no start when hot

[beachbum2425]

1997 Jeep Cherokee Sport automatic Start problem when engine reaches 220 degrees -I replaced spark plugs, spark plug wires, distributor cap, rotor, air filter, oil filter, coil, engine oil and transmission oil, also checked engine computer and found no trouble codes. After above work we took vehicle out for a test drive. When engine temperature gauge read about 220 degrees F, engine stalled at traffic light while idling. Engine would turn over but would not start for 45 minutes after hood was opened and engine allowed to cool. During no start condition found no power going to the coil. Automatic Shutdown Relay, on front passenger side wheel-well in engine compartment, powers the coil and was not closed. The engine computer actuates this relay after receiving information from certain engine sensors. I believe the crankshaft position sensor and camshaft position sensor will allow auto shutdown relay to close but am not sure if anything else is required. Is anyone familiar with what is required to close the Auto shutdown relay? I did manually closed the auto shutdown relay, but still would not start. Found evidence that engine computer, camshaft position sensor and coil had been replaced in the past. So I'm thinking that the Crankshaft position sensor should be changed. For now,to keep engine from stalling; I electrically disconnected the air conditioner compressor clutch and then turned on the air conditioner with dashboard controls. This allows electric radiator fan to run, cooling radiator and engine, without the air conditioner actually running. I also removed the engine thermostat; this allowed engine to run at about 170 degrees, we did not have any further stalling problems. The problem is definitely heat related but what is causing the no start problem? Anyone have any ideas? I guess, I should probably include this: the vehicle is in the Dominican Republic and used by home building missionaries; I live in Florida. I need to know what to bring with me before I head back. Also oil pressure gage varies all over place sometimes steady but sometimes zero and sometimes full scale. Thanks in advance.

[beachbum2425]

If no one has any new ideas , at least does it seem like I am on the right track? Any help would be great. Thanks

[tjwalker]

It certainly could be a flaky crankshaft position sensor that is sensitive to heat. I think that is what I would focus on, especially because it is a very common component failure in a Cherokee. This sensor is located on your transmission bellhousing.

Use the "search" function for more info and tips on installation. Trying to test or troubleshoot this sensor probably wouldn't work in this case as it could test out fine while engine is cold and then fail again as soon as it gets hot. I think if it were me, I'd just replace it.

As far as the oil pressure gauge varying, that's an easy one. Start with replacing the sending unit for the gauge; it's right by your oil filter. They aren't that expensive and again are prone to failure in your Jeep. 9 times out of 10, that takes care of it. Very rarely is it the gauge itself.

Good luck! Keep building those houses!

[CharBroiled]

my 2000 FSM says the ASD can be tripped when the CPS signal is "lower than pre-defined values.." so the CPS could certainly do it.

[beachbum2425]

Thanks guys, I will be bring along a crankshaft position sensor, oil pressure sending unit, new thermostat and gasket, radiator flush kit and new antifreeze, and a bunch of socket extensions and universal joints. It seems to be a tough job getting to the CPS.