exhaust is too hot, not engine

My 87 XJ has been running so hot that the carpet inside above the mufler caught fire. I have been trying to solve this problem for 6 months with a severe lake of results so any suggestions will be helpful. The engine temp seems to be fine (as long as I remember to hit the swith for the electric fan while I'm wheelin' ) Here is what I have done so far to solve this:

New muffler & cat
Had the fuel system power flushed
New coil and did a major tune up
New O2 sensor

Still after a freeway run or a run up a tough trail you start to smell the foor getting hot and when checked it is too hot to touch. Last night I checked my friend's XJ and his floor was warm but nothing like mine. I took it to a shop and paid them to run a diagnostic on the thing. That is where I had them do the fuel system flush. It runs better but still heats up. I can't think of what else to do other that take it to the dealer and pay them to check it out. You have no idea how much I hate doing that but I am at a loss here. HELP!

Mine started doing this after installed the flowmaster. So I put in a heat shield. You can find them on tons of other vehicles in a junkyard. I took mine out of a newer F-150. It's helped reflect alot of heat away from the floor.

My suggestion is to take your XJ to a mechanic who can hook up the test set and have him verify the engine is working correctly.

You did not mention what MPG you are getting. You could be running rich. Even with the new oxygen sensor if there is a broken wire the computer will not get the signal.

I think a visit to the mechainc and paying an hour of diagnostic fee will help you know where to attack. The problem with our engine controls is no error codes are read and the customer can not read the computer. What ever mechanic you use make sure he understands the renix engine control system

I thought about welding on a heat-shield but decided that was not correcting the problem just masking it. It shouldn't run this hot. I did take it to a mechanic but now I'm not real confident they knew JACK about the Renix system. The only place I can find around here that is experienced with them is the Jeep dealer. Could it be dumping so much fuel that it is burning inside the muffler? About all I can think of now is the computer unit itself might be bad or the fuel injectors. MPG is crap, about 10. Throttle response is bad and it has NO power climbing any type of grade on the road, never has. How do you test the O2 sensor?

If you have a high flow type muffler it is normal for them to run hot. Flowmaster even states that a heatshield should be run.

You can use one form a '97 or newer XJ that is an easy install over the muffler. Runs about $20 at the stealership. I run one over the muffler and now run one over the cat as well.

Also check the cat. Sounds like it could need replaced as well.

Bones :skull1:

You guys were right

I went and bought a universal heat shield from a muffler shop ($15) and a couple 12" hose clamps. Took care of the problem, at least on the road. I'll try it on the trail tomorrow and let you know. By the way, the Jeep dealer could not figure it out. THey did a diagnostic, told my it was the harmonic balancer. Said it was broken and slipping on the end of the crank. Therfore the timing was fluctuating all over the place. I replaced that but it did not help the heat problem. Runs a heck of a lot better though. Anyway, you guys were right all along about the heat shield. How could I ever have doubted you

Thanks.

Don

http://www.cascade4x4s.com

Running that hot is usually a result of either a stuffed catalytic converter, or just running REALLY lean. What are your coolant temperatures like?

5-90

Re: You guys were right

masterdon said:

...THey did a diagnostic, told my it was the harmonic balancer. Said it was broken and slipping on the end of the crank. Therfore the timing was fluctuating all over the place. ...

Don

http://www.cascade4x4s.com

Click to expand...

HUH? Way late timing might well cause hot exhaust, but how do they suppose the harmonic balancer affects timing? It might affect the position of the timing mark on the pulley, but the CPS and computer determine timing.

Re: You guys were right

masterdon said:

By the way, the Jeep dealer could not figure it out. THey did a diagnostic, told my it was the harmonic balancer. Said it was broken and slipping on the end of the crank. Therfore the timing was fluctuating all over the place. I replaced that but it did not help the heat problem.

Click to expand...

You need to find a new dealer ASAP. The harmonic balancer does not affect the timing. Timing is controlled by the CPS (crankshaft position sensor), which is mounted on the bell housing and reads revolutions from the flywheel.

That much heat together with lousy fuel mileage suggests that you are running too rich, and that unburned (or partially burned) fuel is being burned in the catalytic converter. That fits with the suggestion above that possibly the connection between the O2 sensor and the ECU is faulty. When my O2 sensor went bad, I would hear occasional "POP"s from the exhaust as fuel hit the cat. I caught it before it failed completely, so in my case I noticed that primarily when I would remove my foot from the throttle at speed, transitioning immediately from accelerate to decelerate.

the only time i saw a red glowing header is when the cat is clogged. maybe you have a really thin exhaust? that is weird.

Have you checked your MAP sensor?

i remember some earlier jeeps had leaking fuel pressure regulators. disconect the vacuum hose on the regulator and see if gas leaks out. the diaphragm inside may have ruptured.