Electric Oil Pump Test Proceedure

[Hunter#1]

First, check the yellow wire for voltage. I don't think there will be any.

Then, set the meter on the continuity scale with one probe to the engine block and one probe to the yellow wire. Turn the key on and see if the yellow wire is one and the same as the block ground.

Yellow is normally key on power. In this case I don't think that it is.

ok, interference removed. Thanks for the quick reply. Standy for test results shortly.

[Hunter#1]

First, check the yellow wire for voltage. I don't think there will be any.

Then, set the meter on the continuity scale with one probe to the engine block and one probe to the yellow wire. Turn the key on and see if the yellow wire is one and the same as the block ground.

Yellow is normally key on power. In this case I don't think that it is.

Alright, 12V continous with key on at the r/y wire. We have continuity on the yellow wire (and has no voltage on it) to ground. It opens after about 5 seconds.

[rodbolt17]

ok, so now we know the control side of the relay is working.
any r/y wire will have 12V to engine ground at key on.
the ECU then completes the relay control ground path via the yellow wire.

the black wire is for the fuel pump ground to the engine block.
that relay,when the yellow wire is ECU grounded ,closes the circuit between the black and the blue for the fuel pump ground.

yes some of the diagrams bite but its way way better than the 80's and 90's.

if the key on power yellow wire to the ECU fails or has low voltage,the ECM wont communicate.
same if the ECU ground path is bad.

[Hunter#1]

ok, so now we know the control side of the relay is working.
any r/y wire will have 12V to engine ground at key on.
the ECU then completes the relay control ground path via the yellow wire.

the black wire is for the fuel pump ground to the engine block.
that relay,when the yellow wire is ECU grounded ,closes the circuit between the black and the blue for the fuel pump ground.

yes some of the diagrams bite but its way way better than the 80's and 90's.

if the key on power yellow wire to the ECU fails or has low voltage,the ECM wont communicate.
same if the ECU ground path is bad.

Bosco and Rod - This is the kind of help I needed. My problems seem to occur when this thing sits for the night and is cool in the morning. Any ideas where to go from here?

[rodbolt17]

is the ground path on the relay black wire good?
can it maintain 12V on the y/r at key on?
can it maintain the ground path from the ECU yellow wire?
can it maintain the fuel pump ground path across the relay contacts to the fuel pump?
does the fuel pump yellow red wire maintain its 12V+?

lots of things happening all at once.
lose any of it and the pump quits.
remember that pump draws over 7 amps,way more than what the ECU transistors can typically take.
so the used a relay to operate the fuel pump ground path.

that distribution block is one of those big square black doohickys with wads of wires.

there is also one for various block grounds.

at key on the ign yellow wire wakes up the ECU which wakes up the main relay which powers up that distribution block and supplies 12V+ to any device with a yellow/red wire.

about the same time the ECU drops a dime and sends a ground signal to the fuel pump relay via that yellow wire to the relay.

this causes a current flow in the relay magnetic coil closing the relay contacts.
now that blue wire from the fuel pump is,or should be,connected to the relay black wire which is or should be connected to the block.

the ONLY function of a relay is to use a very low operating current to control a much higher current.

we would not need trim relays if the operator did not mind wiring the helm with 6GA wire and switchs the size of a battery switch.

with a relay for the trim we can control a 30+amp draw with a control amperage of less that 1.

on the ECU it goes back to heat,7+ amps is a lot of heat.

[Hunter#1]

is the ground path on the relay black wire good?
can it maintain 12V on the y/r at key on?
can it maintain the ground path from the ECU yellow wire?
can it maintain the fuel pump ground path across the relay contacts to the fuel pump?
does the fuel pump yellow red wire maintain its 12V+?

lots of things happening all at once.
lose any of it and the pump quits.
remember that pump draws over 7 amps,way more than what the ECU transistors can typically take.
so the used a relay to operate the fuel pump ground path.

that distribution block is one of those big square black doohickys with wads of wires.

there is also one for various block grounds.

at key on the ign yellow wire wakes up the ECU which wakes up the main relay which powers up that distribution block and supplies 12V+ to any device with a yellow/red wire.

about the same time the ECU drops a dime and sends a ground signal to the fuel pump relay via that yellow wire to the relay.

this causes a current flow in the relay magnetic coil closing the relay contacts.
now that blue wire from the fuel pump is,or should be,connected to the relay black wire which is or should be connected to the block.

the ONLY function of a relay is to use a very low operating current to control a much higher current.

we would not need trim relays if the operator did not mind wiring the helm with 6GA wire and switchs the size of a battery switch.

with a relay for the trim we can control a 30+amp draw with a control amperage of less that 1.

on the ECU it goes back to heat,7+ amps is a lot of heat.

Explaining the therory of operation is much appreciated. Gives me a better understanding of what is occurring and why. But what tests can I do (what would you check specifically?). Remember right now it is all working, or I believe so. I'll have to wait until the problem reappears to continue my troubleshooting, which based on how it has acted will be tomorrow morning for the first couple hours of light, or until I force that pump on by defeating the system components i.e. a wire directly to battery.

[rodbolt17]

easiest way?
use the volt setting,use paper clips to back probe the connections at the pump.
place the red lead on the blue and the black lead on the engine block.
turn the key on.
you should see 0V for 3-5 seconds(or very close to it) then switching
to 12V.
what you are doing is measureing the voltage DROP along a wire.

if every connection between the pump blue wire connector and the engine block was perfect you would see 0V when the pump was running,if you see 12V that means the voltage path is to the pump,through the pump but NOT to the engine block.
that is the SAME path the current has to take.
remember Voltage DOES NOT flow its ssimply a measure of electrical pressure.
CURRENT flows and is measured in amps, current is what does the work.

think of that blue wire circuit to ground,electrons don't see connectors and relays,as far as the electrons are concerned its simply a piece of wire.

so from the pump blue wire to the engine block with the relay energized you should see less than .5V..
now open the relay or introduce a bad ground connection and you will see the voltage climb ,depending on how bad the connection is it will climb to supply voltage.

resistance checks are ok, I prefer watching a voltage drop when the device is operating,or supposed to.


think of it this way, them electrons are caddilacking down the old wire heading from a source(bar maybe) to home.
if the path is clear there is no resistance and no pressure from the source.

now them trons see a bad relay connector or the bridge is out.
they either have to slow down,pressure from the source is now pushing, or they stop.
if stopped full pressure is pushing but they cannot move.

[Hunter#1]

easiest way?
use the volt setting,use paper clips to back probe the connections at the pump.
place the red lead on the blue and the black lead on the engine block.
turn the key on.
you should see 0V for 3-5 seconds(or very close to it) then switching
to 12V.
what you are doing is measureing the voltage DROP along a wire.

if every connection between the pump blue wire connector and the engine block was perfect you would see 0V when the pump was running,if you see 12V that means the voltage path is to the pump,through the pump but NOT to the engine block.
that is the SAME path the current has to take.
remember Voltage DOES NOT flow its ssimply a measure of electrical pressure.
CURRENT flows and is measured in amps, current is what does the work.

think of that blue wire circuit to ground,electrons don't see connectors and relays,as far as the electrons are concerned its simply a piece of wire.

so from the pump blue wire to the engine block with the relay energized you should see less than .5V..
now open the relay or introduce a bad ground connection and you will see the voltage climb ,depending on how bad the connection is it will climb to supply voltage.

resistance checks are ok, I prefer watching a voltage drop when the device is operating,or supposed to.


think of it this way, them electrons are caddilacking down the old wire heading from a source(bar maybe) to home.
if the path is clear there is no resistance and no pressure from the source.

now them trons see a bad relay connector or the bridge is out.
they either have to slow down,pressure from the source is now pushing, or they stop.
if stopped full pressure is pushing but they cannot move.

Do I unplug the pump and insert paper clips in the connector, turn key on and read voltage on blue wire to block. Is that what you are saying to do? If so couldn't I just attach the red lead from the meter to the pumps terminal with the blue lead, and then take the black meter lead to the block? How do you suggest I open the relay or intro a bad ground while doing this test?

[Hunter#1]

Question - If I repeat the test in the morning when the problem has been typically presenting that Boscoe had me do earlier (with key on and relay removed check r/y wire for 12V and yellow for ground continuity) would that tell me if the ECU was bad? Or not getting 12V on the yellow lead?

[rodbolt17]

slip a paper clip down the wire on the back side of the connector.
leave the connector plugged in.
use jumper leads with alligator clips.