My 2001 SLK320 sat unused for a year. It was on a maintainance battery charger during that time. Now the startercranks but will not fire/start. I replaced the crankshaft position sensor but no luck. What else should I look at ? What is the correct way to measure fuel pressure at the shraeder valve?

Thanks,

George

 

I'm fighting a similar problem on a SLK230. It sat for several months, also on trickle charger. I determined that there was no fuel flow. I cracked the banjo fitting on the fuel rail and had my wife crank the car and there was no fuel in the rail.
I then checked the fuel pump and found no power to the fuel pump. Then I checked the solder connections on the K40 relay module and found the connections all in good shape and no corrosion or bad solder joints (apparently a common problem on SLK230's)
At this point I am down to checking the crash sensor, if I can locate it.
Good luck on your problem.

 

Firststep.

Cranks well or only just?
If later battery is likely defective. i.re. Low volt under cranking load.
If cranking well

Got a spark? Remove plug, position on adjacent engine and observe whilst cranking.

Got fuel at the schraeder valve (under pressure)? Gauge is just like a tyre pressure gauge but using your normal tyre gauge is not a good idea. Should have a dedicated one. Not sure of correct pressure for your model but would expect itto be a few psi above atmosphere assuming petrol.

Any codes in OBD memory.

I go for 1.

Stuart

 

Umm...is the fule good? Did you use a fule stablizer?

 

possible cause not engouth fuel pressure flowing,check the fuel pump rely which is in the trank on right hand side,see if it clicks when ignition is switch on..........( its a small block rely)

 

The battery is strong and the starter cranks strong.

I have good spark.

I have no fuel pressure at the fuel rail.

I opened the K40 relay module next to the battery and the K1 fuel pump relay does not energize. there is 12V to the switch contact and the high side of the relay coil, but the low side of the coil is not being pulled to ground (reads 12V) therefore no 12V output to pin B3 of the K40 module. WIS shows that B3 goes directly to the fuel pump. Depending on which WIS diagram I look at, the ground side of the K1 coil is controlled by either the N3/4 ECM or the N3/10 ME Control Module.

I do not see another relay in the wiring diagram that is in the trunk unless this is part of the ECM or ME module. Any ideas?

Also, does the fuel pump start energizing when the ignition is on or only once you start cranking? Does is stay energized at the K40/K1 relay indefinitely or does it time out?

Thanks,

George

 

By looking at a different diagnostics source, I have confirmed that the low side of the fuel relay coil gets its signal from pin 36 of the ECM(ME-SFI). Can anyone tell me what sensors/inputs are read by the ECM before deciding whether to energize the FP relay in the K40 box so that I can determine if the ECM has failed or if an input to the ECM is at fault? I am going to try and get trouble codes this week to see if that helps.

Thanks,

George

 

Hi,

Haven't been following your thread BUT a key input into the fuel pump supply is the "accident fuel cut off" inertia switch. Sure this hasn't tripped?
Your handbook will identify location.
I assume you have testedthat the pump runs when directly connected.

Stuart.

 

Update.

No trouble codes.

The output from the K1/K40 relay to the fuel pump only energizes for 2 seconds after the ingnition is turned on (no start). It will not re-energize again unless the starter is engaged and then again for only 2 seconds. The relay stays energized the entire time that the starter is engaged. If you are looking for 12 volts at the fuel pump with only the ignition on, you will not see any power after 2 seconds.

Turns out that there is nothing wrong with my K1/K40 relays or the ECM. There is power and no fuel pressure so its on to the fuel pump and filter.

I'll post again after they are replaced.

George[/align]

 

Hi,

The other thing to bear in mind is that the pump power supply is not simply ON with the ignition ON!!

The pump is activated during ":cranking" by a feed from the starter circuit and once the engine runs engine oil pressure works a relay to maintain power to the pump. No oil pressure and the supply is cut.

Oil switches do occasionally fail.

Some models do run the pump for a few moments at ignition ON in order to pre-pressure the fuel system to reduce cranking time but this activation is time constrained by the ECU for safety reasons.

Filter acts as a pressure relief valve and if stuck open prevents the system attaining the correct pressure.

I suggest you power the pump direct to see if you get and maintain fuel system pressure.

Ifthe pump runs OK but you have no power supply check the Inertia (Accident) switch as I suggested.

Fuel pump (quite expensive) and Filter failure is uncommon although if a car is left unused for several months the pump can corrode (rust up) due to water in the fuel.

Stuart