fuel pump relay question 420sel
 

I have narrowed down my problem to a weak fuel pump relay. The number on my 88 420sel relay is 003 545 25 05. Looking at replacing it I see relays that look the same, are said to be the same, but the number is not the same. How does Mercedes number this part? I do not know the Mercedes system. I realize that aftermarket parts are numbered differently, but what numbers interchange? Thanks, Steve

have you jumped terminals 87 & 30 at the fuel pump relay to be sure of your diagnosis.fp relays usually just stop [sometimes will go again after leaving for periods of time] can you tell me what you mean by "weak"?

fuel relay again
 

My '88 420sel was running fantastic, and then left me on the side of the road. Would restart, go about 30 feet and die. Restart go about 50 feet and die. The more I did this the shorter the distance it would go, and it took a longer time to restart. Had it towed 20 miles, it started and drove of wrecker into driveway. Now it will restart instantly, but only drive about 30-40 feet without stalling. Changed fuel filter. No difference. Changed idle air control valve that I had and no change. Jumpered the terminals you mentioned and PRESTO! car runs fine, drives around the block and sits and idles until I shut it off. Sure appears to be fuel pump relay, but all the ones I have seen for same age car as mine have a different number! Mine matches what the shop manual calls for--has six pins on one side and four on the other. Thanks for any help on this. Steve

ok now i understand.any of the other relays will work.that relay is held in electrically when you crank and then when you let key go a signal [denoted TD by benz] around 6-7vdc comes out of ignition unit and holds fuel pump relay in.