GOT_CAMARO?

So my car has an interesting new problem. If I'm slowly rolling into the throttle in any gear, as soon as I get near 3000RPM then engine starts to act as if it's misfiring then clears up and pulls strongly to 5000RPM. The peculiar part is if I go WOT the car will pull right through 3 grand no problem. At any point after it has its fits and coughs it will backfire out the exhaust. If I am parked and rev the engine, it will cough and sputter all the same.

I talked to my mechanic and he felt that the carb (q-jet) was leaning out at the point where it sputtered and suggested disconnecting the accelerator pump and giving the throttle a quick twist, if it bogs it's lean... So I followed his recommendation and it did bog. Since the problem arose rather quickly after it was sitting for a 1.5 months we figured there may be debris in the primary metering jets/passages. I pulled the whole carb apart and cleaned all passages with carb cleaner and compressed air, put it back on the car, issue still exists.

Then I started to suspect that such regularity of the sputtering was due to my MSD box, so I disconnected it to remove any suspicion... Hit the key, car cranked, and cranked, and cranked, nothing. Hooked the box back up and the car fired right up. At that point I was confused, tired, and overheating so here I am. I feel like I may have missed something, or maybe it's just dehydration...

P.S. Here are two videos of what I'm trying to describe (secondaries were wired shut):
http://youtu.be/qfTnbO9DRcY
http://youtu.be/OmHwLSsYB7I

Ozz1967

iTrader: (4)

When you disconnected your MSD box, your dizzy wasn't getting any spark...so naturally it won't fire up.

If it's ONLY at a specific RPM, I highly doubt it's the carb. if it was, it would be at all RPM's.

Have you changed your cap, rotor, plugs and plug wires recently? Also, it "could" be a fault with your MSD ignition coil. But I'd start with the others first.

If a plug wire gets too close to hot metal, it can eat away at the insulation causing it to arc, thus the studdering etc. Also, if a cap/rotor goes bad, you get spark scatter where it won't fire right or arcs internally causing issues. That's where I'd start.

GOT_CAMARO?

I had suspected that it was not the carb since I had never had an issue with it but a good old cleaning never hurts. When I disconnected the MSD box I reconnected the stock wiring (power wire, tach wire, and ICM wires) and it ceased to start. The plugs and wires are a year old, I had an issue with the a wire or two melting on the header, but have since routed them in a loom miles away from any hot metal. I'll give the cap and rotor a look see, I would think spark scatter would get worse at higher RPM and heavier load. BTW, I have an Accel coil I installed 2 years ago, I realize it's not in my sig. I'm curious if a failing ICM could cause low load failure at a specific RPM but acts "normal" when I stomp on the gas.

GOT_CAMARO?

UPDATE: I've done some more poking and prodding on the car. As stated above when the MSD box was taken out of the ignition circuit, the car wouldn't start. I checked for spark with a timing light, and it flashed. BUT I remember having a similar issue a few years ago when it appeared I had spark but the spark quality was not good (couldn't jump the .060" gap). So I used my handy spark tester set at .060" with the MSD out cranked the engine, no sparky spark. Hooked the MSD back up, cranked, engine fired, but the spark wasn't a nice hot blue bolt of lightning...

Which brings me to my next theory, the coil is at fault, or atleast beginning to fault. I tested the coil, as per my '86 service manual, and read 0.46ohms between C- and B+ terminals. The manual states "Reading should be zero or nearly zero. If not, replace coil." I suppose this is not nearly zero?

I feel the MSD box masked the failing coil by doing what it does best, boost spark energy (or something of the sort).

As far as the cap and rotor are concerned, they both looked to be OK with no carbon tracking in the cap as evidence of arcing. I did clean up the terminals under the cap with a dremel and wire wheel.

Now, back to the coil. This was an Accel Brute Force or something coil that I installed 2 years ago to replace the MSD coil that died. If indeed my coil is on the way out, what manufacturer should I be looking to purchase from since apparently my car is eating the Accels and MSDs? I suppose I could always close the spark plug gap a hair...

Here's what the spark looks like:
http://youtu.be/q4zbXzje8fM
I know it looks like the spark is cutting out, that's just the frame rate on the camera. It really is a consistent spark, just doesn't translate to digital for some reason.

GOT_CAMARO?

Welp, it would seem I made some erroneous statements. Upon checking my ACTUAL plug gap, and not going off memory, I have the plugs gapped at .045". With that new little piece of information, I am almost certain my coil is failing. I've done a bit of research about plug gaps and found that .045" is pretty safe and the coil should have no problem arcing the gap on its own.

This led me to a new theory as to why I have misfiring only around 3000rpm: since cruise A/F ratios are usually pretty lean, and a leaner A/F needs greater spark energy to arc the gap, would it be possible that the coil can't supply the necessary energy to fire the plug at 3000RPM because of a heavier cruising load and leaner A/F? Then, conversely, richer A/F ratios don't require as high of spark energy. Thus when I really jump on the throttle A/F goes full rich, load increases tremendously as well, but due to rich A/F, less spark energy is needed.

Therefore, with the help of the MSD box the coil can produce enough juice for idle, light cruise, and wot, but not heavy cruising. Without the box the coil doesn't have enough juice to even start the car.

Or is this all BS?