Hey guys,
Just out of the blue my 92 600SEL refuses to start. The engine cranks but it doesn't fire when I try to start it. The Palm scanner didn't reveal any useful codes and gave me some with "no descriptions". Any ideas what to look for and where to start troubleshooting? Thanks for your help in advance.

 

I have not yet had this situation. Do you have fuel pressure at the fuel pressure test port connection at the rear, toparea of the engine? Are all of the fuses intact everywhere, including fuses in the trunk and on top of the computer modules, under a screwed down cover at the passenger side of the engine area near the windshield? Checking for secondary ignition spark at the wires can be tricky, as you do NOT want to hold a spark plug wire more than a 1 mm or so away from the engine as otherwise you can damage the very sensitive electronics. Are the spark plugs in good condition (no fouling, black look, when you remove one plug, although this may be the case as a result of other problems. Try cleaning the plugs if they look dirty and no other problems exist)? Has the fuel filter been changed recently? Unsure for a 1992, but do you have an over-voltage relay near the fuse boxor batteryin the trunk, as my model does not as it has a Base Computer module that controls voltages? Are the fuel pump relays/fuses ok?
Bill

 

Thanks for all the suggestions Bill. I have checked the fuses and confirmed sparks at the plugs. I have also confirmed fuel delivery at the rail (not sure about the pressure though). The fuel filter was replaced last year so I don't suppose that could be the problem, I'll try cleaning the plugs but that's kind of odd that it stopped working all of a sudden. It's getting frustrating.

 

Agree, usually the engine would not just immediately quit because of spark plugs being dirty, and spark plugs usually wear evenly and gap increases to a point of slight misfire or idle quality problem. Unless, something else has caused an over rich fuel mixture problem that contaminates a few or all of the plugs. A sudden engine stop usually is a fuel off of ignition offcondition.If you do have spark at the spark plugs during cranking and you do have fuel pressure presence at the test port,it should start and run, even if roughly operating, unless a computer control is preventing a normal action. Any luck yet?
Bill

 

No luck yet, actually the battery died (too many cranks) and I'm in the process of replacing it. Somebody suggested it might be the Central Locking system preventing the engine start up (security reasons), have you heard anything like that? Thanks.

 

I checked at www.alldata.com and my paid subscription for repair/diagnostics of my car- The Alarm, door locking/alarm horn system can be engaged or set to be engaged to go off, but in all cases, the starter is locked-out from operation. Not the ignition off or partially off and starter still operates. Did the battery replacement help? Can you get the computer codes reset?
bill

 

Unfortunately new battey wasn't much of a help either and still cranks without firing. Could the wiring harness be the problem behind this? I haven't changed it myself and has had the car for 2 years now and I doubt if the previous owner changed it either. Any idea what the cost of that is and if it's diy job? Thanks

 

Could be the wiring harness. I have always worried about mine and read many stories of the harness insualtion decaying. Each time I thought it was the harness when I would get an ASR/ABS light on, it turned out to be something else. It can be a DIY job, but figure it would take quite a while to ensure everything goes in ok. I would get a hand held test light and read the computer codes next, clear codes if you can and see if it starts. Send a private message to wmercer@***.net and I can explain the process. What did the spark plugs look like (fuel fouled? heavy black look?)

 

best way is to use a star diagnostic computer or the bosch KTS 520, it gives you the precise code. conventional way is to look at it in 3 departamental ways. first: electrical second: fuel system third: fuel distributor and the fuel pump (test for volume per minute)