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914World.com _ 914World Garage _ Fuel Pump Wiring Experts
Posted by: wndsnd May 17 2019, 07:53 PM
My fuel pump is in the front.
It is fed by the original wiring at the rear suspension point
If I power the fuel pump from an auxiliary 12 volt source fed from the rear, the pump runs. That eliminates the wiring from rear to front, and the pump.
If I put a meter on the pump wiring at suspension point I get a reading of hundreds of volts. How do I get Hundreds of volts from a 12 volt circuit. I am guessing a short would cause amps, not volts.
I have been changing relays, and the board. I did what Dave Darling mentions and checked out the #30 at both board relays. I had constant 12 V there I changed the fuses.
Car was run hard in the rain for a couple of days. I suspect water got into something but where? Relay board was covered. Everything else seems ok. Maybe it is not water. What do you guys think? It has to be somewhere between the board and the wiring at suspension point. Is there another connector between the suspension point and the board? Lots of questions..... Sorry.
Thanks
Posted by: Dave_Darling May 17 2019, 07:56 PM
Hundreds of volts should only be possible if you're reading off a transformer like the coil. Something very strange is going on, but you obviously know that...
--DD
Posted by: wndsnd May 17 2019, 08:04 PM
Dave, I see that pin 13 off the board feeds the pump off the board. Shouldn't I get a 12 vdc reading to ground there? I am getting like 45 volts.
Posted by: wndsnd May 17 2019, 08:09 PM
There is no coil but high voltage twin plug coil packs.. I would think if they were shorting to ground I would have more problems than just the fuel pump. They are also fused.
Posted by: Spoke May 17 2019, 08:10 PM
I assume the car won't start because the fuel pump isn't running, correct?
What type of connection do you have at the original location? Cut and spliced wire? Crimped?
What fuel system do you have? Carbs? FI? If carbs do you have a jumper on pin 3 of the FI power connector?
Follow the fuel pump power path starting at the 25A fuse. Measure voltage on both sides of the fuse.
From there check the voltage at pin 87 of the fuel pump relay K75. You can do this by pulling the relay and inserting a very small wire in the pin 87 socket hole and replacing the relay.
You may want to check the ground wire at the original location. When you measure hundreds of volts, measure each wire to chassis. For the ground wire, you should have zero volts and 12V on the other wire.
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Posted by: wndsnd May 17 2019, 08:15 PM
I assume the car won't start because the fuel pump isn't running, correct? I used a jump pack and fed the pump directly and the pump and engine ran fine.
What type of connection do you have at the original location? Cut and spliced wire? Crimped? I use crimp connectors with heat shrink I crimp twice.
What fuel system do you have? Carbs? FI? If carbs do you have a jumper on pin 3 of the FI power connector? Running Webers yes have the jumper, no changes made.
Follow the fuel pump power path starting at the 25A fuse. Measure voltage on both sides of the fuse. Have not done that.
From there check the voltage at pin 87 of the fuel pump relay K75. You can do this by pulling the relay and inserting a very small wire in the pin 87 socket hole and replacing the relay. Will do this tomorrow.
You may want to check the ground wire at the original location. When you measure hundreds of volts, measure each wire to chassis. For the ground wire, you should have zero volts and 12V on the other wire. Good Idea.
Posted by: wndsnd May 17 2019, 08:23 PM
I assume the car won't start because the fuel pump isn't running, correct? I used a jump pack and fed the pump directly and the pump and engine ran fine.
What type of connection do you have at the original location? Cut and spliced wire? Crimped? I use crimp connectors with heat shrink I crimp twice.
What fuel system do you have? Carbs? FI? If carbs do you have a jumper on pin 3 of the FI power connector? Running Webers yes have the jumper, no changes made.
Follow the fuel pump power path starting at the 25A fuse. Measure voltage on both sides of the fuse. Have not done that.
From there check the voltage at pin 87 of the fuel pump relay K75. You can do this by pulling the relay and inserting a very small wire in the pin 87 socket hole and replacing the relay. Will do this tomorrow.
You may want to check the ground wire at the original location. When you measure hundreds of volts, measure each wire to chassis. For the ground wire, you should have zero volts and 12V on the other wire. Good Idea.
Posted by: wndsnd May 17 2019, 08:24 PM
I assume the car won't start because the fuel pump isn't running, correct? I used a jump pack and fed the pump directly and the pump and engine ran fine.
What type of connection do you have at the original location? Cut and spliced wire? Crimped? I use crimp connectors with heat shrink I crimp twice.
What fuel system do you have? Carbs? FI? If carbs do you have a jumper on pin 3 of the FI power connector? Running Webers yes have the jumper, no changes made.
Follow the fuel pump power path starting at the 25A fuse. Measure voltage on both sides of the fuse. Have not done that.
From there check the voltage at pin 87 of the fuel pump relay K75. You can do this by pulling the relay and inserting a very small wire in the pin 87 socket hole and replacing the relay. Will do this tomorrow.
You may want to check the ground wire at the original location. When you measure hundreds of volts, measure each wire to chassis. For the ground wire, you should have zero volts and 12V on the other wire. Good Idea.
Posted by: worn May 17 2019, 08:29 PM
Hi Spoke,
Is it reasonable to assume some sort of inductance is creating the high voltage? Also, is it reasonable for me to copy your diagram?
As for the car, I think I would ask if 12 volts is present at the relay board and whether providing 12 volts at the fuel pump relay, bypassing said relay will run the fuel pump. Then one could keep swimming upstream towards the key switch.
Posted by: Spoke May 17 2019, 08:37 PM
Hi Spoke,
Is it reasonable to assume some sort of inductance is creating the high voltage? Also, is it reasonable for me to copy your diagram?
As for the car, I think I would ask if 12 volts is present at the relay board and whether providing 12 volts at the fuel pump relay, bypassing said relay will run the fuel pump. Then one could keep swimming upstream towards the key switch.
The large wire coming to the relay board on pin 14 comes directly from the battery. This provides the 12V to the 25A fuse and then to the fuel pump relay. 12V power from the ignition key comes in on pin 8 and powers pin 86 of the FI power supply relay K74.
Agreed the only way to get a high voltage is with inductance and changing currents. Maybe the high voltage coil packs are causing some disturbance on the relay board.
Posted by: wndsnd May 17 2019, 08:38 PM
Hi Spoke,
Is it reasonable to assume some sort of inductance is creating the high voltage? Also, is it reasonable for me to copy your diagram?
As for the car, I think I would ask if 12 volts is present at the relay board Yes I have 12 volts at socket #30 and whether providing 12 volts at the fuel pump relay, bypassing said relay will run the fuel pump. To do this I would direct wire from socket #30 to pin out #13?[i]
Then one could keep swimming upstream towards the key switch.
Posted by: wndsnd May 17 2019, 08:42 PM
Hi Spoke,
Is it reasonable to assume some sort of inductance is creating the high voltage? Also, is it reasonable for me to copy your diagram?
As for the car, I think I would ask if 12 volts is present at the relay board and whether providing 12 volts at the fuel pump relay, bypassing said relay will run the fuel pump. Then one could keep swimming upstream towards the key switch.
The large wire coming to the relay board on pin 14 comes directly from the battery. This provides the 12V to the 25A fuse and then to the fuel pump relay. 12V power from the ignition key comes in on pin 8 and powers pin 86 of the FI power supply relay K74.
Agreed the only way to get a high voltage is with inductance and changing currents. Maybe the high voltage coil packs are causing some disturbance on the relay board.
Coil packs aren't firing if engine isn't running?[i]
Posted by: wndsnd May 17 2019, 08:46 PM
I will do the suggested tests tomorrow. Thank you for your help. I will report back. At this point I am thinking of finding a new good board with new relays. Both boards that I have have lousy sealing so moisture could be raising havoc underneath.
Posted by: mtndawg May 17 2019, 11:31 PM
How many volts do you have on the positive (15) side of the coil?
Posted by: Specracer May 18 2019, 03:42 AM
LONG SHOT question, is the battery fresh in your multimeter, and giving you solid correct info?
Posted by: wndsrfr May 18 2019, 05:31 AM
LONG SHOT question, is the battery fresh in your multimeter, and giving you solid correct info?
Posted by: Spoke May 18 2019, 05:54 AM
Hi Spoke,
Is it reasonable to assume some sort of inductance is creating the high voltage? Also, is it reasonable for me to copy your diagram?
As for the car, I think I would ask if 12 volts is present at the relay board Yes I have 12 volts at socket #30 and whether providing 12 volts at the fuel pump relay, bypassing said relay will run the fuel pump. To do this I would direct wire from socket #30 to pin out #13?[i]
Then one could keep swimming upstream towards the key switch.
Shorting pins 30 and 87 on the fuel pump relay should make the fuel pump run with our without the ignition key turned on.
Posted by: wndsnd May 18 2019, 09:43 AM
How many volts do you have on the positive (15) side of the coil?
No Coil, Hall Sensor on crank, electronic XDI2 ignition with HighVoltage Coil packs.[i]
Posted by: wndsnd May 18 2019, 09:43 AM
Hi Spoke,
Is it reasonable to assume some sort of inductance is creating the high voltage? Also, is it reasonable for me to copy your diagram?
As for the car, I think I would ask if 12 volts is present at the relay board Yes I have 12 volts at socket #30 and whether providing 12 volts at the fuel pump relay, bypassing said relay will run the fuel pump. To do this I would direct wire from socket #30 to pin out #13?
Then one could keep swimming upstream towards the key switch.
Shorting pins 30 and 87 on the fuel pump relay should make the fuel pump run with our without the ignition key turned on.
[i]I will try this[i]
Posted by: wndsnd May 18 2019, 09:44 AM
Hi Spoke,
Is it reasonable to assume some sort of inductance is creating the high voltage? Also, is it reasonable for me to copy your diagram?
As for the car, I think I would ask if 12 volts is present at the relay board Yes I have 12 volts at socket #30 and whether providing 12 volts at the fuel pump relay, bypassing said relay will run the fuel pump. To do this I would direct wire from socket #30 to pin out #13?[i]
Then one could keep swimming upstream towards the key switch.
Shorting pins 30 and 87 on the fuel pump relay should make the fuel pump run with our without the ignition key turned on.
I will try this[i]
Posted by: wndsnd May 18 2019, 09:46 AM
LONG SHOT question, is the battery fresh in your multimeter, and giving you solid correct info?
I know it it not. I will change out now[i]
Posted by: Superhawk996 May 18 2019, 10:29 AM
If your meter is operating correctly and you are getting voltages significantly higher than 12 volts, you are getting flyback voltages induced from somewhere.
Flyback is when the magnetic field around and inductor collapses after being turned off. Most relays have a flyback diode in them that will short this high voltage spike to ground to keep it off the supply line. Cheap relays from Radio Shack or auto parts stores often don't have proper flyback diodes.
Induced Voltage = L dI/dT where L is the coil inductance and dI/dT is the instantaneous change in current. Shutting off current to a coil (or relay primary) via switch (or points) equals a very high dI/dT and high(er) voltages up (potentially to hundreds of volts) can be induced from a 12 volt source.
Do you have any relays that are being opened and closed rapidly?
If you have a defective ignition coil with a bad (open) secondary you can get induced voltage spikes onto the 12 volt primary line as the primary circuit is cycled by the points (mechanical or electronic) and the flyback voltage is induced on the primary line rather than being "absorbed" into the secondary.
https://www.allaboutcircuits.com/textbook/direct-current/chpt-15/inductors-and-calculus/
Posted by: wndsnd May 18 2019, 10:50 AM
Fixed!
I pulled the relay board and WD40'd the whole thing. I continuity tested between pin 14 and the 25 amp fuse, then to socket pins 30 on power and fuel pump relays. All well.
I went to front and pulled two known good headlight realys and replaced both relays.
Replaced battery in Meter for good measure.
Powered everything up and went down to suspension console. Found 12V!
Turned off ignition and went back to console, connected fuel pump wires and went back to ignition. Turned on and the fuel pump kicked on.
Thinking water saturated board and with the WD 40 and cleaning it got sorted out.
BTW Replacement board had no continuity between pin 14 and 25 amp fuse socket or power relay socket#30 and fuel pump relay socket #30.
Now on to other productive stuff.
Thanks again World.
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