Fuel Pump Voltage Problem

[nuts4nine14s]

OK, I bought a new fuel pump for my 70, 1.7 with FI. I bolted it in and cranked the car over. Car fired right up and dies after about 10 seconds. Well, I found the problem. I hooked up a Multi Meter to the fuel pump power and ground wires and when the car is cranking it jumps to 12 volts. Right after the car starts it emmediatly drops to 0 volts. I know I can run a pair of wires to the battery and put in a toggle switch but the problem has to be something that someone else had and resolved very easily. It has to be something stupid but that I am missing.

I have checked all the relays on the relay board. My fuel pump fuse is of course good. I have checked all my grounds and cleaned all the terminals and applied dialectric grease.

Help me Obeone, your my only hope :-)

Luke

[bperry]

I have a 74 which has been converted to Carbs but
from studying the diagrams, I can make some
suggestions/guesses.
This is from looking at the 74 diagrams
(They are the only complete set I can find)
but I think the earlier versions are all the same in this area.

The ECU activates/drives the fuel pump relay.
It does this by sending a gound signal to T4bIII
(This is upper left pin in the four pin connector of the relay board
as you stand behind the relay board facing tward the front of
the car - The pin closest to the driver side door)

The ECU will drive this pin low when the distributor is spinning.
It also has a pulse detector. If the engine stops or dies this is
what shuts down the fuel pump.
To get car the started, the ECU has an override to ground the pin
and activate the pump while the starter is cranking.

Based on your symptoms, it sounds like the ECU is confused
and doesn't "see" the running engine and shuts down the
fuel pump.

I can't verify this, since mine isn't hooked up, but it looks like
there is a wire from the distributor (perhaps on the points
side of the coil) that goes to the ECU that is used.

My recommendation would be to check the wires around the
distributor & coil, and just to be safe all the contacts of the
relay board connectors. (4 pin, 12 pin, & 14 pin)

BTW, this same distributor input that is used to shutdown the fuel pump also drives some other fuel metering, so you probably
do want to track down the real problem and not just hot wire
the fuel pump - unless its only temporary.

Not an exact answer, but perhaps it will help.

--- Bill

[nuts4nine14s]

Here is more information that I gathered.

When I turnt he key to the ON posistion the pump does not run, nor get any voltage. When I crank the car it sits at 12-13v. After the car starts the voltage drops to 0v.

[John Rogers]

When you say you checked the relays, what did you do? The best test is to remove the relay and jumper pins 30 to 87 than try to start the car. If you get voltage when the key is on or cranking then either the relay is bad or power to pin 86 is missing. Good luck

[Dave at Pelican Parts]

Brad Anders has a troubleshooting flowchart on his website: http://members.rennlist.com/pbanders .

Go through that, and you should find the problem.

--DD

[philinjax]

Unplug T4, the 4 pin, 5 wire, connector in the left rear of the relay board in the engine compartment. Spray clean the contacts on the plug and and recepticle with contact cleaner (Radio Shack), reconnect plug.

This may not fix the problem but it is a potential source of the malfunction. If this doesn't fix it, then diconnect the computer plug, repeat the contact cleaninig, as above, and see if this might fix the
malfunction.

If neither of the two procedures above fix it, your computer is likey
the problem.

Hope this helps,

Phil

[philinjax]

Actually, it might be a broken white wire also. While you have the computer plug disconnected, check continuity between pins 18 on the computer plug to pin T4I and pin 24 on the computer plug to T4I. One of these wires might be the culprit.

Good luck,

Phil