Megasquirt users thread to discuss all things Squirty

[Ken_T]

I've recently, bought and built a MS3 + Xpander board with a DIYBOB. Got it to fire up today on an SR20 using a diyautotune RWD SR/KA trigger wheel. Need to weld and wire in the wideband and air temp sensor before I can start tuning.

Pretty funny watching the closed loop idle do it's job holding 800rpm then stall out because air temp swings from -40c to 77c in less than a second.

[thechuckster]

ECU wiring query:

I'm assembling my ECU in an old 22RE ECU case. The ECU is a v2.2 board with MS1 chip and will run MSExtra HiRes code. With this firmware/hardware combo the injectors are run as hiZ only so I'll have a resistor pack in the +Ve supply to the 4AGZE injectors.

The injector drivers and coil-pack ignitors are mounted on the side of the cast alloy case away from the board. What gauge wire should I use for the:
A- injector FET drivers (to & from board)
B - IGBTs (from connector to IGBT and then back to plug for earthing)

I'm thinking that the the HiZ injector scenario only means 1-2 amps going thru the FETs? But what about the IGBTs that will be driving 4AGZE coipacks?

I have some 25 and 16 gauge wire to choose from atm but there's a jaycar store not far away. I'll take some pics later on today to show where I'm at.

[timbosaurus]

Genuine 16 gauge will be perfect for the coils,18 would be fine for the injector wires. You can always go heavier, and even going lighter (within reason) wouldn't be an issue. Believe it or not, its the allowable voltage drop, not wire damage, that determines wire size, as you've gotta be very undersized before you actually burn out a wire.

[oldcorollas]

has anyone used the inbuilt(ldable) boost controller?
pulled trigger on new MS2 with the fancy v3 PCB and various other bits, but hadn't heard of the EBC thing before.
got one anyway tho

pity the 18% off thing is only until US time saturday noon... need more time to think.. or organise GB's for extra bits

[o_man_ra23]

OlRollas, I too bought the EBC, but am yet to put it into full use. So if you get it going before me, let me know how it runs.

Timbo, both voltage drop and current to burn out the wire need to be taken into consideration when determining the wire size. The current to burn the wire isn't to do with the actual operational current of the device on the end, rather the size of the fuse protecting the wire (fuses protect wires, not devices). If you have a short circuit on a wire, the fuse is supposed to blow prior to the temperature of the copper conductor rising beyond the maximum allowable temperature of the insulation. If the end device fails to a short and the insulation is allowed to burn out, then you have a fire on your hands.

Choosing a fast blow fuse will allow you to run smaller wires, but at the risk of nuisance tripping under short time overload situations (blower fan startup for example)

EDIT: for this purpose, better quality wires use better insulation (ie the wires I am using utilise cross-linked Poly Ethelene (XLPE) rather than the usual Poly Vinyl Chloride (PVC) which is slower to dissipate the heat of the conductor, causing a quicker temperature rise)

[timbosaurus]

Owen, you are correct that fuses protect wires, but your design process is actually back to front compared to OEM.

Wire size is chosen to suit the load... more often than not to allow an acceptable voltage drop. Fuse rating is then chosen based on wire size... not the other way around.

[o_man_ra23]

I'm not going to argue this one properly - the reply will be too long and in-depth for this thread. All I can say is that Timbo's method is flawed - you size the fuse to the load, then the cable to the fuse. You will also need to size the cable based on the maximum let through energy of the fuse during a short circuit, and finally, if you have a really long run, or a device very sensitive to having a low voltage applied, then you calculate for voltage drop. As most devices in a car are rated to 12V and during normal running you are sourcing from 14.4V, the voltage drop on most items isn't too critical. You will be surprised how low a voltage will acheive a spark capable of ignition during cranking.

[timbosaurus]

Yeah, what would I know... I'm just a senior electrical engineer in australia's largest OEM auto manufacturer

[drew22]

Hello all thought I'd make my first post an interesting one Was running a MS2 V3 pcb on the old rolla now I have upgraded to a MS3. Running a modified cam pulley as a crank angle sensor machined to give a 36-1 setup at cam speed allowing for sequential spark and injection. All of the original sensors are picked up with a patch loom and extra wires run for the rest of the gear. Holden alloytec COP's are used for ignition along with standard injectors. Idle air controlled with vn stepper motor setup. Im happy with the results so far ticks over quite nicely just need to get it back on the rollers when I get back to work. How have you found your setups?

[o_man_ra23]

Is the VN IAC the correct unit for the DIY Autotune IAC body? The AC151 valve I purchased appears to be incorrect in its fitment down the tube (Oring fitment is incorrect - and looks different to the VN ones I found on Ebay)

[thechuckster]

drew22: very interesting to see another example of the cam pulley used as a missing tooth wheel. Just list night I was going thru the general queries thread on the MS forums and noticed someone mention that they were going do the same with a chain-driven cam.

Out of interest, why not use the factory dizzi as a CAS? or is it going to be deleted completely?

And any problems using the factory MAP sensor? I'm going to do same with my RA65 and was wondering whether it's a 0-100kpa or something else for it's range?

[drew22]

Not quite sure about the DIY autotune IAC setup, its based on a jeep one so im sure its just different enough that a gm one wont fit and jeep can charge a fortune for theirs. Ive got a mate that's a tool maker to machine up the one in the pic, just copied the dimensions from a v6 throttle body and turned up the cube . Have you taken it to an engineering place to see if they can adapt the vn one in? If you want to be really rude about it you could cut out the iac portion of a v6 throttle body tap the holes and fit barbs just looks quite rough.

With the CAS that 4AGE cam pulley was made for it with 36 teeth!!! Just had to -1 on the miller .2mm at a time. It took a few passes Really it was convenient to set up and ill ditch the distributor later on to make some more room in the front. The cam gear also has a few more teeth so it helps the resolution a bit.

I used the on board map sensor on the v3 mainboard but setting up the oe map sensor should be no probs. I was thinking of using the toyota map sensor as the baro sensor.

Its good to find some people enthusiastic about the megasquirt setup. Ive had many ppl can it thinking its a dodgy homebuilt ecu that wont preform.

[drew22]

Hers a pic of the inside of the IAC its not too difficult to machine up.

[o_man_ra23]

I have a machinist at my disposal, and bought the jeep IAC - but it doesn't fit, and I need to get off my arse and design a prototype PCB for said machinist before I can realistically ask him for further favours... Might try getting onto that this week...

[oldcorollas]

Yeah, what would I know... I'm just a senior electrical engineer in australia's largest OEM auto manufacturer

LOLburgers

Drew, thats some nice work there!
At first I was thinking "hey, you can't take teeth off the pulley"... but then I realised.. why not?
what CAS are you using with it and how close is it to the belt? or is that it poking up from behind the radiator hose?

i'm hoping to go COP with MS2 on a 4A but still undecided on how to do CAS.. crank with waste spark is easy, but cam pulley looks nice!