My 85 has been running rough, I changed the plugs, wires, rotor, distributor cap, it runs better but now it has way over heated. 240, and after I shut it down (this was after 6 mile drive) the radiator started to gurgle, overflow filled up etc.
I timed it and think it should be in good shape. The only change is that it's now getting louder when I drive it. Could this be the catalytic converter being clogged?
It idles well but just dogs out when I step on it. fuel pressure is 42, injectors are relatively new but cleaned anyway. Done a ton to it but it doesn't seem to fix it. Now I've thought that maybe the exhaust is not getting out. would this cause the over heating?
Oh, I replaced the water pump last winter and the fan too!.
Sorry to ramble on, it's late and I'm frustrated, been working on it for a couple weeks!
Very definitely could be clogged CAT. My 1988 C4 pre-CATs disintegrated and clogged my primary CAT right in the middle of the Apache Reservation in AZ (like no where with no service, no cell phone, and not even any Highway Patrol).
Lost power eventually to the point of not being able to make it up hills. Overheated badly. Kept stopping letting it cool down for another run. Finally couldn't make it up a hill, hitched a ride to the Casino, and eventually got a tow to Globe, AZ.
"Seems to me that an increase in exhaust back-pressure would be accompanied by a decrease in intake manifold vacuum. Do you have a gauge to measure vacuum? Anybody have any numbers for comparison?"
I think you're on the right track. I just went through this two weeks ago, and noticed a substantial increase in needed brake pedal pressure to actuate the brakes, which could indicate a lack of vacuum. Once I gutted the cat, all other symptoms including increased brake pedal pressure immediately disappeared.
My other symptoms included an unwillingness to rev freely which worsened as the car got hotter, higher than normal engine operating temps, a hissing sound (I have no idea why), high fuel consumption, and waaay down on horsepower. I don't know the correct way to test it while on the car (I suspect vacuum), but after removing the cat and starting it up as a test, it instantly revved freely and ran like a completely different car. After gutting it and re-installing it, I can say that the car really runs well and gets great mileage. I'm going to buy a new cat to keep it legal, but what a huge difference in eliminating that 19 year old cat with over 90k miles on it.
I hope for your sake (i.e. $$$) that the cause of your rough running, poor performance and high temps is a clogged cat, but I'd be suspecting something else with the high temps and gurgling coolant. Check for white smoke at the exhaust, moisture at the exhaust tips, and a possible sweet smell of coolant at the exhaust - maybe a head gasket or intake gasket. Also, if there is a coolant problem happening, check your thermostat - it might be stuck closed and this will cause an overheat/boil over condition pretty fast.