Tinodea

My ‘07 ML320 CDI was running perfectly without issue until last week when I tried to start it and all I got was cranking, no fire. Zero. It was as if I parked it and a switch was flipped by the time I came back to start it. No warnings, no lead-up symptoms of any kind. No codes in the diagnostic system. Fuel filter has < 2000 miles on it. Fuel pump relay and all fuses in the engine compartment box and rear cargo box appear to be sound. There is power to the fuel pump relay. The fuel gauge is also working so I assume there is also power to the assembly unit, but I do NOT hear the pump turning on when I turn the key. I also pulled off the fuel line at the filter and turned to key briefly to confirm- no fuel coming out the line. It seems like it’s all pointing to the the low pressure fuel pump, but I wanted to make for absolute sure there were no other precursors I might be missing before dropping a $400 part into my fuel tank.

The only other thing I’ve done otherwise recently was temporarliy delete the swirl flap motor/assembly until I can get the time to replace the servo motor (otherwise causing limp mode). But this seems unlikely to be related (I think).

Also how do you properly remove the access cover to the pump under the rear right seat? It has no nuts to remove, just a silicone type seal on it. Are you just supposed to pry?

Thanks

Maj. Dundee

There are so many factors & components that control the actuation of the fuel pump. Just because the pump is not supplying fuel DOES NOT mean the you have a faulty fuel pump.

You must own your own scanner to at least pinpoint the problem. Without one, everything is costly guess work.

texterted

Bang on the tank or that access panel with your fist or a rubber mallet. See if you can get the pump to kick on.

Tinodea

Thanks texterted- I will check to see tomorrow what happens if I do this.

Thanks Maj Dundee. Your response highlights exactly why I posed the question. I do already own a scanner, an iCarsoft EU Pro model: https://www.icarsoft.eu/eu-pro. I’m not sure if it’s powerful enough of an interface to diagnose this, but I will dig deeper with the info you attached to see. Hopefully it is.

Maj. Dundee

You have a scanner and with this problem, you didn't check for codes?

Tinodea

Yes, of course I checked for for error codes first- this was mentioned the original post: "...no lead-up symptoms of any kind. No codes in the diagnostic system."

From what I've read so far, the fact that there are no codes being thrown for this issue sounded additionally indicative of an issue with the low pressure pump. A number of places have mentioned that the a failed low pressure pump itself will not throw a code.

My scanner can read real-time data output from a number of the car's sensors (though this car and scanner is relatively new to me, so I'm still learning), and that's what I was referring to when I said I'd look into the scanner's output further re: the information you sent.

Thanks

Maj. Dundee

I don't know what scanner you have, but the AAC Cont. Module stores its own codes. If your scanner cannot read this module then you will be in the dark.

Tinodea

Thanks Maj Dundee- my scanner was capable of that level of detail, and I think I may have found the culprit. I was looking in the ECM/CDI module for originally but just found these codes in the Rear SAM (Error 9153 - Relay 15R) and Front SAM (Error 9043, 9045 - circuit 30 undervoltage), and thanks to the sheet you attached previously describing fuel pump actuation components, it seems to line up under the section:

"Direct input signals:
- Terminal 15
- Circuit 30
- Circuit 31
- Fuel pressure sensor (B4/7)"

I will let you know how it turns out.

Tinodea

To no avail. Replacing the terminal 15R relay did not help. The only possible other indicators I got out of the real-time data from the modules were
1) Electronic Fuel Pump: OFF (when It presumably should have been running
2) Output Terminal 50: OFF (from ignition system data, not sure if that was as it is supposed to be; all others were "YES" or "ON")
3) Synchronization State: DID NOT INITIALIZE; TIMED OUT (

Still stumped, and not understanding what the above might actually be indicating.

Maj. Dundee

The relay you replaced has nothing to do with fuel delivery.

Please explain above sentences 1-3. Code numbers only and what module did they come from?

Tinodea

Yes, I realized after the fact that I misunderstood what the Error code was indicating. I initially did not have an index for the codes, so looked for the relay the rear fuse panel chart that was associated with circuit "15R". So I actually replaced relay R, rather than K. I realized it was relay K after finally finding some more comprehensive information. After that fail, I probed the diagnostic system more. So there is no question, I attached the photos below from the diagnostic output from the Engine Control Module and Electronic Ignition Switch module below:

Diagnostic data options in ECM > "Starter rotates and engine does not start" option



Data streams 1-4 under "Starter rotates and engine does not start" option in ECM output. Could not crank starter at the moment, battery was too low. During cranking all numbers increase, but "Synchronization State" does not change, nor do I don't know what "Synchronization State" is.


Data streams 5-7 under "Starter rotates and engine does not start" option in ECM output. Could not crank starter at the moment, battery was too low.


Diagnostic data options in ECM > "Test engine at idle speed" option.



Data streams 1-4 under "Test engine at idle speed" option in ECM output- only selected Electronic Fuel Pump since the car is clearly not able to be tested at idle at the moment.


Electronic Fuel Pump data stream under "Test engine at idle speed" option in ECM output. Electronic fuel pump should be presumably be "ON" & running at the moment (?) as I had just turned the key to position 3. I don't know if the electronic fuel pump reads "OFF" because it's not working/functional, or if it is not switched on by something upstream from it.


Electronic ignition switch module.


Data streams 1-5 under ignition system module. All looks good here.


Data streams 4-8 under ignition system module. I'm not sure if "Output Terminal 50 (CAN)" should have been "ON" here?

rolfnordnes

Hi
Did u find the source for your problem? I have similar problem with my 2008

lkchris

Fuel pump relay failure is fairly common. That’s all I needed.

Green Line

Finaly were you able to get this solved for your 2008? Was it the Fuel Pump Relay ?
Thanks