94 FZJ80 will not set codes (1 Viewer)

[Matthew Spencer]

I have been having a recuring issue with my 94 (OBD1) cruiser. It will intermittently throw a CEL and go into limp mode. The issue I am having is that it will not set the code after I shut it off so I can not read the code to find the fault.

It only happens when the truck is started and before it is up to operating temperature. Even if I warm up compliantly it will sometimes still throw the code.
Beat of all (insert sarcasm here) it is intermittent.

Here are some of the changes that have been made.

O2 sensors in the exhaust manifold
Single aftermarket cat (deleted duel cat setup)
"air" pump disabled.
EGR disables and resistor installed in harness.

Any ideas on where to start will be appreciated.

 

[Malleus]

The system description is provide below. Although it's not named a sensor, the VAF is a sensor.

 

[Malleus]

Based on your description, the code has been "set". You're clearing it when you turn of the ignition and you don't see it again because the problem doesn't exist.

Next time, try jumping the DLC1 terminals, while the MIL (check engine light) is lit, and see if the code flashes on the MIL.

 

[Malleus]

FWIW, this is the only mention of the engine related fail safe mode in the FSM. The ABS system has a fail safe mode, and so does the automatic transmission. You can search the most excellent recent posted FSM (thank you @SmokingRocks) for "Fail Safe" and read through the non-engine related conditions for yourself.

 

[Matthew Spencer]

Thanks for the ideas and information. I did not know that you could check the OBD1 codes when the engine was running.

 

[Malleus]

NP. FWIW, my SST is two paperclips and an alligator test lead.

 

[Matthew Spencer]

NP. FWIW, my SST is two paperclips and an alligator test lead.

Mine too!