Hi Guys
I have a 99 Cherokee 4.0 auto that has been giving me problems. About a week ago it started a intermittent problem after it had been driven for a while and was parked. When I went to restart it, it spit and spurred and it sounded like a vacuum cleaner under the hood. I found that the air valve was not opening, flooding the motor. I would turn off the ignition, wait a minute and it would restart fine.

A few days later, it did this but after I turned off the ignition, it would not restart or even try to fire. I did not check but it sounded like the motor was not getting spark. I let it sit for a hour or so but it would not restart. It was in the evening and I could not leave it in a parking lot, so i towed it home. The next morning it fired up fine. It has a rebuilt ECU with a lifetime warranty, so I sent it for a replacement, thinking this may be the problem.

I installed the replacement ECU and the same thing happened today after driving it for a few hours. I left the jeep in a parking lot and came back it 2 hours. Luckily it rained and cooled everything off. The jeep fired right up.


Anyone have any ideas ?

 

I had that problem with my '94. Turned out to be the computer. Try icing the computer next time it happens.

 

Maybe the ignition coil is going bad?

 

I'm just plain curious what you mean there. "Air valve"...

I'm about to put it in my signature. I own two 1990 Renix Jeeps, (one for over 13 years), with a different type of CPS. Both, occasionally will present me with a no start that is resolved by simply unplugging the connector and putting it back. We can test the pre 91, and they both test OK.

Just putting that out there. Maybe try that on your HO and see....

 

go to auto zone and have them hook it up to a scanner thing and see what that says. they do it for free. my 97 started doing that last summer. i changed the fuel pump and a few other things. took it to a friends shop, he hooked it up to his scanner thing. ended up being the crank position sensor on my 97.

 

He didn't fill out his info. In CA and Hawaii they won't read your codes free.

 

The air valve is the idle control air valve on the throttle body. When the jeep died the first time, we did ice the ECU down, still no start, I disconnected the battery and un plugged the ECU for 10 mins, still not start. The check engine light did not come on and the auto zone guy said there are no error codes,
It has a newer accell coil, cam sensor, crank sensor, ignition switch and fuel pump. Unless I got 2 bad ECU's in a row, there is got to be something I am missing.

 

Was the crank position sensor aftermarket or dealership? I ask because there is a lot of discussion around weak magnets on aftermarket units failing to send back the right signal. Have you checked to see if you are getting spark?

 

that is true, i went through 2 napa ones. they would only last a week. some dealerships say they are on a national back order but you can find them. i got one from a small town dealership over in new hampshire.

 

I have a spare crank sensor that i will give it a try, I am going to crank it up and see if it will get hot enough to affect what ever is causing it not to restart.
I tried to get a new ECU from the jeep dealer and he said they are no longer available.

 

You do not have an ECU problem.

 

The ecu would not likely cause a temp related starting issue. Stick with the basics first. Spark, Fuel pressure, CPS as they are much more likely to be an issue.