Hey guys,
I had a leaky heater core in my 2001 cherokee sport causing my windows to condensate pretty bad to where I couldnt see. I just pulled my dash apart and replaced the heater core and ac evaporator. Everything seemed to be fine but after starting it back up, its not blowing hot unless Im driving. Also it seems to be idling a little rough and is stalling out at idle practically everytime. I checked the little vacuum line that comes out of the heater box and through the dash and it seems to be hooked up fine. Do you guys have any suggestions on what to check to fix the stalling and no heat?

 

Was it blowing hot air prior to replacing the heater core?


How old is your water pump?


Are both heater hoses in the engine bay hot to the touch when the engine gets up to operating temp?


Is the blower functioning at all speed settings?


When it stalls, what selection do you have on your AC/Heat mode selector? Does it stall with the mode selector OFF?

 

Check for a cracked head. Your Jeep has the 0331 head on it, which has a fatal casting flaw from the factory.

 

I replaced the cracked 0331 head with a "0630" a couple months ago. I have had no issues since then. Everything was fine until I changed the heater core. It is acting like a vacuum leak. The only vacuum line I disconnected was the one fitting through the firewall from the heater box. I also replaced the AC evaporator while I was in there. One of the AC lines didnt feel like it popped back in right. Would the AC line cause the stalling problem if the ac line isnt properly reconnected?

I think the heat not being there may be from air in the system. The stalling issue is much more important since it is my DD.

Thanks again to anyone that is able to help.

 

The AC line will not cause stalling. The stalling could be caused by a vacuum line being unplugged. Try capping off the line going to the airbox. Does the air only come out of the defrost vents? It is designed to default to there if there is not vacuum pressure.

For the no heat, it sounds like the system is low on coolant. When cool, fill the radiator to the top (or run and fill until the engine starts to warm up, then cap it before it gets too hot). Fill reservoir to full. Trick I usually do when replacing a thermostat is to drill a 1/8" hole at 12'o clock and it will self - bleed slowly.

 

In that case you probably have electrical or vacuum lines under or within the dash that are not plugged in properly.

No heat could be caused by that. If you system is through "burping" and your coolant container is at the proper level, that's where I would look next. Please don't drill the thermostat. By doing that, you are keeping it from doing what it is supposed to do.

Your A/C has nothing to do with the above.

The stalling/missing is likely caused by something that was left undone or wrong if it was fine before the dash came out.

 

My heater was blowing hot before, It was just leaking causing some serious condensation on the inside of the cabin. The water pump has never been replaced but the jeep isnt overheating and I have coolant pressure. The upper and lower radiator hoses get hot, but I did notice that the hoses hooked up to the heater core were only warm. All of the fan settings are working properly. Is there a way to test the "blend door motor"? Some other threads pointed towards it to get the heat back.

The main issue I am looking to fix is the stalling which I am assuming may be a vacuum leak due to a slight bounce in idle RPM and the random stall.

I hope this additional info can help you help me haha. Thanks again

 

- Thanks for the suggestion. When I get home I will pull that vacuum line and plug it to see if it has an effect. I tried adding coolant after the job. While it was cold, I took the rad cap off and as soon as I started it up, the coolant started overflowing out the top so I just put the cap back on. I will thoroughly burp the system asap.

What should I be looking for after I plug the vacuum line? increase in rpm?

Thank you

 

Thanks for that! It looks like there is no way around pulling the dash apart again and doing some investigation. Are there any plugs that I can specifically target? Also, where are the vacuum lines within the dash? the only air line I saw was the one coming straight out the back of the heater box and through the firewall.

 

If a 1/8" delays engine warm up by more 1 second I'd be shocked. Could use smaller if you want, but I've been doing that on at least 6 thermostats in 4 different cars and its bled great and never caused an issue. Bleeding is a bigger issue on some cars more than others though and may not be needed on a 4.0, but I wouldn't suggest it if I though it could hurt.

 

On my '87 and '92 XJs, and my daughter's '97 and '06 Grand Cherokees, there was a bunch of color-coded vacuum lines that went behind and attached to the climate control panel.

If you had the radio out you could see them.

After your initial radiator fill, monitor and "burp" the system through the coolant overflow tank. Two or three hot/cold cycles should be enough to stabilize the system.

I always figured that if a thermostat needed extra holes in them, the manufacturer would put them there. I know that some have a loose rivet in them. I have heard that you put that at 12 o'clock. Just because someone drills extra holes, then says that they haven't experienced "burping" issues, is not proof that drilling extra holes prevented air pockets.

 

If you cap the hose going into the firewall at the engine or the T in the vac line (capping the side that goes to the engine), the engine RPM will immediately change. You can use your finger to plug and unplug the hose and your RPMs will change. It affects the reading to the MAP sensor, which is how your computer measures load on the engine.

edit: Low RPM is unlikely to be an interior wiring issue. There is your ignition wiring. Its on or off. Can check your bulkhead connector, but if you have a wiring issue in the dash, it either runs or it doesn't, not misses.

Did you check to see if you only have defroster vents blowing? That's usually the easiest way to check for bad vacuum in the dash. No vacuum = defrost vents when you have panel or floor selected.

 

Ok guys,
The heat is working again! just had to burp it. Unfortunately the stalling issue is still occurring.

Update:
I pulled the T line off and checked it. It seemed connected fine. It was definitely sucking air after I pulled it off. However I did not notice much of a change in how it ran when I plugged it. TODAY I tried to drive it to school and it started stalling on the interstate eventually shutting off. It starts right back up but continued to stall another 2 times while driving it back home. While on the side of the road, I popped the hood and realized that there was NO coolant in the upper radiator hose and the Radiator cap wasnt even hot. I had topped off both the radiator and the overflow tank before leaving. The thermostat read that the engine was running at 210 degree so nothing un-normal there. also the check engine light was coming on and then turning off after dying just to come back again. It runs fine until it just randomly turns off.

Any input is appreciated, You guys are really helping me out.
Thanks

 

Oh and all of the vents blow fine. Not just the defrost vent. It continued to stall even with the heat completely off.

 

It was blowing hot before changing the leaking heater core.
Water pump is original
Upper radiator hose and radiator cap DID NOT get hot!
The blower functions at all speed settings
It stalls with or without the heat on.
The heat is back after burping but still stalls.