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Trying to diagnose this new to me mighty max, been threw a few people who couldn't get it to run when I acquired it for free , I've replaced the IAC on the throttle body and had the ecm rebuilt and installed a new mpi relay just below the ecm. Truck will start without hesitation, idle up for a couple seconds then die off. Any thoughts on where to focus my time? Thanks in advance! Truck ran fine before original ecm fried. Been sitting for a couple years.
Try fooling around with the throttle position sensor.
unplug the MAF sensor, also try the cam position sensor.
Ok so still cant figure out the issue, ive been all over the engine compartment checking grounds, checking MAF and TPS......the only way I can get it to stay running is by taking test light to ground and probing the red/white wire on either the ecm or engine control relay.....at that point truck stays running but stays at a high idle 3000rpm. Any other thoughts?
Try to find out when it first stopped running and then what happened just before that.
I just saw this advice in another thread.
If you can't find out how it stopped running check that timing is set right bring it to TDC and make sure the timing marks are in the right place, if they are then the rotor is pointing to the right cylinder wire.
I'm having an identical issue with the same 1991 4x4 3.0 motor. It sometimes dies shortly after starting ussually after a 1.5 hr trip. I'm thinking a slight squeaking noise is my belt and could also be messing my timing.
Is it possible that a loose belt can throw off timing that may cause the motor to petter out and die after starting/running hot?
If a timing belt jumps it throws the timing period. It normally will strip a few teeth out of a section of the belt and then grab again but once that has happened, it's game over and time for a new belt (hopefully without a bunch of bent valves...)