86 300E-new fuel relay-still won't start
 

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.

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?

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.

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

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.

fp-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.

300e
 

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!!!

Is it possible the ECU is at fault? I am puzzled with this problem due to the fact the car will sometimes start normally with all components in place and it appears the relays are getting the appropriate signals.

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

Yes, I am guilty of not troubleshooting thoroughly in the beginning. When I jumpered the fp relay pins and the pumps ran I made an assumption it was the fp relay at fault. In addition, the fp relay was original (1986) and have a reputation for failure.

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.

300e
 

call me at 2149567007 and i will walk you thru it. david poole e.p. dallas tx.

300e
 

call me at 2149567007 and i will walk you thru i9t. david poole e.p. dallas tx.

Thanks Dave, I will call you when I get home from work which will be 6-7 pm EDT. I live in eastern Pennsylvania.

Isn't 10V a little low? Just saw a pic of the fp relay for a 201 and it says 12V on it.

Some relays don't activate unless it gets its rated voltage though I'm not sure if it applies to this relay.

Thats what I am wondering, pins 10 and 11 should have greater than or equal to 10V while cranking according to the manual. I have 10v with the switch on but it drops to 7v only while cranking the engine. When I relaese the key it jumps back to 10v.

Based on the manual 6-12V is acceptable between pins 10 and 11. This is for the rpm signal.

It's the power input to the coil of the relay that's low at pins 9 and 11. Reading should be 11-14 V. Probably you have a poor ground connection or the incoming power is grounded somewhere. Also what's your battery voltage?

Just wondering, are your electrical centers (battery and fuse box areas) dry?

Oops, my bad. I'm talking about my car. 87 190E 2.3

Confirm the values for your car.

aussiebaz
 

Hi Guys not sure if your 86 300e is simular in electronics as my e220 but i was haveing simular problems until i replaced the OVP relay behind the battery, problem solved . cheers baz

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. :o 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.

OK...I'll take a shot at this one. Likely a "distant shot", but maybe worth thinking about.

Alarm.

You say behind the glove box. On a 126 and I'll bet on the 124 as well, the stock alarm system is beneath the passenger side foot well. That's "beneath" the glove box...sorta. Noises and their point of origin can be confusing.

Could this be the alarm controller yacking at you?

This suggestion may not be valid if the alarm system is the original factory unit. I want to say that the factory system would not stop the car from starting, but simply sounded an alarm in the event of dampering. Someone correct me if I'm wrong.

If your alarm is after-market, there's a much stronger possibility it could be involved here.

Well I decided to take a break from my electrical problem and find out what the mysterious noise coming from the glove box area. I removed the glove box and the vent duct to the passenger dash vent.
What I found was a little fan located directly under the passenger vent but not connected to the vent. I was able to see it with a small mirror and it runs when the key switch is on. There is a grill opening under the dash which allows air to/from the passenger footwell. So what does the little fan do? Circulate air under the dash?
By the way, my car is completely stock with the factory alarm system.

There have been many posts here that discuss this "little fan". Here's pointer to one.

http://www.peachparts.com/shopforum/tech-help/18071-sheeesh-its-hot.html?highlight=small+fan

I still vote for the grounding problem

Problem resolved
 

After hours of troubleshooting and finding nothing wrong I had a friend tow my car to a local foreign car specialist. I couldn't get the car to start even with the fuel pump jumpered and it appeared it was getting good spark and fuel delivery.

The indy checked fuel flow and ran his diagnostics. I received a call today informing me the problem was distributor cap and rotor. This was a surprise to me as the cap and rotor were replaced about 10k miles ago. The car is still at the shop and I will provide an update when I get it back.

Got the car back
 

The car had a weak and intermittant spark. Since the cap and rotor were not that old and my timing light indicated a signal I ruled it out while troubleshooting. Now I know a weak spark will cause a no start situation, you live and learn.
Next is to troubleshoot the a/c and replace the water pump. The a/c has a good charge of R12 but the compressor has a mind of its own. My water pump is not leaking but the bearing in it is noisy and slinging grease.

Many thanks to all who contributed their advice as I learned much more about my car.