1989 300SEL

I'm having an intermittent problem with power reaching my fuel pump. The problem has only occurred at start-up. When it is going to have one of its episodes, the car starts, dies in about 1 second, then will not fire at all (cranks but no fire).

During an episode, the fuel pump gets no power (checked with multimeter) with the key in either the "run" or the "start" positions.

If I jump power directly to the fuel pump (when this problem is occurring) the car starts and I can disconnect the jumper wire (immediately after starting) without the car dying.

Also, it seems that if I walk away for a while (sometimes just a few minutes will do, sometimes though it takes much longer) and come back, the problem usually has gone away.

Any thoughts on what this might be?

Thanks.
Brett

Hi Brett,

Your car has a fuel pump relay located in the cavity between the inner and outer firewall in the engine compartment, just about the center of the car. It’s a black plastic box, a little bit bigger then a pack of cigarettes, easily visible with the hood open. It’s right next to another relay, the Klima relay, that’s just about the same size. I think the part number on your fuel pump relay may be, 002 545 92 05, if that helps identify it. If it were me I’d pull that relay and check the pins for corrosion or loose fit. I‘m not sure on a test procedure for the fuel relay, but I know they do fail. You may try tapping it as well when the pump fails to energize to see if that action helps it along.

Good Luck,

Outofspec

Isn't this a classic OVP symptom?

__________________
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

Thanks for the help.
The pump stopped while driving (for the first time). And then it refused to work at all. I replaced the relay you mentioned with one from a 420SEL I have. It seemed to fix everything. I noticed the numbers on the relays were slightly different (old is 003 545 17 05 and new is 003 545 25 05). I put it in anyway. Is that going to be an issue at all?

I looked at the old one and pin 87H is noticeably corroded (looks like it was subject to high heat).

Brett

Hi Cal.

I had to look up OVP. When I did look it up I noticed a couple posting stating that the "check engine" light always comes on if the OVP relay is bad. Do you know if that is accurate?

I replaced the fuel pump relay and that seems to have fixed things.

Thanks for the help.

Brett

Hi Brett,

I’m very glad to hear that you’re up and running again, and thanks for following through on your thread by posting the results. I use the archives of this forum all the time to help me figure things out and it’s always a lot more rewarding to read through threads that have some kind of conclusion.

I tried to look up your part numbers, but didn’t have much luck. They look close enough to me that one might have just superseded the other. My guess is that whether a 300 SEL or a 420 SEL, the relay simply energizes the fuel pump, or pumps, when necessary and it shouldn’t much care what engine it’s working for. I’m not certain though, so maybe somebody else can tell for sure.

Kind Regards,

outofspec

Huh.... I thought there was no FPR on that year 300SEL. I thought it was part of the fuel computer. Somebody correct me!

__________________
-tp


1990 300SE "Corinne"- 145k daily driver - street modified differential - PARTING OUT OR SELLING SOON - PORTLAND OR. AREA - PM ME FOR DETAILS
1988 560SEL "Gunther"- 190K passes anything except a gas station
1997 S420 - 265k just bought it with a rebuilt trans. Lovely condition

Hello Tinypanzer,

I’ve owned three 300 SEL’s; two 1989’s, and one 1990. Both the 1989’s had the FPR while the 1990 has the fuel pump controlled by the MAS Control Unit. I think 1990 was the first year for MAS on the 103 engine.

outofspec

Hey hi an Happy New Year to you all,
My 300 SEL stopped running abruptly. Unable to diagnose or see visible problems I had the 88 sel towed to a "mercedes mechanic". I informed them the fuel pump, rotor, distrib. cap, and wires had just been replaced.
After 1/12 hrs and $140 they incorrectly told me the plugs were probably fowled. I explained that was unlikely as I had replaced them prior to towing it to them.
They never tested the fuel pump relay which after jumping 30-87 pins car fired right up and ran fine. Ordered new fuel pump relay.
Can't cancel neww fuel pump. They also informed me the coil was bad.
I explained to them I was still getting sparks across the new plugs and the timing was good. Timing light worked too.
Question is what should this company do to rectify their obvious bogus diagnosis on my car . I paid $140 to them for nothin and another $75 to tow it home. Turns out the business had been bought and the good name with it. "Good will" equity is what its called in busines transfers or sales.
I feel I am owed a refund. I do not think they tested anything. They said the 300 sel has no error codes plug to connect to.
input greatly appreciated.

As stated above - 88/89 300-SELs had indepdendent fuel pump relay(FPR). In 1990 - MB moved that function into the MAS - silver box a little bigger than a pack of cigarettes back along firewall - more on drivers side.

MAS contains 6 or 7(forget the exact number of circuits). You test the FPR circuit in the 90/91 MAS jumpering pins 1 & 2. It's "hot" so be careful inserting your jumper wire. You'll get a spark if the wires are caddy-wompus

The system has no "plug-in" as you see in OBD2, but there is a black box back on poassenger side of firewall that display a series of blinks that indicate a given problem. Been awhile since I've had to do this - search thru archives here.

Sounds to me like the shop you went to is not familar with M103 systems.

Not surprised.

I drove into an MB dealership the other day with my ride(see sig) and they looked at the car like they had no idea what it was.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"