Stumbling on hot start

[mackamitsu]

I had to change my catalytic converter and its run fine ever since. Turned out that a partially plugged cat won't throw a code, but will raise the under hood temp with slower moving exhaust gasses. This problem even happened in -40 weather after the engine had been running warm for at least an hour. I used a generic walker cat with a 2.5" ID.

 

[ShaunBaker]

I have a 2000 limited does this exact same thing, when mine does it there is a pretty violent pop coming out of the intake. then i have to crank it over for about 6-8 seconds unlike usually it fires off after about 2 good cranks(whum..whum...bam). So when it happens it does the same...runs like Sh1t for about 15-30 seconds then clears up. This sucks everyones having this problem, there has to be a cure. I'm gonna try insulating my fuel rail and injectors then see what happens. I'll post my results.

 

[techno1154]

I have a 2000 limited does this exact same thing, when mine does it there is a pretty violent pop coming out of the intake. then i have to crank it over for about 6-8 seconds unlike usually it fires off after about 2 good cranks(whum..whum...bam). So when it happens it does the same...runs like Sh1t for about 15-30 seconds then clears up. This sucks everyones having this problem, there has to be a cure. I'm gonna try insulating my fuel rail and injectors then see what happens. I'll post my results.

My solution so far is to hot wire the thermostat switch hot fused of cource. What this does is to run the fan when the water tempetature reaches 185* until it is reduced to 170*. This happens wether or not the engine is running. As a matter of fact, it is not uncommon to have the fans come on 5 minutes after I have left the XJ. I have not had that problem for several months since I did that. :repair:

 

[techno1154]

I have a 2000 limited does this exact same thing, when mine does it there is a pretty violent pop coming out of the intake. then i have to crank it over for about 6-8 seconds unlike usually it fires off after about 2 good cranks(whum..whum...bam). So when it happens it does the same...runs like Sh1t for about 15-30 seconds then clears up. This sucks everyones having this problem, there has to be a cure. I'm gonna try insulating my fuel rail and injectors then see what happens. I'll post my results.

My solution so far is to hot wire the thermostat switch hot fused of cource. What this does is to run the fan when the water tempetature reaches 185* until it is reduced to 170*. This happens wether or not the engine is running. As a matter of fact, it is not uncommon to have the fans come on 5 minutes after I have left the XJ. I have not had that problem for several months since I did that. :repair:

 

[parkeruph]

My solution so far is to hot wire the thermostat switch hot fused of cource. What this does is to run the fan when the water tempetature reaches 185* until it is reduced to 170*. This happens wether or not the engine is running. As a matter of fact, it is not uncommon to have the fans come on 5 minutes after I have left the XJ. I have not had that problem for several months since I did that. :repair:

I thought the 4.0 eng calls for a 192° thermostat. So, I am confused, are you not running a thermostat? and why would you want to run it below the normal operating temp. Sounds like your fan is going to be running all the time once it gets above 185°. Operating the eng below normal operating temp could cause other problems, Sensors? Any body else have an opinion on this???

 

[techno1154]

I thought the 4.0 eng calls for a 192° thermostat. So, I am confused, are you not running a thermostat? and why would you want to run it below the normal operating temp. Sounds like your fan is going to be running all the time once it gets above 185°. Operating the eng below normal operating temp could cause other problems, Sensors? Any body else have an opinion on this???

You are 100* correct. I infact have a 195* thermostat in my XJ. The water coming out of the 4.0 going to the radiator varies between 200 and 210* here in South Florida.
The thermostat switch which turns the fans on and off is located in the bottom of the radiator. It measures the water tempeture after it have been cooled by the radiator. This switch turn the fans on when the water returning to the engine reaches 185*. This setup works very good for me for 3 years now. I choose this location instead of the top of the engine or radiator because under hard excelaration especially going up hill the engine coolant could suddenly spike to as much as 115* while the water from the bottom of the radiator returning to the engine could be less than 160* depending on the ambient tempeture and vehicle speed.
I had problem with it just once. I was out of the country for 9 months. On returning to the US I took the XJ up to Tampa the very next day at speeds exceeding 90 MPH. The fans came on at this speed and off when the speed was reduced to 75 MPH. A quick flush the next day brought this to an end.
Finally, take a tip from AMC now DC. On the renix XJ, the manual fan switch, the same fan switch I am using is located in the cool side of the radiator.

 

[ewander]

You are 100* correct. I infact have a 195* thermostat in my XJ. The water coming out of the 4.0 going to the radiator varies between 200 and 210* here in South Florida.
The thermostat switch which turns the fans on and off is located in the bottom of the radiator. It measures the water tempeture after it have been cooled by the radiator. This switch turn the fans on when the water returning to the engine reaches 185*. This setup works very good for me for 3 years now. I choose this location instead of the top of the engine or radiator because under hard excelaration especially going up hill the engine coolant could suddenly spike to as much as 115* while the water from the bottom of the radiator returning to the engine could be less than 160* depending on the ambient tempeture and vehicle speed.
I had problem with it just once. I was out of the country for 9 months. On returning to the US I took the XJ up to Tampa the very next day at speeds exceeding 90 MPH. The fans came on at this speed and off when the speed was reduced to 75 MPH. A quick flush the next day brought this to an end.
Finally, take a tip from AMC now DC. On the renix XJ, the manual fan switch, the same fan switch I am using is located in the cool side of the radiator.

Has anyone else done what techno1154 did to resolve this problem? I'm REALLY curious.

Eric

 

[scoobyxj]

I thought the 4.0 eng calls for a 192° thermostat. So, I am confused, are you not running a thermostat? and why would you want to run it below the normal operating temp. Sounds like your fan is going to be running all the time once it gets above 185°. Operating the eng below normal operating temp could cause other problems, Sensors? Any body else have an opinion on this???

The way I understand it is. From the factory the fan temp switch has power when the ignition is on, but does not when the key is off. So therefor the fan would act completely normal with the vehicle running. What is happening is he is providing power to the switch even when the key is off. That makes it think the key is on (but only in regards to the fan circuit), and will let the fan run without the vehicle running. So the fan would operate just like it would when the vehicle is running, and shut off when the water temp falls below the normal non fan running temp.

Or does it run all the time once the temp reaches 185* I think I might play with this 'cause I have wanted to do a timed fan overide for a while now anyway.

 

[byadao]

It seems that this is an ongoing battle. Our temps up here in Chicago are in the 70s and today my 2001 had a nice little hot rough start while out at the store. It only happens when it's warm out. I just started and let itself clear on it's own then all is fine. I would like to get more information on rewiring the switch also! Thanks for all the information.

Ben

 

[XJXJ]

Fan switch rewire is good/simple mod and remember that fuel quality will play a role in this issue if it's cook-off heat boiling fuel in the lines. Alcohol vaporizes at much lower temperature than gasoline so it doesn't take much heat to cause these issues. Especially alcohol blended fuels and/or alcohol based additives.

Cat is another good thing to check. And anytime I drive highway in hot weather and stop, I usually pop hood and give the heat a chance to escape. A couple minutes with the hood open will dissipate a lot of heat that would normally be trapped under hood.

Investigate your fuel source and make sure you're putting 100% gasoline in the tank.

 

[2kLimited]

ok mine does this too now:doh:

just started

new plugs didnt help

im gonna replace the cat

 

[ewander]

I might put new plugs in tonight....then I'm off to the CAT also. Let us know how it went.

Eric

 

[spcustoms]

arg... 60s 70s now mine did it again... it was fine all winter, and today on my way home from work I stopped for a bite to eat and misfired when I restarted it 10mins later... didnt throw a code yet... Hmmm cat? havnt thought about that....

 

[2kLimited]

mine wouldnt do it today

ran like a champ



this is confusing

 

[spcustoms]

wonder if its the gas?
I use wawa.. I think it has some ethonal, 10%?

 

[2kLimited]

im using wawa when it happens ive figured out

 

[tupton]

Has anyone replaced their cat to see if it helps?

 

[techno1154]

Has anyone replaced their cat to see if it helps?

My XJ do not have a cat for 2 years no inspection here in FL. I have one coming as we speak that I will install this weekend. I would say the cat or lack of it have no effect on this problem.

You guys who have hood vents do you have thhis problem? Those who have the problem do you have the OEM insulation onn the underside of the hood? I am look things in common to point a finger at.

 

[dcXJ]

Well, it's not just a problem with the 2000s...my 2001 does it as well...I haven't thought about replacing the cat...but might to see if that helps...I have new plugs, and everything else checks out..no leaking injectors, no misfires, nothing out of the ordinary. Heat soak can be a bitch to nail down and correct...it happens once every few days to me, and only when it's been run for a while, and the temps are over 70 degrees....keep us posed as far as replacing the catalytic converter for anyone that's doing it. I'd like to hear the results.

 

[Ben H]

Well, it's not just a problem with the 2000s...my 2001 does it as well...I haven't thought about replacing the cat...but might to see if that helps...I have new plugs, and everything else checks out..no leaking injectors, no misfires, nothing out of the ordinary. Heat soak can be a bitch to nail down and correct...it happens once every few days to me, and only when it's been run for a while, and the temps are over 70 degrees....keep us posed as far as replacing the catalytic converter for anyone that's doing it. I'd like to hear the results.

I've replaced the catalytic converter a few times once from being clogged, and it has never fixed my heat soak. Insulating the fuel rail seemed to help some. Wiring the auxiliary fan to run for a few minutes after shut down is something that I am looking into now. After a few years of dealing with this heat soak issue, it is pretty much normal operation, almost to be expected.