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Fuel Pumps not Working Need Help!

No start this morning. I jumped the fuel pump relays and engine fired. Replace relays and no start. I assume the rotation sensor is not engaging the relays. How to I check this out?
Old 12-03-2017, 07:36 AM
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Crotchety Old Bastard
 
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Pull the fuel pump shut off plug on the back of the air meter assembly then turn the ignition to the run position. The pumps should be running. Check each pump, front and rear. If not running jumper one at a time to see which relay is the problem. Also clean and check your fuses.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 12-03-2017, 03:57 PM
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check out the car will not start sticky. look for my post. I tell u how the FP system works and how to TS it.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 12-04-2017, 03:10 AM
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If the car has Bosch k-jetronic injection or CIS then it may be the white wire where it connects to the speed relay under the left side seat.
CIS is a type of Bosch mechanical fuel injection so there is no "rotation sensor".

CIS is short for constant injection system or constantly irritating sh_t

Old 12-04-2017, 11:43 AM
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Wow! I have owned this 930 for many years and do not remember ever seeing anything electrical under the driver seat, but I will look. Did Porsche use this on 1979's?
Old 12-04-2017, 01:37 PM
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Pulled the air meter connection. Key in on position. Neither or the fuel pumps run. Tried spare relays none run. I pulled the Delay Cutoff Relay and do not get any continuity between any of the 4 terminals. Assume the relay coil is open. Not sure which connection points to jump to bypass the relay. The plug has 12v on two connections. I'm thinking a bad Delayed Cutoff Relay. What else is there?
Old 12-04-2017, 01:44 PM
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I'm not sure what electrical stuff is under the seat of a '79. There wouldn't be any lambda stuff from the factory since that started in 1986 but I'm going to guess the speed relay would be there.
The speed relay is the factory rev limiter that disconnects the ground connection to the fuel pump relays around 7200 rpm if I remember correctly.

The white wire from the over boost sensor goes there too where it trips a relay that disconnects the ground connection to both fuel pump relays.
There were two small relays on a printed circuit board inside the speed relay I had and I don't know why there's two of them in there.
At the same time my experience is from a 1987 model so maybe none of this stuff was in a '79.

There's other folks here that know 930 electrical stuff better than me.
I'm just bored and trying to help
Old 12-04-2017, 02:54 PM
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nothing under the 79, good reason to list your year.

the delayed relay is for the ignition not the FP.

you REALLY need to just read the sticky, everything I can tell you about the FP system is already there. read and ask questions here.
there is also a nice block diagram there for you to look at.

pulling the connector brian said just activates the FP circuit, of course with the key on. leave it off for now.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 12-05-2017, 02:55 AM
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Crotchety Old Bastard
 
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Follow the electricity. If the pumps are not running with the air meter assembly plug pulled and the key on trace the power back to where it is live. You can defeat every relay and control switch that kills power. Once the pumps are running you can check the control devices one at a time.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 12-05-2017, 03:48 AM
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OK the problem is solved. It was the over boost switch. Thanks for all your help.
Old 12-05-2017, 11:50 AM
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