Ignition System Issues (bouncing tach and dying idle)

[JaxLax]

As always, long post incoming, but I want to give as much background and specifics as possible. Fast forward to CURRENT PROBLEM HERE below to bypass story time.

Last time I drove her a few months ago, on the way home, idle was fine and smooth after leveling back out, but under accel it would bog down and at higher speeds often felt like it was missing cylinders or just running super rough. So I parked it and put on the cover and said I'd get to it when I could.

Yesterday, the boy and I had a day of nothing so we decided to go after it. Got out there and tried to turn it over - nothing. Popped the hood and found the battery at 0.40V. Yanked it and plugged in the charger. Came back 30 minutes later and set the charger to 75a starting and it wouldn't crank, but not turn over. Also during charging we noticed an electric sound behind the dash. After an hour of other chores and we took the battery off the charger and watched it lose voltage sitting still - so we went and got a new battery. Swapped it out and kept moving forwards.

Now the engine was again cranking, but never turning over. Fuel in tank, fuel at the glass filter would bubble/move at crank, but getting nothing in the bowl. So we pulled the old filter at the carb and it was HEAVY. Swapped it out for a new one (that you could see through into the screen) and a few cranks later she fired up for maybe a half second. Then died. So I pulled the multimeter out and started checking the ignition system and quickly found out the coil was way off spec on both the first and second windings. Went to the store AGAIN and got a new blaster coil. Got it in with some alligator clips to test and she went right over on the third click, but faded off. Fine, it's been months. Had to keep going a time or two (note: there were some stumbles here, but I thought it was due to maybe carbon on the plugs/sitting issues). Let it idle for maybe 10 minutes and it burned off some oil and the smoke cleared out and she sounded fine.

Went to take it on a test cruise. The issues still remained. Idle/coast is generally fine after a few seconds, but accel or speeds above idle are rough and feel like it's skipped cylinders/fouling? So we're a half mile from home and it straight DIES at stop sign. Pop the hood and nothing looks/sounds/seems wrong. Figured I'd just give it a couple of minutes to settle/cool down. Next start turns over and then fades off at idle. For the next 30 minutes or so we go from starting to no idle fades in between me pushing it 25 yards.

CURRENT PROBLEM HERE
Items replaced: battery, fuel filter, ign coil.
So during the idle fails I noticed that with my key in the ON position my tach is bouncing all over the place (0 to 1500 to 400 to 2000 to etc). When I remove the ignition system from the overall electrical system (this truck had 3 kill switches I've removed, but this one I couldn't trace so it remains) with a kill switch and leave the truck in the ON pos the tach correctly pegs to zero. When it does start and run the tach does bounce like before (all over the place).

There was a time about two years ago when this was my daily and all these systems worked fine and well w/o issues. I understand the battery/filter being almost considered consumables. The coil is old and for all I know the ign box and volt reg are stock. So have they just finally given up?

Going to search now, but wanted to see if anyone had a definitive idea or solution to this problem before.

 

[Speedrdr]

I’m assuming you are grounded well and checked their‘cleanliness’ at connection points hearing the noise behind the dash and the tach needle jumping around sounds like an electrical issue. The engine refusing to run sounds like a fusible link that’s got a flaw and when It heats up allows the fusible link to create an open circuit. I’m certain someone wiser than me will have better info. Good wishes and best of luck. Electrical gremlins are a bear.

Randy

 

[Broncobowsher]

Disconnect the tach and see what happens. I've seen bad tachs playing feed back issues into a perfectly good ignition system

FYI, and engine cranking and turning over is the same thing. Go back to the start of the terms, back in the model T days. There was a hand CRANK that was used to TURN OVER then engine. The hand crank was later replaced by the electric starter, but the term cranking the engine still means the same thing, just using an electric motor to do it. If you want, you can turn over an engine with a ratchet, useful for setting the engine to TDC for setting up an ignition system.

Sounds like you are having issues with the engine failing to start, firing off, starting, etc. Other than the dead battery it sounds like the engine would turn over fine. When a battery is low, the engine may turn over slow, but it is still turning over.

 

[JaxLax]

Replaced the ignition box.
It turns over, but ROUGH IDLE and eventually dies (maybe 15-20 seconds on a good run or almost instantly on others).
The tach continues to bounce all over the place. Pegs to 0 when in run, starts, then jumps all over during idle (anywhere from 0 to 2000). Even after the engine dies - the tach continues to bounce.

I'll remove the tach from the system next and see if that clears it up, but I don't really understand how (unless it's a bad ground) how that could be the problem.
If that doesn't work - then I guess I'll start back with plug wires and the dizzy.

Thanks for all the help so far!

 

[DirtDonk]

A tachometer is connected directly to the ignition coil. If there is a problem within the tachometer, it can affect how the engine runs because the coil is a very sensitive switched on and off device that works literally in milliseconds.
Yes, a tach can kill an engine while it’s running. Easily…

It’s also one of the easiest things to check because you only have to disconnect one wire instead of replacing parts.
The fact that it’s continues to bounce after the engine is off is almost a guarantee that there is a problem with the tachometer, the tachometer wiring, or the ignition switch and it’s wiring.

 

[Rustytruck]

every time I dealt with heavy battery drain it was a bad diode in the alternator. might want to take it to the parts store and have it tested. have you ohm checked the stator in the distributor. hows the ground on your ignition module. most aftermarket modules eliminated the redundant ground wire in the wiring but now need good grounding from the module case to ground. I once had ignition failure from a short inside the tachometer that grounded the ignition signal unhooked the tach and all saw right in the world again.