145K miles, ran ok until 2 weeks ago and was parked for 2 weeks prior to that.
will crank but no start, things Ive done: fuel pump relay tested and cleaned the contacts, ovp relay, removed and tested with 12vdc I can hear relays open/close, cleaned body grounds. If I try to start it once in 20 times it starts and starts easily and runs great but dies after 20 minutes. when it does not start, no fuel pump running and even if I close relay by hand it does not start and power to fuel pump is shut off by car during start attempt, cel light on during start attempt. ODD things: AUX Fan fuse blows often, also found a disconnected vacuum hose, blue ,, one end to an electric device behind the brake booster other end down by the trans. I was getting car ready to sell when this occurred and the body has rust, radio volume doesn't work,driver seat broken and some interior cracks so I wont go crazy with parts but hate to give it to junkyard, newer tires brakes and a/c works great.
Any ideas on what to check? Thanks

If it would crank OK cold, then conk out when it heated up and not start again until it got cool - I would guess crank position sensor (this is what I had on my Land Rover). But not sure on a Mercedes and not sure it matches your symptoms.

Thanks for reply CPS is a canidate

Another clue? when key is turned to position just before start, there is no power sent to close the fuel pump relay to run the fuel pump, even if I close the relay by hand and hear pump rub and I can hear the fuel injectors spraying even trying to start after that I get no start or even a stumble, it just cranks....

If there is no movement at all in the tach while cranking that is a symptom of a bad CPS.

Good luck!!!

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

just tried it, tach jumps @during attempted start, Thanks still hunting

Attach a voltmeter to power input of hfm control module, monitor and see if your losing power, if you loose power try a overvoltage relay

You have 2 fuel pumps, they both have to run, third try a good hfm airflow meter

Sounds like a MAF problem. Can you pull some codes from the LED diagnostic board by the battery?


Sent from my iPhone using Tapatalk

When my 94 maf went out it just was jerky , wouldent start, I unplugged it and started and ran, it goes into fixed 50% when its unplugged

Thanks for tips I have the OVP out and opened, I will test and observe, maybe resolder the joints. Only code I have obtained was 17 blinks with the built in test button, my code reader stopped working

I just installed a new OVP relay, started right up and drove around the block.

I am an idiot, and should know better as I am an aircraft mechanic and troubleshoot daily. My first test of the OVP relay was only with power and since I heard the relays closing I ASSUMED it was ok. After reading about this "special" component I decided to take a second look.
The full test I did: 12vdc to pin 1, pin 5 to ground, checked all other pins and only pin 9 had 12vdc (correct per diagram on relay)
Now add 12vdc to pin 3, pins 2,7,8,9 should have 12vdc and 4-6 should have continuity. My K3 relay would not close!!!! No power at pin 2!
Ordered a new relay and went for a drive.
A little embarrassed but glad it is fixed, thanks for all the help and I hope my story helps also.

someone said BOTH fuel pumps must work for the car to run and I wanted to correct this for general info. I had BOTH fuel pumps fail after just testing and having both of them working. Drove me nuts BC it seemed so unlikely. The car would run if either of the pumps were working. It totally threw me because I could not imagine both failing in a short time span but I finally replaced one pump, and while the other was still bad the car ran fine and I ordered the second pump and installed it. Will run on one pump. No noticeable performance change.