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Question: 1986 C4 Rough Idle/Running and A/C Compressor Clutch Issue

DS75

Member
Joined
Dec 31, 2010
Messages
15
Location
Millersville, MD
Corvette
1986 Coupe, Auto, Metallic Red
I'm looking for help on two issues.

1) I think my A/C compressor clutch is beginning to fail. Is there a way to verify or check this and can just the clutch be replaced as opposed to the whole compressor (or is that not worth it)?

On two separate occasions when I've started the engine with the hood open I've seen whitish smoke come from the A/C compressor. I think this is the clutch starting to fail. Other symptoms include that occasionally while driving or stopped the temp of the air coming out of the vents (when the temp control is set to max cool or 60F, any fan setting from 1 to 10) begins to warm. I've checked the pressure while the compressor is running and the refrigerant is at ~30-35 psi (can't remember exactly). When the A/C seems to be working right the air temp seems to be right, in other words it seems to be working right most of the time right now. Of course in 100 deg heat at 90% humidity working right all the time would be better.

2) My vette has been having an issue lately with rough idle and while idling or driving the engine feels as if it is running a little rough (I base "rough" on the feel/vibration of the car and the sound of the exhaust). For completeness sake I've recently (past 4 weeks) replaced the oxygen sensor (I unwittingly drove for 3 weeks with the oxygen sensor broken off the exhaust, long story...), the air intake housing (cracked over the winter at the bracket where the filter is held on), the air filter, and cleaned the throttle body (this was done with throttle body cleaner and the unit removed from the car).

Additionally sometimes when I restart the engine when it was warm/hot (i.e. after a short drive) there is a hesitation in the start where it seems like nothing happens for half a second and then it kicks to life.

It's been 5 years/15k miles since I last serviced the spark plugs, wires, distributor, etc. I just opened up the distributor and there was no play or carbon build up. The cables seem to be in good shape and are making solid/seated contact. One at a time I ran the engine with one of the cables removed at the distributor end. At no point did I notice a difference in the sound of the engine running or the vibration. I did notice that with the cable removed the terminal arc-ed into the distributor housing on several of the terminals - is this normal?

I've checked all the vacuum lines/hoses and they all seem to be connected and seated well, with no cracks in the lines.

Mt father-in-law thinks it sounds like the engine is mis-firing. I can't really tell - I'm not sure what to listen to. There is no backfiring though.

I'm in the process of getting a timing light to check the timing. Also I've put some fuel injector/system cleaner in the gas tank.

What else should I be checking or looking at? I have a chiltons manual and FSM for reference.

Thanks.
 

boomdriver

Well-known member
Joined
Dec 18, 2008
Messages
1,888
Location
texas
Corvette
87 z-51
I'm looking for help on two issues.

1) I think my A/C compressor clutch is beginning to fail. Is there a way to verify or check this and can just the clutch be replaced as opposed to the whole compressor (or is that not worth it)?

On two separate occasions when I've started the engine with the hood open I've seen whitish smoke come from the A/C compressor. I think this is the clutch starting to fail. Other symptoms include that occasionally while driving or stopped the temp of the air coming out of the vents (when the temp control is set to max cool or 60F, any fan setting from 1 to 10) begins to warm. I've checked the pressure while the compressor is running and the refrigerant is at ~30-35 psi (can't remember exactly). When the A/C seems to be working right the air temp seems to be right, in other words it seems to be working right most of the time right now. Of course in 100 deg heat at 90% humidity working right all the time would be better.

2) My vette has been having an issue lately with rough idle and while idling or driving the engine feels as if it is running a little rough (I base "rough" on the feel/vibration of the car and the sound of the exhaust). For completeness sake I've recently (past 4 weeks) replaced the oxygen sensor (I unwittingly drove for 3 weeks with the oxygen sensor broken off the exhaust, long story...), the air intake housing (cracked over the winter at the bracket where the filter is held on), the air filter, and cleaned the throttle body (this was done with throttle body cleaner and the unit removed from the car).

Additionally sometimes when I restart the engine when it was warm/hot (i.e. after a short drive) there is a hesitation in the start where it seems like nothing happens for half a second and then it kicks to life.

It's been 5 years/15k miles since I last serviced the spark plugs, wires, distributor, etc. I just opened up the distributor and there was no play or carbon build up. The cables seem to be in good shape and are making solid/seated contact. One at a time I ran the engine with one of the cables removed at the distributor end. At no point did I notice a difference in the sound of the engine running or the vibration. I did notice that with the cable removed the terminal arc-ed into the distributor housing on several of the terminals - is this normal?

I've checked all the vacuum lines/hoses and they all seem to be connected and seated well, with no cracks in the lines.

Mt father-in-law thinks it sounds like the engine is mis-firing. I can't really tell - I'm not sure what to listen to. There is no backfiring though.

I'm in the process of getting a timing light to check the timing. Also I've put some fuel injector/system cleaner in the gas tank.

What else should I be checking or looking at? I have a chiltons manual and FSM for reference.

Thanks.


Change the compressor. A compressor w/clutch is only about $30 more than a clutch kit.....if the clutch is burning the compressor could be dragging.

The white smoke? sure its the clutch. Why would you start the car with the a/c ON ? Thats how you kill compressors and clutches. Always turn the a/c OFF before shut down and turn it ON after start up. Compressors get destroyed by the chugging and dragging of low rpm start up and cranking. Makes starting harder too with a compressor dragging on the engine.

Rough idle...possibly tired fuel injectors, (stock inj are trash/junk from the factory) and eventually wear out. Driving around in open loop with the broken o2 sensor probably caused some degree of plug fouling. The GM HEI likes Delco wires and AC Delco spark plugs. Delco ign modules too.

Arcing to dist base?
sure. The HEI puts out as much as 40,000 volts at low rpm and its going to try to ground somewhere. The more resistence in the wires or plugs the more arcing between the rotor and cap.

Start up...
injectors, coolant temp sensor, fuel pump relay. If you have a REAL FSM go thru the flow chart and follow the path for diagnosing a misfire. The FSM covers everything. Use the Chitlins manual for a table leg.

As far as the a/c being erratic....thats a C4. The condensor has to have fresh air flowing across it at all times to be efficient enough to have heat transfer. No heat exchange no cool cabin air. Its removing heat from the cabin, so if it cannot dump that heat to the air flow it just gets returned to the cabin. The fans are not enough to make it work right. The car will work the a/c best at 20 mph or more. Keep the radiator shroud clean, take that apart once a yr to clean and sanitize. That matters. If the cool air is off/on even at speeds where there is good air flow, then the interior air blend door may be sticking. Your FSM will have the location and test proceedure.
 

DS75

Member
Joined
Dec 31, 2010
Messages
15
Location
Millersville, MD
Corvette
1986 Coupe, Auto, Metallic Red
Boomdriver - Thanks. I'll go through the FSM and look through the troubleshooting flow chart with regards to the misfiring/rough running. It may take me a little while to work through it all since this is my daily driver. I'll post whatever I find.

I didn't realize that about the A/C. I'll be more diligent about shutting it off before starting the engine from now on. In general, when a A/C compressor like this goes how does it fail - by which I mean will it lock up and cause any issues on the belt or because it's clutched will I just lose A/C but the engine and belt won't be impacted? I ask because I may have to just drive with it for a little while until I get it fixed.


Change the compressor. A compressor w/clutch is only about $30 more than a clutch kit.....if the clutch is burning the compressor could be dragging.

The white smoke? sure its the clutch. Why would you start the car with the a/c ON ? Thats how you kill compressors and clutches. Always turn the a/c OFF before shut down and turn it ON after start up. Compressors get destroyed by the chugging and dragging of low rpm start up and cranking. Makes starting harder too with a compressor dragging on the engine.

Rough idle...possibly tired fuel injectors, (stock inj are trash/junk from the factory) and eventually wear out. Driving around in open loop with the broken o2 sensor probably caused some degree of plug fouling. The GM HEI likes Delco wires and AC Delco spark plugs. Delco ign modules too.

Arcing to dist base?
sure. The HEI puts out as much as 40,000 volts at low rpm and its going to try to ground somewhere. The more resistence in the wires or plugs the more arcing between the rotor and cap.

Start up...
injectors, coolant temp sensor, fuel pump relay. If you have a REAL FSM go thru the flow chart and follow the path for diagnosing a misfire. The FSM covers everything. Use the Chitlins manual for a table leg.

As far as the a/c being erratic....thats a C4. The condensor has to have fresh air flowing across it at all times to be efficient enough to have heat transfer. No heat exchange no cool cabin air. Its removing heat from the cabin, so if it cannot dump that heat to the air flow it just gets returned to the cabin. The fans are not enough to make it work right. The car will work the a/c best at 20 mph or more. Keep the radiator shroud clean, take that apart once a yr to clean and sanitize. That matters. If the cool air is off/on even at speeds where there is good air flow, then the interior air blend door may be sticking. Your FSM will have the location and test proceedure.
 

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