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Old 12-19-2008, 05:57 PM   #1
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Default 1.6 MX5 Wiring Problem need Help ????

Hi all, First up i would like to say what great forum you guys have here, i was lucky to find it lol

Anyways here is my problem, I have brought a 1989 1.6 fuel injected 5 speed MX5 motor, My plan is to drop this engine into a another mazda body which is non injected and no ECU.
As far as i can see i have two options here, One is to use a after market ECU like the Megasquirt Kit, Or Two is to use the Factory ECU and loom that i got with the motor.

Now with Option two is how much of the factory wiring harness can i use ie: AFM, TPS, coils, ingniter, CAS, Fans, Fuel pump, temp.
By removing what i don't need from the harness will the ECU still work ??, what i would like is a diagram of the wiring in its cut down forum to make this work.??


Option one is using the megasquirt what i need to know is what xtra's or mods do i need to do or get to make this motor run on basic sensors,TPS, coils, ingniter, CAS, Fans, Fuel pump, temp. Also with the megasquirt once installed can i Not use the Air flow Meter or is this not possible.

I am trying to keep cost of this project low at the moment as funds are short at this time of year, So the megasquirt is going to be my last option or untill funds come avallible. So if anyone here can shed some light on my problem or a easy way to get this project up and running it would great.

Cheers
Dr.

Last edited by drbogg; 12-20-2008 at 03:42 AM.
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Old 12-19-2008, 09:37 PM   #2
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Originally Posted by drbogg View Post
Now with Option two is how much of the factory wiring harness can i use ie: AFM, TPS, coils, ingniter, CAS, Fans, Fuel pump, temp.
By removing what i don't from the harness will the ECU still work ??
With the OBD-I cars, you can remove pretty much everything that's not directly related to running the engine. There are a couple of things (like the charcoal canister purge solenoid) that you'll need to put a resistor across to prevent a CEL, but for the most part the wiring in these cars is pretty privative.

Quote:
what i would like is a diagram of the wiring in its cut down forum to make this work.??
Then draw one.


Quote:
Option one is using the megasquirt what i need to know is what xtra's or mods do i need to do or get to make this motor run on basic sensors,TPS, coils, ingniter, CAS, Fans, Fuel pump, temp.
You will ideally purchase a GM-style intake air temperature sensor to replace the stock one that's built into the AFM. $22.25 including pigtail. That's it for parts. As to mods, they're all Right Here. You need to do the "purple box" PWM IAC mod, you need to configure two spark output channels, and you need to set up two input channels for the CAS. Everything else is optional.

Quote:
Also with the megasquirt once installed can i Not use the Air flow Meter or is this not possible.
The Megasquirt operates on MAP alone. It wouldn't know what to do with an AFM signal. Toss it.
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Old 12-20-2008, 03:27 AM   #3
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With the OBD-I cars, you can remove pretty much everything that's not directly related to running the engine. There are a couple of things (like the charcoal canister purge solenoid) that you'll need to put a resistor across to prevent a CEL, but for the most part the wiring in these cars is pretty privative.
Thanks Joe for your info what type of resistor should i use ?? and is there anything esle i need to look out for ?? also i may not be the sharpest tool in the box, could you please explain what you mean by this "prevent a CEL" as i am not up with all the terminolgy.

Cheers
Dr.

Last edited by drbogg; 12-20-2008 at 03:40 AM.
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Old 12-20-2008, 11:37 AM   #4
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Well, even the privative OBD-I ECU does have some basic diagnostics in place to tell when a solenoid has failed completely- either an open or short circuit. It does this by measuring the current flow through the appropriate channel with the device in question is active. If there is zero current, it will assume that the device is disconnected or has failed open. It will thus store a fault code and illuminate the Check Engine Light (known in MazdaSpeak as the MIL or Malfunction Indicator Light) to alert you to this condition.

Here is a list of the relevant fault conditions for an OBD-I Miata. The list is slightly in error as the '90-'93 cars obviously don't have EGR, and codes 4, 25, and 36 don't show up in the '92 factory manual either, but you get the idea.

Assume that you have decided you enjoy murdering baby seals and adorable kittens, and have thus removed the charcoal canister and purge valve. You'd need to place a resistor between pins 1B and 2X of the ECU (where the purge valve used to be) to prevent the ECU from noticing that it has gone. The value of said resistor will be determined by the DC resistance of the purge valve. I just measured mine at 24.6 ohms, and I'd expect that a 100 ohm, 2 watt resistor would probably be sufficient.
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Old 12-20-2008, 07:19 PM   #5
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Well once again i thank you for your very informative reply to my post, as i have had no exprerence with these mazda miata, and only using the engine for another project because it was dirt cheap, i have found finding good information is very hard.

As for murdering baby seals and adorable kittens, i am not sure if you are having a go at me or what ??, compared to your country, were i live We contribute less than 1% off total world greenhouse gases,This is equal to only six months' growth in China's emissions. Natural uptakes of CO2 over Australia's land and exclusive economic zone area absorb half again more than this. Our net contribution to global CO2 emissions is already negative, Beside all the B/S i am hoping to run this engine on LPG or Methenol to cut my emissions.

I thank you again and i have to say this is one of the best forum i have found for information on this make of car, keep up the great work.

Cheers
Dr.
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Old 12-20-2008, 08:46 PM   #6
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As for murdering baby seals and adorable kittens, i am not sure if you are having a go at me or what ??,
Relax, it's called a joke.

(or, What Would Jeremy Clarkson say?)
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Old 12-23-2008, 02:57 AM   #7
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Originally Posted by songli View Post
Now that is a lot of brass air fittings Wholesale Tools With Free Shipping World Wide From China Distributor there is just about every type
of air fitting that you could want. Wholesale prices too. I guess these could be used as small water pipe fitting also. I
used some of the parts to make my babington wvo burner.
What has this got to do with my post ?? it looks a bit like spam to me


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Old 12-23-2008, 10:22 PM   #8
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Yup. He's banned.
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Old 01-04-2009, 09:15 PM   #9
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Hi all once again lol

Ok i am slowly working this wiring out, but i have come up with another small problem its to do with the engine check light, in the wiring diagrams its showing two yellow/black wires one goes to the injectors and one goes to the engine check light now in my wiring loom i only have one yellow/black wire that goes to the injectors ?? what am i missing here ? also can i add a wire to the ECU plug for the Check light there is a spare spot in the plug ??



Cheers
Dr.
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Old 01-05-2009, 03:05 AM   #10
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There is no provision on the MS to drive a check engine light. What exactly do you want to do with it?
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Old 01-05-2009, 03:11 AM   #11
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thats the beauty of a MS, no CEL. I sigh in relief every time I turn the key on my standalone to never see that light come on for even a second before cranking.

99% of the time, especially with obdII, the CEL is for something stupid and emissions related.
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Old 01-05-2009, 03:26 AM   #12
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For what it's worth however, the CEL is tied to +12 internally within the instrument cluster, and the other side goes on the yellow / black wire to ECU pin 1E, which provides a closure to ground to turn it on.

There are only so many different color combinations, and some of them get re-used for different functions. Just because two wires are both yellow and black does not mean they go to the same places. The Y/B wire that drives injectors 2 & 4 is a whole separate entity from the one that drives the CEL.

Last edited by Joe Perez; 01-05-2009 at 10:52 AM. Reason: CEL tied to +12, not +5
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Old 01-05-2009, 03:38 AM   #13
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Sorry for the misunderstanding guys, at this time i am not trying to use a MS (later i will when the dollar gets better) What i am doing is installing a 1.6 MX5 motor into my Mazda1000 ute and need to incorporate the new motor wiring into my utes wiring, and i wanted the check light to work to help diagnosi any problems with the STOCK ECU if i get any as i had to strip down a full wiring loom. Most people that run these utes(pick ups) here in Oz use rotary's but i wanted to a bit diff, as there is not alot of helpfull forums around that mod these engines that is why i am asking here. I don't want to step on anyone's toes here i know you miata owners are pretty sensitive going by some of the post i have read lol.

"There are only so many different color combinations, and some of them get re-used for different functions. Just because two wires are both yellow and black does not mean they go to the same places. The Y/B wire that drives injectors 2 & 4 is a whole separate entity from the one that drives the CEL."

I understand that mate thats why i posted the pic's it shows two y/b wires at two diff locations on the ECU , but as i said my wiring loom has only one But has the spare slot in the connector that corresponds to pin 1E, ??



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Old 01-05-2009, 11:03 AM   #14
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I'd forgotten you were working with Aussie hardware, there. Most of what I have in terms of documentation is specific to the North American cars, and while all the cars are usually pretty similar in terms of wiring, I have observed differences in the RHD vehicles before.

No idea what to tell you, other than that the CEL has its own connection to the ECU, I'd wager that it's 1E on all the cars, and it sounds like it's time for some investigative work. Since you've still got the whole MX5 there, I'd start by tracing the wire back from the instrument cluster. The first stop it should make is at X-19, a large 14 position connector which, on the LHD cars, is located as shown:



If you're lucky, it might just be exactly opposite on your (presumably) RHD car.
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