Thread: Missing at top end

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I have a 67 Camaro with a 327 engine. I am having a recurring issue with the engine cutting out and missing at the upper end of the rpm range starting around 3500 rpms. The issue is worse when the engine is cold but will still do it when warm and pushed harder. I have an Accel supercoil on top of a stock electronic ignition type distributor. No other mods. I have checked the rotor and cap for obvious defects but that is a far as I have gone. Any ideas on where to start? Perhaps even where to begin testing for a most probable cause.

Thanks in advance for any ideas you may have.

CT

I would check to make sure the total advance of the distributor is within specs. Make sure the vacuum advance (if used) is operating correctly. Carefully run all the plug wires to assure no issues there. Is the distributor in new condition with tightly bushed shaft? A high pressure oil pump can wreak havick with a worn distributor shaft making the timing act erratically.

The problem could also be fuel related. Install a fuel pressure gage at the carb and prove to yourself that it is seeing 6 psi throughout the speed range. If you are running a carb with a power valve, is it the right power valve for your cam/vacuum conditions? Finally is the valve train within the engine fresh? Tired lifters/springs can bring down the onset of valve float and cause erratic operation. This should not be an issue with a properly rebuilt fresh engine.

Good Luck, Kitz

and after you check all those... i'd have the coil checked out too.... accel products can be a major pain, their quality control doesn't do too well and sometimes you have to get a part a few times before it actually works right.... the secondary windings in the coil might have too much resistance..... if you have access to throw the car on a scope, you can diagnose a miss really easy....

Originally posted by thesals
and after you check all those... i'd have the coil checked out too.... accel products can be a major pain, their quality control doesn't do too well and sometimes you have to get a part a few times before it actually works right....

IMHO Accel super coils are JUNK. They have a terribly bad habit of breaking down when they get a little age on them. Ran through two of them on a '66 Mustang. Also their inexpensive plugs wires are no better unless you consider a 5k drop in resistance in a foot and a half or less to be acceptable.

Wow, a lot to look at. Thanks a 1/4 mile for all the suggestions. The engine was rebuilt 4000 miles ago so issues related to an aging engine I will skip until I have run through all the others. Of course, there could have been an error in the rebuild as well....At any rate, I will begin with the ignition system and work from there. The neighbor has a used stock one on the shelf since he is doing a rebuild now. He says it worked fine. This might tell me a little or tell me a lot. Will have to see and it won't take long to find out.

Thanks everyone. If interested, I will let you know what was going on when I find out.

Chevytuner......

If your fuel and electrical system checks out another thing that could be wrong is a cam lobe worn out due to improper breakin or plain ole bad cam and or lifter.

Originally posted by DennyW
Run problems, 90% electrical, 10% fuel. Providing you start with a good mechanical base. Top end miss, plugs, wires, or coil....

...or even a bad ground.

The stock HEI module under the cap is junk, that needs changing one way or the other. You can get a good one for about 40 (accel) or a great one for about 75 (MSD). Go ahead and change that first. Make sure you have a ground from the engine to the firewall and from the engine to the frame. Those missing causes all kinds of crazy problems. The next thing to go to is fuel. Sounds like its leaning out. Check to see that the vacuum actuator diaphram is working and that the butterflies open and no bent linkage. If you have a 3310, order a secondary metering block kit for $30. and a power valve plug for it. Then you can easily change jets. A fuel related miss on the top end is usually a lean condition.

After a long diagnostic testing of the electrical I couldn't nail anything down. I took it for a hard drive and it still was having some issues. The next morning I entered the garage and there was a strong smell of gas everywhere. It took an hour to find that there was a loose fitting at the fuel pump where a fitting was actually too short for the line connection to the carb. I couldn't tighten it due to the fitting rubbing on the corner of the block and I am assuming that the engine builder may not have gotten tight originally. I wonder if the lean condition described in some posts on the fuel side could have been caused by this fitting being loose and allowing either air to be sucked into the fuel flow or even reducing pressure allowing not enough fuel to get to the carb. Just found it and haven't been able to get a longer fitting to put into the pump to allow the fuel line to be tighten by clearing the block. Could this be the issue?

yes ,it could very well be the cause of a lean conditiion under full throttle!