280E help needed, will not start - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 09-13-2012, 11:28 PM

I normally hang out around the Diesel Discussion forum (I hope no one minds if I ask a question here), as I am a Diesel head. However, I had an '85 280E that I sold to a good friend of mine (yes he still is a good friend, even though his car does not work!). He called me the other day and asked me if I knew what was wrong with his car. He told me the symptoms:
Every once in a while, it would not start again right after being driven. He would wait fifteen minutes or so, and it would start right up. He drove it to a family members house the other day, and when he went to leave, it would not start. He waited the fifteen minutes, but it still would not start. The family member suggested putting gas down the intake. It started and ran for a few seconds, and then died. That tells me it does have spark. I know a lot about Diesel injection, but not much about the fuel injection system on the 280E. Can someone point me in the right direction as to how to troubleshoot the problem? A basic description of the components of the system, and/or what to check and how. To show how much I know/don't know, I don't even know if the car has an electric or mechanical fuel pump! All the time I had the car, it ran so good that I had no need to learn about the engine. I am very acquainted with the 123 chassis, but with the Diesel engine. Any help would be appreciated. Thanks, Rich

P.S. He is having the car towed over to my place tomorrow (Friday) morning. I will have a look at it then....Rich

alabbasi · #2 09-14-2012, 12:29 AM

If it's not spark then it's fuel. It sounds like either the fuel pump or the fuel pump relay.

Frank Reiner · #3 09-14-2012, 12:40 AM

First step: assure fuel supply to the fuel distributor. The pump is electric, controlled through a relay that will be printed "6 ZYL.".

Suggest you read through these current threads:

1978 280SL Fuel Pump Relay and Wiring Info

1980 350sl Starting and idle problems

(I have not yet learned how to link the threads)

ROLLGUY · #4 09-15-2012, 02:18 PM

I looked at a thread : http://www.peachparts.com/shopforum/tech-help/322947-1978-280sl-fuel-pump-relay-wiring-info.html, and determined that I should jumper terminal 30 & 87 on the fuel pump relay connector. I did just that, and it started right up and ran until I removed the jumper. Does that mean the relay is bad? I also read something about an "air horn safety switch" or something like that. The car is an '85, and not a '78 that the thread was talking about. Any ideas before I order a fuel pump relay?

Frank Reiner · #5 09-15-2012, 09:03 PM

Can you describe the relay? How many pins? Stamped or printed with a part#? Does it say "6 Zyl." on it?

These questions are asked because the car is non-US spec., and some of the components may differ from US spec.

ROLLGUY · #6 09-15-2012, 10:19 PM

Quote:

Originally Posted by Frank Reiner

Can you describe the relay? How many pins? Stamped or printed with a part#? Does it say "6 Zyl." on it?

These questions are asked because the car is non-US spec., and some of the components may differ from US spec.

Yes the relay says 6 zyl on the top. I removed the cover to expose the innards. I tried to manually operate the two relays inside, and still no power to the FP. Either the FP relay part of the circuitry is solid state, or one of the two mechanical relays does the job (supposed to). I just want to make sure there is not something else I can check before laying out the $ for a new relay. Anyone have a good used one for sale?

Frank Reiner · #7 09-16-2012, 12:55 AM

The relay has two functions; the fuel pump, and the heater for the O2 sensor. If the heater circuit is grounded or shorted, the solid state portion of the relay will be damaged, and both functions cease to operate. If a replacement relay is installed without insuring that the O2 heater wiring is OK, the new relay may suffer the same fate.

ROLLGUY · #8 09-16-2012, 10:14 AM

Quote:

Originally Posted by Frank Reiner

The relay has two functions; the fuel pump, and the heater for the O2 sensor. If the heater circuit is grounded or shorted, the solid state portion of the relay will be damaged, and both functions cease to operate. If a replacement relay is installed without insuring that the O2 heater wiring is OK, the new relay may suffer the same fate.

How can I test the O2 heater wiring? I think (although I may be wrong) the car does not have an O2 sensor or cat. It is Euro spec.