Help! Truck still shutting off!

ouh, what truck, what year, what engine?

 

Have you checked the coolant level?

Just sayin'

 

Deffinatley sounds like it might be a bad ECM, but have you actually tested the batteries??? it could be that the battery your ECM is powered up by has a bad cell and it does not maintian enough power first thing in the morning to run the ECM, but does fine after your altenator has charged the batteries for a few hours....but that is just a possiability.

 

You might consider the fuel solenoid.

 

This is a Star right? Replace the fuse holders for the ECM power. I had a problem like this as well. Also, have you checked the connector at the ECM? When truck is cold but running, try wiggling wires and connector and see if it shuts down. I, stupidly, when diagnosing the fuse problem stuck the multimeter probes in the ECM plug's terminals, which caused intermittent ECM power loss as well. A little tin foil in the plug terminals provided a quick fix, but a new plug was in order. When I put the new plug on, I ran new power wires to the firewall, as the previous owner already had done a halfass job of it already.
Altogether between ECM plug, wires, fuses and holders, you should be under $20, so why not do it anyway to see if it works.

 

Well if I was a betting person which I am not that sounds like engine speed sensor fault. They had a tendency to not log faults. The other question I have is when you turn the key on during this no start condition does the check engine light come on. CAT went thru several engine speed sensors because of erratic signal causing engine shutdowns. (the tolerance and cam movement would actually cause a shadow signal that shut the engine down) I believe the latest engine speed sensor for that engine had a green tip and required a shim washer which corrected the tolerance and air gap issue. .

 

Floyd: When you said you wiggled the wires and it shutoff.. Where were you moving the harness at? If it was just above the ECM there is a junction where all of the five volt reference wires splice together and it has been known to lose its crimp and cause the shutting off/electrical problem. There is actually a wiggle test in CAT ET that allows you to put the ET in a test mode and as you wiggle the harness it will record the event. There is a mechanical sensor push pull test for the speed sensor, can't remember exactly what it is this moment. There is an adjustment on that sensor. If I remember correctly, you must align the cam gear in the sensor window so you see a full tooth. Gently pull the sensor probe out to full extension. Leave the o-ring and washer off the new sensor and install the sensor to snug tightness. This will set the initial air gap adjustment. The washer gives it the necessary air gap tolerance that corrects the ghost reading by the sensor. Remove the sensor, reinstall the washer and oring and install the sensor. You really should have the sensor calibrated for cam to crank calibration. The engine will run, just not sure it will be 100%.