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Old May 2nd, 20, 12:50 PM   #1 (permalink)
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Engine losing power at highway speed

I've been having a bit of a fuel (I assume) issue for a while now but it's been getting worse lately. Previously, the car would start to lose power and sort of surge at about 80mph. This wasn't that big of an issue to me until it started doing it at about 60mph recently.

I thought that something may have been clogging the fuel lines, so I switched out the sending unit in the gas tank because it still had the original one from 1978, and it still acted funny at highway speed. My next attempt at a solution is to install an 5psi electric fuel pump, but still wanted to get thoughts on other things that may be causing the issue.

It's a 1978 Camaro with the 305ci engine. I installed a more aggressive cam, intake, and a 4 barrel quadrajet. Engine runs great until it gets to higher speed. Timing is correct and even had a shop confirm it recently.

Any thoughts?
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Old May 2nd, 20, 01:38 PM   #2 (permalink)
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Is your gas cap venting? Could possibly be that simple. Does it die completely? Or just stumble?
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Old May 2nd, 20, 03:28 PM   #3 (permalink)
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Re: Engine losing power at highway speed

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Originally Posted by X-77 keith View Post
Is your gas cap venting? Could possibly be that simple. Does it die completely? Or just stumble?
If it's as simple as the gas cap venting I'll be ecstatic, i'll take a look at it

It stumbles more than dies, but it has gotten to a point to where it shut off on me and refused to start back up

Essentially, when I'm gradually pushing down on the gas, it'll get to a point where it seems like it's only getting intermittent fuel to the motor (probably 1 second increments), and if I keep pressing on the gas, it'll get unresponsive until I back off the gas and drive it a bit more conservatively
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Old May 2nd, 20, 03:31 PM   #4 (permalink)
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Re: Engine losing power at highway speed

Clogged catalytic converter?
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Old May 2nd, 20, 03:32 PM   #5 (permalink)
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Re: Engine losing power at highway speed

What happens at 60mph with the engine surging... and you push on the gas pedal to accelerate?. Does the surge go away?... or get worse?

If the surge goes away on acceleration... but surges on cruise/light throttle, try disconnecting the vacuum advance line to the distributor and plugging the vacuum line with something. Test drive the car again trying to duplicate the condition where the engine surges.
- If the surge goes away, your distributor's vacuum advance is providing too much advance.

Are you running an HEI distributor?... If so, stock or aftermarket?
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Old May 2nd, 20, 03:39 PM   #6 (permalink)
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Re: Engine losing power at highway speed

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Clogged catalytic converter?
I wouldn't assume so but you never know. I will say that it's got a whole in it and occasionally will spit out some black soot when I start it up
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Old May 2nd, 20, 03:42 PM   #7 (permalink)
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Re: Engine losing power at highway speed

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Originally Posted by oldschoolchevy View Post
What happens at 60mph with the engine surging... and you push on the gas pedal to accelerate?. Does the surge go away?... or get worse?

If the surge goes away on acceleration... but surges on cruise/light throttle, try disconnecting the vacuum advance line to the distributor and plugging the vacuum line with something. Test drive the car again trying to duplicate the condition where the engine surges.
- If the surge goes away, your distributor's vacuum advance is providing too much advance.

Are you running an HEI distributor?... If so, stock or aftermarket?
I should've worded it better. It's doing the opposite of surging. It's intermittently losing power (roughly 1 second intervals) when I try to get it up to speed. When I try to get on the gas more at that point, it'll basically nose over and lose power until I back off the gas.

I'm running an HEI distributor and I assume it's not the factory one, but I don't know for sure. The person that owned the car before me passed away before I even got it
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Old May 3rd, 20, 05:42 AM   #8 (permalink)
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Re: Engine losing power at highway speed

You stated you checked the fuel lines for blockage and you're running a quadrajet. I suspect your carb has an internal filter (sintered bronze like Holley?). Did you check/replace it? Assuming you have some sort of inline filter too, try removing the filter in the carb and run the car to see if it makes any difference. Could you have stuck fuel floats and is the float level set correctly?
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Old May 3rd, 20, 06:07 AM   #9 (permalink)
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Re: Engine losing power at highway speed

carb float level ?
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Old May 4th, 20, 11:41 AM   #10 (permalink)
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Re: Engine losing power at highway speed

May be the carb float level as y'all have suggested, I'm gonna take a look at it tomorrow and see if helps
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Old May 5th, 20, 06:37 PM   #11 (permalink)
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Re: Engine losing power at highway speed

If it's a quadrajet, it has a tiny fuel filter in it. Change the filter but use caution with the threads of the fitting. It's large, and has super fine threads. It's easy to cross thread the fitting. It also has a thin clear plastic seal on the end of the steel fitting. Take care to not lose it.
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