Welllll. I finally got the W124 I just bought ("Elaine" ) up and running, so tired, worked on her this entire week. She drives, and feels... Freaking... AMAZING!!! It's literally the W124 of my dreams, EXACTLY how I wanted my old (in my sig) W124 to be JUST like.

I've encountered a small problem though and had her towed back to my garage.. . While I was driving back from work, the RPM's slightly hesitated and she turned off. I turned her back on and the same thing happened after a while, until finally she just wouldn't turn on anymore. I would of sworn it was the fuel pump because the symptoms were exact of a bad fuel pump.

I just jacked her up and checked out the fuel pumps (while they're connected to fuel lines) with a battery. They BOTH work, and when they turn on there's pressure on the fuel line! I immediately thought the relay might be bad or something electrical. When I turn the key to on though, I can hear them humming, and she turns on for a few seconds then turns off. I plugged the fuel pump (just one) to the battery and turned the car on. And she stays on perfectly fine, as if nothing ever happened. What the heck? :S

Is it possible for a fuel pump relay to kind of "go bad" while the car is on and then work the next crank? What do you guys think?

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And by the way here's a little clip I made of her

http://www.youtube.com/watch?v=4ydzM-hFMOw

P.S. I heard humming from the driver's seat when I turn the key, so it might be humming from some other component? Any way I can kinda "test" the relay, and where it's at? Been searching and so far I found out it's behind my battery? Found a few things but not sure which one still, lol. (Nubcakes here)

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yes...that is possible

I finally found the relay, and am disappointed that I have the MAS integrated $300 relay. lol.....

I was reading about jumping the two pins together to get the fuel pumps to work, is it still pins 7 and 8 on the MAS version of the pump relay?

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You do not say what year the car, how many miles, or what you know of it's past repair/maintainance history since this is a "new" car for you.

Log in and using the search option up in the header, search overload protection relay or OVP or overload protection relay. See if any of those threads relate to your issue.

If you do not know for sure that the OVP relay has been replaced and is not the original one, I rec you spend $80 for one. Not just check the fuse(s) in it, but buy a new one. As that thing fails, all kinds of intermitant electrical issues arise. When it dies, your car does not run at all.

Did you check for error codes??

After that, then test MAS relay.

It's a 1990 with 117k on it. Hmm, I thought just the MAS controlled the fuel pumps.

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fuel pump is mas controlled you are gonna have to do this

test current draw of the fuel pumps
swap in a known good mas and air conditioning relay(corrison)

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

JCD, Not sure how the MAS is put together, but the earlier fuel pump relays do develop bad solder joints internally that can act up as the relay warms up with the motor running. That may also be happening inside the MAS. Also, the earlier relays would shut off if engine speed (TDC) signal were interrupted for 1 second. Consider that possibility, too, that the TDC sender unit at the front of the block is getting hinky.

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1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't

92 300te 4matic. same problem. fuel pumps both work with direct power from a battery. mas tested & ok. seems like wire/ground to fuel pumps is defective but how do you trace as wiring seems to go thru the frame. car runs if fuel in distributor so don't think its tdc sensor

Check the # on your MAS....if you do need one, This one is priced right $20. I know the description does not match the item, but neither did the one I received from him today for my SL. I did get a good one, and what was pictured.....Good Luck and keep up posted.....gene2
http://cgi.ebay.com/ebaymotors/MERCEDES-W124-W126-W202-MAS-RELAY-FUEL-AIR-A-C-COMPUTER_W0QQcmdZViewItemQQhashZitem414c6bbd73QQitemZ280455003507QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5 fAccessories

to have complete reliability the fuel pump relay ,the over voltage relay, and finally all the perfectly good looking fuses in the fuse box be replaced with fresh ones . All seem to be age related failures in these models.
mak

You know, that's not a bad suggestion.
Pull and either clean the terminals on all the fuses or replace them with new ones, and clean all the fuse box contacts as well.
I did that on mine after it sat for only a year, and I've done it on other cars. It'll at least be one less thing to think about.

A good way to clean the fuse ends is to clamp a tight wad of medium steel wool in the chuck of an electric drill. Can't say I know an easy way right off hand to clean the box contacts.

A few easy thing to test that may also be helpful to eliminate...

It's marginally possible a bad AIC valve (Air Idle Control) might contribute to your problem. Its a metal cylinder shaped part located on your intake manifold adjacent to the fuel pressure regulator (about the same size too). It's clamped in and has a rubber hose on the left coming from the cylinder head (under the manifold), and a hose on the right that goes to the rubber boot that throttle body sits on. On the end it has a two-prong connector.
With the car off, disconnect the plug on the end. Connect a 9v transistor radio battery to the valves contacts. You shuold be able to hear or feel it "thump" as you make/break/make contact with it.

Another easy to test item that affects the fuel mixture is the temperature sensor for the CIS (injection system). I think it's the last of the three sensors (by the firewall) sticking up out of the head. It has a round black connector with four pins.
With the engine cold, take a multi meter and measure the resistance between each set of [diagonally] opposite pins on the sensor. The value should be the same between the two sets. The actual resistance value depends on whatever the ambient temperature is when you do it, but I think it would be something like 4500@40°F to 2800@60°F. The important thing is that they be the same between either pair. Plug it back in and run the car up to temp. Shut it down and measure them again. The value should drop with the rise in temperature to about 220@190°F (88° on the car gauge?). I'm really not sure of those numbers, but again the important thing is the value should once more be the same between the two pairs, if the values are much different the sensor is failing.

I'm not sure that either of these things could make your car shut down as you describe but they're easy to test, not uncommon to fail and certainly crucial to the performance of your fuel mixture delivery.

BTW, how's the bad head gasket situation?

Thanks for all the responses guys. Going to try all the suggestions. For now (you're all going to hate me for this, but) I installed a straight wire from the battery to the fuel pumps, with fuses and switch of course. She's working fine, besides an occasional rough idle when in gear if she's warm (and a blown shock). Ordering parts soon and hopefully all should be well!

@Long-gone. Got a full set of new fuses . Gonna try cleaning the connectors on the components, see what happens.

I replaced all the coolant and flushed it out. I can just see/feel slight oil from before. Doesn't seem too bad. Gonna save up a couple or three paychecks and get it all sorted out. Can't wait for the day where I just turn her on and know NOTHING is wrong

Here's a few pics

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