Tompop

I have an odd problem. When I use the air conditioner, and stop say to go into the store, when I start the engine, sometimes it's fine, and runs great. Sometimes when I start the engine after it sitting for a little while, it starts and runs very rough. It's so bad, it shakes the whole jeep. I drive it for 2-3 blocks, and it smooths out, and runs fine. It's random. It doesn't happen all the time. Today, I had driven with the AC on, it runs fine. I stopped and went into a store. When I came out and tried to start it, it wouldn't start. It seemed like it was trying to turn over and start, but no dice. After trying for about 15 minutes to start it, it finally started, and ran rough, like it does until I drove it for a couple of blocks. Then it smoothed out. I drove it home, about 12 miles in fairly heavy traffic, without the AC. When I got home, I shut it off, and started right up again without any problem. It seems to be related to the use of the AC. I'm at a loss, as to why this would happen. Any ideas, or suggestions welcome.

JPXJMOAB

How old is the battery? You should get a charging system test done.

Tompop

I just recently had the battery tested, it's ok. The engine would crank great, it was just not wanting to catch. It would try, but not quite start. After a while, it finally started, then ran rough until I drove it a few blocks. Then it soothed out. Sometimes it starts and runs rough, and sometimes it starts and runs fine.

JPXJMOAB

How is fuel pressure at the rail? Sounds like your fuel pressure regulator could be leaking down. Have you also checked spark and the spark plug gap?

Tompop

It usually starts and runs ok. It seems to be possibly heat related. I think if it was fuel pressure, it would happen more often. I had a tune up done just a few months ago. New plugs, wires, distributor cap, fuel filter, and coolant sensor replaced. I have noticed that the temp gauge is reading 210-230 degrees. Coolant reservoir is full. It seems to happen when it's hot.

dave1123

You know, I hate to say this but YEAR, MODEL, ENGINE, and LOCATION sure would help!

Fill out your signature block so we don't have to go back to your previous posts to figure it out! 94 ZJ 5.2, right?

Tompop

Oops. Sorry. Yes 94 Grand Cherokee 5.2

Tompop

Location. Albuquerque New Mexico

JPXJMOAB

Check fuel pressure. My girlfriend has an XJ that needs a fuel pump.. Starts fine, runs like hell for a few blocks and smoothes out. Check the pressure at the rail.

dave1123

See? Even that helps! You're talking about a LOT of underhood heat! One guy in Arizona vented his hood by using a hole saw in the stiffeners and slotting the back edge of the hood. You can see if that will work by putting spacers under the hood hinge bolts to raise the back edge to vent some heat.

What's probably happening is the fuel rails are getting heat soaked after you shut it off and the fuel is boiling. That causes bubbles in the fuel rails that have to be removed by driving it until they cool off.