Bad running after manual swap

[JPVortex]

Well I’m really spamming this chat up lol….

But big update here, not a good one.

Found a stud to use as a firewall ground, ran the one from the frame and back of cylinder head to it, confirmed it had a good ground with the old volt meter.

Started it up, same exact problem.

So next I tried the new coil to ICM harness I got on Amazon. Nope! Problem still persists.

Cut the tach output wire on the coil and insulated both ends, nothing. Still wants to die/does die 1/2 the time.

So that leaves me with having to check the main ign wire to the coil. Will direct wire it in tomorrow. The wiring under the dash is still super sketchy, so I’m not ruling it out.


One thing I did notice today, is when it happens and the truck wants to stall or does stall(with coil next to dizzy and intake) it makes a weird noise to an extent. Almost like it’s coming from the dizzy like an electronic noise or a spark sound. Hard to describe.

The troubleshooting continues!

 

[JPVortex]

Update folks! Got alligator clips and tested the main 12v keyed coil wire to ignition switch under the hood. Power was fine, wiggled it all over and brought it near the dizzy/intake area, power didn't drop.

So I went in the cab, peeled back some insulation and tested there and wiggled some more. Voltage stayed steady.

Kept it plugged in under the dash and started the truck and waited for the issue to occur. When it did, I looked at the multimeter and found that the voltage was still steady! So, this ruled out the wiring from the part I tested in the dash back to the ignition switch as good. I didn't test while running under the hood because I'm an idiot and didn't buy insulated alligator clips, y'all can guess what would happen lol...

So,

I took the AutoZone dizzy cap off of the new AutoZone dizzy I had put in a few weeks back, and was like eh, screw it, I still have a $40 Chinese amazon dizzy I didn't end up using. So, I robbed the ICM off of it and threw it on the AutoZone dizzy. From there I found something a lil weird, seems like the plastic on the outside of the dizzy rotor has some scratches on it, like the cap has been rubbing on it a bit or something. So, I said screw it and threw the cap from the Chinese dizzy on it. Fired it up, and it's too late to run for a while, but I ran at idle for 3 minutes. In that time there was no tach flutter, almost dying or stalling. So, fingers crossed baby. I'll run her till nice and warm tomorrow.

VERY cautiously optimistic, we'll see tomorrow for sure. If it's not the problem, then honestly, I'm a bit lost.

The next thing I'd probably do is clean up the distributor hold down tab that stops it from moving. It looks a bit rusty and crusty, and that seems to be where the ICM gets its ground from.

 

[1998_K1500_Sub]

VERY cautiously optimistic, we'll see tomorrow for sure. If it's not the problem, then honestly, I'm a bit lost.

I hope this all works out and you find it's a problem in the dizzy.

Is the coil wire making good contact with the center electrode?

Sorry for the late reply, I've been out all day and am just getting to reading your remarks.

 

[JPVortex]

I hope this all works out and you find it's a problem in the dizzy.

Is the coil wire making good contact with the center electrode?

Sorry for the late reply, I've been out all day and am just getting to reading your remarks.

I sure hope so! And the coil wire seems to be making fine connection, it was also happening with multiple wires, so that wasn’t the problem.

And no problem!

 

[JPVortex]

Good morning! Update time, and this one is a good one!

Fired up the truck and let her warm up completely.

The issue seems to be totally gone based on 30mins of idling!!!

Tach no longer bounces and glitches at all, and it no longer wants to die!

Seems like it was a bad out of the box new ICM in the replacement dizzy I had put in it.

I would've never suspected a bad ICM, because my original ICM failed in such a similar way. The issue started with the original ICM, the bouncing and glitching of the tach. So I replaced the whole dizzy with the new ICM, there was no change and I noticed over time the problem seemed to get worse and worse, to the point of stalling the truck. So I threw in the ICM from a cheap $40 dizzy I ended up now using, with the cap from that cheap dizzy, and she seems to be fine now!

My guess is the ICM was bad and was shorting out when I would move the coil near the dizzy, creating interference and all kinds of problems.

 

[1998_K1500_Sub]

Good morning! Update time, and this one is a good one!

Fired up the truck and let her warm up completely.

The issue seems to be totally gone based on 30mins of idling!!!

Tach no longer bounces and glitches at all, and it no longer wants to die!

Seems like it was a bad out of the box new ICM in the replacement dizzy I had put in it.

I would've never suspected a bad ICM, because my original ICM failed in such a similar way. The issue started with the original ICM, the bouncing and glitching of the tach. So I replaced the whole dizzy with the new ICM, there was no change and I noticed over time the problem seemed to get worse and worse, to the point of stalling the truck. So I threw in the ICM from a cheap $40 dizzy I ended up now using, with the cap from that cheap dizzy, and she seems to be fine now!

My guess is the ICM was bad and was shorting out when I would move the coil near the dizzy, creating interference and all kinds of problems.

An ICM issue makes completes sense. The exact nature of the issue (internal fault; poor external connection; infant mortality) would be nice to know.

 

[JPVortex]

An ICM issue makes completes sense. The exact nature of the issue (internal fault; poor external connection; infant mortality) would be nice to know.

Yeah I do wonder what happened to it; it’s so strange.

 

[JPVortex]

Update here again. Tach flutter is still completely gone, drove the truck for almost an hour no problem.

I guess I’m back a bit to needing to find a compatible PROM for the manual swap though lol… while it’s not doing what it was doing the idle does still smoothly come up and down a bit at idle, totally unrelated to previous problem.

 

[JPVortex]

Truck is still doing good today, rpm’s at idle still fluctuate a little bit just because of the computer with the manual swap, but it’s fine for now.

When warming up or restarting the passenger bank definitely does have a misfire. Nothing new, but a misfire that is stubborn nonetheless lol.

I’m guessing the misfire is 1 of 2 reasons

1. The plugs in it are pretty carbon fouled, they have seen better days.
2. There are multiple exhaust leaks on that passenger side. The header gasket leaks, and also the flange has a crack so that’s leaking aswell. Both are before the O2 sensor which is on that side, so maybe the O2 is not getting a proper reading from losing the exhaust fumes at the header and flange.

All in all she’s doing good, and she’s my daily for now again lol.

 

[1998_K1500_Sub]

Both are before the O2 sensor which is on that side, so maybe the O2 is not getting a proper reading from losing the exhaust fumes at the header and flange.

I wonder if you're getting some reversion and a bit of air's getting sucked into the exhaust, altering the O2 reading.

All in all she’s doing good, and she’s my daily for now again lol.

It's nice to believe that the problems appear to have been put to rest.