Car and engine have been running great all year. Have not done anything to the engine since spring other than changing oil, checking levels, etc.

This morning I took the car out and the idle seemed to be a little off. I attributed that to the cold temp we had. Drove about 2 miles on the highway, and all seemed OK. Getting off the highway (to get gas), the car still seemed rough while slowing to a stop. Pulling out from the stop sign to go to the gas station, the car almost stalled -- running rough, seemed to lack power. I left the car running while I topped off the gas tank and it seemed fine. When I pulled out, it again seemed to be lacking power. By the time I went another mile things really got bad. I could barely keep it running. At one point, at about 35mph, it couldn't hold speed, and sounded like it was running on just a couple of cylinders. My first thought was I had gotten some bad gas (I put about 5 gal in to top it off). As I got off into a parking lot, it shut itself off at idle. A quick check under the hood didn't show any obvious problems. No leaks, all the hoses and wires looked fine, oil looked fine. Restarted the car, and it seemed to run OK as long as I kept it above idle - and I was able to drive it home. I continued to have problems at or near idle - most of the time. Curiously, there were sometimes the car would idle just fine, and only start acting up after the throttle was touched to pull out. Sometimes, at speed, the engine seemed to be running as it always has, and other times you could tell something was off. Only the one time (mentioned above) did it refuse to run at speed.

With the car back in the garage, I checked all the basics again and every thing looked fine. When I popped the air cleaner, I did find some oil on the base of the cover just above the breather. The PCV hasn't been changed in a few years - so I changed it, but it had no effect on the car.

Thoughts?
(big block, original quadrajet - rebuilt 3 years ago)

 

Fuel or ignition? Where to start? Check the timing. Make sure the timing advances with rpm. I found my dist weights frozen once from just sitting so long. Easy to see that i had no advance as i revved the engine.

If fuel then something is wrong on the primary side as this problem occurs at cruise. Look over the choke as see if it operates. Check the fuel filter. Measure the fuel pressure (6-7psi). Check the needle and seat - u can remove the carb and give it a shake upside down to free up a stuck needle or float. U can open the top hat for a look - see if the primary needles are free to move, anything inside the fuel bowl and check the float floats and set correctly.

At least u dont have anything major mechanical and the fix should be fairly simple and cheap.

 

You say it lacks power, does it feel like the engine is breaking up a bit? Could be something small like a cracked porcelain on a spark plug or two, or a frayed plug wire. Make sure everything is seated well. I also like the idea of checking your timing.

Lastly, are you on points or hei?

 

Thanks for the suggestions. I will put a timing light on it the next time I have it running. I've been pretty locked in fuel but it's certainly worth checking something like the ignition.

I plan on replacing the in-line fuel filter and the one in the carb inlet. If no luck, I'll pull the carb and take a look inside. I don't think fuel pressure is the problem as it runs stronger at speed than at idle. I did check the choke operation and it seemed OK.

 

Thanks for the info. Points. Everything is pretty much like it came from the factory (no AIR pump). Plugs get changed every spring. Points, condenser, rotor and cap every other spring. -- About 2k to 3k miles a year.

 

I finally got the car back out on the road today and it's running fine now, and so it's time to update this post.

While waiting for a carb rebuild kit I did check all the items suggested and didn't find any problem (or cure). Yesterday I finally got the time to replace the needle valve, seat, float and accelerator pump, as well as the fuel filter. While nothing appeared to be wrong with the parts I removed, the car is running great since replacing them. I suspect I had some leakage at the needle valve.

 

Glad to read the news. Now your the carb expert for that kind of lo mi driving. Ya know the more i learn about our "blended" gas these days i would change the fuel at least quarterly.