🚗 Mercedes-Benz SLK 200 — 💻 Crank/No Start

This 2005 Mercedes-Benz with 83k miles arrived on a flatbed with an intermittent crank no-start complaint. According to the owner this has happened before and he’s had it looked at, but he has no documentation showing what the issues were at that time or what work was done then to get it running. Of course, I can’t assume it’s the same problem as before anyway — so I start by looking for the issue as if this is the first time it’s happened.

Finding the issue ❓

When I got the car off the back of the tow truck it started right up. But it struggled to run above 1,000 rpm. A code scan showed no fault codes whatsoever, but in live data I could see the O2 sensor remained lean of WOT. Straight away I’m suspecting low fuel pressure. So I turned the vehicle off to connect my fuel pressure gauge, but when I went to restart it to see my pressure readings, it turned over fine but wouldn’t fire up.

As suspected — I have no fuel pressure.

Next I checked powers and grounds to my fuel pump. Luckily these vehicles are easy to get to the wiring in the luggage compartment, I added a substitute load and my multimeter back there and turned the engine over. I have full power, ruling out a wiring issue. I’m sure at this stage that I have a faulty fuel pump.

In conclusion

With the data collected it’s fair to say the fuel pump is at fault. Nothing fancy, just a clear and concise diagnosis. I don’t know what the earlier issues were as the owner didn’t know anything except it stopped and when he got it back it was running again. It did have a lot of new parts fitted, like plugs, coils, a MAF sensor, and possibly some cam solenoids. There’s no evidence these were fitted without being needed, but I have my suspicions.

Chances are it needed all those parts or was going to soon. It is a 2005 car after all. For now the owner is happy to have it back for some trouble-free driving. Oh, and we got his roof working again too, so he may even get a chance to get some sun!

 

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