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91 4.0 no spark still :(

J

jeeptorino68

NAXJA Forum User
Location
Lebanon OR
ok so, i think this has nothing to do with it, but the jeep was sputtering and coughing and literally wouldnt get out of its own way, thought it was bad fuel, since i ran it down low, and maybe sucked up something bad, filled it with fresh gas from the pump, and a bottle of techron, and it ran good for about 3 days, then started getting worse,

my dad pulled the tank, fuel pump/sender, and cleaned the tank out, as well as putting in a new filter, but now the jeep has no spark!!!


so we tested the CPS and CKS and came up with test results seemingly indicating a bad CPS (cam sensor) he replaced that, and nothing, so he reaplaced the CKS too, nothing.


what else could there be? coil? is there an easy way to test the coil? when he put the timing light on the wire from the coil to the dist there was no light.


what else could there be, everything else is fine, cranking, fuel, etc
just no spark and we have done the common/obvious.
 
Here is how to test the coil

Tests/Procedures: 1. Unplug the ignition coil connector.

2. Check for B+ on the Dark Green/Orange wire at the coil when cranking.

3. If OK, connect a test light to B+.

4. Check for a flash of the test light indicating a pulsed ground. If OK, replace the coil.
 
Try swapping the relays around.
 
also try ohming the coil. pull the connector off and place the leads on the two terminals. you should have something under 2 ohms but not an open circuit. then check from the coil wire terminal on the coil to each of the terminals on the connector. you should have somewhere around 10-13K ohms, not an infinite reading, indicating an open. last try testing each terminal to the case. in should read infinite. if you have any reading, the coil is shorted. also take it off and check it over. if its cracked a lot, you might replace it anyways. i just replaced one that tested fine but had like ten cracks in the case and wouldnt create a spark
 
wildman, what do you mean by the B+ on the dark green/orange wire?


also where is the ASD relay located, the fuse box doesnt say,

finally i will try using the ohm meter on the coil too to see if its bad, is that the last likely cause?
 
there is no icm on a 91. spark is controlled by the PCM. if you have a pulsing 12 V while cranking at the coil connector the PCM is good and the coil is bad. you need to rule EVERYTHING else out though before you replace the PCM
 
Are you getting 12v to the coil? Is the ASD relay working?
 
heres more info,
the coil tested good at the parts store, and seems to test fine, gets 12 volts, has the proper resistance, isnt grounding to its case, but there is no pulsed 12 volts to the connector at the coil.... that seems bad, does that officially point to the PCM, or is there something else that could be causing such a problem



also there is nothing near the fuel pump and sending unit that would cause no spark right? that is the last thing we worked on before the no spark happened, and we did the CPS and CKS and neither brought spark back...
 
one thing that happens on these is one of the terminals will slip out of the connector on the relays will slip out of base, then get to arcing till it finally loses contact, look at the bases for the relays very carefully. seen it on several jeeps in our club.
 
well im out of ideas too, so ill just keep replacing things i guess, until i get it, i can try a new coil and other parts
ill let you know when i find it
 
jeeptorino68 said:
well im out of ideas too, so ill just keep replacing things i guess, until i get it, i can try a new coil and other parts
ill let you know when i find it
Click to expand...

Pin out the PCM and harness--i.e., test it. You will need the FSM or someone to give you the correct info on the OBDI models, I can't help you I'm Renix.
 
i know the PCM to sensor wire testing was the next step, i probably cant help my dad with that over the phone or email, so it will have to wait until thanksgiving.

other then a new coil thats all i can think of to do,
 
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