My 88 E300 suddenly has rough idle after the muffler has got leaks due to rusting from inside. I checked the ignition, fuel injection, and fuel pressure and they were OK. However, I noticed that cylinder 3 not firing properly at idle. Engine would run smoother when the RMP is above 1700.

Would the back pressure from the exhaust system affect the engine performance?
I have heard that Benz's engine is quite sensitive to the back pressure. I would like to find out from anyone in this forum for suggestions in solving this problem.

Thanks in advance,

Wil

 

back pressure will cause poor power during acceleration and backfire.

the cyl#3 could be cause by bad ignition wire or fuel injector.

 

Thanks, sleepwalker!

The ignition wire and injector had been checked and they were OK... The vehicle does not have backfire. However, Cyl.3 is misfiring. The compression reading for this particular cylinder is lower than the others. I suspect that the valves or the piston ring are worned out.

Do you have procedures to check the valves adjustments for this type of vehicle? It is a Straight 6 3.0 liter gasoline engine.

Is there anyway to repair the valves without removing the engine?

 

it can be the valve if the value is still the same during wet compression test.

was it 104 engine? if it is leaking then it must be lapped (grind), therefore the cylinder head needs to come out.

you don't need to remove the engine. it's an easy job if you have good memory on where the bolts go and mark those timings.

 

yes, it should be 104 engine.

I have not done the wet compression test. Just to confirm the procedures, how and where should I inject the oil into the cylinder.

Although I can keep track with what I am taking apart, I normally like to follow remove/reinstallation procedures.
Do you have removal procedures for cylinder head and lapping?

Thanks in advance