This has been one of the most frustrating repairs we have come across. One day the Jeep just plain refused to start anymore. We have had prolonged starting times for a while now where we will let fuel pump prime at least twice before it would start, but it would always start. Nothing really precluded the no start condition, we just turned it off one day and it didn't want to start again. The symptoms don't really point to any particular component (other than the PCM) and without some fancy tools, you'll do exactly what we did - replace the PCM... and it won't fix anything. So we took out our fancy tool, looked up some diagnostic diagrams on alldatadiy.com, and got to work.
A few things to check for right away to see if you're having the same issue we were:
- Check to see if the fuel pump runs during cranking - ours didn't
- Check for spark during cranking - we didn't have any
- Check to see if your check engine light is on (ours WASN'T)
- Check your voltage and fuel gauges with the ignition on - ours didn't register anything
- Check to see if your low fuel light is on - our was
Now, we see the bus is up, the PCM appears to be down - so we replaced the PCM. Unfortunately replacing the PCM did absolutely nothing for us other than lighten our wallets. At this point, we did some digging on AllDataDiy for an appropriate troubleshooting test to figure out what on earth was going on. While I can't re-publish their content due to the ToS agreement, I can tell you how we arrived at our final solution.
Now, the troubleshooting procedure we started out with had us unplug the ECM at the beginning and then test the TPS pin 3 voltage - but these pictures are from us reproducing it after the fact and we forgot to unplug the ECM first... so we logged a code:
I mention this code just as a side note - we cleared the code with the EVO, but if you just ignore it long enough it'll go away after a few cycles.