This morning my 98 SLK 230 would not start.. Checked Ignition spark first and it was good. Then Checked for fuel pressure at Schreader valve on fuel rail. No fuel.. Before I went to connect fuel pressure gauge, which seemed like it would do no good, since there was no fuel coming out of valve, static or cranking while depressing valve. I went over to the fuse box located in engine compartment on driver side, front of firewall.. Reason for that, was more a hunch, since I have had a few (several) problems in that area with radio failure, and some other componentry problems... I bought car used and had to fix several sloppy slice jobs in wiring loom under that fuse panel.. I had previously removed all fuses cleaned and applied dielectric grease, soldered and used shrink tube on aformentioned bad slices.
After the movement of the fuse panel the car started. I did nothing specific just looked (touched) at fuses and maybe moved box a little.. Its been starting harder (cranking longer) than usual now thoughout the day. I have watched this forum for awhile and have been impressed with the knowledge here. ( I have to say right now I have a serious M.B. dealership allergy) so here are a few of my questions.. If you will indulge me?
1. Which publication has the best specific wiring diagrams for mercedes? i.e. Mitchell, Hayes, or maybe even subscribing to Alldata..
2. Any SlK owners have problems with that fuse panel?
3. Where is K40 relay board? Does it have any fuel relays/functions involved with it?
4. Where is fuel pump relay?
5. Is there a oil pressure switch that has to be satisfied to enable power to fuel pump/relay?
6. If DAS system fails I assume car will not crank. or does it just loose fuel?
I am sure everyone is thinking fuel pump, as I am trying not to. Because, I have had GREAT service out of bosch fuel pumps, but I will perform the routine tests.. Car only has 71,000 miles on it and I feel its not the pump.

 

Hi,

From your symptoms I would have the fuel pump relay as culprit No.1.
Difficult to know what's going on in your control box with bad "splices" (not slices) but you seem to have taken appropriate action to correct although I'm not sure about the DE grease.

The fuel pump is located at the back of the car and should see +12v when cranking and also when running. This supply gets to the pump via the relay which in turn is activated by two different circuits. Firstly when cranking (no oil pressure) it is fed 12v direct. Once running it gets it supply with the oil pressure switch as part of the circuit. Safety system = Engine will stop if there is no oil pressure.

If your problem now seems to be resolved there must have been something loose in the control box or components. Relays are suspect at high mileage due to contact arcing/wear.

Suggest you change the relay (low cost standard part) and have a further very careful look at the relay socket etc and wiring.

If the problem returns check for voltage at the pump.

Came across a guy in Europe whose control box had filled with oil. Normally the electronics in the control box look like new as long as the lid has been in place 100% of the time.

Car will not CRANK if DAS is the problem.