ok been battling no spark i get 12v on the positive side of the coil plug and ground when crank signal activates it. could my distributor be throwing it out of sync? i removed the distributor and reset it the way it came out. it was stuck and couldnt be turned clockwise or counter clockwise. put back in and truck fired up i could turn the distributor and change engine tone ok good. truck dies about an hour into running distributor can not be turned again with retainer nut completley out. i can wiggle the distibutor easy just cant turn it again. is this normal. oh by the way the shaft inside the distributor dosent seem to be stiff like its locked up or anything any ideas lol

 

wanted to add that i can pull crank sensor and trigger with a screwdriver the ground pulse from pcm. but with my new coil and old coil i cant make em spark with a 12v hot ran to positive and ground triggering? with a volt meter i can trigger pcm coil ground and read 12v when reading from battery positive so the coil should fire once right?

 

ok been brain racking maybe im not getting good enough ground be cause with all three of my crank sensor yes i got extras lol i can trigger 12v reading when pcm ground pulses by turning the engine over by hand . and .01 when cranking this is with the meter on coil ground and battery positive when i put meter on coil positive and battery negative i get a 9v reading when cranking. but when i put meter on coil positive and coil ground i get .01 on my meter so im thinking maybe a bad ground since i have checked the coil ground to pcm it is good no shorts but i can only find the wire from engine to body were is the wire from ground to the pcm coming from? also i see it splits into two grounds and goes into k11 and k12 one bieng for sensor and coil grounds and the other main pcm ground does anyone know were this splice is?

 

If you're talking about the PCM ground, it is bolted in at the back of the passenger head (not too far from the crank position sensor). That's where it is on my truck, at least. From that same bolt, there's another cable that runs to the firewall and bolts in there.

For general things, check the notorious splice under the power distribution center, check that you hear the fuel pump turn on (sounds like a hum) because the ASD relay powers up the fuel pump and the ign coil.

Check that you're getting a spark from the wire off of the ign coil. If you have a spark there, then start looking at your distributor. If you don't have a spark, take a step back and check that your ign coil is good. If that's good, step back to check the relays. If those are good, step back to the PCM and its ground.

 

i have confirmed the power splice under pdc to be good 4 red white wires i redid the connection just to be sure. get plenty of fuel and 12v on the posistive coil side about 9-10 when cranking but when i read read coil negative to coil positive i get .01 when cranking. but when i take measure coil negative to battery positive i can get 9-10v when cranking. it just seems to me like the ground signal for coil is crapping under load. have tested circuit from coil ground to pcm looks good on the multimeter. are there anyother splices that would cause no spark? i have checked for 8v at cam and crank sensor's it is present the whole time. ps the only ground i have on the passenger head is the braided cable running to the firewall the wire harness was replaced 5 years ago maybe they hooked it up elsewere. going to hunt it down now

 

Regards the ground lead your not alone, our 92 with 3.9L also has only the metal braid from head to firewall near vacuum res. There are two black 16ga leads from the harness that also attach to the firewall nearby. I have looked at other 3.9L trucks in the parts yards and many are similar setup.
If you find where the PCM ground is terminated on yours please post. I can't get to our truck till weekend to look further.

 

ok so i have noticed using the coil negative pulse and a lead from the battery positve to coil plug positive i can read 12v when activating crank signal by hand when i crank with key i get .03 to .06 this is with coil unpluged. ok when i plug in any of my 2 new coils the voltage reading drops to almost nothing when activating signal by hand and almost nothing when cranking. what in the world could be?

 

last couple of posts sounds that when you are trying to test coil function by activating crank signal by hand.
dumb question here; does it need key in run position if using the PCM to trigger spark and not cranking?

Is the meter you are using fast enough to catch a PCM trigger signal? (I don't know what the duration is for the PCM) Any chance you have a running vehicle to do a similar test on and verify what the meter would show?

Any difference in impedance from original coil to replacements?

 

yes the key must be in the run position otherwise the pcm will have no power i simply take a screwdriver and passit over the crank sensor it makes the fuel injectors pulse and the fuel pump run and triggers the ground signal for the coil. that is until you put a light or coil or something that draws power then the pcm coil signal goes away completly although the injectors still pulse and the fuel pump still runs

 

so no one has any ideas?