Bad Stumble at Road Speed

[bucket]

'84 C10, stock 305, headers, Holley 650 (couple years old), Mallory coil (old), recent tune up with good parts (not cheap junk).

There were tiny hints of things to come for the past couple days, but for the most part the trouble all started this evening. The truck was hiccuping and stumbling real bad intermittently while leaning into the throttle while driving down the road. But giving it a little more throttle smoothed it out. It idled just fine a reved normal while in park. If I mashed it off the line everything was normal. Then everything went to hell in a handbasket. It still idles fine, but light throttle it bucks and hiccups something fierce. It's really hard to drive at all. Heavy throttle still smooths it out, but power is certainly lacking.

The weird thing is, when it's bucking and acting up, the tach needle goes nuts. Even at speed. The tach will instantly drop to zero for a split second, then come back to life right as there's a nice healthy backfire out the exhaust. Because of this I'm thinking a bad ignition module. Or a possible bad pickup coil. I'm really no expert on the HEI stuff and what exactly makes it tick. Anyone have any ideas?

 

[RetroC10Sport]

'84 C10, stock 305, headers, Holley 650 (couple years old), Mallory coil (old), recent tune up with good parts (not cheap junk).

The weird thing is, when it's bucking and acting up, the tach needle goes nuts. Even at speed. The tach will instantly drop to zero for a split second, then come back to life right as there's a nice healthy backfire out the exhaust. Because of this I'm thinking a bad ignition module. Or a possible bad pickup coil. I'm really no expert on the HEI stuff and what exactly makes it tick. Anyone have any ideas?

Check those first.

 

[Jims86]

Yup, tis possible that the pickup coil is now a hiccup coil....especially with the tach freakin out.

 

[bucket]

Alright, I'll just stab another dizzy in it in the morning.

 

[bucket]

Put another dizzy in it, seems to be all better now. The one I put in looks like it's not very old at all, I think it only has a few hundred miles on it. The truck still had the original electronic spark control dizzy in it (it felt shot too, clickety clickety as you turn it) and was still all correctly wired up. Truck seems to run exactly as it did before with the ESC. Although the exhaust note just off idle seems a little different to me, could just be in my head.

 

[89Suburban]

Put another dizzy in it, seems to be all better now. The one I put in looks like it's not very old at all, I think it only has a few hundred miles on it. The truck still had the original electronic spark control dizzy in it (it felt shot too, clickety clickety as you turn it) and was still all correctly wired up. Truck seems to run exactly as it did before with the ESC. Although the exhaust note just off idle seems a little different to me, could just be in my head.

Good job!