2001 CLK55 Fule pressure at startup intermitalt.
 

Hi folks, My issue is at start up. Sometimes starts fine, sometimes starts and stalls quickly, sometimes stalls after a second, sometimes no response to the start position at all. With a fuel pressure gauge attached, I turn the key to run and hear the rear pump run and build pressure and stop. But don't see any pressure at the fuel rail. Then turn the start and if it responds I get immediate pressure. After it has run, if I repeat the run before getting to the start position, I hear what sounds like a pump up front run and see the pressure build immediately and it always starts then. Is there a second fuel pump up front that might have a relay I can check?:nix:

Fuel pump relay is a cheap replacement. I'm only aware of one fuel pump on the 2001 model.

The pump noise you're hearing up front is most likely the ESP pressure pump.

System pressurizes the rail for one second on "key on", then de-energizes until the ECU "sees" crankshaft position sensor pulses indicating the engine is turning over, and then re-energizes the fuel pump.

PM me your email address and I'll send you some info. Expect to log into WIS, pay the fee, and pull model-specific info from there.

This morning while trying to start it, I thought of the neutral safety switch. So I shifted to neutral and it started rite up. This could be a coincidence because it always does start eventually. And during the day it usually starts especially when warm and it was 88 during the day. I should know tomorrow morning.

Problem NOT solved. Must have been a coincidence shifting to neutral and it starting because it did not work this morning. I do hear the fuel pump power-up and stop after a few seconds like normal but I do not have any fuel pressure at the rails unless it trys to start. I will get a new fuel relay as suggested by bbirdwell, perhaps it does more than run the pump. One more thing now, it was rainy and the car was not too warm and now, even when I've been driving, if I make a stop, it acts up by not responding to the start position at all. Or sometimes it starts and stalls within a second.

Sounds like you need a new fuel pump.

Just replaced that last year from a different symptom. Turned out that wasn't the problem that time. Could be this time but the fuel does pump up sometimes but still no response to the crank position at the switch. I'm wondering if it could be a bad ignition switch. I should clarify that after it tries to start, when it does respond, I do get fuel pressure at the rails. and sometimes it still will not crank.

Any fuel smell by the rear axle? I've seen some CLK's have the same leakage issue that effects the E class, causing the car to bleed down pressure when off. If the line is getting air in it, the short priming of the pump may not be enough to pressurize it. Doesn't really explain no gauge reading though...

Thanks for your input. No fuel smell. At least one time I had a gauge hooked up, it tried to start (started and stalled within 1 second) the pressure came immediately up and stayed there for the next 20 min. while I kept trying to start it. So I think from that I can say the pump is good, the bleed down idea is out and it is probably an electrical issue. Or at least something keeping it from giving the OK to crank.

This morning it's cooler out and it will no longer start. At all.

I've come to realize when the cabin is hot it works. When the cabin is cold it doesn't start. So this morning I used a hair dryer and heated up the electric portion of the ignition switch and after a few minuets it started. As apposed to yesterday morning when it took 35 min. Seems like it's the ignition switch. Any thoughts?

You can interrogate the EIS (Electronic Ignition Switch) using Star or Xentry diagnostic system for current or stored codes. If the electronics in the switch are failing and you order a replacement, you need to code it to your car. Not cheap; around $450 at factorymoparparts.com.

Problem Solved
 

A few weeks ago I was about to buy the ignition switch parts and a friend in a MB dealership asked an old mechanic about the problem. He said It's it's NOT the EIS or key. It IS however a known problem with a fuse and relay block called a K-40 relay. ilocated in the compartment behind the engine compartment on the passengers side, just in front of the computer.
The MB part # A 000 540 00 72
It's a little over $100 and it took care of the problem.