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Ignition coil issue

DannyD

NAXJA Forum User
Location
Sweden
I'm having a bit of an issue with my ignition and was hoping someone could give me a push in the right direction.
96XJ 4.0 has been acting up with stumbling throughout the rpm range, especially on load. Driving it gives me quite a jolt.
Been testing a bunch of snesors, fuel pressure, compression and so on to no avail. Tonight I got to the coil.

While performing test Test 4 here: http://troubleshootmyvehicle.com/jeep/4.0L/how-to-test-the-ignition-coil-3

Turns out I don't seem to have an ignition driver pulse. Rather it's a comstant 12V no matter if the ignition is on or not.
This would indicate a short somewhere right? But howcome the engine manages to run albeit poorly and without power?
What am I missing?


Not terribly good with electrics. Funny that since 90% of the problems I'm having are just that but it doesn't seem I'm getting any better at solving them.
 
Thinking on this maybe the coil is strong enough to give a decent spark even though it's constantly triggered. Just not strong enough to give the strong spark need when engine is under load?
When I attached the test light it did kind of dim a bit occassionally so maybe the signal is being fed on top of the short or whatever is causing this.

I might disconnect the PCM connector tomorrow and see if I still get 12v. That would have to indicate a short and maybe then I can just run a new cable.

Any thoughts greatly appreciated sine the whole constant 12V things makes me afraid I'm overlooking something.
 
take the dist cap off and look for electrical tracking on the inside. check for corrosion on the pickups inside the cap and for the overall condition of the rotor inside. report back with info and pictures of findings
 
Define "bunch of sensors" and provide test results for each, or at least confirm which ones are within specifications.

Wondering why you are focusing on the coil ? What are the test results of the coils Primary and Secondary circuit resistance ? Have you performed the switching signal test ?

Basic trouble shooting should start with a look/feel/shake test of the wire harnesses and wire plugs looking for damage, corrosion, and the onset of symptoms when shaking a specific section of wire harness. Disconnect and clean all under hood wire plugs. Clean mating surfaces and snug all grounding points.

Typical suspects for stumbling would be old/worn/faulty tune-up parts, fuel pressure issues, and old/weak engine sensors especially the O2 sensors, and other sensors that are affected by heat due to age or infirmity.
 
I'm having a bit of an issue with my ignition and was hoping someone could give me a push in the right direction.
96XJ 4.0 has been acting up with stumbling throughout the rpm range, especially on load. Driving it gives me quite a jolt.
Been testing a bunch of snesors, fuel pressure, compression and so on to no avail. Tonight I got to the coil.

While performing test Test 4 here: http://troubleshootmyvehicle.com/jeep/4.0L/how-to-test-the-ignition-coil-3

Turns out I don't seem to have an ignition driver pulse. Rather it's a comstant 12V no matter if the ignition is on or not.
This would indicate a short somewhere right? But howcome the engine manages to run albeit poorly and without power?
What am I missing?


Not terribly good with electrics. Funny that since 90% of the problems I'm having are just that but it doesn't seem I'm getting any better at solving them.

How are you testing? There is a constant 12V (+) supply. The PCM switches ground.
 
Lets add a vacuum leak in the MAP sensor vacuum line "stumbling throughout the rpm range, especially on load"

and possibly a noisy worn TPS. Also should flow test/pressure test the fuel pump pressure under heavy demand......

Define "bunch of sensors" and provide test results for each, or at least confirm which ones are within specifications.

Wondering why you are focusing on the coil ? What are the test results of the coils Primary and Secondary circuit resistance ? Have you performed the switching signal test ?

Basic trouble shooting should start with a look/feel/shake test of the wire harnesses and wire plugs looking for damage, corrosion, and the onset of symptoms when shaking a specific section of wire harness. Disconnect and clean all under hood wire plugs. Clean mating surfaces and snug all grounding points.

Typical suspects for stumbling would be old/worn/faulty tune-up parts, fuel pressure issues, and old/weak engine sensors especially the O2 sensors, and other sensors that are affected by heat due to age or infirmity.
 
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