Tach Jumping - Engine Dies

[79spider124]

All,
I think I may have been visited by a Halloween gremlin. When the car starts, the tachometer begins jumping all around. As the engine warms up, the jumping get worse, bouncing from one extreme to the other. Then, if the idle drops below about 2000 RPM, the engine dies. I tried to fix by replacing the distributer cap and rotor, coil, spark plugs and wires. But the problem was unchanged. I did not replace the control module...yet.

Any thoughts as to where I ought to look next?

[WYSpider]

Start with really cleaning the grounds with a small wire brush. Also clean the connections at the top of the coil and use dielectric grease. The tach is driven off one of the connections to the coil.

I had a jumping tach until I really I cleaned the connections, replaced the coil and control module. Now it is rock solid. Mine probably just needed a good cleaning but I replace the control module and coil because they were 31 years old.

[joelbert2k]

I had the jumping tach problem a while ago. Turned out to be the electronic pickup wires inside the distributor. The little wires are so fine that they break very easily.

Joel

[leftfield6]

I had the jumping tach problem a while ago. Turned out to be the electronic pickup wires inside the distributor. The little wires are so fine that they break very easily.

Joel

This.

I had the same exact issues, opened up my distributor cap to find those very fine wires brittle and cracked. A new pick-up assembly later, all is good - no jumpy tach, no random miss, no longer randomly dies .

[79spider124]

Thanks, guys. I'll try a new pick-up assembly. I'll post again with results.

[79spider124]

That was it. Finally got around to installing the new pickup. The old one had bare insulation under the wires and the magnet was brittle and disintigrating.

Thought I had the gap right on. But the engine is jumping around and a little rough. I get some backfiring when the accelerator is depressed. Drove around and the power just isn't there. I'm going to start by undoing some of my earlier fixes, like putting the old coil back on.

Seems like all I've fixed is the jumping tach. I still have the initial engine problems where I can't keep it running, no power, backfiring... Wonder where else to look?

[skykng]

Sure sounds like ignition to me: be sure your plug wires are on tight and in correct firing order 1,3,4,2. Also check the plug wires in the right holes in the distributor cap. Are the plug wires old, brittle, cracked, shorting to ground/block?
If any doubt, replace the plug wires double checking the items above (firing order, etc). How about the rotor inside the ditributor? Is it old, cracked, dirty? When the engine quits, do your guages (fuel/temp) go dead? If so, it could be intermittent 12vdc to the ignition coil/from the ignition switch on. I'll bet a sasparilla it's ignition. Steve

[PNWSpider]

Hmmm,

I'm beginning to wonder if this is the issue I'm having with mine, been fiddling with carb thinking that the cutoff solenoid has an issue, not saying it does or doesnt but this might be a good place to look also, sorry you have this issue but thanks for posting this up for the rest of us to learn from.

[PNWSpider]

Just a heads up on my issue it turned out one of the wires under cap was grounding out, fixed it up right and no more issue , good luck with yours!

[James2000Spider]

Sounds like my problem too. I was thinking it was the alternator/battery. Had my alternator tested this morning and it checked good. Battery good too. The car would run good for about 10 minutes and then start stumbling and the tach jumping before dying. I will also try the distributor. Thanks.