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  #1  
Old 07-18-2011, 09:07 PM
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Location: Crook county, Illinois
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M103 throwing me for a loop

Hello all,
I am throwing this out there to see if anybody has experianced this. Yesterday, while driving down the HWY at 75mph my rear tire blew. If you havn't experianced this pleasure yet, then I hope you never do. After I went across the road, into a ditch, and out of the ditch I came to rest safetly on the shoulder. At one point, the car was sliding sideways, and I thought it might roll. I bring this up, b/c it may be pertinent to my problem. After I changed the tire, the car wouldn't start. Nothing looked obviously wrong, and the vehicle was running fine prior to the tire blowing out. I had the car towed home. I pulled the plugs and verified spark, which I had. The fuel pumps turn on, I can here them when the key is turned. When I spray carb cleaner into the throttle body, the car wants to start. Question? Does a 1991 300e M103, have a fuel cutout switch? Any Ideas would be welcome. thank you in advance
Mat523

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  #2  
Old 07-18-2011, 09:25 PM
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Debris could have ruptured a fuel line and/or dented, kinked or otherwise damaged the filter, pump assembly, or accumulator. The only real way to know is to crawl under there and survey the damage.
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  #3  
Old 07-18-2011, 09:34 PM
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Thank you for your reply. I did a complete inspection underneath, and nothing seems out of the ordinary.
Mat523
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  #4  
Old 07-18-2011, 10:16 PM
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I'd lean towards something going on in the fuel system at the back. Run a fuel pump delivery test like I just did:

http://www.youtube.com/watch?v=tMSv7WsaM6s

Make sure to jump fuel pump relay first of course. Pins 87 and 15.
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  #5  
Old 07-18-2011, 10:34 PM
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Jumping fuel pump relay may involve crossing pins 1 & 2 in the MAS if I recall correctly. That's how it works on 1990-1991 M103s in the 126 cars.

Silver box about the size of a pack of cigarettes - along firewall - drivers side.

Unscrews off using knob on top of MAS. Search forum for more detail. Been covered in a number of threads.

Might be interesting to see what happens after it's been allowed to "sit" overnight. If know it's not carbed.....but.
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Old 07-19-2011, 07:50 AM
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Thanks Guys,
I will do these checks as soon as I return from work, and update the results.
Matt
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  #7  
Old 07-19-2011, 10:23 AM
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Also,
do I need to completely remove the MAS relay? Will the car start w/o the relay in and just the pins jumped?
Matt
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  #8  
Old 07-19-2011, 11:03 AM
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Yes you pull the MAS out - then jumper pins 1 & 2 - again - I would fish around here to vfy pins.

First try to start the car again with MAS in place.

With it removed and pins jumpered - if car starts - fuel pump relay in MAS is bad and you get to replace the entire unit. It controls 6 or 7 circuits.

I find it hard to believe that what happened to you killed the FPR circuit in the MAS, but who knows?
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  #9  
Old 07-19-2011, 12:28 PM
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I can't remember - does a 124 have a post-accident safety fuel cutoff which must be reset, actuated by some sort of sensor? Is it possible that it tripped as you were spinning and bumping?

Rgds,
Chris W.
'95 E300D, 344K
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  #10  
Old 07-19-2011, 04:40 PM
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Here is an update: I pulled the MAS sensor, and jumped pins 1 and 2 as Mike suggested. Car started right up. Replaced MAS sensor, ( I had an xtra in the glovebox. Had I realized it was the problem it would have saved me a 50 mile tow). Anyhow, car runs fine again. Thank you for everyones insight. Does anyone have any idea of how/why the MAS went bad? Is it related to the "accident" or is it purely coincedence
thanks again
Mat523

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