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88 XJ won't start warm

R

rpyne

NAXJA Forum User
Location
Provo, Utah
I am at my whits end. I have an 88 Cherokee I-6 that won't start when the engine is warm. It starts fine when it is dead cold. I have noticed that just about the temperature when the thermostat opens it will either cut out for a second or two if I am above idle, or die if at idle, then it won't start until it cools down. It cranks fine, just won't start.

In the last couple months I have replaced the Coolant Temperature Sensor, the Cam Position Sensor (in the distributor), the Crank Position Sensor, the Ignition Module and the Engine Control Unit (Computer).

ANY help on where to look now will be greatly appreciated.
 
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rpyne said:
In the last couple months I have replaced the Coolant Temperature Sensor, the Cam Position Sensor (in the distributor), the Crank Position Sensor, the Ignition Module and the Engine Control Unit (Computer).

ANY help on where to look now will be greatly appreciated.
Click to expand...
How's about the coil itself?
It's another one of those parts that suffer from thermal breakdown.
 
I am still running my original 89 HV coil and ICM.

Check the MAT (IAT) sensor resistance while cold and hot first. It is in the intake manifold, rear. Intake Air temp sensor. See the table in the link below for resistance versus temperature.

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

Also check the CPS cranking voltage while hot with an AC volt meter. Should be over .35 V, some say it needs to be over .5 V.

Lastly, try disconnecting the O2 sensor to see if the warm engine dying stops. It may be bad, and flooding the engine?
 
If you are missing spark (confirm that you are missing spark; very important!) when the engine warms and the crank sensor has already been replaced, TEST the ignition coil as B. Raider mentioned.

But test it only when symptomatic (ie: no spark) The ignition coil can suffer from "thermal" (heat related) failure.

The coil can be tested pretty easily for primary and secondary resistances with a meter and a manual.
 
Also...determine if you have 12 volts to the ICM when you have a failed start and no spark. No voltage means that the problem is further up line before it gets to the ICM.
 
Hair dryer on the test part while engine is running is a good thermal test method.
 
One clarification. Once it is running and warmed up, it will continue to run until I shut it off, then it won't start again until it cools off.
 
rpyne said:
One clarification. Once it is running and warmed up, it will continue to run until I shut it off, then it won't start again until it cools off.
Click to expand...

If the camshaft position sensor signal is lost while the engine is running, the computer will calculate spark timing based on the last CMP signal and the engine will continue to run. However, the engine will NOT run after it is shut off.

It is located inside of the distributor. I know you said you replaced it. Was it a new unit or a junkyard one? I would still test it when you experience the no-start.
 
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birchlakeXJ said:
If the camshaft position sensor signal is lost while the engine is running, the computer will calculate spark timing based on the last CMP signal and the engine will continue to run. However, the engine will NOT run after it is shut off.

It is located inside of the distributor. I know you said you replaced it. Was it a new unit or a junkyard one? I would still test it when you experience the no-start.
Click to expand...

According to 5-90, the Renix will start with out a signal from the Dizzy sensor (CMP?), it will be slow to start, and some times fail to start right away, but will start if pushed, cranked long enough.
 
rpyne said:
I replaced the entire distributor with a reman from O'Reily (Checker).
Click to expand...


Ah Ha!!!! Ding, ding ding!

The notorious Dizzy installed but one tooth off from correct timing set up!

Search here for "Renix distributor installation" issues, and how to get it installed right! It is tricky to install, and easy to get installed, but off but one tooth. ECU tries to compensate, start and run, but causes many issues likes yours!

http://ezinearticles.com/?How-to-Index-the-Jeep-4.0-Distributor&id=1357018

http://www.google.com/search?q=reni...s=org.mozilla:en-US:official&client=firefox-a
 
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