Symptoms of Engine Missing when in 3rd and Fourth Gear
 

I am new to the forum, not mechanical but recently bought a restored 66 427/425. I've noticed that when I open it up and shift to 3rd and 4th, the engine seems to miss and hold back. Is this an indication that it needs a tuneup or something else?

without knowing the maintenance history of the car the cause is uncertain. Do you have the maintenance history to help narrow things down?
how many miles on the plugs, plug wires, cap, rotor, points if not TI system, air filter, fuel filters?
how many miles on the valve adjustment?
when were the floats levels checked?

Could be a tune-up, could be crossed plug-wires, distributor weights sticking and several other things.... A generic miss is hard to diagnosis in cyberspace...you might need to get it looked at...

the engine should not care what gear it is in to have a miss. if it has a miss it will do it all the time. start it up in a dark garage and see if you see a light show coming from the wires.. if not check remove the ignition shielding top cover and see if that helps.

Plug Wires
 

Sounds like old plug wires to me . They tend to be overlooked because the braided ones are expensive .

1st and 2nd are fun gears (at least for gear heads), the miss is generally masked by the relatively light load and higher RPM compared to the lower RPM and higher torque needed in 3rd and 4th.
The problems are unlimited, but the vacuum advance in combination with timing is the only thing I can think of that is dominate at cruising rpm in 3rd and 4th. Thus, timing????, bad canister??? vacuum leak??? weak spark???
Probably more information needed for the real mechanics here on the forum.

What R66 said. Higher gears mean higher load, and marginal issues with fuel supply and ignition will rear their ugly heads. Fuel filter, fuel pump, float level, ignition coil, points/condenser, plug wires, plugs, timing advance are all things to check.

Thanks all. I'm taking it into a mechanic that was recommended on this forum. I'm a recovering lawyer (retired) and know next to nothing about car mechanics but am learning. Had an 88 for years and used to just bring it into the Chevy dealer when work needed to be done. Can't do that anymore.
Starting a little late but better late than never.

Having said that. Cruising in 3rd and 4th are fine. It's only when I step on it that I feel the engine missing.

If he's willing, see if the mechanic will give you some over-the-shoulder troubleshooting experience instead of just dropping it off....it can be enlightening...

Some techs will let you observe, some won't...

Yes but....You still want to keep the RPM's going even in 3rd and 4th!

At least a little from time to time! LOL!

Hope you're able to determine the problem.

Pat

To the OP-

Back when I used to drive as a daily driver, a L78 Chevelle, which is basically the same engine you have, I kept a spare set of plugs in the glove box. A week or two of piddling around town would have them sooted up where it wouldn't get out of its own way in third and fourth. It would misfire, and run like crap. Running it up and down the rpm range at full throttle would cure it for awhile, but the only fix was to put in a new set. I think they were AC 43 XLS. Won't take but 20 minutes to find out.

Had a Honda Accord to exactly this when driving....turned out that the petrified mouse mummified to the ignition coil tower had caused a short circuit, and had been for so long that the coil tower was cracked and grounding through the mouse to the shock tower. Only happened under load in 3rd and 4th. (No 5th, it was the '80's!) Ignition and fuel demands are very high in the upper gears under load.

If your mechanic recommends new spark plugs, I'd recommend AC 45 XLS plugs instead of the book reference AC 43 XLS.

:rofl: that's one for the Ripley's Believe it or not records!

Again, I'm a novice. Why

See post #12.

:iagree: And would suggest the ignition system be looked at first for potential problems.

Thank you everyone for your input. I went to Steve Luvisi, a corvette specialist in Huntington Beach, and he saw the problem immediately. You are right it was an ignition problem. The ignition coil wires were crossed. Positive to negative. Negative to positive. Wondered how it even ran.
It's kind of tough being non mechanical at this stage in my life but I am learning!
Thanks again.
George

He did more then the wires. A car will not run wired backwards.