I'ms surprised that HEI requires three wires to ECU. What's the function?

The key is: *shielded* twisted pairs. And signal or control pulses is usually used in pairs not three wires.

This goes like this:

VR sensor is shielded twisted pair, that's all. But I have exceptions on other three wires:

*And*, EACH wire is twisted pair for one signal each between HEI module and megasquirt that's means two pairs. The power wire MUST be separated from that signal wires that means redo of that wires for HEI. That power wire from HEI could had induced into wirings and bugged out the ECU. The current spikes on the power wire for HEI can do that easily and givng you headaches. That is why I noticed 3 wires which is not right.

Remember, no ground loops. Any twisted pairs using one ground wire is tied at one point. (ground star fashion) And that's at the one point nearest ECU.

The set up is usually had relays and interface in the engine compartment linked via harness between relays and ECU in the passager compartment.

Cheers, Wizard

Hear are the wires that go to the HEI. The ground wire goes to the ground of course.



* tach signal is a purple wire with a white trace [pin R]
* advance control signal is a white wire [pin E]
* override (cranking) signal is a tan wire with a black trace [pin B]
* ground is a black wire with a red trace [grounded to distributor case]

The tan wire with the black trace is the wire with the disconnect. If you disconnect this wire, it runs in base timing, with no timing control. Wizard, according to your principal, should any one of these three wires be left out of the shielded cable? They are all three twisted together now, but not shielded.

Sam

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If you are trying to cut down on noise from the HEI to the MegaSquirt, the only wires that would actually benefit from twisting together are the ground and R wires, if you run the ground wire to the ECU.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

The ground wire is run to the common engine block ground the ECU is grounded to, but on its own wire. The other three are twisted together. Should I untwist them?
Sam

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On a factory GM car, the module ground goes to the ECU itself. I suspect that duplicating that wiring will cut down on noise.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

Would that mean taking it to one of the relay board sensor returns in addition to the engine block ground wire? The HEI is grounded to the engine block as well.

Sam

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Use the relay board sensor returns. The HEI module also grounds through its body - THAT ground needs to go to the engine block.

_________________
"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

Thanks, I will do that.
Sam

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Where can I read about the effects of ground plane differences. This is a bit mystifying to me. I don't know if I used the right phrase. It is interesting that it would make a difference to take a ground right to the ECU instead of the engine block, when the ECU itself is grounded to the engine block. I do not doubt it is different, but would like to understand it a bit better.

Sam

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I've got a short treatment of them in my book - I've also seen them discussed in Mark Rummerick's Car Stereo Cookbook.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

Maybe I will just have to order your book. I have intended to order the trigger wheel, and have not simply because I am not sure which spacer to get. I will try to figure it out, then order both.

Sam

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