SL320 won't go above 40-mph...HELP!! - PeachParts Mercedes-Benz Forum

carloz · #1 01-16-2006, 12:43 AM

I own a 1995 SL320 V6 with about 180,xxx. The other day I was driving around 30-35mph, when I started to go above 40mph, it started to act like it was choking. If I try to push it beyond 40mph, it acts like its dying, but slowly it goes to 42-44mph.

I replaced the fuel filter and air filters, no resolution yet. What can cause this weird problem and how can I properly diagnose it?

thanks!

jjrodger · #2 01-16-2006, 04:45 AM

I assume it is an inline 6 as they did not put the V6 into the SL until 06/1998.

It could be the air mass meter; these are expensive, though.

Mike Miller · #3 01-17-2006, 07:13 PM

There are threads that talk about a "limp home" system that activates when God only knows what happens. I wish I was better at searching threads. As I remember, the the 500 SL at least has this system. It only allows you to go 40 mph to get home. Something to do with traction control maybe. I'll try to look more.

Mike Miller · #4 01-17-2006, 07:26 PM

It appears the Limp Home Mode is related to two things. The Electronic Throttle Actuator (ETA) and the ASR (traction control) system.

tecqboy · #5 01-17-2006, 08:36 PM

With that many miles also consider the possibility of a clogged catalytic convertor.

Marc-1 · #6 01-18-2006, 05:09 PM

Just read a book about the changes made to the '90's' series SL and the transmission has goveners which retard the timing and fuel if certain things do not respond ie; over rev and over speed. This as well might be worth a look even though you didn't go over those limits. Also there are two fuel pumps located just near the passengers rear wheel (under a black plastic cover) There is a presure regulator with those. Also check the distributor cap for cracks and risidual dust (carbon) this will retard the firing.
Let us know what you do find. Thanks

RHLP3 · #7 01-19-2006, 02:03 PM

I had the same problem with a 98 SL600 - Clogged Catalytic Converters...

bwheitman · #8 01-31-2006, 03:37 PM

I had that problem with my SL, but when it goes into limp mode you really know it. The engine is running on 3 cylinders. There are many factors that will cause this. All the ones previously mentioned are correct, but the most common reason for the I6 to go into limp is due to a misfire. Turning the engine off and restarting will resolve temporarily.
First thing to do is figure if it is related to load, 30mph is a certain RPM, with the car in park, run the engine to that RPM, does it start to sputter and misfire? if so it is not related to load or drivetrain. Check the plugs, coils, and ignition wires. If this doesn't resolve check your throttle actuator, and then your speed sensors. Have you replaced the wiring harness? The 95 has the harness issue, be sure to replace it before it ruins anything else. Also check your vacuum lines. Was anything done to the car prior to this condition? Oil change, repair? These are places to start.
Good luck!
Brian