Bucking/Hesitation/Stalling after driving on highway - Pontiac GTO Forum
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post #1 of 3 (permalink) Old 04-13-2018, 01:08 PM Thread Starter
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Bucking/Hesitation/Stalling after driving on highway


Someone PLEASE help me out here.

I have a 1966 GTO with a 455 built by Don Johnson at DCI Automotive in Ohio. The engine has an aggressive cam, and is currently putting out 440 HP at the rear wheels. Don is great and no complaints on the motor.

Here is my issue, after driving the car on the highway for 25-30 miles, and when I go to pull off the highway and let off the gas, the car wants to die. I can keep it from stalling by keeping on the gas but you can all imagine the fancy footwork going on as I'm in town, with a 4 speed, trying to stay on the gas so it doesn't die while braking with my left foot. When this happens, it also gets worse under load, so when I put it in first, even though I'm keeping it at 2,000 ish RPM, it hesitates and is bogging out. If I get it up to 3,000 ish RPM its better but can still tell its running very rough.

It seems to be worse in the summer when its hot, but not exclusive to summer. Also not exclusive to highway driving. It can happen after driving it stop and go for awhile and it heats up. This was happening with the motor at about 190 deg. I'm noting this because I was thinking is this vapor lock? (I have mechanical fuel pump).

It started last summer when I was on the highway and it would start to die even on the highway when I wasn't exiting and letting off the gas. It wants to die.

I have had 2 different large carbs on here and it sthe same with both. My mechanic in Philly (muscle/classic car specialist JD's Performance) thought it might be an electical issue and put a "filter" on it. Didn't fix it.

Can someone help with some ideas here please!!! Its so frustrating I don't want to take the car anywhere as I'm worried about getting stranded (or worse causing a traffic back up).

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post #2 of 3 (permalink) Old 04-13-2018, 06:26 PM
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First, it appears you posted it under the wrong heading "2004-2006 GTO". You might get a better response by posting under the 1964-1974 heading, namely the engine section.

Next, funny how the "specialist" can't seem to figure this out. Guess you just learned he is not much of a "specialist" after all. Sometimes these "specialists" like to call themselves that so they can charge more. Here, were are not "specialists," but can usually guide you in fixing what the "specialist" can't..........and we don't charge.

That said, if you would, re-post your situation in the correct forum area (or get an administrator to re-locate your post), we will get you going and hopefully fix your problem as summer is around the corner and you need to tear up a couple chevies, fords, mopars, buicks, olds, rice burners, etc..! You will be asked more questions about your car and engine so be prepared, the more info, the better we can get you going again.
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post #3 of 3 (permalink) Old 04-13-2018, 07:31 PM
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(I moved the thread - thanks for the suggestion, PJ)

Ok Phillycanuck, please provide us with as many details on your engine as you can. For example - which carb and intake manifold are you using and what have you tried? Which ignition system? As many details as you can on the cam, compression ratio, etc. Hit us with all of it -- we can always ignore what we don't think we need. From what you're describing, I'm very suspicious of a significant vacuum leak somewhere.


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