[DMCForum] Re: very frustrated!! - starting problem
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[DMCForum] Re: very frustrated!! - starting problem

You're making this much harder than it needs to be. First, take
Rich's good advice and give it a shot of starting fluid. If it fires
up you'll know you have a fuel issue to resolve. If not you need to
go in another direction.

The relay isn't necessarily bad, it won't turn on and send power to
the fuel pump unless the engine is running or cranking. You might get
a relay closure for a second or two when you turn on the ignition but
otherwise the RPM relay needs to sample the tach signal from the
ignition system to energize and that only happens when the engine is
running or cranking.

Measuring things: People tend to focus on both wires at a time,
measuring right at the load. (In your case the fuel pump.) Ths is bad
technique because you don't know which side of the circuit is bad,
the "hot" or the ground. Never reference a ground measurment at the
load while troubleshooting what you think is a hot wire failure, go
back to the source. Same for when you're shooting what may be a
ground wire failure, go back to the source with one lead because it's
a known good reference.

In other words, don't place the negative lead of your voltmeter right
at the pump if you're having a problem. Make up a long wire and
connect it directly to the negative battery post or a known good
ground not far from the battery. Now use the meter's positive lead to
walk through the circuit with the RPM relay jumper installed. If you
end up at the pump and have 12 volts you have a bad ground somewhere.
(Better is to just go directly there and work backwards if you need

If the pump has 12 volts with one meter lead connected there and the
other at the battery post, leave the positive meter lead connected to
the pump and now take the long negative lead you made up and walk
through the ground paths until you find the spot where you're losing
it. Again, best to start at the load (pump) and work backwards until
you find the spot where you're losing voltage. It could be your
inertial switch, a bad frame ground for the fuel pump, the wiring
itself, or the connector for the pump...it's well known to corrode.
Step back a bit at a time and check the meter.

Using this technigue you'll find where the problem is. If you both
meter leads at the pump and have 12 volts the wiring is probably OK
but that means squat when pulling current. You should test the
circuit under load. Use the pump (or some other load connected in
place of it), you should still have close to 12 volts when it's
running under load with the RPM relay removed and jumper in. If the
voltage sags under load do the wiring test all over until you find
the bad connection.

If all this checks out try to start the car with the jumper in place.
It won't run right because you're still not powering the Lambda but
if it started with starting fluid it should start now. If it doesn't
then do as Rich says: Push down on the airflow plate and see if the
injectors spray. If so the car should start. If it doesn't you need
to look elswhere besides the fuel system.

If it doesn't start (or if the RPM relay doesn't close while
cranking) with the relay in place you need to check the relay or the
tach input to it from the ignition system, a failure of either will
keep your fuel pump from running. (That or your inertial switch but
you already tested that during the wiring checks mentioned above.)

One step at a time and think about what you're doing, this isn't
rocket science. There are simpler ways than this to trace a
circuit but for beginners this is the easiest and most reliable

--- In DMCForum@xxxxxxxxxxxxxxx, "Brian" <TK581@xxxx> wrote:
> Okay - I didn't bother test starting it because with the jumper (a
> godd one) in place and a full battery I'm getting 9.5volts at the
> pump.  I do not hear the pump either (with ignition turned or
> I might replace the new pump with my old one to check to see if I
> get a different result (I don't think my old pump was ever broken,
> just replaced it as a revamp)  - should I even bother with that? 
> I'm pretty sure that the relay is bad becasue I get no voltage when
> it is place and at least I get 9.5 when I have the jumper in place.
> I hope to have some more info by tomorrow evening...  :)

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