Author Topic: fuel pump issues  (Read 155 times)


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fuel pump issues
« on: 29 December 2019, 04:30 PM »
I am having issues with the fuel pump on my 6.9 not getting any fuel to fuel distributor,  when i bridge relay terminals 30 and 87 i can hear the pump bumping but not pushing fuel through, when i push down on air sensor plate i get nothing, also i put a volt meter directly on pump terminals turn the ignition to on and i get 0 voltage, does the car have to be cranked before voltage is read at the pump? hope this make sense
« Last Edit: 29 December 2019, 07:31 PM by arcijack »


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Re: fuel pump issues
« Reply #1 on: 29 December 2019, 10:12 PM »
...does the car have to be cranked before voltage is read at the pump? hope this make sense

Yes it has.
But another practical option is to place the transmission lever in R or D and then turn the ignition key to ‘start’ position. Obviously the engine won’t crank but you should be able to hear the pump while the key is maintained in ‘start’ position.
If pump is running but still no fuel delivery, then you might have a clogged filter/line. To check the delivery disconnect the in line at fuel distributor. Careful the amount of fuel passing is significant so place a good size container to capture the fuel. 2 people doing this is a good idea, one at the key and another at the hose/container.  Seeing fuel coming out of the line is not enough proof. The right flow spec has to be measured (lt/min). Value available in the CIS manual.
Good luck
W116 1977 280SEL & 1979 280SE


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Re: fuel pump issues
« Reply #2 on: 30 December 2019, 07:57 AM »
It is possible for a worn out pump to make noise yet fail to deliver the correct fuel pressure.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550