Havng a staring issue

[CLehman]

So yesterday I put an aftermarket mechanical temp gauge in my 92 XJ, and the "Check engine" light came on I didn't think anything of it until I had a problem starting my beast this morning and it seemed like it really just didn't want too fire up. Now I took the factory temp sensor out of the Termostat housing and put in the new mechanical setup. The gauge works great but is this causing my starting issue? If so is there another place I can put my new mechanical setup on the engine and just replace the old factory sensor and all will be fine? Please help.

[Mudderoy]

So yesterday I put an aftermarket mechanical temp gauge in my 92 XJ, and the "Check engine" light came on I didn't think anything of it until I had a problem starting my beast this morning and it seemed like it really just didn't want too fire up. Now I took the factory temp sensor out of the Termostat housing and put in the new mechanical setup. The gauge works great but is this causing my starting issue? If so is there another place I can put my new mechanical setup on the engine and just replace the old factory sensor and all will be fine? Please help.

Well I know my 1998 computer wouldn't like a missing sensor. I think your 1992 has two. One on the thermostat housing and one on the back of the head. I only have the one on the thermostat housing.

We'll see what others have to say about it, you know experience with pre 97 XJs but you might want to look into an adapter so that you can run the stock sensor and the mechanical sensor at the same time.

One thing you might want to try is just connecting the old temp sensor to the harness. It's cold when you start, but the computer might not like it if it doesn't see the sensor at all, and that could be causing a start issue.

[4.3LXJ]

Yeah Chris, you have to leave that sensor hooked up. The ECM uses engine temp to change the mixture. Rich when cold and lean when hot. Finding a good port is always an issue on a 4.0. Might have to drill and tap one.

[CLehman]

Thanks for the info...I tried plugging the sensor back in and the "Check Engine" light is still on, I really hope I don't have to drill and tap a new hole in the block or head just to get my temp gauge to work.

[Carves]

X 3 on needing to put the factory sensor back in.

The computer needs to see varying coolant temps as part of, applying the most suitable fuel settings.

Basically ... the computer is trying to pretend its a carby ... and is doing what Cheromaniac states in his post.

If you have a problem selecting a spot on the engine for the extra sensor ... you could always fit an adapter in the heater hose ... for the sensor to screw into.

[Carves]

The CEL probably wont clear until after a few start up, and warm to operating temp, cycles.

Later model XJ manuals state approx 160* is the minimum warmup temp but I dont know what the "92 specs are.

[Cheromaniac]

Now I took the factory temp sensor out of the Thermostat housing and put in the new mechanical setup.

There's your problem. The sensor in the t'stat housing is the coolant temp. sensor for the ECU to properly calibrate the air/fuel mixtures during initial cold start and warm-up. By removing this sensor the ECU thinks that the engine's hot and is providing an abnormally lean A/F mixture, resulting in difficult starting. It's a bit like trying to start a carburetted engine from cold with the choke valve fully open. It'll fire up for a split second and cut out again.
On the '92 XJ the temp. gauge sending unit is on the back of the cylinder head on the driver's side next to the valve cover and has a single wire electrical connector. That's the one you need to replace to operate your mechanical gauge.
Make sure you've remedied the problem first and then if you disconnect the negative battery terminal for 10 minutes, the CEL should go off and stay off.

[Carves]

There's your problem. The sensor in the t'stat housing is the coolant temp. sensor for the ECU to properly calibrate the air/fuel mixtures during initial cold start and warm-up. By removing this sensor the ECU thinks that the engine's hot and is providing an abnormally lean A/F mixture, resulting in difficult starting................................


Dohh .. :bang:

No sensor = No wiring circuit resistance.

PCM reads high temps at low resistance.


Well at least we all agreed the sensor is needed .. :D

[CLehman]

There's your problem. The sensor in the t'stat housing is the coolant temp. sensor for the ECU to properly calibrate the air/fuel mixtures during initial cold start and warm-up. By removing this sensor the ECU thinks that the engine's hot and is providing an abnormally lean A/F mixture, resulting in difficult starting. It's a bit like trying to start a carburetted engine from cold with the choke valve fully open. It'll fire up for a split second and cut out again.
On the '92 XJ the temp. gauge sending unit is on the back of the cylinder head on the driver's side next to the valve cover and has a single wire electrical connector. That's the one you need to replace to operate your mechanical gauge.
Make sure you've remedied the problem first and then if you disconnect the negative battery terminal for 10 minutes, the CEL should go off and stay off.

Awesome!!! Thanks man! That helps alot and makes total sense!!! Why in the hell didn't I think of that? You'd think I've never done this before...oh wait I haven't...not on a Cherokee so new. :bang: