No power to fuel pump (944) help!

It's at my mechanics right now for an intermittent starting problem I've
been having. They didn't hear the fuel pump running so they tested to see if
the fuel pump was getting power, it wasn't. They went backward to see if the
DME relay was getting power, it wasn't either. Funny enough, They tested it
for spark (which it had) and when they plugged everything back in, it
started right up. I just got off the phone with my mechanic and he was
stumped, but thought it could be the DME or some faulty wiring. We just
replaced the fuel pump, DME relay and fuel filter last spring.

When it did this in the past, it seemed like it wouldn't like to start in
colder temperatures, and when you'd pull it into a garage to warm up, it
would eventually start; possibly because some bad wiring was expanding and
contracting?

Any other ideas why the fuel pump and DME relay wouldn't be getting power??
Thanks!

I had a similar problem. Stupidily replace the fuel pump, still didn't
work. Turned out the be the fuel pressure regulator. It went bad, allowed
too much pressure, computer then shut fuel system down but still allowed
spark.
Tested fuel pressure by putting gauge on end of fuel rail, replace pressure
regulator, started right up.
Your regulator may be faulty an allows the pressure to drop while the
mechanic takes the time to check other components. Fuel pressure is easy to
check.
For what it's worth.

Tony



"Elma" <280smercedes (AT) bonesmart (DOT) com> wrote

It's at my mechanics right now for an intermittent starting problem I've
been having. They didn't hear the fuel pump running so they tested to see
if
the fuel pump was getting power, it wasn't. They went backward to see if
the
DME relay was getting power, it wasn't either. Funny enough, They tested
it
for spark (which it had) and when they plugged everything back in, it
started right up. I just got off the phone with my mechanic and he was
stumped, but thought it could be the DME or some faulty wiring. We just
replaced the fuel pump, DME relay and fuel filter last spring.

When it did this in the past, it seemed like it wouldn't like to start in
colder temperatures, and when you'd pull it into a garage to warm up, it
would eventually start; possibly because some bad wiring was expanding and
contracting?

Any other ideas why the fuel pump and DME relay wouldn't be getting
power??
Thanks!

If you figure out the problem, please post the results. I'm sure many are
interested. I would mess with the DME, doubtful it's the problem. I've
opened up mine and resoldered all connections a few time. Even went so far
as to buy a spare DME. Sold the care, still have the DME. They are
rugged.\

Tony



"Tony" <tigerNOSPAMz (AT) att (DOT) nospam.net> wrote

I had a similar problem. Stupidily replace the fuel pump, still didn't
work. Turned out the be the fuel pressure regulator. It went bad, allowed
too much pressure, computer then shut fuel system down but still allowed
spark.
Tested fuel pressure by putting gauge on end of fuel rail, replace
pressure regulator, started right up.
Your regulator may be faulty an allows the pressure to drop while the
mechanic takes the time to check other components. Fuel pressure is easy
to check.
For what it's worth.

Tony



"Elma" <280smercedes (AT) bonesmart (DOT) com> wrote in message
newsPlQh.133875$_73.132721 (AT) newsread2 (DOT) news.pas.earthlink.net...
It's at my mechanics right now for an intermittent starting problem I've
been having. They didn't hear the fuel pump running so they tested to see
if
the fuel pump was getting power, it wasn't. They went backward to see if
the
DME relay was getting power, it wasn't either. Funny enough, They tested
it
for spark (which it had) and when they plugged everything back in, it
started right up. I just got off the phone with my mechanic and he was
stumped, but thought it could be the DME or some faulty wiring. We just
replaced the fuel pump, DME relay and fuel filter last spring.

When it did this in the past, it seemed like it wouldn't like to start in
colder temperatures, and when you'd pull it into a garage to warm up, it
would eventually start; possibly because some bad wiring was expanding
and
contracting?

Any other ideas why the fuel pump and DME relay wouldn't be getting
power??
Thanks!

If you have a factory alarm, check it. It and the DME relay are the two
most frequent culprits.

Kevin
Catellus Engineering

in my experience, every failed DME relay I've examined has failed due to bad
solder connections, I've never seen a different failure mode - of course
I've only examined about 5 relays - resoldering and adding wire to relay
frame is permanent solution
"Martin²" <never (AT) give (DOT) one> wrote

Most probably your DME relay, they can create interminent fault which can
be sensitive to temperature.
This is because the spring loaded contact inside can get weak and the
contact points will burn, this will also happen if you try to start the
car with weak battery.

--
Posted via a free Usenet account from http://www.teranews.com

Martin, you seem to have a good understanding of the DME relay and the
control electrics.

So can you help me?

My fuel gauge works when you start the car up but will suddenly drop to zero
after about 3 minutes. Longer in cold weather and shorter in hot weather. It
may work later in the day if the car is left to stand.

I have eliminated the sender by measuring it when working and when not and
it is reading correctly according to the Clarke's Garage figures.

Is there some circuit which turns on or off as the car warms up which could
directly or indirectly affect the fuel gauge?

Could the DME relay be implicated?

All other circuits seem OK.

Alec



"Martin²" <never (AT) give (DOT) one> wrote

Most probably your DME relay, they can create interminent fault which can
be sensitive to temperature.
This is because the spring loaded contact inside can get weak and the
contact points will burn, this will also happen if you try to start the
car with weak battery.
First think you need to know that the function of the DME relay is to turn
on the fuel pump WHEN the engine starts cranking ( on 968 it also turns on
the idle stabilized circuit and O2 sensor but that may not apply depending
on the age of your 944 ). This is a safety feature, when your engine
stops, so does the fuel pump.
The way it works is that pin 30 of the relay is always on, connected
directly to the battery. The DME computer detects the engine cranking it
grounds pin 85 of the relay which then switches power to pins 87 (pump)
and 87b (other).
If necessary you can take the DME relay out, connect pins 87 & 87b to 30,
you would her the pump run and you can start the engine and the car will
run normally. Sometimes the DME computer no longer grounds pin 85, in
which case you can wire 87 & 87b into the ignition circuit (the auto
tranny fuse is good for that even if you haven't auto tranny).
Regards,
Martin

did you check the connectors to the gauge cluster? that's one likely
culprit. also possible is defective ground


"Alec" <alechopley (AT) dsl (DOT) pipex.com> wrote

Martin, you seem to have a good understanding of the DME relay and the
control electrics.

So can you help me?

My fuel gauge works when you start the car up but will suddenly drop to
zero after about 3 minutes. Longer in cold weather and shorter in hot
weather. It may work later in the day if the car is left to stand.

I have eliminated the sender by measuring it when working and when not and
it is reading correctly according to the Clarke's Garage figures.

Is there some circuit which turns on or off as the car warms up which
could directly or indirectly affect the fuel gauge?

Could the DME relay be implicated?

All other circuits seem OK.

Alec



"Martin²" <never (AT) give (DOT) one> wrote in message
news:46131487$0$8722$ed2619ec (AT) ptn-nntp-reader02 (DOT) plus.net...
Most probably your DME relay, they can create interminent fault which can
be sensitive to temperature.
This is because the spring loaded contact inside can get weak and the
contact points will burn, this will also happen if you try to start the
car with weak battery.
First think you need to know that the function of the DME relay is to
turn on the fuel pump WHEN the engine starts cranking ( on 968 it also
turns on the idle stabilized circuit and O2 sensor but that may not apply
depending on the age of your 944 ). This is a safety feature, when your
engine stops, so does the fuel pump.
The way it works is that pin 30 of the relay is always on, connected
directly to the battery. The DME computer detects the engine cranking it
grounds pin 85 of the relay which then switches power to pins 87 (pump)
and 87b (other).
If necessary you can take the DME relay out, connect pins 87 & 87b to 30,
you would her the pump run and you can start the engine and the car will
run normally. Sometimes the DME computer no longer grounds pin 85, in
which case you can wire 87 & 87b into the ignition circuit (the auto
tranny fuse is good for that even if you haven't auto tranny).
Regards,
Martin

--
Posted via a free Usenet account from http://www.teranews.com

all ground wires on 944, except the one from the battery, are brown


"Martin²" <never (AT) give (DOT) one> wrote

Alec,
problems with gauges are quite frequent, almost always down to bad ground.
There is a common ground point on the chassis for all of the facia
equipment. The wiring schema in the workshop manual should tell you
approximately where it is located and the wire colours, then you have to
dive under the dashboard and trace the wires in between... good luck.

Absolutely nothing to do with the DME relay.

--
Posted via a free Usenet account from http://www.teranews.com

Elma,

Did you resolve this? Contact me direct if you still need help. The
BOSCH DME kills the fuel to the engine in an accident [if engine
stops]. This is why the DME Relay and fuel pump is powered by the DME.
This can fail in a otherwise good DME.

FR Wilk
Engineering
"Power PROM" Performance Products
http://www.frwilk.com
PowerPROM (AT) frwilk (DOT) com

Performance Chips for Porsches.
944 1982/1985
944/924S 1985.5/1987
944/924S 1988
944 1989 [2.7 liter]

On Apr 6, 9:23 am, "Bill N" <nob... (AT) nowhere (DOT) can> wrote:

all ground wires on 944, except the one from the battery, are brown

I've heard that some of the grounds in the interior (OEM stereo,
possibly others) aren't ground. No personal knowledge of this. But I
believe the above is true for all engine compartment grounds.

"Martin²" <n... (AT) give (DOT) one> wrote


Alec,
problems with gauges are quite frequent, almost always down to bad ground.
There is a common ground point on the chassis for all of the facia
equipment. The wiring schema in the workshop manual should tell you
approximately where it is located and the wire colours, then you have to
dive under the dashboard and trace the wires in between... good luck.

Absolutely nothing to do with the DME relay.

--
Posted via a free Usenet account fromhttp://www.teranews.com