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Hot start problem.

Badmunky

NAXJA Forum User
Ok so I have had it with this hot start problem! :gonnablow

My 2001 4.0 AW4 Cherokee runs great! It starts right up cold. And it starts right up hot.
Be when you let it sit for about 15 min hot, especially on a hot day it srats right up and runs like crap!!!!!!!!!!!!!!!!

I have changed the following parts in the last 1,000 miles.

All O2 sensors with new Bosh.
Spark plugs.
Spark plug boots.
Crank sensor.
Cam sensor.
IAT sensor.
TPS sensor.
IAC unit.
Coil pack. (One used one, one brand new one.)
Oil pressure sensor.
Temp sensor.
Changed the oil and filter.
New air filter.
Sea Foamed it before new plugs.
Ran seafoam in the fuel tank.


It still has this problem.

When its hot and you park it for about 10 to 20 min and then start it back up it runs like crap. Acts like its running on 4 cylinders. Rev it a few times, and or just let it run for a few min and its fine. Clears right up and runs great.

But until it clears up, you can not put it in gear. It will stall. And at times it takes it a few min to clear up.


Today I pumped gas in it and then went in to pay. Had to wait in line. Came back out and I have cars waiting to use the pump behind me. Start the Jeep and it runs like crap. :bs:
Takes it almost a full 2 min to clear up so I can move. People are honking at me, and I feel like a fool.:dunno:


So what is causing this problem?
 
Google Cherokee heat soak. I think the best and easiest solution is to install a e-fan timer that runs the e-fan after the ignition is shut off. There are several threads about them here on NAXJA.

Click here -> ELK-960 e-fan timer

FYI, Bosch O2 sensors are proven to cause issues in the Jeep 4.0L, you should be using NTK O2 sensors.
 
Common issue on 01's

There's a tsb out there for it that specifies wrapping the #3 injector in a heat shield. Part is about 10 bucks. I did it last year and it seems to have solved it for me most of the time. Still have an occasional issue.

Next step would be the Efan timer or hood vents
 
Ok sounds like an easy fix.
I'm planing to go to an E-fan to replace the stock clutch fan any way. Its failing.

Just not 100% sure how I am going to go about it just yet.

I wrapped the entire fuel rail in heat wrap today. But did not do any of the injectors.

This seamed to help a little bit.

But it seams I now have a failing precat. :(

The front cat is getting REALY hot. I used a laser temp gun and the front cat is running a good 120* hotter then the back one. I think this is part of my problem.

And the cause of my low power problem / crap MPG problem. (Getting less then 200 miles out of a tank driving it on the street, and driving like a grandma!)




Question:

How hard is it to convert to a return style fuel system? This would help solve the problem by keeping the fuel temp down.

Thanks guys.
 
The mechanical fan works just fine, there is no reason to swap it out for expensive electric fans, and most e-fans don't have high enough cfms. Just buy a new fan clutch.

So you swapped out the Bosch O2 sensors and still are having cat issues ?
 
The mechanical fan works just fine, there is no reason to swap it out for expensive electric fans, and most e-fans don't have high enough cfms. Just buy a new fan clutch.

So you swapped out the Bosch O2 sensors and still are having cat issues ?

Clutch fans suck. They sap power and MPG. And this one is already failing. It was replaced with a new one about 12k miles ago.
There is a reason no new car uses a clutch fan any more.


I replaced the O2 sensors to try and fix 2 problems.

This hot start problem.

And I was getting an O2 sensor code. I no longer get an O2 sensor code.
But I suspect the last owner drove it for a long time with engine light on and may have ruined the front precat.

I have only owned this thing for about 1,000 miles now. I bought it mostly as a toy and have not driven it much until the last few weeks. Think I put more miles on it in the last few weeks then I did in the almost 9 months before that that I have owned it.


I have also had to fix the rear brakes. The self adjuster on the drivers side popped out.
Replace both power steering lines as the high pressure line started leaking really bad and I ruined the return line trying to remove it from the box.
Had to fix the exhaust system as it started to fall off. (Now held up with a hose clamp and a coat hanger.) I knew it was shot when I bout the Jeep. Just have not had money to replace it yet.
 
I'll refrain from any other comment except that I really wish I could fit a mechanical clutch fan on my V8 swap. I miss the CFM they can produce when needed.
 
Clutch fans suck. They sap power and MPG. And this one is already failing. It was replaced with a new one about 12k miles ago.
There is a reason no new car uses a clutch fan any more.
So many of us have tried replacing the mechanical fan with an electric fan to only find they don't have the airflow that the stock mechanical fan does.
Electric fans add extra complications and more opportunities for a cooling system failure, if the XJ's electrical system isn't up-graded.

The stock cooling system, when if good shape is quite adequate. Find out what your's isn't working correctly.

My 2001 XJ's cooling system is totally stock except for a bigger trans cooler and a added power steering cooler. It never overheats in the high summer temps of SoCal.
And I have the tried and discarded Taurus fan rotting away, behind the garage.

My 2001 also has had the hot soak issue for the ten years I have owned it. Insulating the bottom of the intake manifold and fuel rail helped, along with with hood vents but nothing totally cured the problem except adding timer to the electric fan, having it run for 2-3 minutes after the engine is shut down.
https://www.flickr.com/photos/lwade/sets/72157617434915718
I have used the timer for many years, it hot weather, with success. You have got to love the mini-cats.
 
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Clutch fans work, and are cheap. Good luck with your e-fans and Bosch O2 sensors.
 
I'll refrain from any other comment except that I really wish I could fit a mechanical clutch fan on my V8 swap. I miss the CFM they can produce when needed.

Never had any problems with a properly working e-fan. I have yet to have a vehicle with a clutch fan that did not fail.

So many of us have tried replacing the mechanical fan with an electric fan to only find they don't have the airflow that the stock mechanical fan does.
Electric fans add extra complications and more opportunities for a cooling system failure, if the XJ's electrical system isn't up-graded.

The stock cooling system, when if good shape is quite adequate. Find out what your's isn't working correctly.

My 2001 XJ's cooling system is totally stock except for a bigger trans cooler and a added power steering cooler. It never overheats in the high summer temps of SoCal.
And I have the tried and discarded Taurus fan rotting away, behind the garage.

My 2001 also has had the hot soak issue for the ten years I have owned it. Insulating the bottom of the intake manifold and fuel rail helped, along with with hood vents but nothing totally cured the problem except adding timer to the electric fan, having it run for 2-3 minutes after the engine is shut down.
https://www.flickr.com/photos/lwade/sets/72157617434915718
I have used the timer for many years, it hot weather, with success. You have got to love the mini-cats.

I will look in to the timer. That does seam like it may solve my hot start problem.

As for the clutch fan I have run them on every Jeep I have ever had with 0 problems. As well as converting every clutch fan vehicle I have ever owned with no problems.
Every one of my buddies run E-fans on the Jeeps with no problems.
Its all in the fan you use, and if you sealed it to the core correctly. Many people use the Taurus fan and leave that large gap at the bottom open. This will allow the fan to pull air around the rad instead of threw it. They also fail to trim the shroud so it seams to the rad fully. Again allowing the fan to pull air around the rad. This make its so the fan is on, but only working at about 30% of what it could do. I fixed my buddies fan install do to this same problem. After some trimming and seaming off the lower part that hangs bellow the rad his works great now!



Clutch fans work, and are cheap. Good luck with your e-fans and Bosch O2 sensors.


I plan to replace the Bosch O2 sensors in a few days. I did some reading and found that you where not the only one that seams to hate them on Jeeps.
I have NTK O2 sensors on order that will be here soon.

If you would like I currently have 5 Jeep clutch fans in my scrap pile. All failed. With #6 on its way as soon as I sort a few other problems and have time to yank it off my Jeep. Your welcome to them.



Also is there some reason that this 2001 has the hot start problem, but my 98 and 2000 did not do this?
None of my friends have this problem ether.
They own the following years.
92, 94, 95, 95, 98, 99, 2000< My old one.

All running E-fans in place of the stock clutch fan.
No timers that I know of.


Thanks for the help guys! :patriot:
 
Never had any problems with a properly working e-fan. I have yet to have a vehicle with a clutch fan that did not fail.



I will look in to the timer. That does seam like it may solve my hot start problem.

As for the clutch fan I have run them on every Jeep I have ever had with 0 problems. As well as converting every clutch fan vehicle I have ever owned with no problems.
Every one of my buddies run E-fans on the Jeeps with no problems.
Its all in the fan you use, and if you sealed it to the core correctly. Many people use the Taurus fan and leave that large gap at the bottom open. This will allow the fan to pull air around the rad instead of threw it. They also fail to trim the shroud so it seams to the rad fully. Again allowing the fan to pull air around the rad. This make its so the fan is on, but only working at about 30% of what it could do. I fixed my buddies fan install do to this same problem. After some trimming and seaming off the lower part that hangs bellow the rad his works great now!






I plan to replace the Bosch O2 sensors in a few days. I did some reading and found that you where not the only one that seams to hate them on Jeeps.
I have NTK O2 sensors on order that will be here soon.

If you would like I currently have 5 Jeep clutch fans in my scrap pile. All failed. With #6 on its way as soon as I sort a few other problems and have time to yank it off my Jeep. Your welcome to them.



Also is there some reason that this 2001 has the hot start problem, but my 98 and 2000 did not do this?
None of my friends have this problem ether.
They own the following years.
92, 94, 95, 95, 98, 99, 2000< My old one.

All running E-fans in place of the stock clutch fan.
No timers that I know of.


Thanks for the help guys! :patriot:
 
Never had any problems with a properly working e-fan. I have yet to have a vehicle with a clutch fan that did not fail.

Every one of my buddies run E-fans on the Jeeps with no problems.
Its all in the fan you use, and if you sealed it to the core correctly. Many people use the Taurus fan and leave that large gap at the bottom open. This will allow the fan to pull air around the rad instead of threw it. They also fail to trim the shroud so it seams to the rad fully.

Also is there some reason that this 2001 has the hot start problem, but my 98 and 2000 did not do this?
None of my friends have this problem ether.

Here's my thinking about electric fans.
My wife and I like to explore the distant back roads of the West, usually traveling solo. You can get a long ways from things, so far that some trips require carrying extra fuel.
I want my vehicle to be as simple and dependable as possible.
I also want repair parts to be widely available. You can't get anymore available than late model XJ parts.

Electric-only cooling fans add several extra layers of complexity to the XJ's cooing system with the required heavy wiring, relays, fuses and controllers, plus it puts a much bigger load on the alternator.
A bunch of stuff to potentially fail.
The stock system, with everything in good condition, does work, as many of us desert dwellers and explorers can attest to.
Fan clutches are expendable and cheap, so I carry a $25 new one in the parts box. Never had to change on on the road because I check it before long trips.

As to proper installation of the Taurus fan, I know about how shrouds should be sealed, it's something I do to all my vehicles. I use heavy aluminum mending tape to tightly seal gaps.
The Taurus fan does work but it adds too many new opportunities for problems, compared to the stock system, IMO.

There are differences between various radiators. I have found the HD Mopar radiator to be the most efficient.
The A/C condenser can be so badly corroded and/or jammed with debris, that it significantly restricts air flow. The condenser many times cannot be adequately cleaned and should be replaced.

2001 and some 2000 XJ's have two small catalytic converters, mounted on the exhaust manifolds.
They dump a large amount of heat into the engine compartment, cooking the driver's side, the cause of the hot soak problem.
Running the XJ's electric fan for a few minutes, after shut down, blows enough heat out to prevent the gas, in the fuel, rail from boiling.
It works without hood vents but better with. if installing vents, shield the throttle body's sensors from rain.
 
I tried the TSB method & it did not work for my XJ; The only thing that worked was the "E" fan timer, After setting the timer to make the "E" fan run for 3 minutes after hot shutdown I never had the problem again, In the Winter months I just pull the timer fuse as the 3 minutes of cooling is not needed.
 
I was finally able to solve my issue when my mechanic did the service bulletin that reprograms the ecm to turn on the electric fan at a lower temp and it also has the efan run for about 2 minutes on all hot starts regardless of engine temp. Your mechanic should be able to pull it up. It only applies to the 00-01 xj.

Nothing else worked. Tried hood louvers, service bulletin for insulating injector 3, i even insulated all 6 injectors and the fuel rail. If you can find enthol free gas your problems will also go away.
 
I was finally able to solve my issue when my mechanic did the service bulletin that reprograms the ecm to turn on the electric fan at a lower temp and it also has the efan run for about 2 minutes on all hot starts regardless of engine temp. Your mechanic should be able to pull it up. It only applies to the 00-01 xj.

Nothing else worked. Tried hood louvers, service bulletin for insulating injector 3, i even insulated all 6 injectors and the fuel rail. If you can find enthol free gas your problems will also go away.

Not sure if that is a universal fix.
I run the aux fan in hot weather and have all the 'fixes' you listed and more but still have the hot soak problem, which has only been controlled with the fan timer.
I use ethanol-free gas.
It does get a lot hotter in SoCal than in BC (and we drive a lot faster).

The Factory came up with several 'solutions' but, AFAK, none have worked for everyone affected
 
FWIW I had the same problem and replaced all the injectors Followed the TSB and wrapped everything. Even made my own heat shield. None of that worked.

Once I installed hood vents its been perfect and has never done it again. I would skip straight to hood vents.
 
I was finally able to solve my issue when my mechanic did the service bulletin that reprograms the ecm to turn on the electric fan at a lower temp and it also has the efan run for about 2 minutes on all hot starts regardless of engine temp. Your mechanic should be able to pull it up. It only applies to the 00-01 xj.

I didn't know there was a TSB that accomplishes this, Does anyone have the TSB # or better yet the procedure for reprogramming the ECM to do this?
 
I'm interested as well, my 2000 doesn't suffer from heat soak (that is a pre-cat equipped issue) ... But extra cooling is always good. My cooling system is working fine, but I did add a Hayden 2737 fan clutch to help keep cooler in slow traffic and on the trail. Thought about the Efan route but have had several Efan failures in various vehicles over the years, I prefer the even limited backup cooling a failed clutch still provides.
 
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