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Jeep Wrangler YJ
YJ General Discussion
Do ECM's "Break Down"?
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<blockquote data-quote="DOWNS" data-source="post: 440021" data-attributes="member: 21038"><p>I don't see a year mentioned, but as mentioned above you have no control over the ignition timing in a 4.0 no matter how much you move the distributor around. The ignition timing is fully controlled by the computer. Usually somewhere between 10 and 14 degrees BTDC at idle. This is a common failure mode of various sensors, they're fine cold but when you get them hot they fail, can make diagnoses very difficult sometimes. This failure mode can also happen with coils. Work fine when cool but get some heat in them and they start to malfunction. You could always put a multimeter on it and troubleshoot it that way. But if it's cold it may show good readings. Maybe drive it till it starts to mess up then shoot it then.</p><p></p><p>Your experience of bucking backfiring etc sounds like a possible TPS that has a "dead" spot, it causes wildly erratic readings to the computer about where your throttle is actually at. Put your multimeter on it and slowly open and close the throttle by hand (engine off) and watch for erratic or no readings on the multimeter though the full sweep. An analog meter is easier to use for this, but you can use a digital one as well.</p></blockquote><p></p>
[QUOTE="DOWNS, post: 440021, member: 21038"] I don't see a year mentioned, but as mentioned above you have no control over the ignition timing in a 4.0 no matter how much you move the distributor around. The ignition timing is fully controlled by the computer. Usually somewhere between 10 and 14 degrees BTDC at idle. This is a common failure mode of various sensors, they're fine cold but when you get them hot they fail, can make diagnoses very difficult sometimes. This failure mode can also happen with coils. Work fine when cool but get some heat in them and they start to malfunction. You could always put a multimeter on it and troubleshoot it that way. But if it's cold it may show good readings. Maybe drive it till it starts to mess up then shoot it then. Your experience of bucking backfiring etc sounds like a possible TPS that has a "dead" spot, it causes wildly erratic readings to the computer about where your throttle is actually at. Put your multimeter on it and slowly open and close the throttle by hand (engine off) and watch for erratic or no readings on the multimeter though the full sweep. An analog meter is easier to use for this, but you can use a digital one as well. [/QUOTE]
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Jeep Wrangler YJ
YJ General Discussion
Do ECM's "Break Down"?
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