I have a 2002 Grand Cherokee with 225,000 miles (hooyah!) on an I-6 . After driving for long distances (at least an hour on the road) then idling for extended periods of time, it seems it starts misfiring. RPMs drop to about 500 and will not rev past 1200 without dying completely.
This has happened a few times in the following scenario:
We have 3 kids and often visit family out of state. We’ll drive for several hours before pulling off at a rest area. To minimize the amount of time spent off the road and to save the hassle of unloading/loading all the kids, we’ll leave the car running (to keep heat/cool air in) and either myself or my wife will run in to use the restroom and get snacks. The vehicle may idle for 10 minutes before the issue presents itself. It seems that if we turn the vehicle off and rest for a few (3-5) minutes, the problem will resolve itself and we can be on our way with no more issues.
Check Engine light is on but only throws a code for an EVAP leak.
I don’t know a whole lot about cars. I thought it could be time to replace spark plugs but this issue doesn’t happen often and it seems only in these specific circumstances.
Any advice would be appreciated!
allpar.com is another good place to ask. They specialize in Chrysler products. I have found good help there for my Plymouth and Chrysler minivans.
Is This I-6 a 4.0L engine?
First off, problems with the evap system could cause this symptom, so that needs to be addressed. That code isn’t just a emissions thing, but could also indicate a malfunction that affects drivability. Getting that under control is what I’d do first.
One way to test this idea, see if the problem resolves by loosening the gas cap.
Also, make sure via the coolant temp gauge on the dash that the engine isn’t overheating during these long idles. The radiator fan is coming on during these idles, right? Even if it is, it might not be spinning fast enough.
Finally, ignition control systems can be heat related. And long idles after long drives will definitely test the heat response of all the components. The crank position sensor in particular is a common heat-related complain here. But the ignition module, igniter, coil-packs etc can be problematic w/heat too.
It sounds like the fuel pump is failing when it gets hot. In cases like this we don’t drive the vehicle for an hour to duplicate the problem, just let it idle in the parking lot with the fuel pressure gauge on it until it gets hot. If it is still running after 30-45 minutes I’ll try to drive it while monitoring the fuel pressure gauge. Most of the time the trouble is found.