Hi Folks,

Here is my issue - 1984 Duke 4 speed - When first started car runs nice and smooth. About 10 minutes into a drive, around 2500 rpm car begins to buck and the gauges start to be come erratic - speedometer spins completely around, rpms on gauge and volt gauge also erratic and I here a "ding" from under the dash probably because of the gauges. I just installed a new coil as old one was a little out of spec doing an ohms test. Car runs fine, actually very smooth as long as I'm under about 2500 rpm. Doesnt matter what gear and pulls strong in 4th up hills - again, under 2500 rpms. I'm thinking a grounding issue but nothing is visually apparent. Also replaced wire from coil to cap. I'm lost here and value your thoughts and guidance. Thanks!

Check all the wiring and fusible links at the starter.

I had a similar problem on my '84 Indy.
On the '84, all the supply wires with fusible links for the whole car connect there.

I FOUND the source of my problem causing all the headaches.
An intermittent short of the battery cable near the starter on a heat shield.
So anytime the short touched, the ECM etc. all lost power for a milli-second.

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Check for arcing at the coil. When I changed mine it started arcing from the coil cap to ground at about 2500 rpm. Had to replace the coil to distributor cable.

Thanks guys for the tips. Coil to cap is brand new as of today. No change. That said, I did put a new starter last fall not long before storage. I'll crawl under and check the wiring and report back...

Gentlemen,

Reporting back with some good news - I replaced the coil to cap cable and also as suggested repositioned the positive battery cable eyelet on the starter as we all know there are a few small protruding studs on the starter from manufacturing and although I couldn't see well I twisted the eyelet and re-tightened. Took her out and smooth sailing with absolutely no problems over 2500 rpms. Fantastic suggestion! Just hope I socked up the cable enough (open end 5/8 wrench is all I could get on the bolt) but if the problem returns that will be the first thing I'll check.

Thanks for your help!

Thanks for the report!

Well, unfortunately the problem is back. Once again checked the starter connections to ensure there are no intermittent shorts due to engine movement, etc. Drove the car to work twice last week 40 miles each way. No problems. Last night I noticed the speedometer start to spin around 360 degrees and then the bucking started.

As with last time, when I was light on the pedal the problem was not as bad - but still present. New starter, new battery, new coil - cables appear good and all connections tight and clean. Wondering if the ECM is bad. Nothing apparent visually. Not misfiring but something definitely electrical.

Getting very frustrated....

Remove the tach filter and see what happens.

Thanks Everyone for the input. Throughout all of my efforts, turned out to be a bad positive battery cable to the starter (despite it being replaced). New cable installed, all problems resolved and hasn't run better in a long time. Gauges nice and smoothly operating. sometimes it the simple stuff.

Thanks to all

quote Originally posted by cashmgr: Thanks Everyone for the input. Throughout all of my efforts, turned out to be a bad positive battery cable to the starter (despite it being replaced). New cable installed, all problems resolved and hasn't run better in a long time. Gauges nice and smoothly operating. sometimes it the simple stuff. Thanks to all

It's odd that a problem like that would only show itself at 2500 rpm or higher. If it happens again, suspect a bad regulator/alternator or a loose connection. '84s are special, and perhaps this is just another example of why.