Im at a loss.

My car has been developing a worse and worse high RPM misfire for a while. It was intermittent. When I first got it together in July it wasnt there. By the fall it happened sometimes, by December you could hear it breakup fairly clearly in the 4500-5000 range pretty regularly.

It ran fine other than that, but it was annoying me so I went through the distributor and I set shimmed the dist gear to have .018 play (instead of .068), replaced the module, replaced the cap, and replaced the rotor.

After all that and the car sitting for about 3 weeks during christmas while I was waiting on parts, I got it back together and it's doing the same thing, only now it's a lot worse. It now kicks in bad at 3,000 RPM. It's clearly not firing on all 8, it's the same problem, but it's markedly worse than it was when I took it apart in December.

I set the timing all the way back to almost 0* BTDC static timing just in case my indicated timing was wrong and perhaps way too far advanced, I took about 12 degrees out of it and it made absolutely no change. Mechanical advance is adding about 15 degrees or so like it should. I pulled the valvecovers and all my rockers are moving normally. There's no excessive valvetrain noise and all my cam lobes seem to be there. I put a vacuum gauge on it, and it gives a reading of 16 inches and has a vibration of less than an inch, so it's fairly steady. I replaced the plugs and that made no difference either.

Another point of note is that, for whatever reason, my stock tach and my autometer tach don't read smoothly off this distributor. If I'm cruising at 1500 RPMs the tach will sporadically jump around. Not constantly, but it will give weird readings once or twice every 10 seconds or so. It's not my tachs or the wiring, the distributor is sending out weird readings for some reason. Not sure if that's relevant or not. All the parts I swapped out had no affect on it.

All the vitals seem to be good. And as long as I stay below 3 grand, the car runs fine. I could commute with it just fine really. It's only at high RPMs, and it seems to do it in neutral too. I dont think being under load affects it much.

Is there anything you guys can recommend me try before I buy a cheap crappy Pro Comp distributor off ebay?

 

simple seems like its a voltage issue more than anything else check your starter wires see if they are burnt or cut then check the wires running from the starter to see if they are clean and have a good connnection and let me know what you find

 

I have a remote starter solenoid on the firewall. Everything is bolted to the battery-side terminal, not at the starter. I'll definitely get the DMM out and start probing things, though. Should I just probe the battery wire going into the coil?

 

Get a heat gun and see what each cylinder temp is, and see what one is colder. Have you looked at the plug to see what they look like? that will usually tell u allot about that cylinder.What dist are u using, coil ?

 

i have had issues like this before.. sounds like a coil might be on the fritz.. at least that was my issue.. it just wasnt able to charge back up after all the years of abuse.... if you dont have an HEI distrbutor, and have a timing light that'll read display rpm, try hooking a timing light lead on the coil wire, it' read crazy high rmp's, but then rev it up to where its missing, and see it its showing the same miss off the coil.. if so theres your answer, if not, that's not your answer..lol

or you could just through some more parts at it!

just a thought

 

does kinda sound like a bad coil-if it has some shorted
turns in the secondary winding that can cause the
described problem.could be a bad module also-just sub
out these parts with known good and see what happens
BTW is the distributor original type or something else?

 

It's an old school large cap HEI.

Im about to roll the thing in the street and burn it. Im sick of dealing with it.

Okay I've replaced

1. The rotor
2. The cap
3. the module
4. the coil
5. the plugs

There's nothing left. Nothing has made any difference. Somehow it got much worse after replacing the cap and rotor, I have no idea how.

When the tach jumps the car audibly misses. When I get to 3200 RPMs and the car starts acting crazy, the tach jumps all over the place and it backfires out the exhaust as the pots dont fire.

All the plug wires are tight. There's good connections everywhere. Maybe I need the ohm the plug wires.

The only thing left in the distributor that I havent changed is the magnetic pickup and the radio suppressor. Is there ANY way that either of those can cause this?

I checked voltage going to the battery wire with the car off. Gets a constant 12v from the battery. I check resistance from the hold down bolt on the intake manifold to a ground, and it's an acceptably low number.

The plug wires are only 6 months old. I doubt they could be the issue, but if you think that might be it, speak up.

Im about to just buy a chinese ebay distributor and set the rest of it on fire.

 

check all the resistance in the wires, make sure that they are all not touching anything metal and make sure that they are not touching each other also check for slits in the wires anywhere.

 

a bad pick up is very rare but is possible-could just get
a j/y distributor and swap out the whole works to see
what happens-any j/y dizzy is better than a chicom
knockoff P.O.S. Could also check that you do not have
too much lash in the dizzy gears or too much endplay
in the distributor shaft-either can cause spark scatter,
especially if a high volume oil pump is in place.
Could also power the distributor for a seperate souce,
even direct from the batt in case the voltage from the
original feed drops off as the ignition starts to pull more
amps as rpm increases.

 

I got a distributor from a buddy to test with to see if the problem happens with a known good one.

We'll see what happens.

Also I already set the endplay in the dist gear down to .018 from .058. Big improvement that showed absolutely no change.

If the new dist does the same thing, I'll be running a huge wire straight from the positive battery terminal to the distributor and see if that helps. If not then it has GOT to be a ground issue or a carburetor issue, right?

 

The one thing that you have overlooked, although you did mention it, is the ignition wires. They are a critical component. One thing you can do is run the engine at night (or in the dark) and observe the wires to see if they 'leak'.

A bad coil could also be your problem, but I'd definitely suspect the ignition wires first, especially since you have not done so and changed so many other parts.

 

The wires arent brand new, but they are only a few months old. I've inspected them and made sure there was nothing burnt out on my headers and I've checked for arcing in the dark too when I had some boots that had burnt to pieces. I've replaced all the bad looking plug boots and my wires look fine.

I just threw my buddy's distributor in and the jumpy tach is gone and so is the misfire. Runs smooth as a whistle.

It's something inside the dizzy but i've got no idea what it could be.

ANyway, Im gonna buy a chicom dizzy off ebay and see if it goes away.

 

In case anyone searches and finds this thread, I got a new magnetic pickup and put a new radio interference suppressor in it and the problem went away. I have no idea how taht could possibly do that... but whatever, it fixed it. No more misfire for now although I worry it may come back.

 

I saw you in Warner Robins yesturday. car looks good with that hood