Fuel Pump - Low Voltage Issue

[videobob]

We have restored a car that sat for 12 years.
We have replaced the entire fuel system, pump and everything at the tank, distributor, lines, all fuel accessories, etc.
(we also did the brakes, all hydrolics, cooling system, all rubber, fluids, etc)

So the car was running.
When I took it on the first test drive it was bogging down when I tried to get some speed.
It would buck like a horse and gurggle.
Then it died all of a sudden and seemed to have lost all electrical power for a few seconds.
I couldn't get it to start after that.
I thought it might be low on fuel so I put 5 gallons of premium in it.

After trying to get the car to run we checked the obvious stuff starting with the fuel pump and found that despite the battery being charged (13v)
we were only getting about 9v at the pump.
After some research on the subject, we added a ground wire to the harness but it did not help.

So my question is this:

Where does the fuel pump get it's power from?
Does the pump get full voltage all the time or does another device vary the voltage depending on condition?

We need to trace back all the points where the power is fed and find where the resistance is.
Thanks!!!

[ccurzio]

Have you checked/replaced the RPM Relay?

[Ron]

we were only getting about 9v at the pump.
After some research on the subject, we added a ground wire to the harness but it did not help.

So my question is this:

Where does the fuel pump get it's power from?
Does the pump get full voltage all the time or does another device vary the voltage depending on condition?

If you took the "extra" ground from a confirmed good source, you are on the right track.

Fuel Pump Circuit in Resources Section (http://dmctalk.org/attachment.php?attachmentid=91&d=1306264511)

Power to the pump should be either on or off.

[Bitsyncmaster]

Gets it's voltage from the RPM relay. Check the fuse #7 fuse for good connection. Check the 2 pin connector up near the pump.

You will lose a volt or two with hall the harness and connector drops but your 4 volt loss is way to much.

[stevedmc]

Have you filled Mr Fusion?

On a serious note, I would ground the fuel pump directly to the frame and bypass the RPM relay to see what happens.

[DCUK Martin]

Check that all 6 pins in the RPM relay are solid and don't wiggle. It could well be a simple dry joint which you can fix yourself with 5 minutes and a soldering iron. This caused my friend's car to run one minute and die the next.

[David T]

That circuit #7 can be one of the most troublesome ones in the car. What it looks like to me is when you wind up melting the fuse out of the fuseblock you have a lot of problems in it to fix. When I see that area melted, invariably you later wind up replacing the fuel pump and the RPM relay. The pump because is is going bad and drawing too much current, and the relay because it got too hot and you melted some solder joints. They can be resoldered if you want but most would just rather replace it. Other problem areas include the plug in the wiring harness up in the washer bottle bucket, the inertia switch (older style or attached to the lambda counter), corroded wiring at the fuel pump because water and fuel collected in the pump boot, and the Control Pressure Regulator, the wiring inside it tends to burn up. When the RPM relay starts acting up you also see the Lambda working sometimes and not others. A LOT going on with #7! It is getting to the point that if you see that circuit running hot you should just go over the whole thing! It is really interesting, the SECOND the fuel pump stops the motor DIES. If you have an intermittent connection (bad solder joint) in the RPM relay it can be making the fuel pump (and Lambda) go on and off. Easy to verify, just jumper the RPM relay and test.
David Teitelbaum





Check that all 6 pins in the RPM relay are solid and don't wiggle. It could well be a simple dry joint which you can fix yourself with 5 minutes and a soldering iron. This caused my friend's car to run one minute and die the next.

[DCUK Martin]

They can be resoldered if you want but most would just rather replace it.


If it got hot enough to melt the solder, it'd have a heck of a lot more problems than a simple dry joint!

Repair rather than replace if you can - it'll keep the supply of new parts out there for longer for those who really need them.