It has the 2.8 liter 6 cylinder. The cold start valve is fine. How do I adjust it to make it run less rich? During acceleration, it spits and bogs down quite a bit. I assume it has to do with to much fuel. During idle, black smoke pours from the tail pipe. The car sat for 1.5 years, someone suggested that it might be the injectors dripping fuel constantly.

__________________
"BECAUSE KNOWING IS HALF THE BATTLE"
G. I. JOE.

Injectors can be cured by a tank of clean premium with a bottle of Techron or RedLine injector cleaner. Don't bother with other brands, they don't have the right detergent.

Unfortunately, the problem is very likely to be a broken mixture adjustment "screw" -- someone turned it with the engine running. This causes it to strip off ("mechanical fuse") and drive to full rich. Can be repaired cheaply (there was a thread here recently about that).

There is also a warmup regulator (has heater hoses to it) that can fail, leaving you in startup mode all the time, and that means RICH on these cars. Make sure it is getting hot.

You might also want to post this on the Tech Help section, too -- some of the professionals may be able to help more.

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 truly feel your pain. I have a '70 280SL and i foul plugs like nothing else. Black smoke and all! I had a raher large post a while back about this. I ended up replacing distributor, points, condencer, rotor, plugs, plug wires, FI thermostat... still no luck.

I'm sure i had started annoying a few people. They kept telling me to give up and take it to a shop. Anyway, maybe we can get through this together

psfred, no one had ever mentioned anything about the broken Mixture Adjustment Screw in the past post, but I just checked and I may have that problem.

Is this thing at the very bottom of the FI "unit"? .. brass color, about an inch long with a 6 sided disc at the end of it? Mine doenst do anything when I turn it; it's actually very loose. I can push it in, and the spring will let it come right back out. Does all of this mean its busted?

I'll try to find that mentioned thread about it.

Thanks for the burst of hope!

I dont thing the screw I mentioned in the previous post is the mixtureadjustment screw. I did some searching and I read that you need a 3mm allen to move it.

Does anyone know what I'm looking at? I'll try to post a pic soon.

Rad-man:

I believe that is the "screw" -- six sided doodad on the rear of the IP.

If it is free, it is stripped and must be repaired. This is probably the only repair you can do on this system without the proper tools....

The reason everyone is telling you to find a tech who knows these systems is that it will be impossible to get it working properly without either considerable experience OR a complete shop manual, and the manual has been out of print for 30 years. Benz stopped using the six cylinder mechanical system in Oct. 1972 when the last W108 rolled off the line.

I cannot help you much more without some pics or more detailed info, and that will only be to ask questions of my benz tech!

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!

The mixture adjustment screw is at the bottom of the IP at the back. In order to make adjustments, you need to push the screw in and turn it counterclockwise (to lean the mixture) maybe one or two clicks WITH ENGINE OFF. Start the car and see if it's any better from there. Make sure the screw pulls back out after you make the adjustment. When the screw is disengaged, it will "freewheel" when you turn it. One possibility if the car has been sitting for so long is that the rack in the injection pump is stuck. This can either cause a no start symptom or a rich running symptom as you describe. The way to check the rack is as follows:

At the front of the IP, near the top you will find either a black rubber plug or an alloy cap with a 10mm head on it. Remove whichever your pump has and with a small screwdriver (or preferably a special tool which is actually a long bolt meant to thread into the front of the rack), push the rack back and see if it returns to it's former position. If you have free movement of the rack, that eliminates it as the culprit. If not, the pump has to be overhauled.

If somebody ran the engine with the mixture screw engaged, the pump will have to be removed and recalibrated.

One other thing to mention: Rather than the Bosch W7 plugs, we've had good success with NGK B7ES spark plugs as far as fouling goes.

You might also check the altitude compensator and the air filter at the back of the IP. Both of these things, if amiss, can lead to poor running.

__________________
Regards,
Aaron

THANK YOU! That's exactly what I needed to know!

I checked the rack behind the black rubber plug and it would move back and forth. not much, though. maybe 1/4"

I had also messed with the screw before I knew what it was, so I had no idea where it had been. I started off by turning all the way to the left (to get it as lean as possible). When it is the tightest, it would not "freewheel". So then I decided to turn off a few notches.

Then, I got her started, butshe would die in idle. Turned off a few notches again and it would still die in idle, but it wasn't lean at all. I couldnt get it to cause any black smoke.

I tried a few more positions, (along with the idle air screw) but I couldnt get it to idle.

Should I try some new plugs again? any other suggestions?

Well, without actually being there I can only say that you might go ahead and try a new set of plugs, since the car was running rich, the plugs are most likely gasoline fouled, but before you change them, pull each one and smell/look at the electrode tip to see if there is evidence of fouling. If some are fouled, get new ones, as the only way to clean the old ones is to rev and rev the engine for quite some time to burn the fuel off the plugs. New ones (if this is the case) will make the car run 100% better. And do try to get the NGKs rather than the Bosch plugs.

__________________
Regards,
Aaron

Actually, these plugs had fouled once before I figured out where the Fuel Mixture Adjustment screw was. I cleaned them off with a metal brush, and then started messing with the IP screw.

This will be the 5th set of plugs in 6 months

Rad-man:

I've been told that Bosch plugs won't self-clean after being carbon fouled well enough to bother. They must be cleaned on a plug cleaning machine (minature bead blaster) or replaced. They appear to stay carbon fouled and refuse to properly spark for extended periods of time.

Remember that old rotten fuel, particularly if you added detergents (RedLine or Techron) won't burn worth a damn -- reguardless of engine mixture, that stuff will foul plugs terribly, and the only way to "cure" them is to drive for several hours at 75 mph!

Try setting the fuel mixture again after you get new plugs in.

Basic procedure in the manual is to attach a vac gauge and tach, then set the air screw on the intake to max vac, then check idle speed. If the speed is too high, the pump it too rich, if it is too low, the pump is too lean. You then adjust the IP mixture screw one or two clicks, then readjust the air screw and re-check idle speed. I think (and Aaron will correct me if I'm wrong) and the running (off idle) mixture will match the idle mixture setting via the linkage and the 3-D cam in the pump. This, of course, means you should NOT diddle with the linkage adjustments unless you KNOW what you are doing -- otherwise, you will surely go from bad to worse.......

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!

Thanks again for all the info. I'm glag I'm finally getting somewhere with this thing.

As far as fuel goes, I unhooked one of the fuel lines and let it drain out for a while. Then I put some new Bosch oplugs in and let her run for an hour. (That was before this post; before I learned about the adjusting screw).

I'll go ahead and order the NGK's and try it again this weekend.

Thanks for everything

Are these similar to the NGK BP6ES? This is the one that comes up in FastLane

Rad-man:

They are one heat range difference, but I don't know which way NGK runs -- Bosch I think the number goes higher as the plug gets "colder".

You probably want a hot plug for this car, especially if you don't expect to run it on the highway a lot. MB ran them RICH for extended periods due, probably, to the quality of the gasoline in 1965. Modern fuels are much better burning, and the engine doesn't need to run anywhere near as rich to keep it going cold.....

Peter

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!