My 1986 300E with manual trans will not start after replacing fuel filter and fuel pump relay. When I jumper the fuel relay socket the fuel pump runs and the car starts and runs smooth. My initial conclusion was a faulty fuel pump relay but when I put the new one in today it still won't start. The original relay has part# 002 545 15 05, the replacement part# 003 545 24 05. Any ideas welcome. Thanks.

The fuel pump relay need a RPM signal to make the fuel pump run...


The 003-545-24-05 is a correct replacement number.

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190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
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Thanks M.B.DOC, it appears I am not getting an rpm signal to the fuel pump relay. I have been searching through the forum for a couple of hours now, what I found is a diagram which shows the rpm output signal coming from the ECU to a terminal block to the KLIMA relay and then to the TD pin of the fuel pump relay. Could the KLIMA relay be the culprit here?

ftp://members.aol.com/ajdalton7/fuel.jpg

When you bridge the pins on the fuel pump does the car run & IS the tachometer working? Do you have a signal at the klima relay TD pin with the engine running?

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

I removed the klima relay and checked the solder joints and it appears to be good. A new fuel pump relay is installed. The klima was put back in and for the heck of it I tried to start the car. It started right up and everything was good, a/c, tach, etc. and let it run for about five minutes. I turned it off but it would not restart. I pulled the fuel pump relay again and jumpered the fuel pump. The car started and the tach is working.
I just got home from work and will pursue with your suggestions later tonight. Thanks.

I checked the pins on the fuel pump relay:
with the ignition off
87 and 30 (7 and 8) always have power, showing 8 amps
with the ignition on
TD and 31 (10 and 11) showed nothing

while testing with the ignition on I made a connection between two pins which engaged the starter, might have been 8 and 11, not sure.

Once again I reinstalled the relays and the car started normally, after letting it run for about ten minutes it stalled and would not restart. It will restart if I jumper the fuel pump, and the tach is working fine. When cranking there is a signal to the tach.

I can't seem to make sense of this problem and going to take a break until I find more troubleshooting info.

While troubleshooting I noticed the water pump is slinging grease from the bearing so I got that going for me too!

Been reading this thread but couldn't find what prompted you to change your fp relay.

One more thought.

Electrical portion of ignition switch.

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1U40N9POF1UJ153VY1&year=1986&make=MB&model=300-E-002&category=M&part=Ignition+Switch

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

Thanks Mike, that a good idea. I will check it next and let you know what I discover.

Did you check if there's power going into the relay between socket 9 and 11 of your diagram?

If there's no power try removing fuse 7 and check its continuity with your meter.

I am getting 10v between pins 9 and 11 with the ignition on which is good. I am getting power since I get a good reading between pins 7 and 8.

Also checked pins 10 and 11, I get 10v with the ignition on but it drops to about 7 volts while cranking the engine but I am not sure if thats a sign of a problem or not.

Special thanks to Dave Poole for offering his time to discuss this issue on the phone and to Mike Murrell for suggesting to check the ignition switch.

What I have found is I am not always getting a reading between pins 9 and 11 on the fuel pump relay. I turned the ignition switch on and left my meter to pins 9 and 11 and after about a minute voltage was detected. Wiggling the key in the switch or turning off and on doesn't have an effect but what is unusual is a reading will appear without doing anything but leaving it in the "on" position. One thing I tried was looking for voltage and when it appeared I removed my meter and replaced the fp relay but the car would still not start. At this time I am suspecting the ignition switch and will continue troubleshooting.

Thanks again to all who have contibuted their suggestions to this post.

Sorry but your problem got to me. Can you do one thing for me? Try hot wiring 11 to ground and see if it helps.

Not sure if this has anything to do with my issue but here it is. When I turn the ignition key to "on" there is a buzzing noise coming from behind the glove box, it is not very loud and can only be heard when the ignition is on. The noise is definitely not coming from under the hood.