Jeff1216

I have 1 2007 E350 211 and now have an issue NO START after the car stopped unexpectedly No prior issue and all other systems are working normally. .
1) Replaced the Crank Position Sensor
2) Replaced the Fuel Pump Rely in the trunk
3) Confirmed Fuse #4 in truck is good
4) Removed back seat and fuel tank access cover and confirmed interconnect fuel line were ok
5) Unplugged the fuel pump connector and directly power the fuel pump using a 12V battery charger. The engine started immediately.
Any and all help would be appreciated. Jeff

juanmor40

Great work so far

Any codes after scanning ?

No codes, then you need to check you get 12V at the connector to the fuel pump under seat when the key move from position 1 to 2 (without attempt to start the engine). Since you already took the seat out, try to hear the pump priming when the ignition key move into position 2, the sound last @2sec. No sound, track backwards to the rear fuse box.

In the rear fuse box, at the fuel pump relay there should be 12 V fixed from main battery, carefully bridge to activate pump (careful one connector is from the CAN bus). Does it prime? :
Yes = problem with the relay, or the ECU (back to it later).
No = The cable from the fuse box to the fuel pump is broken.

Primed after bridging? Either the relay is still faulty ( swap with another known to work ). If relay is good, then logic to trigger the relay is failing . I think at this point someone with more experience than me need to contribute ( I would say ECU fuel pump circuit faulty? )

Hopefully I got my sentences straight.

JDM E550

See my thread Fuel pump relay - MBWorld.org Forums. For me it was the ECU.

sdhvb

There has been much discussion about "crank-no start after a short drive" situations on the ML350's, especially Bluetec Diesel Models.
If youhave replaced the FP fuse, checked the wiring, etc. with no luck, you are probably suffering from a Mercedes "non-divulged problem" ---which manifests itself - either after the original fluel pump ages and begins to draw more
urrent than it did when new (typically 5-6 amps,) -- or after a fuel pump replacemnt with an aftermarket (Non MB) fuel pump which draws more current from the get-go.

The pumps themselves, if given voltage from the FP relay, will likely continue to operate OK even if it draws more current (up to 9+ amps has ben observed,)

The Rear SAM Fuel Pump Relay will NOT OPERATE- due to overheating of the relay socknotet " prong-type contacts" in the SAM module itself - which, due to the overheating, "open up" and lose connection with the relay itself . The relay itself will probably be "hot to the touch" partly because of higher amps and due to the faulty connection.

After the engine is turned off - and the vehicle sits for less than 30 minutes or so - the engine will still NOT start on first try - because the overheated relay socket PRONGS have not cooled yet and still are not in contact with the relay.

After 15-30 minutes the car may start, as the SAM contacts have cooled and now grip the fuel pump relay contacts.

This is a royal pain, and all Mercedes will do is sell you a new rear SAM for $600 + labor--and the problem will eventually definitely come back ---because the symptom has been attacked--NOT THE PROBLEM!
THE SOLUTION involves two steps:

1. Use the original FP relay in the SAM to "pilot" a heavier duty relay {external to the rear SAM} (Hella 30 to 40 Amp 4 Prong Style with a suppressor and a suitable socket) This is pretty straight-forward and involves cutting of only one wire going from the Rear SAM to the fuel pump and using that to trigger the new relay coil. Take end of the cut wire that went to the fuel pump and connect it to one part of the Normally open contact of the new relay. Reun a new red wire 12AWG from the other side of the Normally Open Contact to the Main + 12V stud at the bottom right side of the SAM.
This will get the heat out of the SAM and the undersized MB relay and will likely solve your problem..... BUT THERE IS AN ADDITIONAL STEP RECOMMENDED....

2. You will notice that the Rear Relay Compartment is pretty much sealed behind a removable panel on the right rear side of the cargo compartment. Any heat generated in there STAYS IN THERE and is not good for anything electrical.
I cut two 3-inch round holes in that panel and installed a 3" Computer-Style 12 Volt fan in one and left the other open to vent heat and forced-in air out of the comparment. Wire the fans to the 12V+ and ground with a 2-3Amp fuse. This fan will help get rid of heat build -up inside that compartment. ( A closed vehicle in 90 Degree Summer Weather does not help anything electrical.) Remember the Germans pride themselves on "designing to spec" and leaving little extra margin in most cases.

Parts are all available on eBay or Amazon and you do not have to remove the SAM Module to do this. You will need a wiring diagram of the SAM from say AllData or other source to trace wires.

Good Luck--This does work!

This completely solved my long standing problem.

sdhvb

Remember to add a 20AMP inline fuse to the Red Wire to the Fuel Pump Itself.

juanmor40

Q: this red wire will be hot, 12V, when key on the ignition position, and OFF otherwise, correct?

What about after a craso, with air bag deployment? Will it be off, or still HOT?

Direct wiring of the fuel pump is not safe. The SAM should be able to shut it off.

In any case, Thank you very much for the explanation and finding out the root cause of the problem. Very common indeed.