Pontiac 400 problems

[77grandprixsj]

So, Im new at this whole discussion board thing, but I am doing it out of desperation. I have a 77 Grand Prix SJ with a 400. It ran fine the first couple days after I bought it. After driving it a few times, I noticed a slight miss when cruising highway speeds. Soon after, it started cutting out, terribly when the engine was warm and going highway speeds. So, I flushed the gas tank, put on a new fuel pump, and had the q-jet rebuilt. That changed nothing. So, I then installed a complete new distibutor and new plugs and wires. It ran great for few 5 mile trips to town and back, but then started doing the same as it did before. At idle, and reving it in park, it runs just fine. But, once I go about 3 miles up the road, it will cut out intermitantly and want to die. Could the choke possibly be closing and be causing this problem? Could it even be the alternator or a bad ground? It has me extremely confused and even more frustrated. If there is anybody out there that can please help me out, words cannot describe how grateful I would be! Thanks

 

[melsg5]

The car has an electic choke probably so you should be able to see if it opens once the car is warm. When you changed the distributor, I assume it's an HEI, you should have gotten a new cap with a new coil, is that correct?

 

[77grandprixsj]

It is a hot air choke. I guess it runs off of vacuum. But, yes, the HEI distributor came with a cap, rotor, coil, and the works. Thats what is confusing the heck out of me. Thanks!!!

 

[melsg5]

have you done a compression test both dry and wet? have you tried spraying carb cleaner around the base of the carburetor and intake manifold to check for a vaccuum leak?

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[77grandprixsj]

Havnt tried either one of those yet. Sounds like a good idea though.Ill try it out. Thank you