95 wrangler 2.5L....First happened a month ago, first drive of the morning 4 blocks from home engine died. Would crank but not start. after sitting a minute or so it would start and run while sitting still, but die when I drive. Pulled it home, next morning bought a fuel filter (quick and easy optomism) before installing it everything ran normal, after installation, test driving around the neighborhood, hit speed bump, died, started back up and has run without issue for a month.
Yesterday, hit bump on the way into gas station, quit. Put gas in, started and ran fine for 20 minut drive, till I hit a rough road, died, again, would crank but not start, after 1 or two minutes, started fine and ran 3 blocks to friends house where it now sits while I work.
Any ideas where to start with this hard to duplicate intermittent problem!!! PLEASE!!
Maybe pull the batt cable while running and see if the alternator keeps it running. Could be a loose bad cable on the battery as well enough to crank but not enough to start. Happened to me once she would crank and crank. Turned out to be my negative cable wasn't tight enough to the post.
If hitting a bumb is doing it then you need to get under the hood and under the chasis and shake the harness while its running to see whats killing it. Make sure you check the harness going back to the tank. It could also be fuel. Hook up a pressure guage to the fuel rail. It should have 31-39 psi. Drive it until it happens.
Battery cables seem good and when it dies I still seem to have electric elsewhere. Do to the intermittent nature of the problem, I have yet to determine if it is fuel or spark. I will say that I hear the pump run when I turn the key, even when it wont start for that 1 or 2 minutes.
The answer to your question is a definitive....maybe. The diagnostics were in the infant stage and are OBDI. They have ranges they look for and if something fails out of the range it will throw a fault code. The problem is that sometime things fail in range and dont set a code. The newer OBDII starts looking at rates of change to detect just that kind of issue. So, if you have any codes other than the usually 12,33, and 55 you have an issue. If you dont have a code and its running bad....you have an issue. The bottom line is, you have an issue. LOL
As always you are all. Very helpful, please keep the great advice coming, but the bottom line is it is hard to test or trouble shoot from 2000 miles away, I'm sure one of you have the answer and I will fix it tomorrow (optomist)!
Also if you have a loose connection and can't locate it try looking for it at night with no light and do the shake, wiggle, bounce test since it will probably arc and seeing that in the dark would be real easy