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Should I just start this wiring from scratch?

Old 12-06-2018, 06:54 PM
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Default Should I just start this wiring from scratch?


Hey guys,

My name is Cody and I'm brand new to the forums here. I've had a stock miata for a few years but just came across a good deal (I think?) On a nearly complete turbo miata project.

I am a total noob at wiring but got a car with a half wired megasquirt ms3x unit. I've tried following diagrams to complete the wiring but have just ended up being confused.

this car has the vvt 1.8 and turbo so all the sensor wires come directly into the cabin and arent connected to the stock ecu wiring. Should I just start this wiring from scratch? Is this even the right way to do it? All the necessary wires look insulated. Here are some photos.


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Old 12-06-2018, 06:58 PM
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No photos.

VVT requires some additional wires, so it's not surprising it has additional. But yes, you're going to have to map them all - and I suggest labelling them as well.

Starting over as a newb, you're going to make mistakes, but you're going to learn alot. But ultimately it's probably a wash experience wise - unless the photos reveal the guy did an absolute hack job.
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Old 12-06-2018, 07:14 PM
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Fixed the photos I believe. I traced the wires from the megasquirt (thank God they are labeled!) And they all go to the correct sensor wires. The ms3x only has one power input wire correct? The one from the main relay? Also, because all the sensor wires come in separate from the ecu harness, it is still fine to use the original ground wires on the stock harness right? Does it matter if I ground to the engine block or the chassis?
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Old 12-06-2018, 11:52 PM
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The power wire (should be white with a red stripe) is only to power the MS, it's not for powering all your sensors, injectors, etc. Well, it is, but there's no reason to bring them all into the cabin. Most wiring should happen in the engine bay. VVT solenoid should be powered off the white/red wire on the injector harness, your stock CAS signal wires should split to the CKP and CMP sensor, same with ground and power. The only wire that should end up at the ECU is the VVT solenoid signal (ground) wire. As for ground, I like to keep it as original as possible. Now I have spliced an entire NB engine harness into an NA multiple times, which means grounding nearly everything on the throttle body. But if you don't go that route (don't, unless you're me), keep the stock ground wires. So if you're trying to ground the CKP or CMP, use the same ground wire as the CAS.
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Old 12-06-2018, 11:59 PM
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P.S. I would unplug that harness from the OEM yellow connector, walk over to trash bin, and put that harness there. Then buy a PNP unit and avoid hours of headache down the road.

Test mode is your friend. Check all the sensors/inputs/outputs you can, and if anything doesn't work, trace wiring for that component only, rather than chasing grounds, power, and signal for everything all at once.

Here's your list of items to check:

gauges in TS:
TPS
IAC
CLT
test mode:
boost control solenoid
VVT
ign1
ign2
ign3*
ign4*
INJ1
INJ2
INJ3**
INJ4**
composite log:
CKP
CMP

*only if you're running sequential ignition
**only if you're running sequential injection


P.P.S you need a new overflow canister.
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Old 12-07-2018, 01:13 AM
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Curly, thank you for the very informative reply. Since this had the 1.8 swapped in, the sensors changed from the 1.6. The previous owner ran completely new wires from each sensor into the cabin. (Completely bypassing the stock harness). The only thing that is hooked up the the original harness at this point is the power and some grounds. No sensor inputs come from the original harness as they come into the cabin in completely separate wires. You're saying the correct thing to do would be to splice them into the original harness so they connect with the oem ecu connector?

you're right, that overflow tank is a glorified potato chip at this point.
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Old 12-07-2018, 05:10 AM
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Yikes. I would not want me anywhere near that wiring. Also, (unrelated), the intake manifold volume seems a bit off.
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Old 12-07-2018, 06:11 PM
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Also unrelated, but that little tray that replaces the valve cover breather cross over tube is really cool.

Originally Posted by curly View Post
Now I have spliced an entire NB engine harness into an NA multiple times, which means grounding nearly everything on the throttle body. But if you don't go that route (don't, unless you're me), keep the stock ground wires.
I'm very interested in what this looks like. Do you have a picture perhaps?
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Old 12-07-2018, 06:13 PM
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[QUOTE=tylerkun;1513951]Also unrelated, but that little tray that replaces the valve cover breather cross over tube is really cool.


HUH?
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Old 12-07-2018, 06:49 PM
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Looks kinda like this. I just like how the NB harness stays in a single bundle across the engine, VS the NA branching off in numberous places. I unwrap the entire harness, keeping the junction points, and use 2 dozen too many butt splice connectors kinda where the harness goes through the firewall by the washer bottle. Rewrap it in some split loom and voila. I wired Project Lazarus and Oregonmonís more like the vvt thread, which is just splicing connectors onto the NA harness, but did Storminínormins, my car, and a customers with a NB harness like above.
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Old 12-07-2018, 06:49 PM
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[QUOTE=matrussell122;1513952]
Originally Posted by tylerkun View Post
Also unrelated, but that little tray that replaces the valve cover breather cross over tube is really cool.


HUH?
The front of the valve cover on either side of the exhaust cam gear. Normally there is a cross over tube connecting the intake tube to the valve cover. In his picture, he has a little aluminum plate to hold up wires in place of it. I've never seen that and I think it's cool.
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Old 12-07-2018, 06:55 PM
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Old 12-07-2018, 08:02 PM
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The car does have an ls throttle body so not sure if that makes a difference in ideal intake volume? And curly, that looks amazing. I would love to get some more photos to see exactly how you routed everything. Would that be possible? I'll probably pull everything back and do that same thing.

yeah the wiring isnt done poorly in terms of connections and routing, I just think have two completely different harnesses is excessive and confusing. Splicing into the oem seeks like the way to go.
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