Need help.. 92 with no heat!!
Posting Guru
Joined: May 2002
Posts: 2,450
Likes: 2
From: Baltimore
Need help.. 92 with no heat!!
I have a 92 xlt with 4.0 engine, and the heat quit working yesterday. Blower is ok, controls seem to be ok. Thermostat seems to be opening and closing ok. Both hoses at the heater core are stone cold. Engine light came on so I pulled the codes. I got a 121 (Throttle postion sensor) and 129 (insufficient manifold absolute pressure)errors. Does anyone know if either the TPS or Mass air flow sensor could result in no heat?? Any and all help is greatly appreciated!!
thanks,
Mike
thanks,
Mike
Elder User
Joined: Aug 2001
Posts: 942
Likes: 0
From: South Texas
Need help.. 92 with no heat!!
Codes you mentioned are not likely cause of no heat. Since you stated both heater hoses were cold, there are 2 possibilities for the heater problems.
1. Thermostat is stuck open. Check upper radiator hose after warm up and see if it ever gets too hot to hold on to. If not, replace thermostat.
2. Heater core is blocked shut from rust residue. It is about a $50 item at most parts houses and is easy to replace. Remove heater hoses at firewall. Remove glove compartment unit. Remove 4 screws at bottom of heater box (remove plastic cover)and slip the core back and down to remove. While glove box is out, check cable operation to blend door in the air box. It is easily visible with glove box removed. Capture point is a pinch type arrangement on cable cover that can come loose and cause door function to be improper.
While you are at it, may as well fix the error codes. Work on them one at a time starting with the first code. Check/replace sensor indicated, reset the computer then re-test. TPS is cheap and located adjacent to throttle butterfly on left side of upper intake. (May have to remove the plastic "4.0" cover to see it). I think the MAP sensor is located on the firewall just right of center. Check the atmospheric opening to see it is not clogged. Original had a foam filter which disintegrates over time. Clean/replace as necessary. Not sure what it costs.
Dialtone
1. Thermostat is stuck open. Check upper radiator hose after warm up and see if it ever gets too hot to hold on to. If not, replace thermostat.
2. Heater core is blocked shut from rust residue. It is about a $50 item at most parts houses and is easy to replace. Remove heater hoses at firewall. Remove glove compartment unit. Remove 4 screws at bottom of heater box (remove plastic cover)and slip the core back and down to remove. While glove box is out, check cable operation to blend door in the air box. It is easily visible with glove box removed. Capture point is a pinch type arrangement on cable cover that can come loose and cause door function to be improper.
While you are at it, may as well fix the error codes. Work on them one at a time starting with the first code. Check/replace sensor indicated, reset the computer then re-test. TPS is cheap and located adjacent to throttle butterfly on left side of upper intake. (May have to remove the plastic "4.0" cover to see it). I think the MAP sensor is located on the firewall just right of center. Check the atmospheric opening to see it is not clogged. Original had a foam filter which disintegrates over time. Clean/replace as necessary. Not sure what it costs.
Dialtone
Posting Guru
Joined: May 2002
Posts: 2,450
Likes: 2
From: Baltimore
Need help.. 92 with no heat!!
Dialtone: thanks for the info. I did confirm that the heater core is blocked. I'm going to try and force flush it before replacing it. If that doesn't work, I'll put in a new one.
