M103 suddenly died on FWY at 70mph - PeachParts Mercedes-Benz Forum

NDP 2.6 190E · #1 10-28-2010, 05:18 PM

Car (1991 190e 2.6) was running fine at 70mph on the freeway. With no warning the engine suddenly lost all power and the tach needle went to zero. Managed to pull onto the shoulder. Car would not restart, trailered home.

Where should I start? Check the crank position sensor...?

dynalow · #2 10-28-2010, 05:38 PM

Lots of threads with similar problems. Here's just 1.

Engine shuts down while I was driving: M103

Search "M103 engine stalling" for more.
Could be a few typical things. OVP, MAS sensor, Distributor cap.

In my case, repeated stalling was caused by fuel pump relay till it finally died. Fixed it and problem solved couple of years ago. No repetition.

Gilly · #3 10-28-2010, 07:09 PM

One of my guesses would also be the fuel pump relay.

NDP 2.6 190E · #4 10-28-2010, 07:23 PM

Quote:

Originally Posted by dynalow

Could be a few typical things. OVP, MAS sensor, Distributor cap.....fuel pump relay...

To be clear, the tach needle plunged to zero the instant I lost power, but the engine was still spinning as I slowed from 70mph...

New OVP relay was installed approx 6 months ago and appears to be fine.
Inspected the cap and rotor when I replaced the waterpump last month - both good. Could the FP relay or MAS sensor cause this kind of problem?

kiwi_bloke_nz · #5 10-28-2010, 07:40 PM

Fuel Pump relay or Crank sensor are my votes. You can test the crank sensor when cold.

Should be around 800 ?? Ohms from memory. You can pull the plug at the EZL unit and test here.

You should also be able to jumper the FPR and see if the pump runs.

When you turn the key to the on position, engine off, do you hear the pumps run ?

NDP 2.6 190E · #6 10-28-2010, 08:33 PM

Appreciate the advice. Will try these things when I get home at the weekend and advise the outcome.

sptt · #7 10-29-2010, 12:22 AM

Has happened to my 103 twice now. Just shuts off and dies but I can get it into neutral and do a quick restart. What I found was I was running too lean on air/fuel mixture. However, it could be the fuel pump relay as well. Wiggle it around a little. Do you hear the fuel pumps when you turn the key? Your CPS is right behind the fan on the bottom on the base of the engine. See if its wet or covered in gunk. Cleaned my daughter's off during a water pump change and it starts first crank now every time...don't know why though. Mine doesn't and it's 4 years newer with less mileage. Best of luck.

MBeige · #8 10-29-2010, 03:07 PM

I don't think a 1991 would have the fuel pump relay. I think it appeared up to 1990 only?

The FPR was replaced by a MAS unit that control multiple functions (including fuel pump relay).

Can you hear the fuel pump buzzing when you turn key to position right before starting?

NDP 2.6 190E · #9 10-30-2010, 02:13 PM

Quote:

Originally Posted by MBeige

I don't think a 1991 would have the fuel pump relay. I think it appeared up to 1990 only?

The FPR was replaced by a MAS unit that control multiple functions (including fuel pump relay).

Can you hear the fuel pump buzzing when you turn key to position right before starting?

Cannot hear the fuel pump with ignition on. Cannot find a FP relay.
Behind the battery is the OVP relay, MAS unit and what look to be 2 x control modules - each with a large connector on top.

The crank position sensor reads ~1100 ohms, so assume this is OK.

francotirador · #10 10-30-2010, 02:32 PM

Quote:

Originally Posted by NDP 2.6 190E

Cannot hear the fuel pump with ignition on. Cannot find a FP relay.
Behind the battery is the OVP relay, MAS unit and what look to be 2 x control modules - each with a large connector on top.

The crank position sensor reads ~1100 ohms, so assume this is OK.

If you have a MAS relay, then the fuel pump relay is incorporated into that. You should be able to hear the fuel pump when the key is turned, especially if you have someone else turn the key while you listen near the fuel pump. What # is on your MAS relay? The two pins to jump on mine are numbers 1 and 2. I don't know if yours is the same. I have a 1990 300SE with the M103 engine. Perhaps someone else can tell you for sure which pins to jump on yours.

wagonman124 · #11 10-30-2010, 02:32 PM

Behind your battery compartment is a plastic shield ( just gently squeeze and pull pull the cover towards you) it hide's the relay as well as a number of other items. The relay is about the size of fat deck of cards. Wiggle it back and forth while pulling it up and it should pop right out. If memory serves me right it has seven pins. You can first try a little emery cloth on each of the the pins (the idea being to just score the surface a little not remove material). To expose the circuit board you need to gently pry the housing back on both sides of the unit while pulling the unit apart. Take your soldering iron to all of the contact points on the board.

Hope this is of some help

Quote:

Originally Posted by NDP 2.6 190E

Cannot hear the fuel pump with ignition on. Cannot find a FP relay.
Behind the battery is the OVP relay, MAS unit and what look to be 2 x control modules - each with a large connector on top.

The crank position sensor reads ~1100 ohms, so assume this is OK.

NDP 2.6 190E · #12 10-30-2010, 02:36 PM

The problem is fuel delivery. Removed the air filter and poured a small amount of gas down the intake - she started right up, then died.

Since there is apparently no fuel pump relay, is there a simple way to test the fuel pump?

Gilly · #13 10-30-2010, 03:10 PM

If there is no fpr, then the problem more than likely is the MAS unit. You can simply either get a vom on the pump (there might be 2 pumps), turn the key to on and see if you are getting voltage when the key is turned to the on position. You could also do this with a test light.
OR you can try jumping power and ground to the pump and see if the engine starts, or hell even if the pumps run!
Gilly

NDP 2.6 190E · #14 10-30-2010, 03:21 PM

Removed the MAS unit and jumpered two large pins near the passenger fender (two large pins on the other side of the connector operate the a/c compressor clutch) - the fuel pump ran and the car started

Will be ordering a replacement MAS unit.

Merkey · #15 10-30-2010, 03:36 PM

My $0.02...
This is ignition related, the biggest clue was the loss of Tach signal... and the instant shut off.
I always use the way the car died as a good clue... a slow die off with spluttering and a bit of surging is loss of fuel, and an instant switch-off most likely ignition related.
If it was FPR the electrical side of the engine would have read the tach signal, as the ignition would have not "seen" any loss of fuel pressure or fuel. and the Tach would have just followed engine speed back to stall.
I am calling it ignition related.