I have a 1979 280SE that I recently purchased from an auction for a couple hundred. It's in good shape, except the engine. What I am hearing (how to word this) a robust knocking when at 2500 rpm or above, but levels out with no load. Now, heres a little background information.

Has 213,000 miles.
Doesn't overheat.
Oil is very clean. (no water, particles)
Engine runs good (strong accell., quick responce)
Have changed gas to premium, added drygas.

Symtoms:

At start black smoke, but clears out when warm.
(Also very smelly...)

Engine missis periodicly.

Number 1, 3 have oily spark plugs. (There's alot more to this one. I had recently changed the spark plugs, and found them in normal condition. I changed them and found the knock had gone away, but I ran it down the highway, and in about 2 miles it started knocking again. The next time I checked the plugs they were oily)

The idle speed was set @ 1800 RPMs, now I had lowered it to 800rpm, and was successfull. But when I did, it ran for about 20 mins and stalled, and didn't start back up... so I reverted back to the setting and it started.

Oil pressure is high (as far as I know that's Ok)

Hard to start when hot (running for more than 30 mins)

The engine is overall pretty loud.. possibly lifter noise.

I have not checked any timing, compression (due to lack of funds). But if anyone possibly may have an answer, that would be great. I have found a ton of info, but I have so many variables involved that I overwhelmed. My thoughts were possble heavy deposits on lifters, or advanced ignition timing off... maybe running rich??? (due to oily/gassy smell from exhaust)
Thanks

You have plain K-Jet fuel injection. You also have bad valve guide seals (oily spark plugs).

Here's what I would do:

Clean the air flow sensor housing and make sure the flap is centered. It must move smoothly throughout the entire range. If not, the fuel control plunger is probably scored or the seals are bad -- replace.

Your warmup regulator or cold stard valve is bad, and it sounds as if the mixture is way off (check the plugs). If someone has set the mixture without correcting a leaky cold start valve or bad warmup regulator, the mixture is way too lean hot. This will cause running problems, excessive spark knock, and idle problems. You should have a fast idle cold that drops on it's own -- if not the cold idle system isn't working.

Also look for vac leaks -- the cold start and idle control screw hoses are a good place to start -- vac leaks here will screw up the idle, but not running mixture.

Check the ignition, too -- fried cap and rotors are pretty common, as the car will run pretty well with them in bad shape, just idle rough and miss once in a while.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I have checked a few things... still not alot of luck. What I have found is.

Carbon buildup on distrubuter cap, rotor. (scraped off and it doesn't miss ass much)

Wires off of the cold start valve (still unsure if it even works anything I can do to check it's operabilty?)

I have also retarded the ignition timeing a few degress... have found that almost removed all of the knock.. but it runs @ 500 rpm and it's a little rough, unresponsive. I also adavanced the timing a few degrees.. It runs great but the knock definitly gets louder. So I think the knock is probably due to mixture and timing. I just don't know how to set it correctly.

I need to know how to check the cold start valve. I am not sure how to check the warmup regulator (I actually couldn't find it..)

If you have any kind of troublshooting tips that would be great. I am looking foward to getting this old girl running good again!

Get a new cap and rotor -- if they were carbon tracked, cleaning won't fix the misfire for long.

The warmup regulator will be plumbed in the fuel system -- it lowers the pressure in the bottom half of the fuel distributor so that there is more fuel delivered. There is also a pressure regulator between the fuel distributor and the return line -- no electricals on these.

You can test the cold start valve by applying battery voltage on stopped engine -- it should spray as long as there is pressure in the system. In operation, it should energize briefly when cranking at low temps -- time is determined by the thermo-time switch and a relay.

Fuel mixture is adjsted with a concealed allen screw -- not sure where it is on the M110, but somwhere between the air meter flap and the fuel distributor.

Idle speed will be controlled by a bleed screw in the idle air line. There is also a cold idle system attached to the block, I believe, with two air hoses also. May also be a decel valve to feed air in on hard decelceration, but I'm not sure about that. There was on my Audi Fox of similar vintage.

Timing specs should be on a sticker in the engine compartment if it hasn't shrunk so bad you can't see it. My Childtons' lists ) TDC as the correct timing at 800 rpm

Make sure the vac system for advance and or retard is connected correctly and working before setting the timing! Else it may end up strange.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!