W126 will not stay running
 

I have a 90 300 sel with 140,00 klm. This car has always worked great. One day for no reason it started to stall. Turns out it stopped charging so I put a new alternator on it and same thing. I thought maybe the OVP relay may have failed when the alt went out so I changed that. After it sits for a day it will take off and run great, as soon as it warms up it will stall and then no go. Seems like it is getting to much fuel as it backfires. What could it possibly be??? I have put new injector seals in it and checked everything else. It is charging 14.1 V so that is good. New OVP and still the same thing. Is there any way to pull a code from this thing? I am not sure where to go from here. Very frustrating.

I would start with a basic check and move on . For starters replace the fuel filter and the fuel- accumulator if old.
Fuel Filter may be a partially clogged
Regards
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I will change the filter, I think I have one. Would that make it do what it is doing? Seems like it is getting to much fuel rather than not enough but admittedly it is hard to tell

When the engine won't run:
Is there fuel at the injectors?
Is there a strong spark at the plugs?
Is the cold start injector switching off properly?
Is the distributor cap clean and dry inside? (Damp would usually cause a rough idle misfire, but I had one cut out after a mile once and it wouldn't re-start for twenty minutes).
While unlikely, it could be worth borrowing a known good fuel pump relay, just in case.

I don't think the fuel pump relay (or MAS) is that unlikely. It happened just that way in my M103--fine until today, then random stalls and soon no start.

cap is good, seems to have fuel. This am started right up after sitting all night. Cold start?

Similiar thing happened to our 1988 300SEL last summer... turned out that the coil had went bad.... not sure if thats your problem, but could be?

Now we have started getting a splutter/miss on a cold engine, looking into that now. Its fine when the engine reaches full operating temperature.

Whem I said Cold Start I meant cold start sensor

I've been thru this - '91 300-SEL.

Car started fine in the morning - then after 10-15 miles of driving stalleds/died.

Turned out to be a bad fuel pump.

While replacing that - I changed out everything related to fuel near the pump. Accumulator - hoses - filter - tank screen - etc.

Well, could be. I can hear the thing cycling though

Mas
 

what type of Fuel relay does a 91 -126 have ? A combined unit for fuel and AC?

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It has a MAS

Yep - controls 6 or 7 circuits - lots on info in the archives here.

Used in 1990 - 1991 300-SELs. Not sure what years used in W124 and other MBs that featured the M103 motor.

Here's what it looks like:


http://catalog.peachparts.com/ShopByVehicle.epc?q=1991-Mercedes--Benz-300sel-Body--Electrical&yearid=1991%40%401991&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6223%3AED%7C10000012%3A MBC%7C1515%40%40300SEL&catid=241959%40%40Body+Electrical&subcatid=242017@@MAS+Control+Unit&mode=PD

Thankyou.
MAS = Mass Airflow Sensor?
I'm only familiar with UK / Euro spec M103s and I haven't seen a MAS like the one shown further down the page. In fact, there was just the throttle body / metering head on the M103s that I've had and a fairly basic looking on / off relay.

Subscribed My 300e is doing the same thing :eek: