90 300E serious miss problem - help - Benzworld.org

Andy_M · 08-14-2007, 03:01 PM

OK, so I replaced plugs, cap, rotor, wires and the miss persists. Cylinder 3 appears to be dead. It is getting fuel and spark, but compression is zip, so I assume since this problem went from a minor intermittant rough idle that cleared up to a full time miss that doesn't, that a valve is probably stuck open. May be a piece of carbon. Rebuilt heads look like $940 plus shipping if I reuse my cam/lifters/rockers, $400 to $500 of that being a core charge, so ~$500 to fix.

Before I go that route, what other options might be available? I remember seeing something about a product that can clean the carbon out? Anyone know about that ? Other options? Not sure if I have a local shop that could do a refurb, or if it would even be worth it.

All input appreciated....especially if you have already been through this one....

jhodg5ck · 08-14-2007, 03:38 PM

I'm going to wager this is more then a stuck piece of carbon.. Who is doing your head?

I'm thinking more along the lines of broken or cracked valve..

Jonathan

Andy_M · 08-15-2007, 05:32 AM

Quote:

Originally Posted by jhodg5ck

I'm going to wager this is more then a stuck piece of carbon.. Who is doing your head?

I'm thinking more along the lines of broken or cracked valve..

Jonathan

Probably will buy a rebuilt head. There is a couple of places in California (autoshoppingcenter ) and
Mercedes Rebuilt Engines

that have them.

Out of curiosity, what makes you suspect a broken or cracked valve ?

shavereng · 09-02-2007, 07:36 PM

I also have a 91 300 E with same symptom. 185 psi all cyl. except #3 which is 0.

If anyone has a solution short of head rebuid or major work, I'll try. otherwisw car is too old and banged up to do major engine work.

Don

neanderthal · 09-03-2007, 09:19 AM

we used to pour a small amount of water or brake fluid into the inlet manifold as the engine was being revved. not a lot, barely a trickle.

old school carbon removal. dont even know that it worked but thats what we did.

Andy_M · 09-04-2007, 08:57 AM

Quote:

Originally Posted by shavereng

I also have a 91 300 E with same symptom. 185 psi all cyl. except #3 which is 0.

If anyone has a solution short of head rebuid or major work, I'll try. otherwisw car is too old and banged up to do major engine work.

Don

In my case #3 turned out to have a chipped valve. No damage to piston at all but valve was chipped. Also had traces ov valve blow by in the intake tracks of the 2 other cylinders with lower compression than the others. Valve job most definately indicated. Springs all tested good. Head being completely redone by a local shop for a very reasonable price, so I am not going the pre-rebuilt head route. Should be reassembling this week.

Pulling the head was not especially difficult.....time consuming, but not terribly difficult.