Fuel Pump Or Relay 1980 450SL Died

[xkeots]

Hi All,
I was driving my 80 450SL today all over and when I was about to go home it wouldn't start. I tried cranking it, pushing the plate in the intake down (It wanted to start) I couldn't hear if gas was going in when I pushed the plate as there was a lot of traffic on the street.
I was able to get a cup of gas and pour it into the F.I intake and it started for a moment.
I had to have the car towed.
Would you all agree with me that it is either the relay or fuel pump?
What is my best way to check this and also after 27 years of this car being on the road should I just change them both?
Thanks
Jack
1980 450 SL

[450slcguy]

Could be the relay. Pull the old relay out and put a jumper between pin sockets 1 & 2. Switch on ignition and you should hear the pump turn on for a few seconds. Then try to start the car. If it starts then but a new relay, about $100 bucks.

[xkeots]

Originally Posted by 450slcguy

Could be the relay. Pull the old relay out and put a jumper between pin sockets 1 & 2. Switch on ignition and you should hear the pump turn on for a few seconds. Then try to start the car. If it starts then but a new relay, about $100 bucks.

I will try that tomorrow.

Thanks
Jack

P.S. Can you tell me exact location of fuel pump relay?

[coleyjf]

Was the fuel pump making a noise before it all stoped? If so it points at the pump.

Try htting the fuel pump ( under the rear end attatched to the subframe) with a wooden mallet ( or big sick or the jack handle) whilst the ignition is on. It sometimes works to "get you home".

I bought a replacement pump off eBay for £40 inc postage in the UK (that's about $80 but post from UK could be $20 I guess) so it's not too epensive
Best of luck
Cheers
Jim

[xkeots]

Originally Posted by coleyjf

Was the fuel pump making a noise before it all stoped? If so it points at the pump.

Try htting the fuel pump ( under the rear end attatched to the subframe) with a wooden mallet ( or big sick or the jack handle) whilst the ignition is on. It sometimes works to "get you home".

I bought a replacement pump off eBay for £40 inc postage in the UK (that's about $80 but post from UK could be $20 I guess) so it's not too epensive
Best of luck
Cheers
Jim

Jim,

If the relay crapped out the pump will not kick in.

Thanks
Jack

[450slcguy]

Originally Posted by xkeots

P.S. Can you tell me exact location of fuel pump relay?

Yes. You have to remove the lower right passenger side kick panel that surrounds the fuse box. To do, remove the stainless step sill plate, then the vertical angle stainless piece that holds the panel in place. You might have to drop the under dash panel that the entry light mounts into, depending on clearance. The relay is to the right of the fuse box and is about 2.5" long, rectangular shaped and mounted horizontally. Hope that helps.

[230/8]

When you have the fuse box cover off, why don't you first check the fuse for the relay? The diagram indicates it is #14. See if it is a good brass fuse with no corrosion. My 107 crapped out in a similar way and all it took was a new brass fuse to replace the old aluminum fuse that was installed.

230/8

[coleyjf]

Originally Posted by xkeots

Jim,

If the relay crapped out the pump will not kick in.

Thanks
Jack

Yes but the KEY question is - Was the fuel pump making a noise previous - I've seen loads of posts about fuel pumps dying like this - the noise being the critical diagnistic factor as it was with mine.

Agreed it can be the relay but hitting the pump with the ignition on (normally works) allows you to diagnose which without much trouble.

Cheers
Jim

[xkeots]

Originally Posted by xkeots

Hi All,
I was driving my 80 450SL today all over and when I was about to go home it wouldn't start. I tried cranking it, pushing the plate in the intake down (It wanted to start) I couldn't hear if gas was going in when I pushed the plate as there was a lot of traffic on the street.
I was able to get a cup of gas and pour it into the F.I intake and it started for a moment.
I had to have the car towed.
Would you all agree with me that it is either the relay or fuel pump?
What is my best way to check this and also after 27 years of this car being on the road should I just change them both?
Thanks
Jack
1980 450 SL

In 29 degree temps, no garage I replaced the fuel pump relay and it is back on the road.

Thanks All
Jack

[BenzToy]

Glad to hear that replacing the relay got you going. I've been told that a noisy fuel pump could cause the relay to fail, (too much current?). My fuel pump seemed to be getting louder, so I replaced the pump, filter, accumulator, and pressure relief valve. No relay problems so far. Noise went away and I have a more confidence I'll get home. I think I'll order a relay, just to be prepared.

[Damian]

The fuel pump relay is a very common item to fail.

Jumper the pins as 450slcguy recommends, if the pump fires up you can then save a few dollars and do the following.

Locate the relay module, open up the black platic box and remove the circuit board. Inspect all the soldering joint as per below, you will usually notice several dry joints on the relay connections to the board.

If you have access to a soldering iron or know someone with one, resolder these and you should be in buisness.
Most other connections are usually ok, but I would check them anyway.

The joints should have a consistant, relatively shinny silver apearance all over. If you see any of them discoloured or have a fine ring visable around the component lead give them a touch up (a micorscope, loop or magnifying glass would be ideal to use to inspect with).

I have repaired many of them in the past

Regards

Damian