'98 weird electrical problem - PeachParts Mercedes-Benz Forum

mtglick · #1 02-14-2011, 05:29 PM

Hi, guys--nice place ya got here!

I'm having a problem with my '98 SL500, and I don't exactly know where to begin. The problem is electrical (probably), and intermittent (of course). I'm not even certain if this is one issue, or multiple ones, but what I do know is that I'm afraid to drive it any more--nothing makes sense and I can't just keep throwing parts at it.

The history: The car has about 125K on the odo, I've put about 10K on it since purchasing in 2007. In the summer of 2009, we started noticing a small starting problem--it would crankandcrankandcrankandcrank for a few minutes, then if you walked away for about 10 minutes, it would fire. This got progressively worse over a few months, until finally it refused to start altogether for a few days and sat in a parking lot over a weekend. On Monday, it fired up as if nothing had happened. I drove it home, and on advice, replaced the CPS. Engine fired right up. It ran great for a few months, but the problem started up again, needing a few minutes to start after refusing.

Then it had a big problem. While running, the CEL came on, lots of lights flickered, the car lost power, and ended up being carefully driven to an independent's shop. Two coil packs and a brake job later, the car was returned. The independent noticed the same refusal to start, and thought that the key might be the cause, but the car didn't throw a code, so he couldn't confirm it. Parked it for a while, tested it every so often, always started up. Somewhere along the line I misplaced the alarm fob, so I started using the straight key. No appreciable change in behavior

Continued using the car, with the occasional starting issue, and on the way to work one morning it died cold while running. Nothing, no starting, no action at all. Didn't crank. Car had power, battery was OK, LED odometer worked, headlights worked, but the rest of the electronics were out. Parked the car, and came back later, the power was back, car would crank, but no start. Did that for a week, sometimes the power was on, sometimes not, finally it started and I drove it home. Once home, it died again and refused to start, sometimes it would crank, and sometimes not. I started to try to isolate symptoms, but they were intermittent and I couldn't put my finger on a root cause. Found the alarm fob, tried to use that instead, no change. At that point it seemed like there were two separate problems--a cranking no-start, combined with some other larger electrical problem. So I parked it, covered it, and ignored it. For about a year.

Last weekend, I decided that it was time to revisit the Benz. Uncovered it, hooked up a battery charger, and left it alone for a day. Came out the next morning and tried it, and the damn thing fired right up. No problems, other than running slightly warm at first, just sitting in the driveway. Slight valve tick that self-resolved.

WTF?

tecqboy · #2 02-14-2011, 09:38 PM

I don't know where it is physically located on your vehicle, but if it's an automatic, check the nuetral safety switch. It prevents cranking unless the car is in nuetral or park. Early 90's cars have issues with the ignition switch. There is a lot in the archives on that problem. Use the search tool. Welcome to the forum and good luck.

mtglick · #3 02-15-2011, 04:56 PM

Quote:

Originally Posted by tecqboy

I don't know where it is physically located on your vehicle, but if it's an automatic, check the nuetral safety switch. It prevents cranking unless the car is in nuetral or park. Early 90's cars have issues with the ignition switch. There is a lot in the archives on that problem. Use the search tool. Welcome to the forum and good luck.

Thanks, car is an auto, NSS could be a possibility, willl look into it, but would that cause the whole car to die? That's my main concern--I was willing to live with the cranking no-start, it's annoying but I would have eventually thrown enough parts at it to solve. The shuts-off-while-driving thing could be potentially lethal on the roads I drive, so that's what stopped the whole process. Anybody got any ideas?

TIA,

Matt

tecqboy · #4 02-15-2011, 06:09 PM

Well, probably not the NSS, as the car cranks OK most of the time, no? Some guys have reported that moving the steering column up/down or in/out while in the "dead" mode would restore power. This is indicative of a bad ignition switch. Moving the column flexes the switch mount and wires.

mtglick · #5 02-16-2011, 01:12 PM

Quote:

Originally Posted by tecqboy

Well, probably not the NSS, as the car cranks OK most of the time, no? Some guys have reported that moving the steering column up/down or in/out while in the "dead" mode would restore power. This is indicative of a bad ignition switch. Moving the column flexes the switch mount and wires.

Didn't try that, the power is currently on across the board, so there's no way to test.

By the way, thanks so much for the efforts thus far-I really appreciate it!

The cranking no-start is annoying, but otherwise not going to kill me. I'm leaning towards an ignition switch fault for that, one of the keys faulted it the other day, and then another key immediately started the car. This was after a key-in-door locking cycle, the car locked normally, but did not unlock normally-just the doors unlocked, and the key I used got it to crank, but not start. Switching keys solved, as soon as I put the second key in all of the central locking popped open and the car started.

What's frightening me is the dead-car phenomenon. Once running, my understanding is that the ignition kill is not supposed to be able to, well, kill the car. My concern is that whatever stopped the engine the last time won't just kill the car, but it could take me with it!

Just to clarify, even when "dead", the electrical system still had power, but NONE of the central console switches operated, the radio was out, the rear bar was out, the top motors were out--pretty much the entire interior, as well as the engine, which wouldn't crank. When I inserted the key, there were a couple of lights on the lower dash that would flash 2-3 times when I turned the key to ON, but that was it.

If it was just dead, I could work from there, but the intermittent nature is throwing me for a loop, so I'm hoping for a lead from somebody who knows more than I do.

johnflight1 · #6 02-17-2011, 06:33 PM

Hi, The part about losing your alarm key fab I find interesting.It has alot to do with the DAS,ECM,Immobilizer systems which identify the ECM and lock it out. You can crank and crank away and the car will never start. Do a search on some of the DAS posts and see what you come up with.

mtglick · #7 02-18-2011, 07:03 PM

Quote:

Originally Posted by johnflight1

Hi, The part about losing your alarm key fab I find interesting.It has alot to do with the DAS,ECM,Immobilizer systems which identify the ECM and lock it out. You can crank and crank away and the car will never start. Do a search on some of the DAS posts and see what you come up with.

Will do, thanks.

Couple notes, I did find the fob, it didn't necessarily change anything, and last night, on a slightly weakened battery, a new symptom emerged. Got in the car after locking and unlocking a few cycles, put the key in the ignition, and all hell broke loose. LOUD rapid clicking sound from somewhere in the cabin, all of the lights flickered, and I don't remember the rear bar being up, but there it was, not sure if it popped up like in a rollover or if I left it there, but the noise came from slightly behind me, so I got the sense that the bar had popped up when I turned the key. The battery was too drained to start after that.

Anybody have that particular experience and want to share?

johnflight1 · #8 02-19-2011, 02:43 AM

You can not really do any diagnosis with a weak battery. Get the battery charger on it or a new battery. There are a lot of relays that are going to click away in the trunk and under the rear seat compartment when the battery is weak they will not make full contact and they will clatter.