jhoward924

2001 ML320, 140K miles


It all started when the truck died while at a stop light in traffic. I tried restarting it multiple times but it would run for 1 second then die. I did notice if I held my foot down on the gas it would spike the RPM but then die. I was able to finally get it to start and throw it into drive but it was not responsive to the throttle. It paced along at <5mph until I could pull into a parking lot. My first thought was a crankshaft position sensor but I had replaced it about a year prior. After about 30 minutes while sitting in the parking lot I was able to get it started with a response to throttle position, although it was slugish. At this point the check engine light came on but I was able to make it home (~9 miles). Once I got home I checked the codes and received P0100 and P0110. Both related to the mas air flow sensor and intake temperature (both contained in the MAF sensor). 2 months prior to this I replaced the MAF sensor, fuel pump and filter. While the car was still at temperature sitting in the driveway I tried to start it and it would run for 1 second and then die. I disconnected the MAF sensor connector and the car started normally. While running I reconnected the MAF sensor and nothing happened, the car continued to run normal. With it still connected I turned off the engine and tried to restart but it would die after a second. I repeated this series of events 2 more times to make sure it wasn't a fluke. At this point I assumed I had a defective MAF sensor but figured I could drive to work the next morning with it disconnected. The next morning the car would crank normally but would not start regardless of crank time. Going for a long shot I replaced the CPS but this resulted in no change.


To begin the diagnostics I started from the top. The spark plugs were firring during the cranking operations. Next I check the schrader valve on the fuel rail and quickly realized there was no fuel pressure. Next I listened for the fuel pump to make noise when the ignition was turned on, nothing. I got access to the fuel pump connector and detected .7V with the ignition on and during cranking operations. Chasing the rabbit further I located the fuel pump relay and fuse in the passenger side sub fuse box. I could here the relay switching over when the ignition was turned on. I then checked the voltage at the fuse when the ignition was turned on and then cranked, essentially no voltage. I checked the relay as well and had 11V at the top pin location which matched the diagram on the relay housing. This is where I am stuck. There has to be something upstream of the fuel pump fuse that is not allowing voltage . I usually can find answers to all of my problems on these message boards but after a day of searching I can't find exactly whats going on. Many people suggest the ignition switch (transponder) and AAM. Is there a way to check both of these? I almost refuse to take the truck to the local MB shop because of the terrible service and lack of customer focus. I know this is a lot to read but I wanted to provide all relevant information. Any help is greatly appreciated.


Thanks,


John

Maj. Dundee

The first thing you have to understand is that the prime circuit for the fuel pump is only activated once during the test cycle. It will not come on again until you have started the engine (see pdf)

The fuel pump relay is actuated by the ECM which then powers up the fuse and then to the fuel pump. So, while cranking the engine, test to see that there is battery voltage at both contacts of the fuse. If there is that means that everything is in order with the wiring, relay and fuse up to that point. If not................

With the key off remove relay K2 in the right side kick panel fuse and relay box. With a test light test and a fashioned jumper wire, test all four cavities of the vacated relay and only 1 cavity should lite the test light.

Then turn the key to the on position and check the remaining 3 cavities and one should lite the test light. Does it?

Sagostinho

Hi!

Just to finish this post, on the last 4 days I've been fighting with the exact same problem, and the solution is to replace the CPS (crankshaft position sensor).
5 minutes job and problem is gone!

Hope that this helps someone with the same symptoms in the future

Cheers to all

m1943

I just had a similar situation a couple of days ago. I was driving 600 miles away from my home and still had to cover about 50 miles to my destination. The time was 4 a.m. and my engine just quit. The car is '04 ML 350. I've replaced the CPS some 3-4 years ago, and the way the car quit (like running out of gas, losing power first) did not seem like that was it. By 6 a.m. I had a flatbed pick me up, by 7:30 I was at a Lada repair shop, the only shop open 24 hours in town. Took me an hour to convince them that they should touch my truck despite the fact that it's not a Lada but a Mercedes. First we decided to replace the fuel pump as it did not make any noises and the fuse box showed 13 volts. Of course they didn't have a Mercedes fuel pump, but we decided to try and stick in a Lada fuel pump. I'm talking about not the complete fuel pump assy but of the electric motor that makes it run. It's made by Bosch and it turnes out it's a one size fits all. Lada-Bosch fuel pump motor fit perfectly and connected to the Mercedes fuel pump assembely. So the car didn't start. Mechanic took a tester to the fuel pump motor and saw that the current was weak under load. So he put back the OEM fuel pump motor, took a piece of wire and connected the pump directly to the fuse box on passenger side. The car started; it was not a fuel pump problem but a fuel pump wiring harness issue, which apparently is located somewhere in the left rear wheel well. So I left the shop with jerry-rigged fuel pump and now need instructions on what to do with the proper wiring harness and so on. Apparently it is exposed to the elements and sometimes gets damaged after a decade or so of use in poor weather and on rough roads. The snow melting chemicals and salt can do that damage, or it just might be a poor design.
My question is, where does the wiring harness run from, what is the procedure to diagnose and locate the broken harness, can it be repaired or replaced only?

Maj. Dundee

The connector you are looking for is X18/3 located at the left rear wheel well (must remove liner).

With your jumper wire removed, separate the connector, clean and recheck proper starting. If not..................

Separate the connector, crank the engine and test for B+ at the green wire. If not, you must trace that wire back to fuse #13 in the fuse box.

If you get B+ at the green wire then your problem lies from the X18/3 connector to the fuel pump.

m1943

Tried some of that, checked the connecter that's right underneath the lower corner of the plastic liner. Did not pull off the liner completely, kinda pried it open, did not see any other connectors, saw wires and fuel filter. The connector seemed very nice and clean on the inside, by the way. Have not tried to start the car without the direct wire, will drive back and than have the truck go up on a lift. Prior to that need to power wash the undercarriage, as mud and crap is all over the smaller parts.