Stuck in Salt Lake! - PeachParts Mercedes-Benz Forum

Jeremy5848 · #1 12-22-2007, 12:46 PM

The '96 performed beautifully yesterday and made it to Salt Lake City yesterday with no problems. We crossed Nevada (Reno to Wendover, 400 miles) at an average speed of 74 MPH and got 29 MPG for that tank.

This morning it is 15F and the problem with the engine not wanting to start occasionally has now become permanent. When I turn the key switch to position #1, the ABS light comes on as usual; when I turn further to position #2, the other idiot lights should come on but in fact do not. If I turn the key further, the starter will engage and crank but the engine will not start.

This problem has occasionally occurred but I have always been able to get the engine to start eventually by trying the switch again and again. Today, it is not interested.

The K40 module has been suggested before; this is possible but I'm not sure whether that would also cause all the dash lights to not work or just the fuel injection. I could try removing it and bringing it inside to warm up.

Any additional suggestions would be appreciated. I don't see any alternative to taking it to a local dealer and paying through the nose while they replace expensive modules one at a time until they fix it.

Jeremy

Matt L · #2 12-22-2007, 01:04 PM

It could be the ignition switch. These are also known for problems, and would indeed cause the idiot lamps to fail to illuminate.

TMAllison · #3 12-22-2007, 01:09 PM

Cold weather = contraction.

Raise hood and listen for the click of the shutoff valve opening when the key hits pos 2; no click, no start.

If no click, try pulling the SOV elect plug then turning on ign to pos 2, then pluging back in and then going to pos 3 to start.

Be very careful with the plug, is it delicate and part of the overall wiring harness.

alfa 75 · #4 12-22-2007, 01:09 PM

I'm in SLC. I've PM'd you my phone number if you need anything.

PS- DO NOT take it to Garff Mercedes!! Werner's Mercedes is the local independent shop and they're better and more affordable. Either way though, most shops are closed until Wednesday..

romansek · #5 12-22-2007, 01:24 PM

As the first step I will recommend to clean ground connection from the battery to the body. Good luck.

Jeremy5848 · #6 12-22-2007, 01:39 PM

Quote:

Originally Posted by romansek

As the first step I will recommend to clean ground connection from the battery to the body. Good luck.

I don't suspect a ground problem as the engine cranks strongly, however I will check anyway.

Jeremy5848 · #7 12-22-2007, 01:41 PM

Quote:

Originally Posted by TMAllison

Cold weather = contraction.

Raise hood and listen for the click of the shutoff valve opening when the key hits pos 2; no click, no start.

If no click, try pulling the SOV elect plug then turning on ign to pos 2, then pluging back in and then going to pos 3 to start.

Be very careful with the plug, is it delicate and part of the overall wiring harness.

Good analysis, thanks. No clicking at all in position #2. What is the "SOV elect plug?"

Jeremy5848 · #8 12-22-2007, 01:43 PM

Quote:

Originally Posted by Matt L

It could be the ignition switch. These are also known for problems, and would indeed cause the idiot lamps to fail to illuminate.

I have long suspected the switch itself. Wiggling doesn't seem to help. I wonder how electronic it is? Some of the later cars have really complex switches covered with tiny pc boards.

TMAllison · #9 12-22-2007, 03:04 PM

Jeremy - If the Shutoff Valve (SOV) doesnt open when key hits pos 2 there is no fuel to the IP. You should hear a definate click (with hood up and door open) as it opens.

The most common cause is the K40 relay failing to provide the elect signal to the SOV; this is why cycling the key or pulling the elect connection (as I described) to the SOV sometimes works.

Just be very careful with the elect plug. I had to get a new harness (comes from fatherland) because of fiddling with mine too many times.

SOV elect plug = electrical connection (plug) at the shutoff valve

michakaveli · #10 12-22-2007, 03:13 PM

Do the easiest thing first, the K40. Just don't know how you will find one currently...

Jeremy5848 · #11 12-22-2007, 03:54 PM

Quote:

Originally Posted by TMAllison

Jeremy - If the Shutoff Valve (SOV) doesnt open when key hits pos 2 there is no fuel to the IP. You should hear a definate click (with hood up and door open) as it opens....

SOV elect plug = electrical connection (plug) at the shutoff valve

I removed the K40 module and brought it inside, warmed it in the sun, put it back, no joy. There's no clicking at all when the key switch is turned to position #1 or #2.

The shutoff valve is on the IP, I suppose? meaning, buried under the intake manifold? In any case, I don't think a K40 problem would prevent all of the idiot lights on the dash from working.

The block heater has been connected for two or three hours now and has the block nicely warmed up. The trickle charger has the brand-new battery in a high state of charge: it really spins the engine but that's all that happens. It's gotta be either the key switch or a relay/module that the key switch activates, which then powers everything else. Sure wish I had an electrical diagram for the car.

Other things that work or don't work in switch position #2:

Works
Windshield wiper
Radio
Windows, sunroof, seats and seat heaters
Headlights and other external lights
[These are all things that also work in switch position #1]

Doesn't work
Headlight flasher ("light horn")
Climate control
ScanGauge II (ScanGauge connects to and is powered from the electrical socket under the dash, reads codes, displays engine information, has tripmeter functions--I just got it, used it on this trip for the first time--disconnecting it does not help, BTW)

I can turn on the ScanGauge manually and use it to check codes -- but none have been set.

The temp here is up to a balmy 31F.

Jeremy

Jeremy5848 · #12 12-22-2007, 05:31 PM

The '96 started! We were about to push the car out of the way so my sister-in-law could get her car out of the garage. I tried one more time (maybe it heard the threat, maybe the block heater helped) and the dash idiot lights came on and it started.

Now I'm back to the intermittent version of the problem. If it continues to cooperate, we'll leave for home in a week or so and I'll deal with it there. I may still go see the recommended Mercedes indy,

Werner's
3113 S West Temple
Salt Lake City, UT 84115
(801) 467-8220

TMAllison · #13 12-22-2007, 05:39 PM

I think I would get yourself a K40 relay Jeremy. No click of the SOV opening = no joy. Classic.

Jeremy5848 · #14 12-22-2007, 07:29 PM

Quote:

Originally Posted by TMAllison

I think I would get yourself a K40 relay Jeremy. No click of the SOV opening = no joy. Classic.

I agree that the K40 is certainly a suspect but ask one question: would its failure also cause the other symptoms (failure of dash idiot lights except SRS, failure of climate control)? Lacking schematics for this car, I don't know what K40 is supposed to control except for the fuel injection subsystem. My personal list of suspects also includes the "ignition" switch.

TMAllison · #15 12-22-2007, 08:13 PM

The K40 performs the duties of the old OVP. I can't tell you what all it feeds powers to but know it is numerous devices.

The K40 costs ~$80 and is a high fail part; an ign switch is going to be considerably more and I don't remember anyone ever needing to replace one....

The fact your SOV wouldn't open during numerous cycles of the ign and then all of a sudden did open is pretty classic of the intermittent type failure caused by the K40 relay. Another common failure is the SOV closing while driving which occurs when the K40 signal is interrupted closing teh SOV; results in shutdown very suddendly, as if key were turned off with no warning.