Recently got a 95 gc laredo v8 from a family member trying to get it back into decent shape. 240k miles. Drives fine for about 20 minutes (enough to get to and from work) but anything after that it tries to stall, has no guts and idles around 50-100 in gear stopped. Tried taking it to a mechanic friend but he cant duplicate the problem. Replaced IAC, new fuel system, seafoam treatment. Seems to be electrical not mechanical. Not a cat problem, she ran away. Only thing showing in VIC is "service 4wd switch" and she's not putting out any codes.

I have noticed if I turn the power off then immediately back on while in motion it will drive like a champ again for a few minutes. Is this the distributor going out?

HALP!

 

Try cleaning the idle air control (IAC) if you haven't already. If it's got dirt in it, it gets sticky after it gets hot.

 

Dave, any recommendations on "how to's" cleaning the IAC. I usually use brake cleaner on my brother in law's tooth brush and just clean the outer pintle. I'm leary of sqirting a solvent into the works.
I've some similar symptoms on our 95ZJ 4.0L
Seems to get chuggy, low idle, won't power up, after heat soak conditions. All is well on longer runs. It's the short run, long idles, stop and goes that it transitions into chug mode.
If I disconnect the water temp sensor, will go into a default mode and smooth right out. Checked resistance on the temp sensor, seemed in line with charted reference values.
I've replaced the IAC, TPS, CPS, Temp Sensor, AMP sensor, plugs, wires, rotor, cap. Did not correct the problem.
So I installed an OEM heat shield between intake manifold and injectors fuel log. Helped a little.
I wrapped the fuel delivery line and a couple of most exposed injectors with fibre glass strip and metal foil type duct tape. Helped a lot, but not a complete cure.
Thinking of wrapping the whole fuel log and rest of the injectors next.
My theory is it is a heat soak and fuel line vapourization / vapour lock condition. ???
I'm looking for an affordable fuel pressure gauge to check system presure and look for variations. (The fuel pump and fuel filter are also new, pressure regulated at delivery from the pump)
Just can't figure on why it ran without this problem for 20 years and has had a gremlin for last 3 years?
The fuel delivery of the ZJ (and also our WJ) does not have an inline presure regulator and a return to tank line, as does my XJ. The WJ not having any issue.
Driven 1400 km weekly. I can drive around the problem (seems to clear out if it occurs and I can get the revs up and maintain a fuel flow to clear and suspected vapourization), but it totally messes up my wife or kids driving of the ZJ (well my ZJ is a little rough and prime use is me and the dogs; the wife will barely ride in it much less drive it).
If parked for 15min and cools down, restarts and drives no problama again until another heat soak opportunity.
Oh yes, changed the thermo to 165 unit, with 1/16 dia bleeder hole drilled so no air pocket in block, no engine over heat (almost no heat in winter, and what a cold winter it was, just enough to maintain the defrost of the windshield but not my toes, lololol).
I am open to suggestions.
Sounds to me like Sevtron could have a fuel line heat related issue.

 

Wonder, what is the actual fuel pressure?

 

Actually the WJ does have a pressure regulator and return line to tank, but it's in the fuel filter. If you have less than nominal fuel pressure, the fuel will boil at a lower temperature. This could be your problem.

The proper thermostat to use should be a 195*F. This is the proper temp for the PCM to set fuel trim. Otherwise you're running on preset data in the chip.

 

Originally by TJWalker of CherokeeForum & JeepForum



The Idle Air Control (IAC) is mounted on the back of the throttle body (front for ’87-’90).

The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is retracted, the air control passage flows more air which raises the idle speed. When the valve plunger is extended, the air control passage flows less air which lowers the idle speed.

Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea. This should be part of a normal tune-up procedure and whenever idle/stalling issues are present.

CLEANING THE JEEP 4.0 IDLE AIR CONTROL

1. Remove the air filter cover, associated hoses and the rubber boot that goes from the air filter cover to the throttle body. Remove the IAC with a Torx driver (2 bolts; one can be kind of hard to get to). On ’91 and later, it may be easier to just remove the whole throttle body. Be sure to use a new throttle body to manifold gasket when reinstalling.
2. “Gently” wiggle out the IAC from the throttle body. Gasket/O-ring on the IAC can be re-used if it is not damaged
3. Clean the IAC with a spray can of throttle body cleaner; inexpensive and available at any place that sells auto parts. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, safe for throttle body coatings and oxygen sensors. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle that protrudes from the IAC as it is fragile and you could damage it.
4. Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner.
5. It is also a good idea to clean the entire throttle body bore itself, the butterfly valve inside of the throttle body and it’s edges, and all associated linkage as long as you have things disassembled.

Revised 1-31-2016

 

TB Cleaner, less harsh than Carb Cleaner, good to know, thank you!
My brother in law tooth brush works the best. Remember when borrowing tools, return them, I always put it back in his suitcase.
My IAC replacement with new was not a resolution for me.

I don't yet have fuel pressure data.

I'm willing to try replacing the thermostat back with a 195 deg to check results. My objective was to lower temps away from a heat soak condition, although winter heat would be nice.

I'd like to hear back from Sevtron if any of the suggestions are working for the V8ZJ?

 

Annnd there goes the OP.