Bad running after manual swap

Thanks for the info guys! This may have to take the back burner for a bit as I will need equipment to burn a chip. Still something that needs to be done sooner than later.

Actually, I found the problem(s) making my idle so poor.


1. Low fuel pressure - I only had like 8psi, ended up being a bad regulator. Replaced the regulator and have 12psi now.

Would run really good, but then started doing the same thing again. Then I noticed when it happened, everytime I moved the ignition coil(wasn't bolted down for testing).

So I peeled back the 2 wires going from the coil to the ICM, turns out the previous owner did a terrible job splicing in a tach wire for a remote start that it had with the automatic transmission. He left the bare wires, wrapped in a zip tie with loose electrical tape. I got shocked by it just looking at it while it was running. Also tugging the wire and moving it made it misfire and stumble.

Ok so I’m REALLY lost now. I replaced both the coil wires and it’s still happening. But I now found what is causing the problem….

For some reason when the coil is next to the distributor cap and touching the intake in it’s normal resting place it misfires and surges like hell. But as soon as I move it in the air and hold it there it runs completely fine. I can now make it run crappy and then make it run good. But I don’t know what’s causing it.

I’m so confused why it is doing this.

You mentioned that you cracked the ICM when the engine fell back against the firewall. Could that be your problem and did you check the dist. cap. I cracked a cap once doing a tranny R&R.

Scooterwrench said:

You mentioned that you cracked the ICM when the engine fell back against the firewall. Could that be your problem and did you check the dist. cap. I cracked a cap once doing a tranny R&R.

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I ended up finding the issue. There's a short somewhere in the red wire on the gray connector going into the coil.

The red wire should have constant 12V keyed on, it does until I bring that wire down to the intake area near the distributor, then it loses all power.

Does anyone know where that specific red wire on the gray connector leads?

JPVortex said:

I ended up finding the issue. There's a short somewhere in the red wire on the gray connector going into the coil.

The red wire should have constant 12V keyed on, it does until I bring that wire down to the intake area near the distributor, then it loses all power.

Does anyone know where that specific red wire on the gray connector leads?

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just traced that wire all the way up to the bulkhead, and theres no obvious breaks in it or anything

JPVortex said:

when the coil is next to the distributor cap and touching the intake in it’s normal resting place it misfires and surges like hell. But as soon as I move it in the air and hold it there it runs completely fine. I can now make it run crappy and then make it run good. But I don’t know what’s causing it.

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Ohmmeter testing of the ignition coil, between primary winding and ground.

Connect one lead to a primary terminal, the other to the coil mounting bracket. There should be no continuity--an open circuit. ANY continuity means the coil is faulty.

IF there's continuity, the primary winding is grounding to the engine, which means the primary windings have a short-circuit to ground. Kinda surprising that the short-circuit to ground didn't pop an ignition fuse.

Another possibility is that the wires have a break in them, that opens up when the coil is near the manifold, but connected when the coil is raised-up from the manifold. Kinda unlikely, though.

Schurkey said:

Ohmmeter testing of the ignition coil, between primary winding and ground.

Connect one lead to a primary terminal, the other to the coil mounting bracket. There should be no continuity--an open circuit. ANY continuity means the coil is faulty.

IF there's continuity, the primary winding is grounding to the engine, which means the primary windings have a short-circuit to ground. Kinda surprising that the short-circuit to ground didn't pop an ignition fuse.

Another possibility is that the wires have a break in them, that opens up when the coil is near the manifold, but connected when the coil is raised-up from the manifold. Kinda unlikely, though.

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I don’t believe it to be the ignition coil itself, I’ve tried 4 different ones at this point.

The original distributor was literally sparking here and there from the body of it into the bracket.

Also looked through the red wire and did in the cab find a bare piece of exposed wire where the previous owner had put a remote starter. I reinsulated it.

But yeah literally it’ll run fine and all of a sudden the tach will start fluttering, like glitching and it’ll start stumbling and misfiring.

Schurkey said:

Ohmmeter testing of the ignition coil, between primary winding and ground.

Connect one lead to a primary terminal, the other to the coil mounting bracket. There should be no continuity--an open circuit. ANY continuity means the coil is faulty.

IF there's continuity, the primary winding is grounding to the engine, which means the primary windings have a short-circuit to ground. Kinda surprising that the short-circuit to ground didn't pop an ignition fuse.

Another possibility is that the wires have a break in them, that opens up when the coil is near the manifold, but connected when the coil is raised-up from the manifold. Kinda unlikely, though.

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Just tested the 12V coil wire again, its not losing voltage at all anymore, so that's good.

Now I am starting to get suspect of the parts store ignition coils. I just swapped out YET another one, and this time it doesn't even run the truck.

My OEM one runs the truck but you can literally see the spark coming out of the side of the coil. So the primary windings probably have a short.

Im going to order an OEM one...

JPVortex said:

My OEM one runs the truck but you can literally see the spark coming out of the side of the coil. So the primary windings probably have a short.

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Sounds like the insulation's broken-down somewhere on the coil and/or there's too-high spark voltage, possibly on account of...

JPVortex said:

Im going to order an OEM one...

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Have you checked your ignition wires with an ohmmeter? In particular I'm wondering if the spark is having trouble finding a path from the coil to the dizzy.

Another test is to clip a "test" spark plug to the top post of the distributor (or, depending on the cap style, stick it upside down in the hole) and then attach the coil wire to the test plug. The test plug will spark with every cylinder firing, and should spark equally for all cylinders. Yes, the engine will run if you do this.

1998_K1500_Sub said:

Sounds like the insulation's broken-down somewhere on the coil and/or there's too-high spark voltage, possibly on account of...



Have you checked your ignition wires with an ohmmeter? In particular I'm wondering if the spark is having trouble finding a path from the coil to the dizzy.

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What would cause too high of a spark voltage?

Also I have not checked the wires with an ohmmeter, I did just replace them about 2-3 months ago, and none of them seem bad at first glance. Will certainly check them though. How much resistance am I looking for to know they're good?