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#1
11-06-2016, 03:43 PM
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New FP relay, pump runs when jumped. But...
Once again, cranks but wont start...
Jumped relay (pins 7 & 8) and fuel pump indeed runs (but wont start car). Plugged in NEW FP relay - but pump wont run when key turned. Further: Sprayed a little carb cleaner into throttle body area - no help. Replaced ignition control unit last year (Huco). Next checks? Ragtopper 1982 380SL 
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#2
11-09-2016, 03:17 PM
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I would check that the relay coil is getting energized with the key on (12 volts coming in at pin 6 and good ground at pin 5). If either is missing, the relay won't make contact to send voltage to the pump.
If the ground is bad, look for broken or corroded wires between the relay and the chassis. If there's no voltage to the relay coil, then we need to review the wiring diagram to figure out where it should be coming from. Edit: Check this post from Chuck Taylor if you haven't already: Checking 380SL Fuel Pump Relay Instead of "with the key on" I should have said "while cranking the engine." According to Chuck, pin 6 is only energized while the engine is spinning.
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#3
11-10-2016, 10:05 AM
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Thx for reply, J.
Will go thru checklist. Also just remembered: a few months ago, had issue with fuel leaking from gas cap after fillup. Assumed gas cap gasket bad so replaced with new cap. Now wondering if filter is clogged and fuel backed up...but not sure how/why this would prevent pump from running. Ragtopper 1982 380SL
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#4
11-10-2016, 06:36 PM
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Back up...
If you jumper the fuel pump and it runs BUT THE CAR WON'T RUN, you don't have a fuel pump relay problem! If you sprayed carb cleaner in the intake and didn't even get a burp, you definitely have an ignition problem of some sort, even with no fuel present the carb cleaner should get some sort of reaction out of the engine. On your vintage car, the fuel pump only runs when the engine is revolving, there is no prime period when you turn the key. The only way to check the operation of the relay is to have someone cranking the engine and go check if the pump is running.
__________________
Current stable: 1995 E320 149K (Nancy) 1983 500SL 120K (SLoL) Black Sheep: 1985 524TD 167K (TotalDumpster™) Gone but not forgotten: 1986 300SDL (RIP) 1991 350SD 1991 560SEL 1990 560SEL 1986 500SEL Euro (Rusted to nothing at 47K!)
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#5
11-13-2016, 12:24 PM
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Thx D300.
The pump wont run when cranking. Again - however, it will run if I jumper pin slots 7 & 8. When pump DID run, I could hear it buzz for a few seconds before car would start. FP relay is new. Wondering now if recently replaced HUCO Ignition Control Module has already gone south.... Ragtopper 1982 380SL
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Linear Mode
