Having spent ALL DAY metering the megasquirt wiring loom on my car and finding NOTHING fundamentally wrong with it I wonder if any electronic
guru's would be willing to speak to me online or via U2U about a couple of niggles I'm having.
Basically electrics to me are no problem but electronics are a higher level and I'm finding it hard to comprehend where I may be going wrong or
making a mistake. I need advice on why it's better to ground one end of a screen cable rather than the other and how to go about getting rid of
electrical noise (If I have it I'm just not sure)
Getting desperate now as I'm ready for sva if I could only get to the stage that the engine would start first time every time the key is
turned.
I don't want to offend anyone but I'd rather if you were not a guru that you didn't reply with what may not be a logical answer.
IF you connect both of them to earth you can get something called a ground loop.
My brain doesn't work beyond that point but if you look it up on the net you should find some answers...
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IF you connect both of them to earth you can get something called a ground loop.
If grounding the screen on the VR sensor is preventing the car starting, this would tend to suggest you have a short between one of the signal wires and the screen.
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If grounding the screen on the VR sensor is preventing the car starting, this would tend to suggest you have a short between one of the signal wires and the screen.
Ah see now you are all asssuming I have ground loop problems. I reckon I have fuel pump interference problems that are affecting the spark moment. I
also nee to find out the pro's and cons of which/what items to use to filter out any noise. Where I should and should not group items of
equipment (relays and sensor wires. Whether I can feed certain items off of one fuse without risk of a feedback interference to more sensitive
electonic items etc etc.
This is why I wanted to speak to a Guru. I don't want to spend a whole weeks holidays trying to get this thing going by having various stabs in
the dark at what MAY BE a guesstimate of an answer.
But thanks for your input anyways so far.
This is one of the trickiest areas in electronics and vehicles.
Vehicles are a perfect noise generator and it is not always possible to turn off the noise source to achieve a result.
If you know anyone with an oscilloscope you can borrow then this is the best visual way to check noise input. Some is inevitable but the level of
noise is the key.
Grounding the shield at the engine is a way of 'extending' the shield protection along to the input. This is because it's the engine
end that is generating the noise signal, so extending the shield affords protection.
ECU's in their own right are also 'noisy' that's why design is important, along with signal isolation and seperation.
Personally I didn't get a clean crank signal till I completely isolated the wiring of the sensor and gave it a seperate route.
Battery main cables should be avoided and the worst culprit, alternator wiring should be given a wide berth.
FI pumps are noisy but if kept clear of any MS inputs should be OK. Not heard of this as a specific item to avoid. Again a scope on pump wiring would
show this up.
Bit general advice but hope it helps.
EDIT: Re-read your post again, I'm assuming you are having trouble with the crank signal, right?
It's important it is the correct way round, there is even a special section on this in MS manual.
[Edited on 30/10/08 by Rob Lane]
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EDIT: Re-read your post again, I'm assuming you are having trouble with the crank signal, right? It's important it is the correct way round, there is even a special section on this in MS manual.