RE: 1993 600 SL one cylinder misfiring

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RE: 1993 600 SL one cylinder misfiring

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RE: 1993 600 SL one cylinder misfiring - 2/15/2005 1:55:39 PM

CRC 1993 600SL

Posts: 8
Joined: 2/14/2005
Status: offline

I had a re-program of the electronics and changed the air intake filter (changed it to a filter that lets air
pass more easily than the standard factory filter). It is no longer complying with the
EU regulations on emissions but goes much faster. It is a package my mech sourced in Germany, I can try to
get more info, In any case it isn't a huge improvement, just about 6% on power (the big change however
is on torque). The supplier also declares that mileage should get somewhat better (from 5.5 Km/Lt to 6,5 Km/lt)...

< Message edited by CRC 1993 600SL -- 2/15/2005 1:57:50 PM >

(in reply to Lugnut)

Post #: 11

RE: 1993 600 SL one cylinder misfiring - 2/24/2005 6:03:46 PM

CRC 1993 600SL

Posts: 8
Joined: 2/14/2005
Status: offline

The mystery gets deeper!
I had all the wiring changed (the old one was completely destroyed by the heat, you could get the insulation off just by bending
the wire...) and it still gave me 11 out of 12 cylinders working!
The pattern is as follows:

Cold motor: all 12 cyls work OK for about 5 to 10 minutes. Then switches to 11. We have checked the sparkplugs and they
work perfectly (even when the 12th cyl is not working the sparkplug is still giving the spark). It is the injector that stops operating.

Hot motor: all 12 cyls work for three to five seconds on turning on the motor, then revert to 11.

It would seem it could be related to the starter heat up program in some weird way...

Mad & Desperate experiments:

1: wire swapping

We tried inverting the sensors on the right front of the motor (marked 1 and 2, I believe they are camshaft magnetic sensors).
The motor, strangely enough, works constantly on 12 Cylinders but, obviously, goes into limp-home mode. It will work on
12 cylinders indefinetely, however, which rules out compression, mechanical or electrical problems altogether.

2: ASR electronics removal
We entirely removed the ASR electronics motherboard from it's socket (upper left corner of the motor bay). The engine runs
on 11 cyl constantly and now doesn't even give the cold 10 minutes or the 3-5 seconds 12 cyl operation on hot we got with the ASR in.

3: Direct connection of the motor motherboard pin to the injector
This was done to rule out any possible problem with cables and connectors between the motherboard and the injector.
We get exactly the same pattern as with the normal connection (we also tried inverting the boards supposing we would
shift the problem from one side of the motor to the other but it didn't happen and we still got the same cyl. misfiring).
With this test therefore we ruled out all electrical and connection problems and motherboard electronic problems.
It would seem that there is some weird info that tells the motherboard controlling the injector on cyl number 12
to just stop operating (it actually stays shut).

My mechanic decided to send the car to a BOSCH specialist in Italy and have a full diagnostic to see what we get out of that...

Any suggestions or ideas?
Is there a shop manual available somewhere for the electronics for the SL 600?

Thanks

Robin

(in reply to CRC 1993 600SL)

Post #: 12

RE: 1993 600 SL one cylinder misfiring - 2/24/2005 7:47:06 PM

sleepwalker