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billjam's Avatar
 
Join Date: Aug 2007
Location: Perth, Western Australia
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Fuel pump relays controlled by which gizmo?

Today is not a good day.

Apart from my coke problems (in a separate thread), sorry - my car's coke problems, my engine won't start.
I just went out to shift the car around so I could work on it and it fired up for about a second and then died. It wouldn't restart.

Plenty of spark but no fuel. I bridged both pump relays and it started up straight away (although it did run a bit roughly).
Put relays back and it started again but died shortly after - I guess when fuel pressure ran out. Thereafter, no start.

Obviously, the pumps aren't getting the message to go.
Question is ... where is the gizmo that controls the pump relays?
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Bill
1988 Carrera - 3.6 engine (with ITBs, COPs, MS3X) and a whole set of turbo body panels waiting in the attic.
Day job ... www.sspowdercoat.com.au
Memories: '68 912, '72 911T, '80 911SC, '84 911, '85 930, '86 930, '87 911
Old 02-21-2009, 06:38 PM
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Rocket Scientist
 
Join Date: Jun 2008
Location: Detroit
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Here is some background so that you will understand what follows. You don't want the fuel pumps on when no air is flowing through the engine, and you don't want the fuel pumps on when the engine has stopped turning. Both of these are bad from a safety standpoint, so remove from your mind that current flows to the fuel pump relays from the ignition key.

There are two "relays" that can cause your problem. One is the Air flow sensor charging pressure relay. It takes inputs from a switch that is mounted on the airmeter, and a speed signal from the speed relay. It removes the ground from the fuel pump relays if there is no engine speed, or the airflow switch is closed.

So, you have three possibilities, airflow switch (easy to jumper across to test), speed relay (mounted under seat, no fun to diagnose), or Air flow sensor charging pressure relay (easy to get at in the engine compartment).

Fortunately, our hosts here carry these parts (last I looked).

Or you could get REALLY mad and replace all this stuff with EFI, which is what I did!
Old 02-21-2009, 08:27 PM
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Quote:
Originally Posted by Speedy Squirrel View Post
So, you have three possibilities, airflow switch (easy to jumper across to test), speed relay (mounted under seat, no fun to diagnose), or Air flow sensor charging pressure relay (easy to get at in the engine compartment).
I started working through these. Airflow switch OK.
Removed the air flow sensor charging pressure relay, removed its cover and confirmed it was working OK.
Put it back in the car and tried another start. Hey presto, problem fixed - whatever it was!
Don't you just hate that Spent hours tracing lines through the wiring diagrams trying to figure it out and it fixes itself!
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Bill
1988 Carrera - 3.6 engine (with ITBs, COPs, MS3X) and a whole set of turbo body panels waiting in the attic.
Day job ... www.sspowdercoat.com.au
Memories: '68 912, '72 911T, '80 911SC, '84 911, '85 930, '86 930, '87 911
Old 02-22-2009, 02:19 AM
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possible corrosion problem on the pins of the relay!
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1980 930 Turbo
1993 Corrado
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1984 944
2001 VW golf TDI
Old 02-22-2009, 04:10 AM
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Quote:
Originally Posted by h20cooled7 View Post
possible corrosion problem on the pins of the relay!
That very same relay has caused me problems twice in the past...and each time all I did was unplug/plug back in. Dirty contacts. Suggest getting some electrical cleaner and squirting into the female socket and onto the male pins. I believe there is a way to remove the relay and jumper across a couple of points to get the pumps to run in an emergency dead-on-the-roadside kind of thing, but where to jump I would have to trace the wiring diagram. I think I saw someone on the forum here mention doing that.
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Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 02-22-2009, 06:34 AM
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