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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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!

I have been unable to find the source of the fuel delivery issue with the 300E, it appears there is an intermittent break in the circuit somewhere. What is puzzling is the car will start and perform normally at times with everything in place (all my testing is using a new fuel pump relay since I had the old one apart.) I am considering buying a new klima relay or take it to a local shop. When I was at the dealer last week to buy some small parts they told me they do not have a klima relay in stock for my car so going to the dealer would be a last resort. I am waiting to hear back from a local shop on whether they have diagnostic equipment to determine the problem.

I had a problem like this with an old Nissan pickup. Replaced the relay, would work for 5 mins and stall. Tried the old relay on it again and it'd do the same thing. Even when I jumpered the relay to run, it'd stall after a few mins.

Wiring to the FP was cracked, and the pump was only getting ground intermittently. Drove me NUTS. Just a suggestion to check.

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Thanks for the tip, I will crawl under and recheck all fuel pump connections. I'm ok with mechanical repairs but when it comes to electronics I always struggle. I'll keep troubleshooting this week as time permits, it would be nice to get the MB back on the road since I have have using my Ford F250 to get around and it is a gas guzzler.

Early in this thread, M.B.Doc mentioned RPM signal. Check out the following thread for more comments from Doc. He mentions a part well known for causing all sorts of problems. Has it been changed?

http://www.peachparts.com/shopforum/showthread.php?t=158050

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

Thanks Mike, the tach functions properly when the car is running. When the car does start with all components in place the tach works along with everything else. While cranking the engine I see the tach needle jumping slightly so it looks like a signal is being passed. If I remove the fuel pump relay and jump the pins, the fuel pump runs and the car will start and the tach functions. Thats why I am wondering if there is some kind of intermittent circuit in the klima relay, it appears it is getting the rpm signal it needs but not passing it on to the fuel pump relay.

the td signal that comes from ignition unit and holds in the fp doesn't go through the klima relay it just parallels to it .it is possible that the klima relay is grounding the td signal which will stall the car.have you tried running the car with the klima relay removed? david poole european performance dallas texas.

Thanks Dave , good info. I must have misread the schematic I thought the crank sensor sends a rpm signal to the ECU which sends it to the KLIMA which then sends it to the Fuel Pump relay which turns on the fuel pump when it receives the signal during starting.

To answer your question, I did pull the klima relay while it was running with the fuel pump pins jumpered and the car remained running. I was surprised to find the car would run with both relays out.

okay now put fuel pump relay back in without the jumper and leave out the klima relay see what happens. david poole e.p. dallas tx.

Thanks Dave, I pulled the klima relay and left the new fuel pump relay installed. It would not start and I noticed the tach needle moving while cranking the engine. I put the klima back in and it would not start, sometimes while troubleshooting when I put everything back in place the car will start and function perfectly. I appreciate everybody's support!!!

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