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Old 02-09-2008, 04:09 PM   #1
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Default More wiring problems

I downloaded a pdf from the web claiming to be for the 1995 miata wiring. Half of it is WRONG.



This is part of the performance circuit that I cut out of the PDF to illustrate my problem. You'll notice the ignition coils. Theres a grand total of 5 wires going to the coils. Not on my car. This is out of the 1995 diagram I downloaded. Also indicates that the wires going from the tach output of the coils into the harness to position on the computer marked 2I. Wrong. No 2i exists in my harness. Also indicates a wire going to the datalink connector, gauge cluster (Tach) and back to 2i. Wrong. I've tested the position on teh datalink connector it claims, labeled "IG-" for cont back to every pin on the PCM harness. Nothing. So, with the factory computer, did my tach just MAGICALLY WORK!?
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Old 02-09-2008, 04:14 PM   #2
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You don't have a '95 but a '95-1/2 car. Sorry there is no wiring diagrams for these, not even a factory workshop one.

You have to figure it out yourself, it is kindof like a '95 and '96 hybrid ...

Your tach and coils are controlled like on a '96 car, but your ECU connectors are like on a '95. Most likely the wire colors are different than a '96 too.

Your tach doesn't just magically work. it works like on every '96 Miata: the stock ECU creates a square wave and feeds it to the tach. IIRC you won't have the pin (it is not 2I, and IIRC it is different than the '96 too) in any electric schemes but might find it in forums.

On '94 and '95 Miatas (yours is neither of those), pin 2I is the ECU pull-up, the coils ground this and as a result a square wave is fed to the tach.


I helped BikeInDirt setup his AEM EMS for a '95 in his '95-1/2 and he had to solve the same tach issue. His coils and wiring were stock for an ECU tach driver and the AEM EMS being for a '90-'95 didn't have such. He just ended up with either a couple of bucks for a transistor to generate his own square wave or just paid FM for their tach device (which is the same thing - just assembled and tested). I don't remember but most likely he just bought the premade driver from the FM site.

Last edited by j_man; 02-09-2008 at 04:28 PM.
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Old 02-10-2008, 04:38 AM   #3
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I have this.



Tested on a bench with an oscilloscope for a +12 volt square wave. I can't find the fuggin pin on the ECU harness where its supposed to go. :(
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Old 02-10-2008, 12:12 PM   #4
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Cool Then you just have to find the tach wire.

Some flashback ... IIRC it was an ECU harness pin which in the '95 manual is shown as not used (the pin/wire should be missing in a '95), but it is there in the '95-1/2
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Old 02-10-2008, 05:04 PM   #5
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Well according to my documentation the only unused pin in the harness should be 1F, so I'll have to check and see if theres a wire there or not. Nice to know theres not a wiring diagram for my car.

http://spreadsheets.google.com/pub?k...A0Z3FkV_q0Wjbg
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Old 02-22-2008, 04:48 PM   #6
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wtf is the deal with this?
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Old 02-22-2008, 05:14 PM   #7
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Should be 1F
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Old 02-22-2008, 05:21 PM   #8
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Quote:
Originally Posted by paul View Post
wtf is the deal with this?
The 1.6 and early 1.8 cars took the tach signal from the igniter (which is built into the coils on the 1.8 model.) The later model cars take the tach signal from the ECU. The change between these two systems was made halfway through the '95 model year, not at the same time as the OBD-II transition.

That's the deal.
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Old 02-22-2008, 09:39 PM   #9
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Originally Posted by olderguy View Post
Should be 1F
I'm back in town but still haven't had time to further investigate this.. It snowed agian while I was gone. Soon as I know, I'll definatly report back but I believe you're correct.. the only undocumented possible wire is 1F because in my harness as stated what *SHOULD* be the tach wire is empty.
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Old 02-22-2008, 09:51 PM   #10
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elesjuan, are you running a standalone MS? sorry if i overlooked that detail.
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Old 02-23-2008, 03:10 AM   #11
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Yeah, fully standalone. Coils don't even have the tach output pin, either.

Just checked the harness, and 1F does have a wire there. Looked like black and red stripe. Imagine that! Colder than hell outside so thats far as she goes tonight.
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Old 02-23-2008, 02:52 PM   #12
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DING DING DING DING DING DING!!


I didn't wire it up yet, but used a jumper and tested for cont. between pin 1F and the IGN- test point under the hood. WORKS!! W00T!

So in a while, if I feel like it, I'm gonna go ahead and move my tachometer output wire onto 1F and report back again with results.

On another problem note.. I went and powered on the car, no fuel pump running and no connection to my PC. Tested a few point inside and megasquirt IS getting voltage, but won't power up. Took it inside, hooked it up to STIM and nothing. Swapped out the processor which was supposed to be good, I've been using it.. for my old processor that I fried one of the injection outputs on.. Guess what powered on immediately? Yep. Removed that proc, installed the "good" one that I've been using, powered on again. Went ahead and reflashed it just to see if it was maybe bad flash in the ROM.

Gonna let it sit tonight and try again tomorrow, normally if you let it sit for 12 or more hours, it won't power on when you try it. Was actually stuck at a friends house for 2 hours switching ignition on and off over and over and over and over until it finally powered up.
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Old 02-23-2008, 06:04 PM   #13
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Quote:
Originally Posted by elesjuan View Post
DING DING DING DING DING DING!!

I didn't wire it up yet, but used a jumper and tested for cont. between pin 1F and the IGN- test point under the hood. WORKS!! W00T!


Nice Now go put it in some of the FAQs of this site - I might forget what it was until the next time someone asks me again ...




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Old 02-23-2008, 06:24 PM   #14
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Always carry a back up EMB for when your MS takes a ****.














j/k
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Old 02-23-2008, 06:56 PM   #15
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Quote:
Originally Posted by olderguy View Post
Always carry a back up EMB for when your MS takes a ****.
j/k
You mean the stock PCM? I'm honestly not even sure the car would run with the stock PCM anymore. Removed all emissions controls, about to remove MAF from the intake tract, wideband.. I think it'd run in limp mode if I gave it narrow band o2. I don't care.. I've got Unlimited tow service with my auto insurance.

Btw.. Dick..
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