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Discussion Starter · #1 ·
Overheated my XJ, now it won\'t start!!!!!!!!

Ok, well, yesterday I overheated my 87 XJ (with the 4.0) while driving
down the road. As I turned into a parking lot to let it cool off, the engine
died. Well, since it was cooling off, i got a ride home and left it for
about 3 hours. When i got back, i replaced the thermostat and coolant bottle
cap, and started for home. Well, about a mile down the road, i was sitting
at a stoplight when i tried to accelerate from a stop and it died. I cranked
it, and it wouldnt fire up. If I pressed the gas peddle down, it would crank
then stumble and die. It is acting like it did when the vacume line to the
map sensor was disconnected. But the map sensor was connected, and I tested
it and it tested ok. It stumbles when trying to start at full throttle. I
have no clue what the problem is. Its acting like it is running too rich,
too much fuel and not enough air. It puts out lots of nasty smelling black
smoke when it half-stummbles and dies a few times. This was last night.
Today I worked on it some more and these are my new findings: When I
went to start it cold after it sat all night long, it started up fine. But
then, as it warmed up, it got to runing worse. It would stummble and
hesitate if I tryed to rev it a little. It idled ok. Then, i turned it off.
Well, after that it went back to cranking and stumbling like it was flooded
or like if it had vapor lock or something like that, but it only even
stumbles at full thottle. Its still spewing bad smelling gases. Right now,
I am thinking TPS, Coolant temperature sensor, or MAT sensor. WHAT SENSORS
CAN BE DAMAGED BY HIGH HEAT? Could the coil have gone bad? What about the
ignition module?


PS: The CPS and pick-up coil in the distributor are all new, as well as the
cap, rotor, wires, and plugs. The oxygen sensor is about 6 months old, but i
dont think it's that.

· Registered
2,680 Posts
Re: Overheated my XJ, now it won\'t start!!!!!!!!

At the rear of the engine, the sixth cylinder, gets the hottest since it's the farthest part of the water jacket from water inlet. The greatest heat will be near the firewall. Unfortunately there are many crucial wires from the ECM back there -- including the CPS (which this could just be.) of course, heat could MELT your vac. lines. I'd start at the vac lines and make sure they're all flowing completely.

If not that, I'd hunt back on all the wires, not just sensors (which all might need replacement) but the connecting blocks as well. Like the relay box. The heat could have caused a resistance that could blow a lot of sensors. Do you have gauges or idiot lights? Gauges might give a clue to the problem.

Trace wires to make sure none have melted together. Make sure grounds haven't been burned off.

Oh, hell, I just remembered -- trouble codes!!! Give the key turn trick a shot. Do a search for trouble codes -- someone has the list and has put them up recently.

If I didn't have a Jeep, I wouldn't have a life.

'88 MJ SporTruck
Rebuilt 2.5L: 40 over rings, 10 on crank, 10 on bearings
nearing 400K
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