Intermittent misfire, stall, and no-start condition

[jrschatz]

thanks for the next steps —- I will tackle these when I get a chance and report back.

- jeep is a '99

- I haven't tested cam sensor...as far as I know it is the original

just ordered the cam sensor, tune-up kit, and ignition coil

 

[jrschatz]

just as a note I will say I've monitored open vs. closed loop & it goes into closed loop pretty quickly (within about 5 minutes), and the issue usually does not surface until about 15 minutes. It hasn't ever seemed to correlate with open/closed but I will try your suggestions for sure...

 

[ItchyDong]

Yeah, the open loop thing is unlikely, but that's troubleshooting. You can keep throwing parts at it, or you can isolate exactly what you're missing. 99% of the steps in troubleshooting are going to be wrong, but they eliminate a concern, cost nothing, and helps hone in on the actual problem.

Also, unless these parts are OEM, you're likely to introduce new issues. Stop throwing parts and figure out what you're missing before you chuck anything else at it.

Doesn't yours have a distributor? Don't take my saying "coil" as a reason to throw a pickup at it. Later years use a one piece coil for all 6 cylinders. This is why providing the year, engine, tranny are applicable. Basically, I was just saying "check for spark" when it fails.

 

[jrschatz]

I'm not trying to throw parts at it, trust me..... It's not a daily driver so I wasn't pressing to get it back on the road and was trying to take my time and troubleshoot step by step, but after months of no results I was running out of options.... also aware of the fact that 'new part' doesn't necessarily mean 'known good part'.....


it is a '99 2.5L 4-banger manually transmission — which has the distributor with one ignition control for all 4 plugs...


During the crank/no-start I have checked and confirmed that I have spark and fuel pressure at the rail. It almost seems as though it is flooded at that point...

 

[jrschatz]

update on this issue.....

short answer: the problem seems to be a poor connection of the throttle position sensor at the PCM


how I found it:
In an effort to troubleshoot, I wanted to check the signals from my crank and cam sensor again — but this time I decided to do it at the PCM by back probing the connector to make sure it wasn't an issue in the wire harness. While checking the pin-out diagram, I decided as might as well back-probe the TPS wire as well at the PCM. In doing so, I noticed I was not getting good continuity from the back of the probe to the front pin.... after fixing this, the issue seems to have been eliminated. I test drove the jeep for 25 minutes and could not replicate my stalling issue.


hopefully this is a final solution.... this ultimately was a patience-testing endeavor but I definitely learned a lot about electrical & sensor troubleshooting.

Hope this helps someone — thanks again for all of the suggestions