Hi jeffsr, the cap and rotor are newly installed when they did the head. They scoped the engine and all cylinders are firing evenly according to the Sun machine. BTW, can I remove the pistons from underneath the engine in order to do ring replacement? I don't know enough about engine rebuilding, is there any point or even can somebody replace the rings without boring the cylinder wall?

Nope, pistons gotta come out from the top. Don't even start thinking about that yet.. You didn't mention the plug wires and resistor ends. Did they get done? If you are really convinced that adding a few PSI to each cylinder is what you need then rip into it. If your cylinders and pistons are not worn out of spec. (I doubt that they are), then it's ring replacement, cylinder honing and while your there, check the connecting rod bearings and wrist pins in the pistons. How much do you want to spend!! :D Please advise re: plug wires.
BTW a couple of other thoughts. Fuel system is one. Dirty injector, low fuel pressure. Are all of your vacuum lines back where they should be. A remote but possible cause could be a worn lobe on the cam. Did they check the cam when they had the head apart. Did you have the valve springs replaced? Are you confident that the valve job was done correctly? Persevere my friend, we'll figure it out.. 18 MPG is not very good mileage, but you did say stop and go was your forte..
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Jeff L
1987 300e
1989 300e
1987 BMW 325

[This message has been edited by jeffsr (edited 04-23-2000).]

[This message has been edited by jeffsr (edited 04-23-2000).]

Hi jeffsr, I think you are more thorough than my family doctor. Sounds like you want to hear my complete struggle with this problem. It all started when I complained about the misfired in front of traffic light. Remember those so-called Mercedes expert? One of them told me the exhaust system was plugged up, therefore I replaced everything after the exhaust manifolds, Ouch! Later a Mercedes dealer told me the fuel distributor and the injectors were rusted and luckily I managed to find a rebuilt unit from Bosch, still ouch! You guessed it, it made no difference. Then another Mercedes expert with a heavy German accent told me he knew exactly what was wrong. After the camshaft, 8 out of 16 lifters and rockers, timing chain, chain guide and tensioner were replaced, with little to nil differences ( looks like he was trying to cover all possibilities with my $$$). So the only thing I can think of is the wires like you suggested. With all the new parts it is a waste to give up on the car now. BTW you mentioned I should be getting more than 18 mph, now I am beginning to think the lower compression is affecting both the power and the gas mileage as well. I will be getting some wires tomorrow, thanks again

Try this also. Run the car until the tank reserve light comes on. Get 2 bottles of injector cleaner and 2 bottles of dry gas. Dump all 4 into the tank and fill it up. Did you actually replace the injectors or just the fuel distributor. Remember those vacuum lines. If all of this fails to produce any improvement, get it to a benz dealer and get it plugged into a computer and see if it will output any diagnostic fault codes. Also, do you have the correct heat range on the plugs? When replacing the wires, make sure you get a set with resistor tip/shields as part of the assembly. These can fail and cause misfiring..

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Jeff L
1987 300e
1989 300e
1987 BMW 325

It sounds to me like a timing problem. Since timing isn't adjustable on that motor no one has monitored it I'm sure. Temp sensor or control unit problems can effect timing. Its rare but it sounds like you have done everything else.

I don't believe you have a compression problem with 150psi uniformly on all cylinders. Any reading you get at cranking speed plays little value at driving speeds. If you had 150 at cranking and 180 was appropriate, it would only affect idle if that. Once things get moving the leaks do not have time to be of consequense unless there are great differences between cylinders.

Unfortunately you are changing parts and exploring but you really need a diagnostician.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

Hi jeffsr & stevebfl, I replaced the spark plug wires this afternoon but with no luck, I also traced all the vacuum routes with a 124 service manual, they were all intact as well. BTW, what is dry gas? I also checked the spark plugs again, they are factory spec Bosch, I also tried platinum Bosch before, they are actually worse because of the smaller center electrode. I think I will be going back to the dealer next week unless miracle happens soon! Thanks

Dry gas is an alcohol solution which absorbs any water in the fuel system, allowing it to pass out of the fuel system. If there is any water trapped in the fuel system, this will help to remove it. Injactor cleaner speaks for itself. Sometimes it will clear a dirty injector orifice. It won't hurt to try it.

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Jeff L
1987 300e
1989 300e
1987 BMW 325

Hi to everyone who helped, I used the x-66 stuff today and now only cylinder 4&5 has oil spilled onto the spark plug electrodes, but the sad thing is the slight shake came back ( I assume it is because cylinder 1,2,3&6 are firing better now). I might use more x-66 next week on cylinder 4&5.Thanks

Well, the plot thickens. If your compression rings are good enough to give you 150 or so PSI, then I can't see how enough oil is getting past them to cause the fouling you are describing. even if the oil control rings were gunked up, the compression rings should take care of most of the oil on the cylinder walls. The oil control rings are there to keep most of the oil away from the top or compression rings where it won't be exposed to the heat of combustion and turn into a carbonized mess. I'm starting to think your rings ain't in such good shape afterall. Try a new set of plugs, see if this eliminates the rough idle. Set your trip odometer to zero and see how long it takes for the roughness to return. If new plugs don't smooth things out, then something else is causing the problem.

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Jeff L
1987 300e
1989 300e
1987 BMW 325