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#1
12-11-2011, 07:40 PM
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85 380SE fuel pump relay testing
On Friday night, after driving for about 5 minutes, my car stalled and restarted right away. I drove another 5 minutes and it stalled again. This time it took about 10 minutes of no starting and then it fired up without a problem. I got it home after a couple more times of it doing this, I pulled the relay and tried bridging across terminals 7 & 8 and the pump worked.
I checked in the manual and went through the steps in 07.3-165 checking fuel pump relay. I have 12v at jack 8 - good Pump runs when I bridge jack 7 & 8 - good Ignition on, I have 12v at jack 9 - good I have 12v between jack 8(pos) and jack 11(neg) - good I have dwell angle of 13.4 at jack 10 while cranking - good I have almost 10v at jack 12(pos) and jack 11(neg) while cranking - not good, should be 12v, but the test shows 0v as repair interrution to wiring. The last step is checking the kickdown shutoff which I can't do because it's not running. According to the wiring diagram in 07.3-165, jack 12 goes to 'Cable connector engine terminal 50' Should I be checking to see why the voltage is only 9-10v at jack 12 by tracing back towards the ignition switch? I haven't had any other issues with components that are on that circuit. The circuit is only hot during cranking. Thanks in advance.
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Democracy dies in darkness, you have to kick at the darkness till it bleeds daylight Last edited by Kyle Blackmore; 12-11-2011 at 09:05 PM. Reason: re-tested after charging battery 
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#2
12-12-2011, 08:24 AM
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Sounds like the pump is "heating" up the solder in the relay & it is going open circuit.
Very common failure of the pump relay. Make sure that the pump draws approx 8A.
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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
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#3
12-12-2011, 08:47 AM
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Thanks mbdoc, I tried resoldering the relay but it still won't start. The pump is drawing 6.5 amps, that's within spec.
I'll get another relay for it and let you know how it goes.
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Democracy dies in darkness, you have to kick at the darkness till it bleeds daylight
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#4
12-13-2011, 08:55 AM
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Quote:
on a 300se i reresoldered the joints ;worked for a year then required a replacement relay as the intermittent cutting off returned. Guess end of relay lifespan.
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#5
12-13-2011, 12:27 AM
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I picked up a new relay today from my indy. He asked if I had tested it to make sure it was the relay
 . I installed it tonight and she started right up. I went for a short trip and it seemed to be running smoother too, I've had a warm rough idle for a year or so. I've changed plugs, rotor, cap, coil and control unit to try and cure it.... hopefully this does.
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Democracy dies in darkness, you have to kick at the darkness till it bleeds daylight
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#6
12-13-2011, 08:37 AM
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Good feedback!
Hope your car stays 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
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#7
12-13-2011, 08:45 AM
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Thank you mbdoc for your help
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Democracy dies in darkness, you have to kick at the darkness till it bleeds daylight
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