|07-05-2013, 03:39 PM||#1 (permalink)|
How to bypass Fuel Pump Relay on '84 280SE M110.988
Apparently my fuel pump relay 001.545.43.05 KAE# 3.301.310 has crapped out. Is there a way to "fake-out" the system to think it's there? Jumping terminals 7 and 8 gets the pump running. It sputters then dies, so there must be more to it. I (think) I've attached a circuit diagram for the FPR. It's a 9-pin relay, with an awful lot of stuff inside the box. I've re-soldered everything twice now, and the problem went away for a while, but it's back. I'd like to be able to drive it to a repair shop, so I don't have to pay towing...
Dave '84 Euro 280SE M110.988
Dave in USA
1984 280SE M110-989 European Import
|07-05-2013, 03:48 PM||#2 (permalink)|
Date registered: Nov 2007
Vehicle: '73 450SL, '83 300CD, '88 300SE
Location: Upstate Central NY
When dealing with a relay, always look for terminals 87 and 30 if you need to bypass. Put a jumper between them and if that IS the problem, it should get you going.
ASE Master tech, specializing in electronics and driveability.
Certified Diesel Master tech.
EPA 609 certified
1973 450SL - 191K - Summer Toy
1978 300D - 267K
1978 300CD - drove to death
1981 300D - drove to death
1983 300CD -170K
1989 300SE 105K miles..
1981 Coupe DeVille.. just because.
... and many more past and present...
Because Safety is not a luxury. Mercedes-Benz. Engineered like no other car in the world.
|07-05-2013, 04:04 PM||#4 (permalink)|
Been there, done that.
While dissecting the relay (again) it looked like pins 9 and 5 also need to be connected (microswitch circuit) whatever that's for. It has Tach signal, +12VDC, ground all where they're suppposed to be, fuel pump runs when I jump 7 and 8. Troubleshooting chart leads me to the relay NFG. But there must be a way to fake-out the system to get it to drive...
|07-05-2013, 04:28 PM||#5 (permalink)|
I did the jumper between pin 7 (87) and pin 8(30) and the pump runs, but the engine just sputters but won't actually start. So obviously, something is missing from the equation. Like (87->30 + mystery connections) = (start and run).
Last edited by d1hartman; 07-05-2013 at 04:31 PM. Reason: CLARIFY
|07-06-2013, 03:28 AM||#7 (permalink)|
Date registered: Jan 2008
Vehicle: 1983 500 SEC Lorinser 1971 280se w108
FPR on my SEC finally gave up the ghost last week,Ive re soldered it a couple of times
I just bought a cheap generic relay spliced it into the wires underneath the box 87/30 and a switchable power sorce and earthed it on the body
|07-06-2013, 06:12 AM||#8 (permalink)|
BenzWorld Junior Member
Date registered: Jun 2013
Vehicle: W126 4.2 auto sel , trike build
Location: London uk
You dont always have to use merc bits you all need to Do is Step back and think about things I've got a 4.2 sel engine and gear box in a trike frame Volvo diff no wiring to talk about no CPU or idle valv unit and it runs lovely just the etz powering the coil
|07-06-2013, 12:11 PM||#9 (permalink)|
OK so I got the pump running. But it won't actually start up. It sputters a bit at first, then nothing. It just cranks and cranks. I Could this be a fuel injection problem? Like it's getting a start up squirt, but no running squirts?
|07-07-2013, 09:55 AM||#10 (permalink)|
BenzWorld Senior Member
Date registered: Apr 2009
Vehicle: 1984 280SE, 1990 300SL, 1988 260E, 2014 E350
FWIW, I also have an '84 280SE, and when i've had M110 specific questions, I went to the W123 forum since those cars came with the M110 in the US. Bigger knowledge pool. No offense to anyone here...
Good luck with the fuel issue.
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