2007 Mercedes SLK 280 Random Misfires Cylinders 1-4

[Big T]

I know this is a truck forum, but I've found that the best mechanics reside here and may be able to help me. I posted this problem on www.slkwork.com, but those guys can't hold a candle to the mechs that frequent here. So here goes.

Started with codes for intake tumbler flap problem. Car was not running bad at all, but the wife was freaking out about the CEL. This is a common problem on these Mercedes as they use plastic parts and the actuator eventually breaks as the resistance increases from gummed up or warped tumblers. They have aftermarket kits with aluminum actuators to repair this. The dealers just install new manifolds and it's a $1,200 job.

I first did the manifold tumbler flap actuator repair job and after reinstalling the manifold the engine ran extremely rough at idle and generated codes for random misfires on cylinders 1, 2, 3 and 4. I took it to my independent mechanic who said that when people attempt to repair the manifold, they typically come back with a misfiring engine because the tumblers are warped. He said that I needed a new manifold. Beyond idle speed it will accelerate to full rpm, but there are misfires and the exhaust smells like it's running lean.

I purchased a new OEM manifold on-line and installed that. No change at all. It was suggested that I may not have seated the injectors properly and that I should install new seals. I purchased both lower and upper injector seals. I was able to find and replace the green seals which appear to be lower, but I have no idea where the black seals go.

I applied some engine oil to the seals and reinstalled the injector rail. No difference whatsoever. Same codes for random misfires on cylinders 1-4.

I disconnected the harness plug from injector #2 on passenger side and noted a difference in the engine (hard to do as it's really running rough). Then I started disconnecting engine coils one-by-one while it was running. Really no discernible change on the passenger side, but when I got to the driver's side the engine dropped rpm when I disconnect the front and the second coil.

I'm told that the only real way to fight....err figure this out is to have it diagnose on the STAR system at a dealer. Independents don't have the STAR system and thus are generally left plugging in parts. Is this correct?

On the other hand, it would be much cheaper for me to plug in new coils with internet parts prices.

Where should I go from here?

P.S. This is my wife's care and I really hate it.

 

[ak diesel driver]

sounds like your issue is on the passenger side. you said you thought it was running lean, maybe a vacuum leak. take a propane torch (unlit) and run it around the gasket areas with it running. engine should speed up when you get close to the leak.

 

[Big T]

Tried the propane torch thing with a hose on the torch. Thought maybe the brake booster hose might have a leak at the connection as it sped the engine up several times, but not every time. I'm going to pull the manifold and redo the gaskets. I can do the job now in about an hour, but it's a PITA.

 

[THEFERMANATOR]

Sure sounds like an air leak to me as well.

 

[Big T]

Sure sounds like an air leak to me as well.

I got the same issues installing the repaired manifold (see pics) as with the new manifold. I only touched a few things and I've checked them all. I think it's down to redoing the gaskets, as they easily shifted around when dropping in the manifold. That or the intake snorkel below the MAF may be leaking or cracked. I removed that by twisting it slightly, then pulling it off. It's plastic and all the plastic crap on this engine is brittle at 100K miles.

 

[ak diesel driver]

I've used thread to hold gaskets in place. Then cut and pull it out when your there.

 

[Big T]

Yep, intake gaskets were askew. The gasket is coated metal and suloosedly held to the manifold by pins you press it onto. That works poorly. I ended up tying it in place with fishing line and that worked great. Thanks.