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Speedo Issues Still


Guest mcramsay

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Guest mcramsay

Right so still having my speedo picking up interference from the fuel pump. Even though I run a new shielded cable it is still picking up interference however not as bad, at standstill it only reads 30mph rather than 160.

 

I have done some reading and I think adding a capacitor into the circuit may help filter out the noise.

 

Do I put the capacitor across the speedo signal wire to earth or the speedo / Hall effect sensor +12v and Earth?

 

I am about to set the car on fire if I can't fix it...

 

My last resort is the move the speedo pick up and wiring but that is a major job with iva 3 weeks away...

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I would next try to work out if it's stray lectric from the pump itself or its wiring which the speedo is picking up. If you have a few meters of spare wire disconnect the pump wires at both ends and loop new wire direct from the battery terminals to the pump outside the car. Both earth and live. The pump will now run continuously. If no interference take the live from ecu to the pump relay but keep the loop earth. If this makes no difference then its probably not the wiring and its the pump. What sort of pump do you have? In tank should be shielded by the tank itself if the tank has a good earth and is metal. Does the tank have a good earth? Where have you earthed the pump? Is it a good earth? If the pump is an exposed type you might try shielding it with aluminium foil to earth. Do you have two pumps? If so have you tried disconnecting each one in turn to see which is the offender? Last resort try new pumps.

Don't know spit about electronics/capacitors so nothing helpful to say about that.

 

Nigel

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Guest mcramsay

The pump is a facet posiflow mounted on the rear bulkhead and earthed pretty well to the chassis. The pump runs straight off the ignition live, not through a relay, only around 1.5A operating current, the main injection pump is controlled via a relay but the wiring for that is well out the way of the speedo wiring. The main problem is my whole wiring loom for the rear of the car is taped together under carpet, and all the wiring runs past the pump. I ran a new set of shielded wiring for the speedo yesterday but I cocked up as where it goes through the bulkhead it still runs past the pump, all be it the affect on the speedo is now much less. I will try and cure with some capacitors tomorrow, if no luck then I will be running more cabling down the transmission tunnel which should get me well clear...

 

 

Things should not be this difficult to sort out!!

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Guest mcramsay

So fixed I think, I remembered I had an old acewell reed switch type sensor in my spares box, it bolted in the same hole as the Hall effect, stuck a magnet on and connected up the original wiring that has been causing the trouble. The Reed switch is non powered and simply switches between the signal wire and Earth. With the electrics turned on and everything the same to recreate the same conditions and hey presto it worked ran for an hour with the speedo in calibration mode and not picking up any signals and only counting pulses when the magnet passer the sensor, previously I have managed 5 mins without the thing going haywire. So it looks like I can rebuild the car and put the issue to bed.

 

I'm guessing because the signal is

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