A little trouble shooting...

[Chevelle454]

This is a little off topic, but I need to get this car fixed quickly. My '84 Caprice has a 305 V8 (carb.).

I recently changed the valve cover gaskets, and when I put it all back together it runs rough. I changed plug wires and the O2 sensor, but it still is not how it was. When I first start it up, it runs perfect, like it supposed to. After about 10-15 minutes of driving, it will have no power until about half-throttle. It will cut out and backfire out the carb a little bit sometimes. I have to push the gas way down before it will go anywhere.

All vacuum lines are leak-free and connected. Emissions lines and harnesses are all intact. The only thing I can possibly think of is the ignition timing. But it wouldn't run good for the first few minutes if the ignition timing is off, would it? Or could it be the electric choke?

I need help, quick. I am getting 10mpg instead of the 20-25 like I usually get...

Thanks...
Scott

[acloco]

May seem ridiculous...but which valve cover gasket did you change? What was removed to access the valve cover.

First.....does this have the electronically controlled quadrajet (2 or 4 barrel). If so...check the connector at the throttle position sensor.......

[Gordo]

Double check your firing order, # 5 and #7 are easy to cross without knowing. If you didn't move the distributor, the timing will not be affected.

[Chevelle454]

Originally posted by acloco
May seem ridiculous...but which valve cover gasket did you change? What was removed to access the valve cover.

First.....does this have the electronically controlled quadrajet (2 or 4 barrel). If so...check the connector at the throttle position sensor.......

I did both gaskets. I didn't have to remove much to get to them, and what I did remove, I put back the same as it was. It is a 4 barrel carb, and all electronic connectors on it are tight.

The firing order is correct.

Could the catalytic converter possibly be plugged? The exhaust seems to get louder(like a leak near the converter) after it runs for 10-15 minutes and it smells like sulfur sometimes...

[JimKshortstep4x4]

I would not suspect the catalitic converter. When they plug, it affects high rpm and it makes the car sluggish, no missing.

It acts like the computer is not getting all of the inputs. My first thought is the temperature sensor, and then the oxygen sensor would be next on my list to check out, and then the map sensor.

Jim

[Chevelle454]

What would happen if the temp sensor is bad? The wires for the temp sensor(if it is near the waterneck) are exposed...

[JimKshortstep4x4]

If the temperature sensor is bad and it is signalling the computer that the engine is still cold it will cause an over rich condition when the engine is warmed up. I am not sure of all the effects the temperature sender can have but the computer needs the temperature of the engine to properly adjust the fuel, either lean or rich.

Jim

[Chevelle454]

It is not fuel injected, are you sure the mixture is computer controlled? But it is running rich... It blows out black smoke when I step on it hard. Here's a pic of the carb:

[Chevelle454]

I know the temp sensor works, or at least it did last summer. The dummy light came on when the car was overheating(bad radiator).

[acloco]

Double/Triple check the TPS - Throttle position sensor....the one on the right in your picture.

Any wires pinched under the left valve cover? ....especially at the rear corner of it.

[jimfulco]

Might check the electronic connections for corrosion, looseness, etc. And run a can of fuel injector cleaner (I like Berryman's) with the gas.

[bpmcgee]

The temp sender wire is right down where it would get bumped off while changing valve covers. You didn't do that did you?

Brian

[walker]

Anytime I fix something worse than it was when I started I always suspect what it was that I repaired. I would go back and check the ignition wires first, then on to the oxygen sensor. Also, those carbs are nothin' but trouble, if you ask me. It may have been bumped, or had a connection in it that was dying to go bad and you encouraged it by working near it. I can't remember if those cars had onboard diagnostics or not. If it does, I'd scan it.

[Longhorn Man]

It has on board diagnostics, pretty much all GMs from 82 on up had it.
It sounds quite a bit like a messed up EGR valve to me...or one not hooked up properly anyways.

[Perchjerker]

Hell, boy, try this:
Those 80 somethin' year models all had what they called a computer under the dash. In that year, the CPU has a "reset" button on it. Many times, if you have one of those CPU controlled carbs, you will need to push that reset button if you had disconnected anything, like a wireing harness. Make sure you have a flashlight; the CPU on that Caprice should be under the dash kinda behaind the glove box. GOOD LUCK WITH THAT THING.

[acloco]

Or...make it easy on yourself...and disconnect the negative battery cable for a few minutes. This clears the memory and any stored codes on the ECM.

Have you pulled the codes yet? Jumper A & B together on the ALDL connector under the left side of the dash......with the key on, engine off....then start counting the number of flashes on the check engine light. Will start out with 1, pause, 2 (code 12)....will flash this number three times at the beginning.......then any stored codes....then end with code 12 at the end (flashing this three times as well.

Good luck!

[JimKshortstep4x4]

Chevelle 454

If that is a picture of your engine, their is a vacuum line missing off of the vacuum tee for the choke pull. Either put the missing hose back on or plug the tee. With the tee open to vacuum, the choke pull will not work and the engine will flood.

Jim