1978BackToLife

All joking aside, thanks for any help up front. I've had some real runtime issues with this 1978 Corvette, and am almost out of hair to pull out.

In testing some ignition / misfiring problems, I swapped out the ignition coil, and the ignition control module (used dielectric grease on module as recommended). These replacement parts alone added a new problem, creating a bad cut-out issue where you're accelerating (under load) and the engine will literally just cut out like you turned the key off, or it'll cut out for a second and then magically start running again.

So, I decided to immediately put back the old coil and module. Well, the problem has stayed with the old parts now and I can't figure out what is going on.

In the video below, I have the car in drive with my foot on the brake. I accelerate and hold the RPMs up. I never let my foot off the gas - the cutting out is very evident.

Anyone have any idea what's going on? Is it ignition related? Is there a way I put something back together incorrectly? Much thanks again.

VIDEO:
http://vid3.photobucket.com/albums/y...psa2phkvlt.mp4

cv67

had a problem similar once the positive batt cable was grounding out and killing all power to the car. Nice spark show

Check all connections usually something simple

CanadaGrant

The rod from your vacuum advance can is not connected to your distributor. It has dropped below or hasn't been installed back in the hole in the distributor advance.

-sinner-

Seems like it has to be the cap or the module. If the pickup ring was bad, it just wouldn't start. Replace the cap, maybe even spring for the $11 Mallory HO cap. Check all of those wires from the cap to ground and to the module. If one is shorting out when it shouldn't be, especially as the dizzy is spinning faster with more RPMs, the module isn't getting the right cues to provide spark. If that doesn't have any effect, then change out the module again and give it a shot. You might end up actually pulling the distributor, but that is a lot easier than it sounds. If the gear on the dizzy is worn, or the corresponding teeth on the cam are worn or broken, there could be a time when those empty spots just line up exactly right and the dizzy stops spinning in time for a moment, then grabs again. Or maybe loses ground? I had an old ACDelco (not an HEI), that was grounding out in the lead wires exactly the opposite of when it was supposed to kick as the points moved up and down. It was an intermittent problem, until it wasn't! then it wouldn't start at all, but sounded like it should, and the new coil/plugs/plugwires/capacitor/cap/rotor/points and carb rebuild didn't do a thing to change it. Not until I very reluctantly pulled the dizzy and removed everything down to the bare metal did it get fixed. And even then, it was never an obvious problem, but was just cured because I took those wires out and remade their connections when I put it all back together. Then it fired on the first try. With an intermittent problem, it almost comes down to wiring--a bad ground, or a short that only happens sometimes, or when hot, or at or above a certain RPM, or maybe just whenever. I have replaced a module with a brand new module that was bad out of the box, but neither one would start the car, ever. If you have to remove the dizzy, just set the motor on a fixed timing point, like point the timing mark right at a bolt or a mark you make, and mark where the distributor was sitting and how that relates to Plug number one. Then, DON'T move it until you put the distributor back in oriented just the way it came out. If you are lucky it'll slide back in with very minor little shakes of the crank. I'd have to look at my '80 Corvette to be sure, but I think the engine sits far enough forward that you don't have clearance issues moving the distributor up and out.

Good luck!

-sinner-

You shouldn't have any problem with clearance on the distributor. Wouldn't the vacuum advance not pulling timing make for constant rough running and misfires when on the throttle or under load? I usually disconnect it and add weights/change springs to replace it with 100% mechanical advance. I don't like trying to make vacuum on a BB or with anything but a stock cam.

sparky77

Looking at the video you can see when the engine cuts out all the lights are dimming so I would look for an electrical problem maybe the alternator has a short in it .I don't think it's a ignition problem.Inside the alternator there is a voltage regulator that could be bad.

1978BackToLife

Are you kidding! Very good eyes... I took this car in months ago for a cap and rotor from a shop. The cap is obviously new... can't believe they missed reattaching advance rod. I put a vacuum pump on there and said "well, that's working." haha.

Where does this attach? Going to try to look up google pictures but can't always get a good shot.

Speaking of which... how would I check if the rotor is new? I want to see that they didn't just slap a cap on and claim they did the rotor as well. Thanks guys.

1978BackToLife

A very good idea, I did disconnect the alternator and ran if off battery to see if the problem persisted, it did.

1978BackToLife

Thanks for this. Will go through the notes, especially wiring. I did get in there and move stuff around, so perhaps there's now a bad wiring connection. Will also inspect teeth but I recall them looking ok

diehrd

You may have a bad ground , Check bat cable , clean contact on frane , also make sure block is grounded to frame ..

croaker

Not the problem but, heat sink compound is what is recommended not dielectric grease.

sparky77

Was there ever an after market alarm installed on you're car if so it could be the alarm relay,some run the lights and the ignition thru the relay and if it goes bad it could be doing the problem.

speedreed8

i would get a new HEI distributor, that one looks worn out, even the weights are on top of each other, vacuum can disconnected.

Krystal

I'm in the camp that suggests the distributor itself needs to be considered suspect. I had this exact same issue just about 10 years ago in my '79. We happen to own two cars with HEI, my '79 and a converted "69 Camaro. To narrow the problem down we pulled distributors from both cars and swapped them.......sure enough my car was running great the Camaro would fall on it face as my car had.

With the problem narrowed down to the distributor or some component in it.......we did exactly what you did. First the coil, then the module.......when neither fixed the problem a new distributor itself. To this day I can't tell you for sure what was going on.

I can only tell you it wasn't the cap, rotor, coil or module.......it was something to do with the distributor itself that was resolved when we finally ditched it entirely for a new one.

It was weird because the car ran fine until you accelerated.

gungatim

there is more to it than just the coil and module. pickup coil and pole, rotor, ground strap, capacitor, wiring to the B+ (keyed) all need to be tested.

cap button and seal in place properly? have you tested the pickup while wiggling the wires? a broken tooth on the pole can cause weird things as well...

AzMotorhead

its common for those 2 wires on the orange connector at the module to break. They run to the pickup coil

Sluefoot

IF you're gonna leave the advance mechanism, I would at least take it out, clean it good, & put a couple drops of oil on the pivot areas. I had to do this on my Harley years ago when it wouldn't slow down while idling, cuz the weights were dry & needed oiling.

procketus

Here is a write up I used to find a problem I had. My '80 did the same thing yours is doing. Ended up replacing the distributor.

http://www.crankshaftcoalition.com/w...EI_distributor

Scroll down until you get to where they test the wires and connections.

sparky77

How do you account for the lights dimming at the same time the engine quits,I think it's an electrical problem.Start at the battery and look for a bad cable or a loose connection at the starter ,many times a cable will look good but be corroded on the inside,look at the fuse block main wires.Check all you're fusible links .

7T1vette

One WEIRD problem I had in the past is very similar to what you are experiencing. I had a standard distributor rather than HEI, BTW.

There was a signal wire running from the mounting plate in the dizzy and routed under it and out through the wall in the housing. Inside of the dizzy, that wire had chaffed on a metal edge to where it had a bare spot. Normally, it was not touching any metal and all worked fine. When I stomped on it or made a hard turn, that wire would move to where it shorted out to metal in the dizzy and I lost all fire to the engine. Let off the gas and all was fine (because the wire relocated).

It took me weeks to find that bugger! I suggest that there is something similar in your system.