which engine so you have?

so if you attach the spark plug wire from the distributor cap directly to the spark plug and ground the metal threaded part of that spark plug and crank does it make a spark across the plug gap?

 

It's the 4.0. And no, connected directly to distributor and grounding, no spark across plug gap.

 

check for constant battery plus and pulsing ground at the coil wires while cranking
if those are good only leaves

bad plug or bad plug wire or bad cap/rotor or bad coil

 

If the picture is any indication and you are getting just an orange spark in the spark tester, I would say the coil is weak. A good coil should produce a blue/white spark. If you can, try using a known good coil and see if it makes a difference.

 

First of all, you don't have points. It is electronic ignition controlled by the PCM (Powertrain Control Module, "computer"). Maybe you are talking about the contact posts in the distributor cap.

Secondly, there was a thread for "died while driving, now spark from coil but not at plugs" in July & August and it is still not resolved. That guy is talking about buying a new PCM. He's tried a new coil, new dist cap & rotor, cleaned grounds, etc. What we don't know is if the spark from the coil is strong enough, or if it is at the right time. I don't know what is needed to test the coil spark strength, maybe simply a gap-type spark tester.

Don't use the spark tester, do it old-style. I assume you are doing it without a helper. Get the 2 longest of your old spark plugs, put 1 in the coil. Lay a piece of cardboard, or a real board, or carpet, on top of the engine for the wires to lay on. Put the end of the long plug wire from the coil where you can see while cranking the engine. Put one end of the other long plug wire about 1/4" away (5 or 6mm) and connect the other end to a ground point. Clamp it to a bolt or something. Maybe go all the way to the battery negative if it will reach. Crank the engine and see what the spark between the plug wire ends looks like. It should be very noticeable and lively. If so, move the ends a little farther apart 1/8" (3mm) and crank it again. If you get a good spark then, put the end of the 2nd long plug wire in the distributor center post (coil post) and crank it again. What did you see?

What I'm getting at here is that if it sparks strongly when grounded directly but not when going through the distributor, I'm thinking that it means the PCM is firing the coil at the wrong time and the spark is facing too much resistance to jump the gap from the rotor to the post. If you have weak sparks with the gap method and indications are that the coil is good, that would mean the PCM is triggering the coil incorrectly and cutting down the voltage. I don't know if that can actually happen, but it seems like it probably can.

 

Did you read through that long thread by Daggers?

 

Thanks for the responses so far, I'll be testing these this weekend and will report back. Fingers crossed!

check for constant battery plus and pulsing ground at the coil wires while cranking
if those are good only leaves

bad plug or bad plug wire or bad cap/rotor or bad coil

I need to double check for pulsing ground at the coil, good call.

Don't use the spark tester, do it old-style. I assume you are doing it without a helper. Get the 2 longest of your old spark plugs, put 1 in the coil.

This is similar to the process I followed in my testing, but you've got better detail. I will test and report back.

Did you read through that long thread by Daggers?

Yes, and I was hoping that thread would reach a resolution. I went thru all of the weak spark and crank no start threads I could find (as I previously thought I was getting no voltage to the plugs, the tester indicates I'm getting at least some). I did also go thru the dirty dozen and my factory service manual, but a lot of the diagnostic trees just point to the coil. Everything else has been testing good.

I'm hesitant to just put a new coil in since this one is relatively new and has good primary/secondary resistance. Since I've had some crank/no start trouble in the past (mostly better since replacing CPS), I didn't want to potentially miss another issue that could be contributing to this. Perhaps the more logical approach is to just get another new coil and see what happens. Just trying to do a diligent dive before I throw some parts at it.

 

Does your original coil have the same resistance values and the "new" coil, the ~year old Spectra?

I guess something could happen inside the coil so that the resistance values through the windings are correct but it can't generate the correct voltage or current. What exactly was your text method? I'll go check my old "assumed original Mopar" coil that works.

 

For testing, I followed the procedure from this thread to verify primary/secondary resistance. New coil falls within aftermarket spec, and original coil falls within OEM spec.

For voltage on the connector, I backprobed at the plug and grounded directly to the battery. That yielded the results in my original post, although I do need to check that the ground alternates.

 

1.0 & 12650, and it works.
The only number I can see on it is 101015, so apparently it is not an original Mopar.

Did you notice this from Post #2 in the linked coil test thread:
"Roughly 1 ohm on the primary and 12,000-13,000 on the secondary.
Can't always find a bad coil with a resistance test though. They sometimes hold together fine on the low voltage from the DMM but short like crazy under high voltage.

You should have battery voltage (12-13V) on the positive primary coil connector and about half that on the negative while cranking. If the positive and negative primary connectors show the exact same voltage while cranking, the ECU isn't trying to fire the coil. That's often a bad CPS"

You said you have 10.9 on both, didn't you? Was that what you were talking about? Wait, you get a spark from the coil though.

 

Where you said "Green and red wire stay grounded, gray and yellow are grounded sometimes", that's the PCM grounding the negative side intermittently isn't it?

 

You should have battery voltage (12-13V) on the positive primary coil connector and about half that on the negative while cranking. If the positive and negative primary connectors show the exact same voltage while cranking, the ECU isn't trying to fire the coil. That's often a bad CPS"

You said you have 10.9 on both, didn't you? Was that what you were talking about? Wait, you get a spark from the coil though.

Where you said "Green and red wire stay grounded, gray and yellow are grounded sometimes", that's the PCM grounding the negative side intermittently isn't it?

I did a whole bunch of testing today to check. Tried a new coil with no luck, and now I'm not seeing spark in the spark tester either. I updated the original post with more details/pics, but it doesn't look like the gray/yellow wire is correctly grounding and ungrounding at the coil. Looks to be 1V to 3V rather than 0V to ~11V.

My sense is that since the frequency is correct but voltage is off, it has to be the PCM. I can't think of how it could deliver a different voltage, unless you think this is the correct voltage to see from the ignition coil driver.

Definitely in the weeds now...

 

"I can't think of how it could deliver a different voltage"

In some of the "failed PCM" threads for '96-'98 people have reported cracked solder at circuit connections inside the PCM. That could cut down the voltage delivered due to the increased resistance, and maybe cause the noise you saw because of arcing instead of smooth current flow. In "failed PCM" threads for first generation '93-'95 with OBD I PCMs, failed capacitors on the circuit board were reported in a lot of cases. I don't know if '96-'98 PCMs have failed capacitor problems too, it would seem likely possible. A malfunctioning capacitor would alter the output I imagine.