Cold Start in CL-Using O2 Sensors...

[1999]

I have a 99.5 Expy 5.4L EB 225,000 MI, changed Plugs and COP less then 50,000 mi ago.

Recently I had a OL-Fault and after warm up it won't switch to CL.
Now during cold start, it starts out in CL, everything is running fine. Then at ~120 degrees it switches to OL-Fault. Starts sputtering, pull off road, restart then it runs okay but still in OL-Fault
O2 sensors are firing off fine and trim is responsive to acceleration and deceleration while it's cold. Once it hits ~120, switches to OL-Fault and starts sputtering and loses power. I've exhausted the vacuum line search. If there is one it would have to be micro.

I have Sea Foamed vis the vacuum line, short term results but still OL-Fault
I have Sea Foamed the TB and had good results (i.e. Ran in CL after treatment for about 10 mins).

BTW, No Codes have appeared, No CEL, checked every fuse in box fuse boxes, tracked down and did fix 3 vacuum leaks (no results).
This all occurred like a switch flipped, fine one day and running rough/sputtering the next.

I'm leaning toward IAC or EGR(even though no codes or CEL)...Thoughts.

 

[docraymund]

Check the coolant temp sensor.

 

[1955moose]

Did anybody besides you work on vehicle lately? Are you sure your port for checking codes is powered and functioning? If you've got. No power to the port, you won't get codes. A problem as drastic as yours should be shooting a code.

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[1999]

Check the coolant temp sensor.

Via the OBD2 scanner hookup, live data, my air temperature sensor and Engine temperature are reading accurately. Engine temp tops out around 190 degrees.

 

[1999]

Did anybody besides you work on vehicle lately? Are you sure your port for checking codes is powered and functioning? If you've got. No power to the port, you won't get codes. A problem as drastic as yours should be shooting a code.

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Yes, my transfer case motor failed and was replaced by a local garage. He also replaced the speed sensor due to the odometer reading 3X actual speed (both issues occurred at the same time)
I agree it should be throwing codes, that's why I'm so confused. I'm sure I have power because I'm able to pull live data such as fuel status, trim, O2 sensor Voltage.
It's like the Expy is in opposite world where it is starting in CL then switches to OL after warm up.

 

[1955moose]

It's possible he pulled something related to the computer, or maybe shorted something out, due to not disconnecting battery. As much as we love a challenge here, see if you can get them to repair your problem. It's always fun trying to figure out what a prior shop did to a vehicle. They could have shorted out your ecm or bent some pins somewhere.The speed sensor or plug, might be a place to start.

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[1999]

Yeah, that's what I've been trying to avoid. Other then the TC motor, I've done all my own diagnose and work. This one has driven me to the edge. Last resort was input from the gurus on the forum.
I've been a long time member and gathered some great information.
Thanks for the input. I'll post what the garage finds.

 

[1955moose]

It always amazes me how an experienced shop, even a dealership, can gum up the works, by doing one thing, then totally screw up the rest of vehicle. It gets posted here all the time. Simple basic things like disconnecting battery before repair, or don't tap into existing electrical items. But they do continuously. Oh well, if it wasn't for these screw ups, we'd have nothing to chat about!

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[1999]

As promised I am back with the fix. I was beating my head against the wall looking at too much air making a lean condition. I gave up, no codes, no SEL, nothing but the condition of starting in CL and after warm up switching to OL-Fail.

Took it to the garage I trust and told them everything I went through. They kept it for a couple days, they got no codes either. Ran it through its paces and tested the fuel pressure. That's right, bad fuel pump. So the moral to the story, don't get fixated on one thing...keep an open mind...In the end it's fixed. Mileage has increased from 9 MPG to close to 14 MPG (City/Highway mix) so I'll pay for that fuel pump quickly.

 

[1955moose]

Well now you know why all of us bedrk, stamp, myself, always recommend a fuel pressure test with any driveability issue. I've seen vehicles that you'd swear had an electrical issue, just to find out it was fuel. Sometimes it's doesn't make sense, how messing with something else totally unrelated, causes another system in the vehicle to act up, but I've run into into it more times that I can count. The fun part is trying to sell the customer on the new issue. It's supposed to be, but its not always a predictable science. Glad you got it right. Moose

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