Troubleshooting question

[Synthetic Advantage]

I have a good friend that has a 99 grand with the 4.0 and 223k miles on it. The problem he is having is that it will start up and run for about 10 min and then shut down. If you wait 20 min it will start back up but only run for 10 min and shut down again. He also said that the lights inside will act up where they will be on and then shut off and on.

So far he has changed out the fuel filter, fuel pump, plugs, and wires.

Any suggestions? Maybe the ECM is bad?

Thank.

[Matt]

Anyone hook a scanner up to it? What does it do when it cuts out... is it nearly instant or does it start sputtering and just cant recover?

I'd take a look at the coolant temp reading (not the dash, the ECM uses a different sensor) as a possible "quick" fix. Hook a scanner up and read the coolant temp on a cold morning before running it... temp should be near ambient. If its 40 degrees outside and the coolant temp is reading 90 degrees... i'd start there.

[Synthetic Advantage]

Thanks Matt, good start that I wouldn't have thought of. Hopefully it is something simple like that and not an ECM.

One other thing I didn't post so as not to confuse anyone, but he said that if you open and then close the door and walk away, the lights dim down like supposed to but then turn back on and then dim down again a few times. To me that sounds like a possible bad ground as well and don't see that being related to the ECM or could it be?

[Matt]

I'm treating that as unrelated for the moment. Lights are controlled through a different module... so unless it was a battery/charging system issue, its likely a different problem. However, if it was a battery/charging issue, it wouldn't consistently start back up after sitting for a period of time.

[06JeepXKHEMI]

With these Jeeps, sometimes you need to reset the ECM. Start and hold rev at 2500 for 60 seconds and itll reset it. Then he should be go to go

[06JeepXKHEMI]

Or its a bad cam position sensor or bad ECM

[Matt]

He's talking about a 1999 4.0L

[06JeepXKHEMI]

Yea I know, to reset the ECM thats the process. If that doesnt work its probably bad cam sensor or bad ECM

[Synthetic Advantage]

When I get back home I will have him give the reset a try. Thanks again.


Sent from my MaxiPad

[Matt]

Yea I know, to reset the ECM thats the process. If that doesnt work its probably bad cam sensor or bad ECM

I guess i've just never seen a bad ECM or bad cam sensor let an engine run good for 10 minutes and shut down. then repeat; normally it'll run like crap or not run at all.