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"Grace Silver" MPI/06SL2-20G/MegaSquirt


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#161 speedyquest

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Posted 08 October 2019 - 05:39 PM

I think the first thing you should probably do is run a dedicated ground cable up to the front of the car. One of the common mistakes with relocating a battery to the back of the car is poor ground management. Moving the battery to the back and then using the chassis to ground the battery to the rest of the system is that it introduces a large amount of resistance to the electrical system. That ends up creating voltage drop.

And I'm guessing your first thought when I say that is "Well Allen, what about oem cars doing it?" The answer to that is they are designed that way, the engineers have built that into the whole plan for how its wired.

You really want a nice clean voltage from the battery for not just the ecu but for everything including your charging system.

To get more specific about how you might improve your ecu grounding can you tell me which megasquirt you have? That effects how they are made and therefore how they want to be grounded in some cases.

1987 Flatty Starion -- Widebody Conversion -- V-Mount Setup --  JDL Tubular Manifold  --  MX-6 Intake -- MS3-Pro -- AEM FPR  --  ARP head studs -- 3" hood exit exhaust -- Hahn Racecraft 16g --  Tial F38 Wastegate -- Tial Q Bov -- Short route piping -- 5 lug & LSD conversion -- Tubular Front End -- Manual Steering Rack Conversion -- Manual Brake Conversion -- Stack Digital Dash -- AEM UEGO -- D2 coilovers -- full GNT poly bushings & mounts -- four 8" rears -- car lightened significantly...  More to come!


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#162 Turbo Cary

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Posted 08 October 2019 - 06:33 PM

When someone says connect to ECU grounding they are referring to splicing into a ground pin from the ECU to ground.

So long as the ground you are splicing into is not a ground that the ECU does not use for switching a component on or off.

An ECU may control a positive side of a circuit or a ground side depending on what the circuit is used for. For example your fuel injectors have 12v going to them at all times, but the computer is rapidly switching the ground side of the circuit to open and close them. A ECU could apply power (such as energizing a relay for fans) to a circuit.

#163 Preludedude

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Posted 08 October 2019 - 06:48 PM

Using Scotts MS2 Plug-N-Play system....

So if I run a ground cable to front, where would you recommend grounding the battery to at the front of the car?

#164 speedyquest

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Posted 08 October 2019 - 09:16 PM

View PostPreludedude, on 08 October 2019 - 06:48 PM, said:

Using Scotts MS2 Plug-N-Play system....

So if I run a ground cable to front, where would you recommend grounding the battery to at the front of the car?

Hrm I'm not sure where I could find the wiring diagram for that ecu, but I'm sure if you asked Scott how he recommended grounding the ecu he would gladly tell you. As for running grounding cable up to the front of the car I think if you ask three different people you will most likely get three different answers. That being said, here is mine lol.

I'd run it up to the front of the car and then connect it right to the engine block on the drivers side. Then I'd ground the engine block to the chassis with another cable. Finally I'd run a dedicated wire from the ecu's main ground point and ground the other end of it to the engine block as well. For extra bonus points I'd ground the intake to the block if any of your sensors are using the intake manifold for grounding.

Yes, that probably sounds a bit overkill but doing that would ensure a fair chance at having very little voltage drop due to resistance.

P.S. This is roughly how my car is grounded, except for I'm not using the chassis at all for any grounding. Everything is done via the harness.

Edited by speedyquest, 08 October 2019 - 09:19 PM.

1987 Flatty Starion -- Widebody Conversion -- V-Mount Setup --  JDL Tubular Manifold  --  MX-6 Intake -- MS3-Pro -- AEM FPR  --  ARP head studs -- 3" hood exit exhaust -- Hahn Racecraft 16g --  Tial F38 Wastegate -- Tial Q Bov -- Short route piping -- 5 lug & LSD conversion -- Tubular Front End -- Manual Steering Rack Conversion -- Manual Brake Conversion -- Stack Digital Dash -- AEM UEGO -- D2 coilovers -- full GNT poly bushings & mounts -- four 8" rears -- car lightened significantly...  More to come!


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