My buddys 94 inline 6 now my parts truck. Any ways when u would run the AC it would blow black smoke like a diesel and motor go to knocking like it's got no oil check it and it's low. Don't run the AC an it never smokes. It makes no since to me at all. Any ideas?

 

Makes no sense to me either. Separate systems. A/C is a sealed system. Even on these trucks.. I believe the A/C pump is self lubricating, meaning it doesnt have a sump to the crank case... Might just be coincidence.

 

Exactly my thoughts also. Why it makes no since at all to me. It's just weird it doesn't do it with the AC off. But when it's on it and u hit the gas looks like a diesel Layin into it. I'm lost

 

Pull the battery ground and wait about 5 mins to reset the ECU. The ECU does bump up the idle when the AC compressor is running for the engine not to stall out. Hopefully its a random glitch of the ECU. Other than that, not sure what else it could be.

 

Try the computer thing, but another thing that makes no sense is that blue/grey smoke is oil, black smoke is fuel. If the A/C compressor did put a load on the engine and the computer is overcompensating, that could explain excess fuel consumption.. But not oil usage. I am curious. Wish this was something I could physically look at.

 

Yeah this situation makes no since at all. Your right about the smoke which makes no since why it would eat up oil with the AC on. I'd say it's a coincidence but why does it not eat oil with the AC off you know

 

Unplug the wire to the compressor clutch--two pin connector that plugs in right behind the belt pulley on the compressor. Then start the truck and turn the AC on like usual. The compressor won't run and system will not get cold, but it will still send the idle speed change to the computer and run the HVAC fan inside the truck. If it still does the same thing as before, then you know it has something to do with the electrical signal to the computer from the AC controls since the compressor is not running.

 

If that test reveals that the truck runs normally with the AC turned on, but the compressor disconnected, my guess is you have an overheating problem. Have you checked the water temp when you are running the AC and experiencing this heavy smoke problem? The AC puts extra heat load on the cooling system, and if there is a problem that makes the system marginal, then turning the AC on could put it over the edge and cause overheating.

 

Iv never thought to check the engine temp with the AC on. I'll ask him if he ever noticed it or not. Thanks for the replys guys.

 

I talked to my buddy he said he noticed it ran a lil more Warner with AC on then it did off and he sad he burnt more fuel wIth it on also.

 

That's a given!!

 

Well yeah I know that. But with it on it would smoke blac like a diesel. Meaning it's running rich.