fuel pump voltage
Discussion
Thanks for the input, i cleaned up all the connectors and got a drop of .5v at the wire leading from the relay (pin 87 in the middle) to the black bkock connector , all other relay voltages were fine. When i test at the black block connector with the loops and black wires, it increaes to 1.2v, and then on the fuel pump side of the inertia switch it goes up to 1.4v and then then 1.7 at the last block connector behind the seat, which is an improvement on the 3.5v I had yesterday. Didn't have a chance to see if thats enough to get the pump to push enough fuel through.
I did a drop test on the pump by running it on a direct feed from the battery and that alone gave a drop of .6v It's a new pump albeit it aftermarket from Powerspark. Im not really sure if it's any good as it sounds like a rattly bee hive.
I had to call it a day half way through tracking down the fuse, but so far it looks as if it shares the alarm fuse.
I did a drop test on the pump by running it on a direct feed from the battery and that alone gave a drop of .6v It's a new pump albeit it aftermarket from Powerspark. Im not really sure if it's any good as it sounds like a rattly bee hive.
I had to call it a day half way through tracking down the fuse, but so far it looks as if it shares the alarm fuse.
Edited by SwanJack on Tuesday 2nd May 00:04
SwanJack said:
Before I started going through the maze of TVR electrics I made up a test lead from another 12v battery which was charged to 12.33 volts, spade connectors at the end all joints soldered. I had 12.33v at the spade connectors. I hooked the spades up to the pump and it ran, but showed 9v, would this indicate a pump fault?
Your most recent post doesn't tie up with this earlier post?Penelope Stopit said:
SwanJack said:
Before I started going through the maze of TVR electrics I made up a test lead from another 12v battery which was charged to 12.33 volts, spade connectors at the end all joints soldered. I had 12.33v at the spade connectors. I hooked the spades up to the pump and it ran, but showed 9v, would this indicate a pump fault?
Your most recent post doesn't tie up with this earlier post?I did voltage drop tests all along the positive side of the fuel pump circuit and found ever decreasing voltage drops as I got closer to the relay. In the absence of any obvious faults in the wiring, would this drop simply be caused by electical degradation over time, coupled with TVRs inadequate fuel circuit wiring to start with (as mentioned in another post I've read on here)?
Measuring the voltage at the pump is still the right thing to do to see what you actually have, fuel flow will be relative to this.
If you now see that you have a loss of 1.7v from the battery to the positive pump terminal and if we use 10A for current then ohms law of V=IR, then the resistance in the positive line in total is 1.7/10, so 0.17 ohms, if your negative line is good that should leave you with around 12v at the pump if the battery is around 13.7v with the engine running, if you have less than this then you must also have a resistance and associated volt drop on the negative side.
On my pump I have a 2.2uf capacitor connected from the pump negative to earth as well as an earth wire, not wanting to hijack your thread but can anyone confirm if this is correct, do you have one?
If you now see that you have a loss of 1.7v from the battery to the positive pump terminal and if we use 10A for current then ohms law of V=IR, then the resistance in the positive line in total is 1.7/10, so 0.17 ohms, if your negative line is good that should leave you with around 12v at the pump if the battery is around 13.7v with the engine running, if you have less than this then you must also have a resistance and associated volt drop on the negative side.
On my pump I have a 2.2uf capacitor connected from the pump negative to earth as well as an earth wire, not wanting to hijack your thread but can anyone confirm if this is correct, do you have one?
Paulprior said:
Measuring the voltage at the pump is still the right thing to do to see what you actually have, fuel flow will be relative to this.
If you now see that you have a loss of 1.7v from the battery to the positive pump terminal and if we use 10A for current then ohms law of V=IR, then the resistance in the positive line in total is 1.7/10, so 0.17 ohms, if your negative line is good that should leave you with around 12v at the pump if the battery is around 13.7v with the engine running, if you have less than this then you must also have a resistance and associated volt drop on the negative side.
On my pump I have a 2.2uf capacitor connected from the pump negative to earth as well as an earth wire, not wanting to hijack your thread but can anyone confirm if this is correct, do you have one?
The capacitor will have been fitted in an attempt to cure radio interferenceIf you now see that you have a loss of 1.7v from the battery to the positive pump terminal and if we use 10A for current then ohms law of V=IR, then the resistance in the positive line in total is 1.7/10, so 0.17 ohms, if your negative line is good that should leave you with around 12v at the pump if the battery is around 13.7v with the engine running, if you have less than this then you must also have a resistance and associated volt drop on the negative side.
On my pump I have a 2.2uf capacitor connected from the pump negative to earth as well as an earth wire, not wanting to hijack your thread but can anyone confirm if this is correct, do you have one?
SwanJack said:
Penelope Stopit said:
SwanJack said:
Before I started going through the maze of TVR electrics I made up a test lead from another 12v battery which was charged to 12.33 volts, spade connectors at the end all joints soldered. I had 12.33v at the spade connectors. I hooked the spades up to the pump and it ran, but showed 9v, would this indicate a pump fault?
Your most recent post doesn't tie up with this earlier post?I did voltage drop tests all along the positive side of the fuel pump circuit and found ever decreasing voltage drops as I got closer to the relay. In the absence of any obvious faults in the wiring, would this drop simply be caused by electical degradation over time, coupled with TVRs inadequate fuel circuit wiring to start with (as mentioned in another post I've read on here)?
I am of the same opinion as the above posted by Paulprior
You really need to be checking what voltage is at the pump and re-check it every time you clean or repair a connection, volt-drop checks will point to the poor connections but voltage at the pump when it's running is the important thing
There always have been volt-drops and always will be volt-drops along cable, the longer the cable the more the volt-drop, the problem is that if you rely solely upon volt-drop tests you could fool yourself into thinking there is a fault where all is good
If you supply the pump directly from the battery - Does the vehicle run good and is there 12 volt or more at the pump terminals?
If your answers are yes to the above questions, with some fault finding you should be able to get 12 volt or more to the pump with the original car wiring
Check if there is 12 volt or more at the supply side of the fuel pump relay using the battery negative terminal for your multimeter negative test lead
If there is 12 volt at the supply side of the relay you can now test backwards towards the pump
If there isn't 12 volt at the supply side of the relay you will need to test forwards towards the battery
Always use the battery negative terminal for your multimeter negative test lead when checking positives
Always use the battery positive terminal for your multimeter positive test lead when checking negatives
The above saves the confusion that can be caused if there are both bad positives and negatives in a circuit, fix the negatives first and then fix the positives
Belle427 said:
Probably easier to run some better quality cables with no connections in it, the route isn't that tricky.
Good postAs posted above
If by chance you are attempting to run a pump that consumes much more current than the original pump, you will need to check the cables max current capacity and rewire the complete fuel pump circuit if the cable isn't heavy enough
If the pump consumes a similar current to the original pump, the factory wiring will do the job
Bear in mind that should you rewire the pump circuit you must make sure that all the load carrying cables are uprated, it doesn't matter about the size of relay control cables as they can stay as is, also uprate the fuses accordingly
Penelope Stopit said:
Belle427 said:
Probably easier to run some better quality cables with no connections in it, the route isn't that tricky.
Good postAs posted above
If by chance you are attempting to run a pump that consumes much more current than the original pump, you will need to check the cables max current capacity and rewire the complete fuel pump circuit if the cable isn't heavy enough
If the pump consumes a similar current to the original pump, the factory wiring will do the job
Bear in mind that should you rewire the pump circuit you must make sure that all the load carrying cables are uprated, it doesn't matter about the size of relay control cables as they can stay as is, also uprate the fuses accordingly
SwanJack said:
Penelope Stopit said:
Belle427 said:
Probably easier to run some better quality cables with no connections in it, the route isn't that tricky.
Good postAs posted above
If by chance you are attempting to run a pump that consumes much more current than the original pump, you will need to check the cables max current capacity and rewire the complete fuel pump circuit if the cable isn't heavy enough
If the pump consumes a similar current to the original pump, the factory wiring will do the job
Bear in mind that should you rewire the pump circuit you must make sure that all the load carrying cables are uprated, it doesn't matter about the size of relay control cables as they can stay as is, also uprate the fuses accordingly
I viewed the motorsport-club topic you linked to and am surprised nobody pulled the OP up on her/his mistakes
There is no way that anyone should be soldering cables to relays, the heat damages the relay and also the relay can't be quickly replaced or disconnected for testing
If carrying out the modification using crimp on terminals for the relay wiring then yes the modification is a good one apart from one major problem that seems to have been overlooked - If there is a wiring problem on your fuel pump supply cable it can only get worse, by using a supply cable with a problem to switch a relay in the boot will work for now but fail later, you really do need to be sure that there is or isn't a problem with the supply cable.
If the cable to the pump is good yet failing due to it's low current carrying capacity then you can carry out the modification as at the link you posted but if you do carry out the modification be sure not to solder any wiring to any components, use crimp-on lucar terminals for the relay not crush-on
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