Hi, my problem is after running 20 min, hard to start the engine but can start when pressing the gas pedal in and out. When it start it run rough for 2-3 seconds. Basically, everything replaced new except IAC.What is the problem?

Jeep XJ 2.5 manual,93 modal

 

Not saying it's your problem but yrs back after I cleaned my IAC because of the symptoms like you describe they went away. But then came back a couple weeks later. I replaced the IAC and it's been good since.

 

1. You could have a leaky fuel injector. That can leave the cylinder filled with unburned fuel and it takes a few seconds for the engine to burn it off and clear. Some extensive fuel pressure testing could isolate this. The factory Jeep manual outlines how you can do this if you're up for it. Are these original injectors? If so, might be time for new ones.

2. Never hurts to CLEAN the idle air control AND your throttle body while you are at it. Be careful not to pull out the IAC pintle though as that can futz the operation of it up. They aren't all that expensive to replace, but my gut feel is that isn't your problem.

 

Did the 2.5 have the heat soak issue that 4.0 has?

 

What is heat soak??

 

But I can start without any problem in the morning. If leaky fuel injector, i should have the problem in the morning also right? But it only happens when the motor is hot after like 15 min ride.

 

That doesn't sound like an IAC problem.

Heat soak/vapor lock is when the gas is over heated to the point it vaporizes. Maybe try wrapping the fuel rail and leading up to the injector with insulation.

 

What material can be used to wrap the injector?
Can I use aluminum heat shield wrap?

 

Normally the injectors are cooled by fuel flowing through them. Some of the 4.0L XJs have a problem where after the Jeep is shut off and the injectors are no longer being cooled, heat rising off the exhaust manifold boils the fuel left in one or more of the injectors so that it's just vapor. If the engine cools down long enough, the vapor turns back into liquid, and the vehicle starts fine. If you try to start it before it has a chance to cool, however, it will not want to start and will run rough when it does start because liquid fuel is not flowing through the overheated injector(s).

I'm not aware of the 2.5L having the same issue, but the symptoms you describe sound similar.

 

For now I'd use aluminum foil(shiny side out)to reflect the heat. If it helps there are rolls of foiled insulation to be had.

I did search to see if the 2.5l had a problem. Only saw one remark similar to what extrashaky posted. Can't hurt to try.

 

Thanks alot..very informative. What should I do to overcome this problem? Just want to try it.

 

Thanks. I gonna try this.

 

Yeah, it doesn't hurt to try.

As an experiment before the foil, if you want to prove or disprove heat soak as the culprit, next time with a hot engine, pop the hood for 15 or 20 minutes after the engine is shut off.

That always cured my heat soak hard start but its obviously not a permanent or convenient fix just an experiment.

If it still is hard to start after, i'd start looking at injectors next.

Edit: BTW, I installed the official TSB foil fix for the hot soak issue for my 4.0 2K.
It seemed to work in cooler weather.
But in hot weather coming off the freeway and parking for 10 minutes, it was back.

You might have better luck with the 2.5 engine though.

 

If the injector's won't seal they produce drips as they sit with system pressure on them. A very common symptom is hard semi warm restart. They won't effect the cold start much because the engine needs more fuel when cold.

As mentioned, if you get stuck here....consult a factory service manual and get a fuel pressure gauge and do some comprehensive testing. Let testing lead the way here. An injector leak is still in play here. Fuel pressure testing can isolate an injector leak when done properly.

You never answered whether these are the original injectors or do you know?

 

hey guys,
i'm having the same issue with my 97xj 4L.
starts up just fine in the morning or when cooled off but after a drive and then coming back to start it up, its a rough start, sounds like its choking and then it'll kick over. it also died in the dunkin drive thru after sitting at idle for about 5-7 minutes, once it cooled off it started up. the temp gauge never spiked and it didn't seem overheated. any thoughts?