systematic testing of fuel components
 

Is there a way to systematically test each fuel component of the w201 m103 engine 2.6? I.e., fuel pressure regulator, fuel pumps, accumulator (what does the fule accumulator do anyways?) I am having a problem to where my car will randomly shut off while stopped at a light and wont start back up. I dignosed it as a fuel problem because it cranks, and the voltage is correct on battery and all ignition components are new, but when I spray carb cleaner on the air flow plate it starts right up and dies. If I continuously spray the cleaner it runs until I stop

There is a plug on the side of the fuel distributer that you can check fuel pressure with. It's very likely your fuel pumps are shutting down. The fueling system is like a glorified carburetor, not much to check if the car does not run at all

Fuel pumps, fuel pump relay, or wiring problem

wired a small light to fuel pump. will monitor to see if i am losing power to pump. does the 1990 190E 2.6 have a fp relay?

If your fuel system is similar to my W126...

So far as testing each component, that would be a LOT more work and expense - plus you would not know what specifications would be acceptable for each. Best to follow the Mercedes factory service manual testing procedures for the entire fuel system. That will pretty well test everything in the fuel system.

The thing is there are various tests which are buried in the service manual [at least for my car]. So may need to hunt around - fuel system, emissions, fuel system venting... I forget where they all are.

But there should be a fuel pressure and fuel volume test (how much fuel is flowing). That will test to see you have the proper pressure. And the volume test will show that the fuel system can flow enough to provide all the fuel required. For example with a clogged fuel filter or one pump not working (on two pump systems) you may get the pressure, but not much flow or volume.

Then a fuel "internal leak" test. That is connecting a pressure gauge to the fuel distributor, starting and then shutting off the engine, then seeing if the fuel system holds pressure. If the pressure quickly drops, it could be "check valves" or the accumulator.

The accumulator is like a mini pressurized storage tank. It stores pressurized fuel and that is available for start-up and perhaps if you suddenly floor the accelerator. Also it can "dampen" noise.

The thing is... As fuel enters one end, the opposite end needs to vent air. And that air is vented to the fuel tank. If the accumulator is bad - has a leak (or internal leak if you will), then fuel will flow right through it back into the tank. That would show up in the internal leak test - the system would not hold pressure with the vehicle off. And may have lower pressure with the system running.

Also when you first turn on the ignition before starting the engine, it briefly turns on the pumps to "prime" the fuel system - you should see the fuel pressure rise.

And then there is an "evaporative system" - venting and so forth. Tests for that. Perhaps in the emissions section?

With the pressure gauge, you can perhaps rig it up temporarily so you can see it when driving. Then drive around and see if you are getting the correct pressure and if there is no pressure when you stop at a light and the car dies (as you suspect).

If it has no pressure at that point, I would rig up something to monitor the fuel pump voltage. See if it is losing electrical power. And maybe first check the fuel system electrical components. Clean the plug in pins on the electrical modules under the hood, etc. Also the overvoltage relay if you have one of those.

I found a fuel pressure gauge with all sorts of different size fittings at Harbor Freight for not too much $80 or $100. Be SURE you know what size fitting you need and that the testing kit you get has that size.

IIRC in 90, they moved to the MAS relay:
011 545 79 32 - M103 MAS Control Unit - Imgur

Heres fuel pressure testing kit. I have the version that didnt come with a box:
http://www.amazon.com/Tool-Aid-33865-K-Jetronic-Injection/dp/B0002SR5NU

does the MAS control anything other than the fuel pumps?

FSM shows that it also supplies power to the oxygen sensor heater. Beyond that I didn't see anything. So O2 Heater and Fuel Pumps.

I guess I can rule out my MAS then, I haven't gotten any codes about my O2 sensor and my fuel pump test light has yet to go off, but then again I have not stalled again either. any correlation to getting a CODE 11 CEL air injection?

Following is a link to a function diagram of the older "fuel pump relay" and the newer "MAS". They look quite similar to me so far as what all they do. But the old term "fuel pump relay" was not accurate as it also does other things like activate cold start, limits engine speed, and transmission kick-down cut-out (at higher RPM's).

I think they may have changed the name to MAS (Engine Systems Control Unit) as that is a more inclusive description?

http://www.startekinfo.com/StarTek/outside/12264/Program/Engine/103/07.3-0013.pdf

I'm definately getting fuel starvation from somewhere. Car stalled again today, but the light never went off, so I was still getting power at the fuel pump. More suggestions? I just got a working fuel accumulator, not sure if this would help anything, especially since I have not tested mine yet.

Connect a fuel pressure gauge so you can see it while driving and drive with that.

So I think I finally figured out the problem to the rough idle I've been having as well as my stalling: a non-working fuel pump! Even though I rigged up a light to the fuel pump wires, it was not an accurate test. I disconnected the ground wire to each pump one at a time and turned the key to the on position and heard the buzzing of one pump. When I tested the other pump it was dead silence. Since both pumps are about 24 years old I decided to bite the bullet and order 2. I will see what happens and keep this thread updated once I change them out.

Ismalley, I read an article years ago about removing the fuel pump(s) from the vehicle and running it backwards for an instant (powered by a 12 volt battery) with kerosene as the fuel. That effort will clear out any crud that may have accumulated in the pump over the years. May need to repeat the process a few times. It's worth trying to rejuvenate an old fuel pump, rather than buying a new one.

Already ordered 2 new ones. If it were something else that wasn't going to cause my car to stall, I might consider it, but this is a huge safety issue for me. Especially if I'm stalling in the middle of traffic or if I have passengers. Plus this will give me peace of mind. I guess once I get the old pumps off and install the news, I can see what makes them tick and see about trying to refurbish them if possible.

Ismalley, if you get one or both existing fuel pumps running properly you could return one or both new ones. It bothers me to buy a new part when an old part just needs some TLC.