# Engine miss need opinions from the experts



## steve491 (Nov 20, 2019)

Good afternoon,
I woke up a '67 GTO from a 28 year sleep about a year ago and took the first test drive today. Wahoo! It actually drives very well but I have a miss under 2000rpm, over 2000 it's smooth and pulls very well especially in the secondaries.

Little background and specs:
Original 400 HO (it's the original engine), 4-speed, original 670 heads that were reconditioned in 1991. Unknown cam, previous owner said it was a crane cam but he doesn't remember what it was when he installed it (1991).
I installed a new "parts store" points distributor, coil, alternator, water pump, carter fuel pump, entire new fuel system, rebuilt Holley 650 double squirter spreadbore, plug wires, and AC Delco plugs.

Car runs right at 180 degrees, 60lbs of oil pressure at idle (10w-40). It idles pretty good but you can loose a cylinder on a HP engine and not really know.

It seems to have a pretty good miss under 2000 that sounds to me like ignition because once you get over that rpm it's like a switch was flipped. I could be wrong, that's why I'm shouting out to the experts!

Wish I had an original era Quadrajet but it got gone in the 80s. Power valve in the Holley? I have almost 17 inches of vacuum at idle, idle jets are responding well and tuned to max vacuum. DOn't remember which power valve is installed right now.

Sorry for the rambling post. I walked back and forth several times.

Any input will be appreciated.

Edit. I'm a dumbass sometimes. I didn't mean 40 inches of vacuum. That was metric. 16-18.


Thanks, Steve in NC


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## LATECH (Jul 18, 2018)

do a compression test


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## Sick467 (Oct 29, 2019)

Can you get it to miss in the driveway? Adjust the idle screw up and see if it misses in park. If it does, you can start pulling plug wires one at a time and replacing it after it's pulled. If the idle changes, that plug wire is doing it's job. If the idle does not change, that wire is likely dead.

Make sure you use an insulated pair of pliers or a plug puller plier set. Those sparkies can set you on fire!


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## steve491 (Nov 20, 2019)

For some reason my first post (quick post) took a while to show. Updates are on the other post.


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## ponchonlefty (8 mo ago)

points distributor? if so you might can clean them.


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## sameold01 (Jun 21, 2020)

Back in the day if you can have someone put the car in drive and power brake it slightly use a test light to ground out the cylinders at the distributor cap. Obviously the cylinder with no change is the issue.


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## geeteeohguy (Feb 2, 2008)

Ignition misses generally get worse under more load or at higher RPM. Your issue sounds like a vacuum leak or poss. weak cylinder or burnt exhaust valve. First, make sure the tune is right. You DID set the points dwell to 30 degrees and the base timing to 6 BTDC, didn't you? If yes, connect a vacuum gauge to a direct manifold port on the intake and look at your reading. You want a steady 17-21" hg at idle. A bouncing needle means 'bad compression/bad valve'. You can also do a quick 'compression test' by removing the coil wire and turning the engine over with the starter and listening for a 'gallop'. An engine with good, even compression will crank over with no 'hiccups' or 'gallops' in rotation. 
All due respect to sameold, using a test light to ground out wires at the cap ruins the insulation on the wires and will cause you to short the ignition with your hand and groin next time you try to set the timing. I killed the engine with my privates 40 years ago on a Chrysler Cordoba because someone had done just that. My elbow and family jewels hurt for a week. Cordobas had about a 40,000 volt ignition, IIRC. Was doing a routine tune up on a cold foggy morning for a customer. Needless to say, he had to buy new wires.


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