Shuddering when restarting.

Shuddering when restarting.

I recently purchased a 2000 4.0l with 32K miles on it.
On about the 5th tank of gas, it developed a problem.
When the engine is hot and I stop for a couple of minutes, the engine will shudder when started until I kick up the rpm.
Did I get a bad tank of gas?
Could it be the heat (it’s been about 100-105f here for the last couple of days)?
All of the fluids look good.
The air filter is brand new – no blow-by.
I had the dealership change the oil/filter and transmission fluid/filter before I bought it.
I’ve tried not to hard stop/start it. I am letting the engine run for about 15 seconds after parking to let the fan cool the engine off for a bit.
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I already ordered by FSM from Chrysler, but it won’t be here till next week.
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Note: It will not shudder when the engine is cold.

Any ideas???

I found the cause - however, there's no fix at this time. I found a TSB at alldata.com "Fuel System - Rough Idle After Hot Soak." The service manager at the dealership knew exactly what the problem was. He said that the fuel gets too hot when running thru the fuel rail. He said that the problem was fixed in the Grand Cherokees, but there is still no fix for the XJs. He has several XJs in his shop right now for the exact same problem.
What I am going to do it to get some hi-temp exhaust manifold tape and wrap it aroung the fuel rail. Hopefully, that will do the trick!

Also try summit racing equipment. They sell fuel line insulation for this specific reason. I think this problem is refered to as vapor lock. I think you are on the right track.

Dan

DPC said:

Also try summit racing equipment. They sell fuel line insulation for this specific reason. I think this problem is refered to as vapor lock. I think you are on the right track.

Dan

Click to expand...

He's on the right track, but it ain't vapor lock. Vapor lock was from the days of carburetors and low-pressure fuel systems in which the pump was on the engine and pulled the fuel from the tank. If the gas in the line between the tank and the pump got hot enough to vaporize, the pump basically lost its prime and wouldn't work until things cooled down.

In theory, with the pump mounted in the tank and pushing, there's no prime to be lost so vapor "lock" isn't possible. However, vapor pockets in the fuel rail would cause an irregular idle until they get run through the system and the rail is cooled down by cooler fuel flowing through it.

Check pressure

Check the your fuel pressure. Low pressure is one of the causes of fuel vaporizing and is especially critical now with the amount of propane they put in gasoline.

2000 4.0L
What is the thing on the fuel rail between injector 3 & 4?
It's a round piece that faces the manifold? It's not there on my older XJs.

Do the 2000's have a return line? If they do-like the Renix systems, Simply turning on the ignition and waiting a moment to hit the starter would circulate the hot fuel back to the tank and replace it with cool.