I recently replaced the A/C compressor fan in my january 79 240D, I also replaced the compressor belt. I also did an oil change. When I was replacing the belt I realized that the compressor fan belt didn't have a tensioner bolt (like the fuel pump), and I would need a pry bar to tighten the belt. I met up with a friend of mine about 20 minutes away, the car was driving fine. I tightened up the belt and fired it up, it was fine at idle so I started driving away. When I was idleing in drive the oil pressure dropped dramatically. I shut the A/C off and it only went up moderately. I went into the nearest walmart and added oil. It did nothing. I brought it to my mechanic and he said it didnt look like the mounts. I did notice the oil cap was leaking slightly, so I'm going to get another O=ring for it, hopefully that will solve the oil pressure problem. The car does have a fair amount of blow by which indicates it could have some compression issues, but it seems strange that immediately after I adjusted the pulley is when the problem started. I just need some insight before I get a diesel specialist involved. I bought the oil cap today and it didnt help. The oil pressure doesn't drop until the car is warmed up completely, when its cold it still shakes but the oil pressure stays up.

I just looked through the receipts of the previous owner, not only are their new engine mounts, but new engine shocks and vibration damper. not sure what to think.

How low the does oil pressure drop? Its normal for it to drop to 1 bar or 15 PSI at hot idle.

It only shakes with AC on?

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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg

It will drop to 30-35 with the A/C off at idle and 25-20 with the a/c on. It shakes when I am idling in drive or reverse, it shakes more if the a/c is on but shakes pretty damn hard without it. the oil pressure goes back up and the shaking stops as soon as I start moving.

The oil pressure and the shaking have nothing to do with each other. Your oil pressure readings are completely normal, nothing to worry about at all, those numbers are great.

Have you made sure that there are no air leaks in the fuel system? Have the fuel injectors been checked on a pop tester? Have you checked the fuel injection timing?

__________________
1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg

I have had none of those things done, I am going to have to have my mechanic look at it. Could I do any of those things myself? I have limited know how but am good at figuring things out if I have good instruction.

JarydW123, I have to agree with 79Mercy. From reading this, it sounds like when a load is imposed upon the engine (A/C on) the motor seems to become unbalanced (for lack of a better word at the moment). Yes, this could be injector related. Another possibility, although I haven't tested this on my car yet for the A/C's was disconnected when I bought the car, could it be a bad (piston) in the A/C pump.

I don't think it has so much to do with a/c because the issue exists without it being on, the a/c only compounds the issue. my normal mechanic is more of a gasoline engine type of guy, he gave me the number for a guy who works mostly with mercedes diesels, he should know whats up. Thanks for everyones help, im sure i will be back for more in the future.

Jaryd,
Glad to see you are a member of this forum. You have a wealth of information at your fingertips with the knowledgeable members here. I will try to shed some light on this concern of yours when I talk to you on Thursday. Although I did not sell you this car, I do know it. I hope I can help you.
Rob

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1979 240D Caledonia Green/cream gone
1982 240D stick Ivory/Palimino
1999 E300D White/grey

So I followed your advice and adjusted the idle, the car is back to normal, completely fixed. Down the line I am still going to go get a pop test and check the compression and all that, but at least at this point the car doesn't shake anymore. Thanks a lot for the insight and hope to hear from you soon

Glad to help. At least it's tolerable for now until you can do a permanent fix.

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1979 240D Caledonia Green/cream gone
1982 240D stick Ivory/Palimino
1999 E300D White/grey