Bad running after manual swap

[JPVortex]

Yeah, I'm grasping... but d@mn, when you move that coil around the problem is so evident.

Yeah, I dont see how it could be anything else other than a short somewhere in its circuit.

 

[Scooterwrench]

If you're losing voltage to the coil when moving that wire then it's the wire coming from the ignition switch. Disconnect that wire from the coil and put your voltmeter on it. Turn on the switch then go along that wire and bend and wiggle it while watching the voltmeter. if the voltage drops you will have found the bad spot.
Hint, this is a job for a analog voltmeter. Twitches in the needle will be easier to see than the on and off of a digital meter.

 

[JPVortex]

If you're losing voltage to the coil when moving that wire then it's the wire coming from the ignition switch. Disconnect that wire from the coil and put your voltmeter on it. Turn on the switch then go along that wire and bend and wiggle it while watching the voltmeter. if the voltage drops you will have found the bad spot.
Hint, this is a job for a analog voltmeter. Twitches in the needle will be easier to see than the on and off of a digital meter.

I did this test yesterday and the voltage did drop. But then I did it again and it didn’t. So I can’t tell if it’s losing power or if I just slipped the prongs on the multimeter.

 

[JPVortex]

Do you guys think this will be an issue the shop can find fairly quickly?

 

[Scooterwrench]

Do you guys think this will be an issue the shop can find fairly quickly?

You hope!

 

[1998_K1500_Sub]

You hope!

What are shop rates these days for labor, >$120/hr?

I still believe that wiggling each wire one-by-one should allow you to invoke the symptom and thus identify the problem connection.

Alternatively:

Can you easily “hot wire” the +12V lead from the ignition switch to the coil, and just connect that wire directly to the battery?

If the problem persists, then it seems the next likely culprit is the physical connection to the ignition control module.

 

[Scooterwrench]

What are shop rates these days for labor, >$120/hr?

Yeah,and they're going to whine and milk it because he's changed the tranny and tried to fix this issue himself. Everytime I go for a front end alignment they spend most of their time poking around trying to find something they can milk me for. I got pissed at one place and told them to just take it off the rack so I can take it somewhere else.

 

[JPVortex]

Yeah,and they're going to whine and milk it because he's changed the tranny and tried to fix this issue himself. Everytime I go for a front end alignment they spend most of their time poking around trying to find something they can milk me for. I got pissed at one place and told them to just take it off the rack so I can take it somewhere else.

To be fair I don’t think this shop is one of those, the guy is extremely nice and I see him weekly because I deliver parts through NAPA to him. He’s also a Chevy guy and owns a GMT400 himself.

 

[1998_K1500_Sub]

To be fair I don’t think this shop is one of those, the guy is extremely nice and I see him weekly because I deliver parts through NAPA to him. He’s also a Chevy guy and owns a GMT400 himself.

Show him what you've shown us, and I think he'll be able to find it pretty quickly.


My guess:

- the tach "jumps" are indicative of erratic triggering of the coil; the tach is getting more "pulses" than it would otherwise, hence the jump.

- erratic triggering is due to a poor connection; I suspect the "C" connection to the ignition module first, but it could be either of them. I can't completely rule out the switched BAT from the IGN switch, yet, either. Call me ignorant.

- the extra "sparks" you've seen are occurring b/c the rotor tip isn't near enough to any of the 8 posts when the coil's being erratically triggers, so the coil's resulting spark pulse finds another path.

Good luck!

 

[Scooterwrench]

To be fair I don’t think this shop is one of those, the guy is extremely nice and I see him weekly because I deliver parts through NAPA to him. He’s also a Chevy guy and owns a GMT400 himself.

Sounds like you're in man.