2002 sl600 idles rough and hot, lack of power - PeachParts Mercedes-Benz Forum

JohnSL320 · #1 08-12-2004, 11:12 PM

Hello all,

I have a very strange problem with my 2002 SL600 V12 car (r129). It has 14,000 miles, idles rough and very hot. No dealer warranty, status 8. (Storm damage car). I fixed everything myself from the soft top computer, seat controllers etc. Car was running perfect for 8 months, and all of a sudden, it has a throaty type noise on acceleration, lack of power, runs very hot (clutch fan engaged after 5 min of driving) and idles rough and misses. I brought the car to 2 individual MB shops. No codes and could not figure it out. Checked adaptations, MAF, O2's, cylinder firing and all..Nothing.. What do you think??. Please someone help..

John

HitParader · #2 08-13-2004, 12:31 AM

I'm not an MB expert, but on modern cars any significant misfiring should trigger the check engine light. If it's bad enough it will kick the car into open loop, or "limp home mode" - the engine controller declares emergency and changes timing and fuel enrichment to get you home or to a service point for repairs. Improper setup, failed sensors, and trouble codes will send the car into the limp home mode which is in actuality not a very drivable mode.

However, that should be obvious to a mechanic - if no DTC's (diagnostic trouble codes) were recorded that would be very strange.

On an older car, my guess from your description of the symptoms would be either a blocked exhaust system or an issue with fuel delivery, but again the engine sensors should easily detect these problems.....

JohnSL320 · #3 08-13-2004, 11:27 AM

It does misfire, but at idle its hard to detect. How about the crankshaft sensors..? Those round donut shaped metal housings on the cylinder head..? Or the TDC cable that connects to the EZL..? I don't know. Someone please help..

Gilly · #4 08-13-2004, 09:21 PM

See if both banks are operating, this engine will run remarkable well on 1 bank, the whole engine is basically set up as 2 independent engines (left and right side). Easiest way to tell is caefully determine if both exhaust manifolds are hot, or if one side is cold/cool (not hot).

Gilly

HitParader · #5 08-14-2004, 02:48 AM

Exerpt from a recent MB mailing list:

I recently bought a 1993 600SL with 60k miles which developed a lack of
power, means it was unwilling to rev over 5000/min, was getting quite hot in
the process, had some "funny" exhaust noise, shifted the gears very hard and
basically lacked about 200 horses.
Today I got it back from my Indy who replaced the 2 blocked catalysts. He
got the new ones manufactured from someone in Ca for half the price of the
originals, I "only" had to wait a few weeks for them to receive the old ones
as a template and manufacture the new ones.
What a difference!!!!
The car goes like stink, the engine noise is smooth as are the gear changes,
the car pulls up to the red line with increasing torque and the ASR is
working hard to keep up!
I know the V12's are expensive to maintain and to repair but boy, what a
feeling to drive a sorted one.

JohnSL320 · #6 08-18-2004, 11:38 PM

Update-- Changed the crankshaft adjustment solenoid. Donut looking shapped can on passenger side cylinder head. Still runs like CRAP.. bad idle but not that noticable. A little shake like a miss. I cant figure this one out. I think its running on all 12. But I can't tell. Again like my last posts, it has a throaty type noise on acceleration and lacks power. Its like running on 6 cylinders. Keep in mind, it ran great for 8 months. It also seems to be running really, really hot. Temp gauges (Oil and Water) are around 100 C. I know thats ok, but the engine temp or maybee the exhaust manifold is too hot. The Clutch fan engages and sounds like a blower. The passenger side fender was so hot, I couldn't even touch it the other day. Yes the fender.. Does any one here think maybe the cats are bad..? Someone who knows V12 please help, otherwise I think I am inclined to bring her in.

Gilly · #7 08-19-2004, 06:57 AM

SURE you can tell if it's running on one bank, just like I told ya! See if on one side if the exhaust manifold is cold! If it's warmed up and you don't want to put your hand down there, do it when the engine is cold, just kind of monitor the temps as it's warming up, before it's too hot. You could also disconnect plug wires to see if it runs worse with various plugs disconnected. If you end up taking it in, be sure to tell them you did that, it may set misfire codes, which they can disregard. if a bank is dead, probably want to take it in, and it'll probably be a dead fuel or ignition module, there is one for each bank.

Gilly

JohnSL320 · #8 08-19-2004, 01:23 PM

when we had it on the MBscanner, all the cylinders were firing (as I was told).. Maybee its the fuel module..? where is this and how do I check it. I did notice that the passenger side exhaust manifold took longer to get warm while doing the hand test you recommended. Please help someone..

HitParader · #9 08-19-2004, 08:06 PM

Again, I'm not an MB expert, but in general to check for a blocked exhaust (most likely cat converter), you can do a vacuum check at idle and then at 1500 RPM. If the vacuum is say 21 inches at idle and like 15 inches at 1500 then the cat is likely clogged.

Others remove the oxygen sensor and start it up. The hole where the oxygen sensor was will relieve the back pressure and it should run a tad better. If so, then disconnect the exhaust pipe at the exhaust manifold and try it again. If it is a clogged cat it will scream like a banshee and rev up to its normal 4000 rpm.

Kebowers · #10 08-24-2004, 09:50 PM

It sounds like an electric throttle actuator is not working--but that should trigger all the lights ASR, Check Engine,etc.

It's kind of young to have wiring harness problems. What kind of damage was done by the storm?

anthinhk · #11 08-26-2004, 07:08 AM

After days of testing it turned out to be the cat. Changed it - performed like new. Then the other one went - exactly the same symptoms - changed it - perfect.

Re the rough idle - that was a leak from the manifold. Pretty cheap to fix.

There could be a partial problem with your throttle actuators but I would suggest the car is too young to have the typical SL600 problem. I have had mine completely re-wired (both actuators and the main loom) and it is better than ever.

Hope that helps.

JohnSL320 · #12 08-27-2004, 12:16 AM

Update.. Check engine light on now. Still riding rough and no power with throaty noise on accleration. Also noticed the exhaust air is really, really hot and the cats and muffler crackling after turn off. Can even put my hand near the exhaust pipe its so hot.. Verified both side exhaust manifolds getting warm and eventually HOT together. I think both banks are firing. Brought it in today.. Mercedes Dealer Smithtown N.Y. I am about to bend over.. Will let everyone know. I wish I was able to fix her myself. I did everything but solve this problem. Thanks All

JohnSL320 · #13 09-13-2004, 12:55 AM

Update everyone..! Finally turned out to be the clogged passenger side cat. I changed both. Runs great and like new. VERY, VERY HAPPY that I have my V-12 power back. It was very hard to diagnose this problem. Brand new cats were quoted to me for $4500.00 installed. I optioned to get remanufactured (from the Mercedes parts counter for 475.00 each) + install of 600.00 = $1500.00 total. Well worth the price at the Benz dealer. I let no one work on this car other than an MB pros or myself..

Thanks for all your responses on the Mercedes Shop thread.. and the phone call support from Enrique (M.B Motors in Tarzana, California) for guiding me in the right direction. Wished I had someone like him in the Long Island, New York area.

omegabenz · #14 09-13-2004, 04:34 AM

Quote:

Originally Posted by JohnSL320

Brand new cats were quoted to me for $4500.00 installed.

Glad you got it fixed, and didnt pay that much. I think you could probably get a high flow titanium exhaust (which would be a significant weight savings for the Sl600 exhaust) for about that much!!! That exhaust is very heavy isn't it?

c107 · #15 09-13-2004, 07:24 AM

Since you're close to the Smithtown dealer, and I am quite familiar with them (not only because their parts department is open evenings and on Saturday, but their phone number is one digit away from mine, so I get lots of calls from people looking to drop off their car... I tell them they can drop it at my house but no one seems to want to do that....) this shop might not be that far from you:

I take my SLC to Steve at Gerhard's Foreign Car Repair which is on the north side of Jericho Turnpike in Huntington Station, a little east of route 110. 631-271-7744.

It's not a Mercedes only shop. I take my station-car Audi there as well. Every time I've been in there there's always some "obscure" car on the lift... 280SE 4.5, Ferraris, VW Buses, late E38 BMW's... lots of Jettas (I wonder why...) .... so I have no reservations recommending a V12 there.

Nice guy, listens to you, reasonable prices. He did (among other things) the flex discs, trans mounts, shocks and springs on my car and when you look down there at the work, everything related is cleaned and just looks professional. He also had no problems installing parts I had either previously had or bought on my own as part of the job.

Steve