MS in boot -- grounding.

[beefeater]

Hi All,

I'm in the process of re-wiring my car for the MegaSquirt install and had some questions around grounding etc.

I'm moving the battery to the boot/trunk and will be installing the Megasquirt in the same area to keep it out of the way...

All the literature I can find basically says that ALL grounds have to run back to a central point in order to reduce EMI / noise in the vehicle. This will be difficult in this instance as the MS will be grounded direct to battery in the back of the car. Sensors will still be ground to the MS of course...

What I'm wondering is:
1. Why is grounding to the chassis normally advised in all the MS docs -- is it just for convenience?
2. How critical is it for non-ECU circuits to ground to a central point? I'm thinking coil driver grounds, lighting, etc. Can I use a distribution block at the front of the car and run the feed back to the battery?
3. Normally when moving a battery to the boot, you run one +'ve feed to the front of the car, ground the battery to the chassis and ground the engine to the chassis as well. Is this still advisable for the MS, or do I need a dedicated ground from engine -> battery?
4. Is there a 'minimum distance' that I should keep the MS / harness from power or earth leads in order to reduce noise? I was thinking of running the MS harness through the frame on one side, and power / grounds for the battery on the other.
5. Any other advise on reducing noise? Best practices etc.?

Sorry if these are obvious questions... This is my first EFI install and would like to get it "right" while the car is still in pieces, rather than have issues later on

[jsmcortina]

What I'm wondering is:
1. Why is grounding to the chassis normally advised in all the MS docs -- is it just for convenience?

Actually it shouldn't be advised in any docs. All the ones I know of say to ground to the engine.

James

[beefeater]

What I'm wondering is:
1. Why is grounding to the chassis normally advised in all the MS docs -- is it just for convenience?

Actually it shouldn't be advised in any docs. All the ones I know of say to ground to the engine.

James

Thanks -- at second glance you are correct!

Question still stands though -- is there any reason this is preferred instead of to the battery?

i can do either with where the ECU is mounted but would prefer battery if possible...

cheers.

[john.p.clegg]

I have a '60s Lotus elan (fiberglass body) with the battery in the boot...my problems were

1 Low voltage at Ms when starting

2 EMFs causing noise (lots of)

Cured by running heavy power and earth leads to the Ms (front of the car) and shielding ALL the sensor leads ,and then sorting them into two groups those that cause the EMFs and those affected by EMFs and shielding the two groups from each other...grounding the screens at one end only...

John

P.S. Overkill maybe but it stopped it spluttering to a halt after 10 miles of noise confusing the processor..

[billr]

On the other hand, I have a Corvette with fiberglass and the battery in the rear, only ground to it is via the frame (factory stock). I have never had noise issues and even run some wiring in-and-about the wasted-spark coils/wires. I have found the MS3/V3.0/MS3x combo to be pretty immune to electrical noise. Try with the battery and MS in the rear, you can always add heavy cables for power/ground later, if needed.