to be any rhyme or reason - and no drivability issues seem to go with. On a recent trip, I brought along my Tech 2 to see if it could help pinpoint the issue.

Drivetrain is mostly the same as a similar-year 2500 - 454TBI, 4L80E, etc.

Things I know:

The code is always "044" - lean exhaust

O2 sensor voltage hangs out around 100mV, which is obviously quite lean

When the light trips, voltage drops to 0 mV (!), then spikes up to 500mV, then returns to 100mV and the light goes off

Before, during, and after the light drivability is not impacted

Other sensors (TPS, ECT, MAP) all seem reasonable. This is speed-density - MAP, no MAF, right?

No other sensor seems to correlate to the O2 sensor or code - at steady throttle, they are steady, but the light may come and go

Tech 2 reports fuel trim is "Cell 10" - does anyone know what that means?

Fuel level doesn't matter - could be 1/4 tank or full tank or anything in the middle.

Engine has 90k on it. Nothing has been done to it other than routine maintenance (plugs, wires, cap, rotor, fluids, filters, etc.) That stuff is very much up to date with quality parts - nobody wants to get stranded in a 16,000lb monster.

I don't have a way to monitor fuel pressure while driving and there is no OBD reporting on pressure or injector duty cycle or fuel trims (other than the "cell") so that's a black box right now.

Replacing the O2 sensor is easy, but I'm wondering if anyone has any other experience with this code on this engine that might point me in another direction before I order parts? Replacing the fuel pump is daunting but anything else is up for discussion.

I'm pretty good with cars, but don't have much experience with TBI motors... I skipped from diesel to Vortecs. Any thoughts are appreciated!

 

[Supercharged111]

It's intermittent, so likely not the pump. I've had O2 sensors fail lean and fail rich, lying to the OBDII and having it not report a code at all. Drivability was garbage, but only at certain throttle positions. Next time it acts up, give it more gas and see if it goes away. If it runs good open loop, the O2 is to blame. I unplugged an O2 on mine to force open loop and no more black clouds so I replaced the sooty sensor and all is well again.

 

[Schurkey]

I wasted two years--on and off--trying to fix a "lean" condition at highway speed. Everything I tested seemed to be "good". AIR injection wasn't going to the manifolds, no ignition or misfire problems, no vacuum leaks, O2 crosscounts good at lower speed, etc.

After screwing around for WAY too long...I stuffed in a fresh O2 sensor to replace the one that had 80K miles on it.

End of problem. $13 plus my labor.

HOW OLD is your O2 sensor?

 

[thesameguy]

The light remains on for perhaps 30-45 seconds at a time. Nothing happens before, during or after as far as I can tell - the vehicle behaves totally normally at all times. Nothing I do seems to cause the light nor cause it to go away - playing with throttle and road speed neither prevents the light from coming on, nor go away... More throttle, less throttle, all the same.

No idea how old the O2 sensor is - could be original for all I know. Lacking anything better to go with, I'll give it a go.

 

[thesameguy]

I did a little more digging around, and here's where it is now -

I found both grommets in the valve covers were a bit worn, so I replaced them both.
I had no history on the PCV valve itself, so I replaced it too.
I used factory GM parts here, from gmpartsgiant.com (they've always been great)
I noticed that the rubber hoses to the air filter housing and from the PCV valve were old and hard, replaced them too
I installed a new air filter - truck has been out in the desert, so while the old filter wasn't actually very old, it was dusty
While installing the air filter, I noticed that the red (positive) wire to one of the injectors had, at some point, been crimped between the air filter housing and the "extension" - so I replaced the entire injector connector & wiring
While doing that, I noticed that both positive leads to the injectors are crimped together, and that insulation had failed at some point. I replaced the crimp and added marine heat shrink for insulation.
I replaced the O2 sensor. The old sensor physically broke on removal - it left its threaded section behind in the exhaust pipe! I tapped it out, and installed a new Bosch sensor.

Nothing here really screams LEAN MIXTURE but between air leaks (although with speed density it probably doesn't matter) and maybe poor a injector connection and questionable O2 sensor I've got hope. I haven't had time to get it back on the road yet, but hopefully this gets it back to right. Maybe I can find out this weekend.