AWSX1686 (Forum Supporter)
AWSX1686 (Forum Supporter) GRM+ Memberand UltraDork
10/5/22 9:30 p.m.

Ok, so I have a 92 Miata shell, and I have put in the harness and engine from a 95 (automatic) and a manual transmission. 
 

I'm at the point that it should be ready to start, but it doesn't crank from the key.
 

I might be having a fuel pump issue too, not 100% sure. I seem to recall something that the fuel pump doesn't run unless it knows it is cranking? So I'm not sure. 
 

The car has spark. 
If I put power to the trigger terminal on the starter it does crank. 
When cranking that way it will kick off of starting fluid. 
 

I hooked the neutral switch on top of the transmission to what should be the correct wires from the auto transmission plug. 
 

I guess the main thing is, since it was a shell it's barebones and I have a lot of things that just aren't plugged in at this point. (Lights, HVAC, Cluster, etc)

 

Any input appreciated, thanks!

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
10/5/22 10:13 p.m.

It's almost impossible to stop a NA Miata from cranking, it's about the simplest circuit in the car. Ignition switch to clutch switch interlock to starter solenoid, done.

If there's a plug with bit fat wires on a switch on the clutch pedal, plug it in :)

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
10/5/22 10:14 p.m.

Oh crap, auto donor. So there's a brake switch interlock instead. Let me dig that up...

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
10/5/22 10:20 p.m.

It's called the "inhibitor switch" on a 1.6. I need to go down to the shop to get my '95 diagram.

AWSX1686 (Forum Supporter)
AWSX1686 (Forum Supporter) GRM+ Memberand UltraDork
10/6/22 12:23 a.m.

Brake switch interlock makes sense. I wondered if there was something along those lines, but I didn't see any mention in the manual swap pages I've read. 

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
10/6/22 12:54 a.m.

Just the neutral switch. This is 1994. Maybe you wired up the wrong switch. Just for fun, does it start when you're in reverse?
 

AWSX1686 (Forum Supporter)
AWSX1686 (Forum Supporter) GRM+ Memberand UltraDork
10/6/22 1:35 a.m.

In reply to Keith Tanner :

Hmmm, I'll try that in the morning. Pretty sure I got the correct switch, but you never know. I'll double check the wires I hooked to it too. 

AWSX1686 (Forum Supporter)
AWSX1686 (Forum Supporter) GRM+ Memberand UltraDork
10/6/22 1:40 a.m.

In reply to Keith Tanner :

I don't think this is required, since I didn't see this on most manual swap pages, but it is something interesting I came across that I never heard before. 
 

I'm not 100% clear, but I wonder if this undoes the "-10hp detune" for the automatic cars  

Originally Posted by STO962 View Post

Been doing a little wiring diagram and PCM pin out comparison between the manual and automatic versions of a 96 NA. Pin "1O" (That is 1 and the letter O, not a zero.) of the PCM is what tells the PCM if the car has a manual transmission or an auto in it. In the PCM pinout chart, pin 1O is labeled "MT/AT Distinction". On an AT equipped car, this circuit is left open and there should be battery voltage at the PCM pin with ignition switch on. On a MT equipped car, there is a black/light green wire that goes to ground from this pin terminal. On the MT car there should be no voltage at pin 1O with the ignition switch on and the blk/lg wire in the circuit properly connected to ground. When installing a manual transmission into a formerly auto transmission equipped car you would need to run this wire to a good grounding point. This lets the PCM know the car has a manual transmission and keeps it from turning on the CEL and setting any auto transmission codes due to the missing auto transmission control module.

Pin 1L (Brown/White wire color) is the "Load/No Load Distinction" and is used to tell the PCM what gear the car is in. Either Park/Neutral or any of the drive gears. When you remove the Park/Neutral switch of the auto transmission, you need to wire the neutral switch of the MT and the clutch switch to this circuit. Otherwise, it will set a code for this circuit and it could affect the idle quality/rpm.

Just wanted to do an update on this post for future reference for anyone doing an auto to manual transmission swap on an NA and trying to get the CEL to go out. The edited quote above applies to a 1996 Miata. After some more checking to verify the wiring diagrams and pin terminals are the same, this info would also apply to a 1997 Miata as well.

I have also looked up the info for 1994 and 1995 models. Both of these also have the "MT/AT Distinction" pin terminal on the PCM but it is in a different location. The "Load/No Load Distinction" (Clutch/Neutral switch) pin terminal is also different.

1994 uses pin 1K (MT/AT Distinction) which has a Black wire that would need to be grounded when switching from an automatic to manual transmission. 
Pin 1V "Load/No Load Distinction" (Clutch/Neutral Switch) Brown/White wire color.

1995 also uses pin 1K (MT/AT Distinction) with a Black/Light Green wire that would need to be grounded. 
Pin 1V "Load/No Load Distinction" (Clutch/Neutral Switch) Brown/White wire color.

1993 and earlier do not have the "MT/AT Distinction" function for the ECM. Also note that none of this applies to NB Miatas as they are very much different with respect to the PCM wiring and operation.

https://forum.miata.net/vb/showthread.php?t=530965&page=2

Berck
Berck Reader
10/6/22 4:40 a.m.

As I remember, the automatic transmission"detune" was only on the 1.6 engine. It had different cams and lower compression for more low end torque at the expense of top end power. 1.8 engines were the same for both transmissions. No idea what the 1.8 ECU does with the transmission information though. 

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
10/6/22 9:35 a.m.

Yeah, the "detune" is mechanical. The 1.8 auto is electronically controlled, the 1.6 is not. The "MT/AT distinction" is probably there to let to ECU know about the different idle behavior on an auto, you can't idle a stick with the transmission engaged but you can with an auto.

None of that will stop it from cranking. The cranking circuit is not affected by the ECU or anything but that inhibitor switch. You could try just jumping the switch. 

The ECU does need to know the engine is cranking because it turns on the fuel pump relay during that time, but it'll still turn over.

AWSX1686 (Forum Supporter)
AWSX1686 (Forum Supporter) GRM+ Memberand UltraDork
10/6/22 9:59 a.m.

Gotcha. Good to know!

 

So technically speaking, if I put my own push button start to the starter solenoid, and rand my own power on a switch to the fuel pump, it should run. 

 

The weirdest thing to me is that for a little bit yesterday it did actually crank with the key, but then it stopped. So maybe it is the switch going bad. Not sure if I'll get a chance to mess with it at all today, leaving for a weekend trip this afternoon. 

 

Thanks again to all!

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
10/6/22 10:14 a.m.

Just feed 12v into the cranking pin on the ECU, it should run the pump for you when it's cranking. 

Switch going bad is a possibility for sure. I've also got a car that's got high resistance in the wires to the solenoid so it only cranks intermittently when the starter button is pressed. Too many high school Best Buy employees installing alarms in its history...

I'd start with that switch of yours. Is there 12v coming in when you hit the starter switch? Does it close when you think it should be closed? Is there continuity between the switch output and the solenoid? The answer to one of those is going to be "no" :) When they're all yes, the starter will engage.

AWSX1686 (Forum Supporter)
AWSX1686 (Forum Supporter) GRM+ Memberand UltraDork
10/6/22 3:09 p.m.

Looks like either the ignition switch is being intermittent (most likely), or the transmission wasn't fully in neutral. 

I got it to crank a little bit ago after testing if it would crank in reverse. Reverse wasn't the issue, I'm pretty sure the switch is just faulty. I think I have another around here somewhere. 

 

Fuel pump isn't running best I can tell, but I have a suspicion of why. Out of time for today though, I'll check back next week. Thanks!

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
10/6/22 3:43 p.m.

The reason I asked about reverse is because it's so, so easy to get the reverse and neutral switches mixed up on the Miata transmission :)

AWSX1686 (Forum Supporter)
AWSX1686 (Forum Supporter) GRM+ Memberand UltraDork
10/6/22 11:56 p.m.

In reply to Keith Tanner :

And when it comes to times like these it's good to check the stupid little stuff like that. It's a good tip. 

David S. Wallens
David S. Wallens Editorial Director
10/7/22 11:03 a.m.

Not much to add other than thanks for the help, Keith. 

AnthonyGS (Forum Supporter)
AnthonyGS (Forum Supporter) GRM+ Memberand UltraDork
10/7/22 8:34 p.m.

So if you locate a Miata shell, what gotchas do you look for?  There is an 02 SE near me with no diff, trans or engine and kiddo loves a yellow Vert.  

AWSX1686 (Forum Supporter)
AWSX1686 (Forum Supporter) GRM+ Memberand UltraDork
10/11/22 10:02 a.m.

In reply to AnthonyGS (Forum Supporter) :

It depends how much of a shell it is. If it just needs a Diff, Trans, Engine, that's really not bad. You could buy each piece individually. 

In my case with this shell I actually got a 95 automatic for $400, it ran, but the Automatic trans was bad and the thing was rusty. I had planned to manual swap it, but the rust was so bad. Like, control arms looked like they were going to crumble, bad. Pretty sure it was a flood car. 

Then I saw this shell pop up for sale, with title, rust free, overall decent body, but the wiring harness was hacked up, no bumpers, hood, fenders, trunk, or interior. Some of that doesn't matter since it's not intended as a daily, but there were a lot of pieces to put together. So I pulled everything I could salvage off of the rusty car before I scrapped the rest and cleaned it up and started putting the shell together. 

 

So, a parts car is great for working on a shell if you can find the right deal. Separately even just the driveline adds up. ($5-900 for a 1.8l engine, $75-200 for a 5 speed trans, $250-750 for a diff depending on LSD or Open, plus probably a PPF and driveshaft, and exhaust.) 

AWSX1686 (Forum Supporter)
AWSX1686 (Forum Supporter) GRM+ Memberand UltraDork
10/11/22 2:16 p.m.

It's alive!

Definitely seems like the ignition switch was the main cranking issue. It seems to be behaving for now though. 

Fuel turned out to be a clogged pickup sock. 

AWSX1686 (Forum Supporter)
AWSX1686 (Forum Supporter) GRM+ Memberand UltraDork
10/19/22 9:12 a.m.

Hey all, got another wiring issue that I haven't found anything definitive online yet. 

So the harness is a 95 AUTO, pulled from a car, but the gauge cluster plugs don't match my cluster... Now, it is very possible that the cluster I am messing with now is not the one from that 95 auto car. So, is it an Auto/Manual thing that makes the plugs different? I have 2 clusters exactly like this that don't match up. If the auto is different I have to assume I have the auto cluster burried in a box somewhere. 

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
10/19/22 10:03 a.m.

Those aren't the cluster plugs. All NAs used the same plugs for the cluster - and IIRC the NB used them as well with a third one added.

Since I don't recognize them, I'm going to guess they could be to the transmission control unit- I don't mess with many autos and I don't even know where the TCM lives. I don't have a '95 wiring diagram available to me at the moment. One of the guys at work might recognize them.

AWSX1686 (Forum Supporter)
AWSX1686 (Forum Supporter) GRM+ Memberand UltraDork
10/19/22 10:08 a.m.

In reply to Keith Tanner :

Ok thanks. Guess I'm just blind and need to find the correct plugs in the harness. 

AWSX1686 (Forum Supporter)
AWSX1686 (Forum Supporter) GRM+ Memberand UltraDork
10/19/22 1:10 p.m.

Ok, yeah. It was me missing the obvious. There's wiring still attached to the one dash I had sitting outside. Guess the dash kinda has its own sub harness. 

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