Megasquirt users thread to discuss all things Squirty

[knightrous]

With my 20V, I use all the stock ground wires (including the sensor ground wire) in the stock loom and haven't experienced any issues so far with my DIYPNP. No fluctuation of TPS or sensor signals in general while cranking.

What voltage does it sag to when cranking?

[nuk1ear]

good question about voltage flucuation. Ill check the log, heading home from work now. I can post up the log and my MSQ too.

[nuk1ear]

ok my cranking voltage is 9.9V so that shouldnt be an issue right? Still add grounds etc i guess

[o_man_ra23]

You should have the ecu grounded to the body, head, and block. You should also have heavy gauge wire grounding the battery to the body, block, head and alternator (I like to go overboard with these things to prevent future faults). The body to block wire should be a flexible type as it will move a lot. The braided wires seem to work well for this.

[nuk1ear]

I understand yeh, but also the battery is in the front, engine in the rear. Can only ground the battery to the body really. But ill make some better ground wires for the block/head to body

[thechuckster]

fwiw: I once encountered a mid-mounted fibreglass kit car with battery up front - had chronic wiring issues (compounded by a very random and shitty wiring loom). They'd run a heavy-duty earth cable from battery up front to the rear (bolting it to the engine/box subframe and from that to the engine block). Unfortunately they missed an earthing point in the cabin where the big cable terminated onto a bolt and then ran down to the motor. The bolt was covered in corrosion and the surfaces of the two heavy-duty crimped lugs were also covered in crud.

After cleaning up all the surfaces at the bolt and bolting it up tightly (instead of finger tight) at the cabin earthing point, many problems went away.


I'd suggest the thickest-gauge cable you can run going from battery to engine block, then at the battery a thinner cable going to chassis at the battery. From the engine block you can then run a similar thinner cable from block to rear chassis.

You sensor earth solution (taking them to the intake manifold) is ideal. I wouldn't bother changing that bit.

[nuk1ear]

i re-did the sensor/ecu/coil packs ground to a large terminal bolted to the block. Ill add a couple more 4/8ga cables from the gearbox to the chassis and engine block to the chassis. I dont think my earth was ok cause everything went to the earth (sensors, ecu, coilpacks) and it was actually on a support bar which bolted to the manifold and engine block. This time just to the engine block with a more solid mounting.

[WDE_BDY]

Timbo hooked me up on some sweet connectors, pics to come but very very happy.

Callum

[The Witzl]

My sure fire method of solid earthing is:

1. 0ga or 2ga from battery neg to chassis (max. 400mm length). Use M10 bolt
2. 0ga or 2ga from chassis to engine block (500mm length). Use M10 bolts, and chose a SOLID point on the block
3. 8ga from cylinder head to chassis. 300mm max length. Use M8 bolts
4. Earth the ECU, coils and engine electrics to the cylinder head (normally there is a stock point on the intake manifold, or otherwise go directly to the head). Use M8 bolt
5. Earth sensors (TPS, intake air temp, water temp, MAP sensor, AFM, etc) to the dedicated ECU sensor ground output.


Never had any earthing issues following this method.
Make sure all connections are solid, terminals crimped well, bolts securely fastened to a CLEAN metal surface, etc.

[thechuckster]

Ideally you want the thickest cable going from battery directly to the engine block. A rear-mounted battery using chassis to provide earth up to a front-mounted engine can be problematic for some people. However, many have had success (I didn't).

[The Witzl]

Ideally you want the thickest cable going from battery directly to the engine block. A rear-mounted battery using chassis to provide earth up to a front-mounted engine can be problematic for some people. However, many have had success (I didn't).

It's all about how good your connections are, not just the size of the cable.
It's no good having 3000A welding cable, if you bolt it down with an M6 bolt and 10ft-lb of torque to a painted bolt hole..... You need CLEAN metal on metal contact, with good solid torque maintaining pressure and minimising contact resistance.
You also need to ensure you have good quality, tight, battery terminations!


In my RA28, i had a boot mounted battery - just a standard car battery, using those fancy gold plated battery terminals.
It had voltage stability issues, and cranking the engine was shithouse (starter struggled).
... turns out those crappy gold plated terminals didnt contact with the battery terminals very well.

... so i upgraded to a sealed battery with M8 threaded termainls. The difference was instant.

So yeah - tight contacts. Metal on metal.
Cant fail.

[o_man_ra23]

In my RA28, i had a boot mounted battery - just a standard car battery, using those fancy gold plated battery terminals.
It had voltage stability issues, and cranking the engine was shithouse (starter struggled).
... turns out those crappy gold plated terminals didnt contact with the battery terminals very well.

They weren't the Jaycar ones were they?

[The Witzl]

Doesnt matter where they come from.... i dont rate 90% of those types of battery terminals.

[TTV8RA23]

Can anyone tell me whether the factory injector output on an MS2 is high impedance output or low impedance output?
Cheers
Simon

[knightrous]

Factory outputs each will handle 4 hi-z injectors or 1 low-z.