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.

[06JeepXKHEMI]

You would think but my dad and I would find jeeps with same problems and most of the time those were culperates. One grand cherokees we bought was an 07 with 48k on it owned by this old lady that poured money to fix it and all we did was hold at 2500 reset ecm and done

[Matt]

Good stuff. Interested to see if that fixes Nick's issue! Regardless, i'll add that trick to my toolchest :)

[06JeepXKHEMI]

Yea I'd be interested in what fixes it to, it's how we learn!

[The_War_Wagon]

Plugged catalytic converter? Seen a LOTTA those lately...

[Synthetic Advantage]

Well I was able to get over to his house and crank it up, ran it up to 2,500 for a minute and then let it idle. Funny thing is it ran great, nice and smooth up to about the 47 second point then it started to run rough and I had to gas it to keep it up to 2,500 on the rpms for the rest of the minute. We sat there and let it run for about 15 minutes. Didn't get a chance to get it out on the road. I told him to also get a scan tool and hook it up and see what the readings are on the coolant temp sensor. So he is gong to do that as well. The thing has 227k on it. The post above about a clogged cat makes sense with that many miles on it. So that is something else we will be looking into.

Thanks for all the help, when I find out more on how it is running I will let you know. Like posted, the more we find out what causes what, the better one becomes at troubleshooting. :)

Thanks again.

[06JeepXKHEMI]

Awesome keep us updated on it.