fuel pump wiring

[Martin Hoskisson]

does anyone known what the ?"in series resistor " is linking the orange wire to the black/red wire that powers the pump.Its situated just before the pump om the chasis member

[Chassis 33]

Martin, do you have a V8 or V6?
I dont recall having one on my V6 mind, however i would guess it goes in the power side (+12v) rather than the earth side of the circuit.

Regards
Iain

[Martin Hoskisson]

Thanks Ian it's a V6. I'll need a repacement as it's broke, don't know what I'm looking for or where to sorce it,

[dickymint]

Welcome Martin and stay tuned. Can't help you myself but soon enough somebody will

[Chassis 33]

dickymint said:

Welcome Martin and stay tuned. Can't help you myself but soon enough somebody will

WEDG1E...don the leotard and come to the rescure...

hm...sorry to keep asking the questions...is the loom typically all black? What age is your wedge?

Only ask cos before i totally re-did the wiring on mine (series 1 FHC) to my own diagram, the large red/black wire that went all the way from the engine bay to the pump went directly to one of the main ignition relays with no resistor. and the only orange wire is one of the six coming from the ford 'ecu' and i think that was one of the three went to the dizzy. Not aying youre wrong in the slightest, just figuring if im in position to help.

Do you have a copy of Steve Heaths 'Bible'?

Regards
Iain


>> Edited by Chassis 33 on Thursday 7th April 23:48

[wedg1e]

Have to admit that, despite ransacking my files and even the internet, I can't find a definitive answer as to (a) why the resistor is included or (b) what value it should be.
In the case of the V8 cars, some have the resistor and some don't. It's shown on the Rover/ Lucas diagrams, but no value is given.
As for the V6, I don't recall my Tasmin having the resistor fitted. I wasn't in the engine bay or near the pump (IIRC I had to replace the plate that the pump sits on).
The only reasons I can think it was needed are to help interference suppression (though a choke would be better) or (more likely) to limit the current that the pump could take, perhaps for safety reasons in the event of a stalled pump. As far as I know the pumps were rated at 12V, so it's not there to reduce the voltage. The fuel pressure regulator (in the fuel distributor on the K-Jetronic) should take care of over-delivery by the pump, so it's not to reduce the pump speed.

In short: dunno. I'd guess at 10 Ohms and about 50 Watts as a starting point, if I was going to source a replacement.

[martin hoskisson]

thanks again local car people say its probable radio supressor ,the loom is black ,car is '84. so i think i'll just run it and keep my fingers crossed

[GreenV8S]

I think Mark adams mentioned this in one of his many helpfull posts. As I understood it, the purpose was to extend pump life by running at a lower voltage where the pump had excess capacity. If the voltage is dropped too far then there would be a danger that the pump miht be unable to meet the pressure/flow requirements of the engine at peak power, which would be rather disasterous. So to be on the safe side if you aren't sure about the spec it might be better to remove the resister and just plan to replace the pump more frequently.

[wedg1e]

Cheers Peter, I consider myself corrected...
Make the pump last longer? The very idea...

[dilbert]

Wired in series with the inductance of the motor windings in the pump, it'll reduce the power of the sparks in the motor, unless it's brushless.

Even if it's a brushless motor, it'll still prolong the motor life, improve radio reception, and improve the life of the relay that control power to the fuel pump.

It's an anti arc/spark resistor. Don't worry about fuel/sparks, the pump will be designed to be safe even without the resistor.

Edited to say:

This has to do with excess energy in the windings of the motor as GreenV8S says, but it's also very likely to be 10ish ohms at 50ish Watts.

>> Edited by dilbert on Thursday 14th April 00:38

[GreenV8S]

dilbert said:

it's also very likely to be 10ish ohms at 50ish Watts.

I don't know what the normal spec is, but isn't that resistance rather high? If you're looking for a couple of Volts drop at say five Amps, you'd ony want fractions of an Ohm in there. Or do without to be on the safe side. (Wouldn't a capacitor in parallel be a more effective suppressor?)

[dilbert]

GreenV8S said:

dilbert said: it's also very likely to be 10ish ohms at 50ish Watts. I don't know what the normal spec is, but isn't that resistance rather high? If you're looking for a couple of Volts drop at say five Amps, you'd ony want fractions of an Ohm in there. Or do without to be on the safe side. (Wouldn't a capacitor in parallel be a more effective suppressor?)

Spot on, I didn't even think about the math to be honest. But yes, even 10ohms is pretty big for the application.

The actual value is going to be dependent on the actual motor current under normal circumstances, and I have no crystal ball. On the other hand I just considered the 10ohm 50Watt suggestion as being a generic low value high power resistor.

Properly done all of the suggestions about resistors, capacitors and inductors (choke) are probably correct. Calculation of a proper snubber will involve appropriate vector/complex aritmetic to derive a filter with poles and zeros at the appropriate frequecies to absorb unwanted energy. These calculations could lead to any combination of resistance capacitance and inductance, with both series and/or shunt connection.

Capacitors are commonly used as snubbers, but this is due to their comparitive lack of expense compared with coils of any kind.

Sadly most auto electricians have difficulties connecting the wires up right, let alone devising the correct snubber network.