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Modern cars (NC miata) and engine harness


turbogrill
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Hi, 

 

What do you do with modern cars and ECU/harness? Keep the stock harness and try and keep it good condition?

 

This weekend we have annoying electrical issues, the car wouldn't start due to the immobilizer complaining. We also had problems clearing ABS related codes.

The ECU is "hacked" but it still needs to talk to the dash to work, the CAN connection in the harness seems to be flaky.

 

So something is not right with the harness, previous owner chopped up harness to connect AiM dashes and we have also done some work on it.

 

I need to do something with the current harness, can't have these issues.

 

If this would be a simplier car like the NA/NB I would probably do standalone and do a custom harness, pretty simple.

 

But it such a modern car it seems like a lot of work to go standalone and the stock ECU seems very good and tune-able. They do sell a drop in aftermarket replacement but it uses the factory harness.

 

 

 

 

 

 

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the strategy I took with e30 was rip all of the oem harness out and redo it. the drivers behind that were:

1) not wanting the old brittle wiring in there (plus it was crazy heavy!!)

2) i put a motec PDM and AEM ECU in so wiring plan was way simplified

3) I wanted a modular system that would allow a change of motor (i.e. swap to different) without having to redo anything to the rear of the primary engine harness connector at the firewall.....

 

that said if your harness has been really hacked on a lot, i'd say its time to reload. chasing electrical gremlins is not fun....

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E30 harness is a cakewalk compared to newer stuff. No immobilizer, no ABS / TC things which will cause the car to shut off or not cooperate, etc. Also fewer wires than a modern car.

 

No idea about NC miata but I’m sure many have done this before you. @NigelStu knows miatas

 

Edited by enginerd
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2 minutes ago, enginerd said:

E30 harness is a cakewalk compared to newer stuff. No immobilizer, no ABS / TC things which will cause the car to shut off or not cooperate, etc. Also fewer wires than a modern car.

 

@turbogrill what’s the car / engine?

 

exactly, that's why you just rip it out and go with after market ecu. all of the mainstream aftermarket ecu's will handle things like VVT, ABS, TC, etc. I do know @turbogrill's car (spoiler alert we are neighbors :)), and I think he'd prob be better off reloading. also stuffing a PDM into the mix makes it even more simplified, i.e. bye- bye fuses and almost all of the relays.

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5 minutes ago, atxe30 said:

exactly, that's why you just rip it out and go with after market ecu. all of the mainstream aftermarket ecu's will handle things like VVT, ABS, TC, etc. I do know @turbogrill's car (spoiler alert we are neighbors :)), and I think he'd prob be better off reloading. also stuffing a PDM into the mix makes it even more simplified, i.e. bye- bye fuses and almost all of the relays.

 

Car is 2006 Miata (2006-2015)

 

Agree on your setup being the nicest. But Custom harness,PDM and ECU is  quite a lot of $$!

 

I can do a megasquirt install on simple engine (as in datsun) but to much must crap going on with this engine for me to do it my self. VVT, Knock sensors, etc,etc,etc. Would cost a fortune to have someone install it.

 

The ME442 (seems to be decent) has a special NC version, so that would make it a little easier. No messing around with figuring out the knock algorithm or VVT phase sensing and all that stuff. 

 

Maybe buy the ME442 and a new factory harness and just remove poop that the ME442 doesn't need. The only limitation they have is that they don't support cruise control, I guess I can survive without that.

 

It's very frustrating trying to start your car geared up and ready to go and the car accused you of being a theif. All I want to do is dive bomb other miatas och get a heap of trophies :)

 

 

 

 

 

 

 

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39 minutes ago, turbogrill said:

 

Car is 2006 Miata (2006-2015)

 

Agree on your setup being the nicest. But Custom harness,PDM and ECU is  quite a lot of $$!

 

I can do a megasquirt install on simple engine (as in datsun) but to much must crap going on with this engine for me to do it my self. VVT, Knock sensors, etc,etc,etc. Would cost a fortune to have someone install it.

 

The ME442 (seems to be decent) has a special NC version, so that would make it a little easier. No messing around with figuring out the knock algorithm or VVT phase sensing and all that stuff. 

 

Maybe buy the ME442 and a new factory harness and just remove poop that the ME442 doesn't need. The only limitation they have is that they don't support cruise control, I guess I can survive without that.

 

It's very frustrating trying to start your car geared up and ready to go and the car accused you of being a theif. All I want to do is dive bomb other miatas och get a heap of trophies :)

 

 

 

 

 

 

 

I hear you on the dollars for sure. and if that plug and play ecu gets you removal of the street car mode crap that's def a great thing!

 

how much does a new factory harness cost? i mean if you can get the ECU and a new factory harness for ~1500 bucks, that would go a long way towards reducing your break risk.

 

lemme know if you are going to HH this week, we can walk through some of this stuff. i'll def be down there friday and probably weds too...need to see where the paint guy is with my miata.

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3 hours ago, atxe30 said:

 

how much does a new factory harness cost? i mean if you can get the ECU and a new factory harness for ~1500 bucks, that would go a long way towards reducing your break risk.

 

 

That might be a good approach! Seems like the ME442 only needs stuff from the engine harness inside the bay and not the other crap

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  • Technical Advisory Committee

Newer cars, so many circuits and stuff that it is risky to just chop stuff out.  Immobilizer aspect adds another level of frustration.

 

I know na/nb miatas and find even the NBs a pita for wiring - megasquirt on my '03 street/track car and there are a couple things that are still just not right.. I don't want to dig into it all to correct, so I just deal with it.   Engine swaps in NA/NB adds a level of complexity.  No experience with NC yet.

 

Pairing down a stock harness can be done, but it takes time, patience and a REALLY good set of wiring diagrams.   I wouldn't be surprised if something got cut/removed/disconnected that the car wants to see.   

 

With all the extra 'stuff', grounds are very important.  Check ALL of them

 

This is a race car, right?   Not something you'd normally (or ever?) take on the street, gets locked away when not in use?  If your main issue was immobilizer and ABS, carefully go over that set of circuits, especially grounds and any cut circuits associated with them to ensure no accidental ground/closed circuits.  Tip for immobilizer issue is to zip tie a key (with the chip in it) to the dash at the ignition cylinder and use a blank/spare key or button to start the car.  It removes the 'protection' but ensures that the car will see that chip it thinks it needs to safely go to the grocery store.

 

 

With the unknowns of what was done, the easy/quick/cheap button is to put a new complete harness in, being very mindful of ground points (get that wiring diagram out!)  and just do a harness swap.  Don't unpin anything, only disconnect stuff you for sure don't need (audio, seat adjustment, etc) until you want to start searching for those extra tenths of a second.  Reliability far outweighs the ~10 lbs of wiring/components that you may be able to remove.   

 

Options -

Opt 1: Change over to a Stand-alone with a built to need harness - cleanest install method, moderate cost/time to get it right, theoretically most reliable since you are limiting circuits/components to just what is needed. 

Opt 2:  source a custom harness for stock ECU setup you have.  $$$ and time.   There may be a 'race' harness available for the NC, but not likely (at least for a stock engine).  You'd need to find someone willing to do the work.  (such a pita....)

Opt 3: remove your current harness and go through each circuit one-by-one and repair what you need, remove what you don't, re-install.   Buy a good set of connector tools if you go this route, much easier to put a pin back in then it is to solder a wire back together and eliminates potential incorrect circuits/grounding issues (no cut ends to touch).  You'll get a sense of accomplishment, crossed eyes and carpal tunnel syndrome.  

 

 

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The stock NC ECU is pretty good and the tune they have is pretty good, unless you go >300whp turbo there is really no need for standalone from a performance perspective.

So it's a little bit of waste to swap ECU just to get a clean harness, on the other hand a race weekend costs much more.

 

The ECU is about $300 a person. I am sure everyone would gladly pay that to have a shot at the podium instead of crawling around the engine harness trying random things.

 

I think I will do standalone.

 

Thanks!

 

 

 

 

 

Edited by turbogrill
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Not for everyone, but I have found that one of the side benefits of going aftermarket ECU and building an "only what is absolutely needed wiring harness" was that it forced me to learn exactly how the ECU worked for our car.  The result is I am much more confident in trouble shooting and have a single source or truth wiring diagram.

neon wiring.jpg

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  • Technical Advisory Committee

@tneker I think I've seen that diagram before. 

Did you create that for your car?

That's some impressive work, and what a great way to have a visual diagram for comprehension of the system, duplication, and trouble shooting.

Good stuff!

 

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You have not seen a mess of wires until you dig into an C4 Corvette.  Back then on these cars everything had it's own separate power feed (for the 4 tail lights there were 4 separate hot leads and grounds (because the car is fiberglass).  This was the early age of electronic automation so they had a million wires along with ABS, theft control, etc.  We first tried a paired down harness then finally just gave up and made our own.  It is a lot cleaner and also follows common/simple logic so we can trouble shoot a lot easier.  

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