300E Fuel Relay Location

[jim16671836]

Where is the fuel relay located in a 300E and does anyone know the part number...Would it be in the same location in a 87 and in a 90...thanks Jim

[lee polowczuk]

behind the battery...should be the same for both models. there are two relays in the same area...black , rectangular.... one is the a/c relay...may say "klima" on it...

[400E]

Don't know if it's unique to the 400E, or just later-year W124s in general, or what, but on my car, the fuel pump relay is under the rear seat cushion on the right side.

[simmo300e]

Part number for 1987 model is 002 545 27 05 up to engine number A396764 and 003 545 24 05 for engines after that, is what I was told.

However, important to make sure you get the 6 cylinder relay, not the 4 cylinder version. I was using a pattern relay numbered 003 545 24 05 in my 300E and it wouldn't rev over 4,000 rpm. Turned out it was for a 4 cylinder engine.

The correct item should have 6zyl/6350 stamped on the side.

About the location, you'll find it behind the battery in the front on the 4 and 6 cylinder 124s. I'm guessing that the 400E and 500E relays are located in the boot next to the battery because there isn't room under the bonnet

[Duke2.6]

Originally Posted by simmo300e

However, important to make sure you get the 6 cylinder relay, not the 4 cylinder version. I was using a pattern relay numbered 003 545 24 05 in my 300E and it wouldn't rev over 4,000 rpm. Turned out it was for a 4 cylinder engine.

The fuel pump relay contains the rev limiter function, so if you use a four cylinder relay in a six cylinder engine, you will only get two-thirds of design engine revolutions.

Conversely, if you use a six-cylinder relay in a four, the rev limiter will be about nine grand, but I definitely would not recommend this "mod".

Duke

[brewtoo]

Hmmm....Isn't the fuel pump relay a part of the MAS computer on the 1990 300E? And not a separate relay like on the earlier models?

Or am I experiencing confusement?

[Duke2.6]

Carefully check the relays for bent pins and the receptacles for any debris or damage.

I just removed my FPR a couple of weeks ago following a no-start condition. I did a careful inspection, but found no obvious issues, so I cleaned the pins with electrical contact cleaner... reinstalled the relay and it started right up.

I documented the above in the following thread:

Sometimes I call it the "Mercurial-Benz"

Duke

[murphysf]

Originally Posted by Duke2.6

Carefully check the relays for bent pins and the receptacles for any debris or damage.

I just removed my FPR a couple of weeks ago following a no-start condition. I did a careful inspection, but found no obvious issues, so I cleaned the pins with electrical contact cleaner... reinstalled the relay and it started right up.

I documented the above in the following thread:

Sometimes I call it the "Mercurial-Benz"

Duke

thanks for the post.

I removed both relays and the pins are straight and they are not discolored. I took a small wire brush to the pins and then sprayed the pins with deoxit.

The issue I am having is the physical contact of the tangs on the sides of the relays, in particular the two tangs on the sides where the climate relay and fuel pump relay are side by side. If both relays are removed, the fist one in seats fully but then when the second relay is installed the tang from relay being installed next hits the tang of the relay that is already installed, this keeps the second relay from being fully seated.

ideas?

[Duke2.6]

The only thing I can think of is that you might have an incorrect relay... physically larger than original, but maybe functionally correct???

If all else fails I don't think filing or cutting off the interfering retention tangs will cause any problems. The pins themselves should hold the relays in place, and they make removing the relays a PiA.

A couple of years ago I tried to remove the FP relay to inspect when I was having starting problems. I used a couple of small putty knives to carefully pry the tang slots back, so the tangs would clear, but it wouldn't budge. I recall even starting a thread here asking if anyone knew how to get the damned thing out and got no response.

It turned out the problem was the due to an internal leak in the fuel accumulator that was shorting fuel back to the inlet hose from the tank, which prevented proper fuel pressure from building up at the regulator, so no big deal.

For whatever reason, it came out came out last month without much effort.

Duke