My 5.2L was running then while driving abruptly turned off. Then I... swapped the fuel relay with the horn relay and horn worked, but wouldn't start...checked for spark at coil. theres spark...checked for spark at the spark plug and it wanted to start, but it wouldn't??...after replacing the first plug wire and pulling off the next plug wire, it started up and stayed on and idled just fine....then after immediately driving for about 2 miles, it turned off.???...I then tried starting it, but it wouldn't start, so I pulled off the same plug wire I removed before and it started right up. I was able to drive it home for another 4 miles and it ran fine and never turned off again...that was a couple of days ago and it continues to run just fine. My question is: Do I have a fuel pump problem (but it runs just fine now) or a spark problem now? Please any insight would be appreciated. Thanks.

 

Could be a bunch o' stuff. Failing cam or crank sensor, bad O2 sensor..... (not as likely) bad ignition switch, bad battery..... dirty connections at the battery, or alternator, crummy ground....... Pick up a noid light at the parts store, and the next time it does it, (and you just KNOW there WILL be a next time...) see what's missing, spark, or injector pulse.

 

I haven't checked for a failing cam or crank sensor yet (don't really know how to test it) and I forgot to mention in my original post that over the past several months, the check engine light had been coming on (TCode P0138) but I would erase it with a pocket scanner. Prior to the CEL coming on (many months ago) I had R/R one O2 sensor (above the tranny). During this running and not starting and now running problem, the CEL light has not come on.

Would it be wise to not go out at this time and buy a replacement fuel pump at this point? or wait until this problem happens again and use the noid light to test the injectors first or could the O2 sensor be the problem all along?

 

As long as the pump is running and has good pressure (and the truck runs fine, so the filter/screen should be in good shape), you shouldn't replace it...unless you like throwing money around.

Do what HeyYou said and check the spark and injector pulse first. And clean the battery terminals and test it for fun.

 

I will hold off on the fuel pump (don't really have a lot to blow) and I'm so forgetful (only sometimes). I did R/R the battery a short while back because it was aged and wouldn't hold a charge, so I'll scratch this off this list. Noid lights it is. Thanks.