# Engine miss in 66 GTO



## paly57 (Jul 27, 2008)

I have a slight engine miss in my 66 GTO and I am looking for suggestions on what I might be able to do to fix or reduce the problem. The engine and carb are original with about 200,000 miles. The miss is most noticable when I am driving at constant speed and there doesn't seem to be any miss under acceleration. I have checked plugs, points timing and replaced the spark plug wires. Other than rebuilding the carb , which I have not rebuilt in many years, I'm not sure what else to try. 

Thanks in advance for any suggestions.


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## Rukee (Feb 8, 2007)

Perhaps a compression test is in order? With that kind of miles it could be worn rings or a cam lobe, dished lifter, weak valve spring, etc.


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## 66tempestGT (Nov 28, 2009)

set the points with a dwell meter? is the vacuum advance working properly. this wont cause it to miss, but while in the distibutor always check to see if the mechanical advance is working freely and not stuck.


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## geeteeohguy (Feb 2, 2008)

Put a vacuum guage on it to determine engine condition. YOu can look at it as you drive. 18 inches and steady at idle? Steady at cruise? No fluctuation? If you have a weak valve spring, or a burnt valve, it will show up. The needle on the guage will fluctuate rapidly.Is the dwell set correctly? The timing? Plug heat range? How is the ignition coil? is the tower on it cracked or tracked? Is the dist. cap cracked or tracked, etc. You could also put it on an oscilliscope and look at the ignition pattern and see if you have an ign. problem. Could be anything, but probably not too difficult to figure out. These are basic cars. Good luck.


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## topfuel67 (Dec 23, 2008)

I had a similar issue with my 65 Tempest that I put a 389 in. The motor was rebuilt and I did all the obvious checks listed above and still had a miss and it didn't have the power.  I put a new distributor in with the HEI and it solved the problem. These old distributors wear out and are a pain to diagnos. The old distributor even had the pointless ignition upgrade and at one point ran fine.


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## Poncho Dan (Jun 30, 2009)

paly57 said:


> I have a slight engine miss in my 66 GTO and I am looking for suggestions on what I might be able to do to fix or reduce the problem. The engine and carb are original with about 200,000 miles. The miss is most noticable when I am driving at constant speed and there doesn't seem to be any miss under acceleration. I have checked plugs, points timing and replaced the spark plug wires. Other than rebuilding the carb , which I have not rebuilt in many years, I'm not sure what else to try.
> 
> Thanks in advance for any suggestions.


Did you replace the distributor cap and rotor? Those will burn just as bad as points. The reason I say is that when I first got my GP, I took it for a drive one night and started losing cylinders about a block away from home... made it back on 4, maybe 5. :lol:


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