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93 jeep grand cherokee no hot start

5K views 1 reply 2 participants last post by  qldit 
#1 · (Edited)
this jeep is driving me nuts no code come up on scan jeep will not start when warmed up changed all most every thing like coil pick up coil sensers still has this problem any one think of what it can be? thier is no fire has good fule
presure any help would be greatly needed ty
 
#2 ·
Good Evening montie, that is an interesting problem, I would suggest getting an old spark plug and temporarily mounting it on a suitable place, like an engine lifting point etc, and securing it with a suitable retainer, a wire tie or something like that.

The object of the exercise is to let the engine get hot and then disconnect one of the spark plug leads and attach the lead to that plug, carefully observe if spark is present when someone else cranks the engine.

What often happens is that the cylinder compression increases when the engine is hot and the spark has a problem jumping the plug gaps.
As the compression increases spark jump ability deteriorates quite markedly.

When this kind of problem happens it commonly causes the spark to actually track inside many modern coils and is a real nuisance to troubleshoot because the coils often are buried inside distributors etc. and are very expensive and difficult to replace.
When a tracking situation happens it is commonly apparent symptomatically by hesitation when power is applied when the engine load is increased, most often in the higher gears.

So you will appreciate why the extra spark plug trick can be so useful, if the lead is simply held away from the engine it can damage the coil pack etc or the ignitor control circuit.

If your system uses a simple standard old type ignition coil it is quite easy to get caught with reversed primary control connections, the actual high voltage passed to the spark plugs must always be "negative" otherwise your kind of symptom will happen. The spark plug cenre is always cathodic.

You could try regucing the plug gap to a typical hacksaw blade width and seeing if that assists. This is just a trial tip.

Theoretically the computer system should not cause your symptom.

Others will have different ideas.

Cheers, qldit.
 
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