Jeep Wrangler miss hot soak

[delcecchi]

My son's 98 Jeep Wrangler, 4.0 straight 6 has a problem. When started from cold it is ok. but if he drives it for a while then restarts after 30-40 minutes, it runs like a carp. After driving a while it gets better.

He has had it to two places and they say they can't find anything wrong. No codes either. If it was a carb'd motor I would say vapor lock. but I am thinking some sort of sensor, like coolant temp.

Any ideas? Things to check? experiments?

[Jeremy airjer W]

I'd like to see what the fuel pressure is at after it sits.

[delcecchi]

What do you think is happening? What would they be looking for?

An injector dripping gas while it sits, causing a rich or flooding type situation?

[Macgyver55]

Has he pulled the vacuum line off the fuel pressure regulator and checked for fuel in the line?

[Jeremy airjer W]

Isn't that one regulated at the pump?

I can never remember what year they switched that over

[Macgyver55]

I dont think so, I think its on the rail.

[delcecchi]

Has he pulled the vacuum line off the fuel pressure regulator and checked for fuel in the line?

He hasn't done anything. He did take it to two places, but it was running ok, so they didn't do anything. I don't think he has left it anywhere yet.

[Jeremy airjer W]

The key will explaining when the condition happens. Until the shop gets it to act up they will likely not do or recommend anything. The more they know about the symptom the easier it will be for them to replicate and then find a solution.

[delcecchi]

Agreed.

His description reminded me of the old carb'd days when gas would cause mild flooding due to hot soak making the gas in the carb expand. Unfortunately my automotive knowledge is pretty far out of date.

[Macgyver55]

Whatever the case, pulling off the vacuum line from the regulator and checking for fuel intrusion is a simple, no cost way to eliminate a possible/likely cause.

[delcecchi]

certainly worth a check. Thanks.

Does gas in the vacuum line mean a bad regulator? I presume this is the case. How hard is it to swap regulators?

[Macgyver55]

Does gas in the vacuum line mean a bad regulator? I presume this is the case. How hard is it to swap regulators?

Yes it does. Its normally a fairly easy swap.