At my wits end, please help.

[Dinkster]

Coil is about a year old as well

 

[Schurkey]

The crosscounts continually climb. They start at 0 and work their way up to 250, the start back over at 0. They are constantly changing.

Yeah, that's gotta be an artifact of the scan tool used.

Doesn't seem to have a time-related function, so it seems less-useful than crosscounts as displayed on my scan tool. You'd have to estimate the speed of the increasing count to see if it's fast or slow.

 

[PlayingWithTBI]

Doesn't seem to have a time-related function, so it seems less-useful than crosscounts as displayed on my scan tool. You'd have to estimate the speed of the increasing count to see if it's fast or slow.

^^^This. As an example here's a data log showing my WBO2 and NBO2. Time line on the bottom, Cross Counts = 180

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I think some scanners use # of counts in 10 seconds, others use # of counts in one minute. That would explain @Schurkey seeing ~40 max with his scanner, and this example seeing 180. If I take 180/6 I get 30 Cross Counts per 10 seconds. Just a theory here.

 

[Dinkster]

Ok, so I thought because the tach needle was bouncing erratically that it could very well be a bad pick up coil in the distributor. I replaced the entire thing, set the timing at 0, holds steady, but no change in how it runs. I've tried spraying water on the coil and such looking for an arc, but that didn't show anything. Done the wiggle test to all the wires, nothing. Replaced/cleaned all the ground wires, nada. Any other ideas?

 

[Schurkey]

Erratic tach + misfire = ignition problem.

You've replaced all the "parts", and done some inspection of the wire harness.

ANYTHING connected to the ignition system is a potential cause. Including a faulty tach, a faulty ECM, wires that intermittently ground, a circuit that intermittently opens, etc.

This could be on the battery-power side (ignition switch and harness, bulkhead connector, wire to coil, wire between coil + and ignition module +) or on the ground side (coil - to ignition module -, the tach, and the wire harness between coil and tach. It could be on the signal side--wire harness between pickup coil and module, between module and ECM.

Does the misfire go away if you disconnect the tach wire from the coil? That's the easiest thing to check that doesn't disable the ignition system so the vehicle will still run.

 

[Dinkster]

I'll try that but I will say that the idle smooths out when the AC is turned on.

 

[Hipster]

I've tried spraying water on the coil and such looking for an arc, but that didn't show anything.

Not really a valid test. If it's grounding intermittently internally from vibration or such anomaly you won't see anything on the outside. Ohms test for ignition components are often described but inconclusive as well. Ohms test will tell you it's not bad but won't tell you if it can support a working load.

 

[Dinkster]

Yeah, very true but I'm tired of throwing parts at this thing. I replaced the coil about a year ago but of course, that doesn't mean anything.

 

[Hipster]

Yeah, very true but I'm tired of throwing parts at this thing. I replaced the coil about a year ago but of course, that doesn't mean anything.

No it doesn't and unfortunately we live in an environment where new can be bad out of the box.

 

[SNCTMPL]

If you want a second set of eyes on it, let me know, I’m out in Spanish Springs.
One of the next things I would do is verify that the timing mark and tdc are accurate, if so unplug the timing wire and set base timing to 8-10 degrees advanced. I have found that these trucks like some timing at our elevation.