I took the cutlass out the other day and while I was coasting up to a stop light the engine started running really rough. So bad that it will barely idle in drive anymore. The vacuum gauge normally shows a steady 14-15 when in park and now it flutters between 7-12. Before this happened, I had absolutely no issues with it and now it seems like its missing on several cylinders. When I drive it now the whole car shakes really bad, especially at higher RPMs and has no power. I have tested and replaced all of the ignition components, verified that its getting fuel, and checked for vacuum leaks and I cant figure out whats wrong. The engine was rebuilt two owners ago so I don't have a lot of info on it. Supposedly it only has between 25000-35000 miles since the rebuild. Please help.

 

HEI suffering fatigued pickup coil wires?

needs a tune-up?

 

I thought it was the pickup coil too, but I replaced the whole distributor and it still runs the same. I just cant figure out what would all of a sudden cause it to run like crap. I wasn't even driving it hard when it happened.

 

ck fuel flow?
pinhole leak in line from tank to carb can cause it to suck mainly air.

Dirt in the carb is the next obvious suspect but with faltering vacuum, a wiped cam lobe seems quite possible

Is your HEI fed vacuum from the manifold directly?

 

I will try running it out of a gas can tomorrow to eliminate the possibility of a fuel line leak. My Vac advance is hooked up to the carb not the manifold. I did a compression test and all cylinders read 150 so idk if that rules out a bad cam lobe or not.

 

If the vacuum gauge needle is fluttering what you would consider half of crankshaft speed. It could be a broken valve spring. A broken spring can give good compression readings and still float the valve with the engine running. You can try to identify if it is any one cylinder by pulling plug wires one by one with the engine running. Or use a temp gun on each header tube if you have headers and look for one that is cooler than the others. It could be a fuel problem but the vac. Gauge would be sweeping gradually as the rpm goes up and down and not fluttering.

 

Wait just thought of something else. I had a truck that had a bug (insect) in the float bowl, every so often it would plug one of the main jets and the engine would start running on 4 cylinders under load. Then it would backfire and apparently blow the bug off and it would start running fine. Off the throttle it would idle just fine when this would happen.

 

The engine runs bad on and off the throttle. I will check and see if i have a broken valve spring but i doubt it. The heads have been redone recently and the valve springs looked fine when i had the covers off a month ago.

 

I'm envisioning a variation of the "Waiter, there's a fly in my soup"...