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Have been pulling my 99 apart and getting it ready for turbo install, during that time I though t it would be wise to do a wire tuck and doing a mil spec connector on the firewall for the engine wiring. What I want to do is make sure I have all the wiring planned I will need to have done before I start cutting and crimping. Wanted to ask a few questions pertaining to extra sensors.
MS3ProPNP 99-2000, 47pin Deutsch HD30
Sensors removing from engine harness, I may reuse some of the wiring like +12v and possibly others to repin at the ecu.
-6 wire EGR
-2 wire VICS
-1 wire power steering
-4 wire o2
Sensors adding to engine harness to go thru mil spec connector:
+2 wires for sequential ignition(pins 2I and 2J)
+2 wires for VVT(+12v from sensor removed above and a wire to pin 2K)
+1 wire 5v reference(pin H, to be shared with oil temp, oil pressure, water pressure, possibly fuel pressure on the rail)
+1 wire oil pressure(pin C)
+1 wire oil temp(pin D)
+1 wire water pressure(Perfect Tuning gauge or TinyI/O)
+1 wire fuel pressure(Perfect Tuning gauge or TinyI/O)
Questions:
1. Can all three of the 0-100 5v pressure sensors and oil temp sensor share the same +5v ref?
2. From documentation I have seen the pressure sensors state to use chassis ground, would this be an actual ground to the chassis? I believe the grounds on the intake and head are both considered sensor grounds correct? So the oil temp would use one of those sensor grounds.
3. When running the the knock sensor thru the mil spec connector it has a single shielded wire. Would the best practice be to connect the shield wiring to its own pin so that it is only left unshielded as it passes thru the connector? Or would it be better to keep the shield intact and run it with the chassis wiring?
4. Anything else to add to this nonsense that I have overlooked?
Diagrams below are for the 99-2000 Miata from DIYPNP, appreciate the help.
All the sensors that use 5v can share the same 5v wire. From what I learned, if a sensor requires 5v, then you would use the sensor ground (This is 4F on the ecu pinout), not chassis ground.
For your flex fuel, you didn't ask but i'll mention it as I didn't know this initially. You will ground this (flex fuel sensor) to the chassis ground. Like you mentioned, grounding it off the intake manifold works for anything needing chassis ground.
You can crimp the shielding of a shielded wire to a pin and then continue it through the other side of the bulkhead connector.
Since you're already going custom, may I suggest making the ignition coils on a sub harness? That way if you ever decide to upgrade to LS Coils/IGN-1A, then you don't have to run new wires to the bulkhead, only need to re-wire a smaller sub harness section.
All the sensors that use 5v can share the same 5v wire. From what I learned, if a sensor requires 5v, then you would use the sensor ground (This is 4F on the ecu pinout), not chassis ground.
For your flex fuel, you didn't ask but i'll mention it as I didn't know this initially. You will ground this (flex fuel sensor) to the chassis ground. Like you mentioned, grounding it off the intake manifold works for anything needing chassis ground.
You can crimp the shielding of a shielded wire to a pin and then continue it through the other side of the bulkhead connector.
Since you're already going custom, may I suggest making the ignition coils on a sub harness? That way if you ever decide to upgrade to LS Coils/IGN-1A, then you don't have to run new wires to the bulkhead, only need to re-wire a smaller sub harness section.
Thank you for the info, I really like the idea of making a sub harness for the coils. 6 pin deutsch connectors are cheap as well so wouldnt take much extra effort. I think the r8 coils will be good for the power capable on this turbo though.
Have been getting in all the wiring and extra sensors so should be starting this very soon.
If you're looking at the Amphenol equivalent stuff better buy soon, lot of places are out of stock when I was buying DTM/ATM stuff last week.
These are the coils I ended up with, simply have to shave off the lowest O seal on the boot with a razor/box cutter. I'm happy at $25/coil with a lifetime warranty and I grabbed the coil connectors/pins/plugs for like $7 on amazon.
If your input goes to an ADC in the ECU then it needs to be grounded at the ECU and nowhere else. The ECU is trying to measure between what it sees as ground and whatever is left of the 5V reference. The regulator generating 5V is inside the ECU, using it's ground as it's reference. If it's a megasquirt, it's ADC runs on the very same 5V. What all this means is no matter what happens, if the 5V regulator makes 5.1V or 4.9V, the resultant ADC conversion, what actually matters, correctly represents the proportion of the ADC supply voltage. This is good because the vref reg in a MS3 is not a precision regulator, far from it.
The ECU ground is not actually ground. If you measure voltage between the ground at megasquirt and the ground at the head I bet you'll see ~300mV. That's because all injectors, solenoids, and everything else pass current through this ground between ECU and head. When you do that without superconductors you get a voltage drop. This is the 300mV you probably measured.
If you ground a sensor at the head this 300mV is going to be added to all measurements. Since all the ground currents are pulsed, this changes all the time and with load. Further, grounding even one sensor improperly can compromise the entire harness, ruining the signal of anything running on an ADC. This is because the injectors will try and ground through anything they can, introducing a voltage drop/offset. Attaching a signal ground to the head does this. This is bad, do not do this.
So, sensors that run on Vref ground at the ECU/sensor ground and nowhere else. If for some reason your "sensor" dumps more than milliamps of current on it's ground, like a LC-2 o2 heater, it must be grounded at the head and you'll have to deal with offsets or run canbus...
Flex is a digital signal and so long as everything is working correctly a ~300mV offset is not going to matter. So long as the megasquirt sees the signal swing between ~0.9V and ~2.5V or so everything will work properly.
If your input goes to an ADC in the ECU then it needs to be grounded at the ECU and nowhere else. The ECU is trying to measure between what it sees as ground and whatever is left of the 5V reference. The regulator generating 5V is inside the ECU, using it's ground as it's reference. If it's a megasquirt, it's ADC runs on the very same 5V. What all this means is no matter what happens, if the 5V regulator makes 5.1V or 4.9V, the resultant ADC conversion, what actually matters, correctly represents the proportion of the ADC supply voltage. This is good because the vref reg in a MS3 is not a precision regulator, far from it.
The ECU ground is not actually ground. If you measure voltage between the ground at megasquirt and the ground at the head I bet you'll see ~300mV. That's because all injectors, solenoids, and everything else pass current through this ground between ECU and head. When you do that without superconductors you get a voltage drop. This is the 300mV you probably measured.
If you ground a sensor at the head this 300mV is going to be added to all measurements. Since all the ground currents are pulsed, this changes all the time and with load. Further, grounding even one sensor improperly can compromise the entire harness, ruining the signal of anything running on an ADC. This is because the injectors will try and ground through anything they can, introducing a voltage drop/offset. Attaching a signal ground to the head does this. This is bad, do not do this.
So, sensors that run on Vref ground at the ECU/sensor ground and nowhere else. If for some reason your "sensor" dumps more than milliamps of current on it's ground, like a LC-2 o2 heater, it must be grounded at the head and you'll have to deal with offsets or run canbus...
Flex is a digital signal and so long as everything is working correctly a ~300mV offset is not going to matter. So long as the megasquirt sees the signal swing between ~0.9V and ~2.5V or so everything will work properly.
Thank you very much for that explanation, that was exactly what I was wanting to know but was having issues understanding completely. That's why mt.net is the best
I am going to plan everything out on paper to further wrap my head around it and make sure I only have to do this once. I keep buying nice tools to do everything as legit as I can, last thing I want to do is go thru all this and end of screwing it up.
04-20-2021, 12:59 PM
Wiring questions/wire tuck idicocracy
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