So the plan was, since my RX-7 is down for a while, I was going to drive EvanB's Championship-winning Miata at Nationals. Picked car up, got on lift at work to finish skidplate install after the subframe replacement, noticed that the diff mount was broken. 2 days before the GLDiv National Challenge. Oh well, this is what chains are for. Chain up the PPF so it doesn't flop around too much, go to Challenge, win MR after making a few runs pinging off the limiter in 2nd gear because there is no tach and I can't hear/feel the engine over the incredibly washboarded course.
Berk, this thing needs a tach if a rotary doofus like me is going to drive it. 90-93 MSPNP + MSM engine = no simple way to run a tach.
Next weekend (two days ago) we replace the diff mount (which I keep calling the diff uterus). All is well but the trans really hates shifting. Replace the runny silvery stuff in the trans with a special blend of 85W140 and Dexron VI. Trans shifts like butter and no longer makes scary noises. Now about that tach...
MSM engine has "dumb" coils. They get power, ground, and the primary side is controlled by the engine computer. So I splice the two ECU-controlled leads with diodes and supply them to the tach. Of course, this does nothing because there is no 12v on the line for the grounds to switch. So I grab a handy 460 ohm resistor and splice that in from power. Still no tach. I'm not seeing any switched power with the engine running, just a pulsating ground, and I accidentally bump power to the circuit with my Power Probe. Engine stalls. Won't restart. Maybe I fried the diodes somehow, yank those out of the circuit! Nope, no ignition. Check the leads on the coils. The "D" lead on the coil conenctors is a dead soldier, no vague-ground like it was connected to anything.
Berk berkity berk berk berk. Have about 44 hours before I have to leave for Iowa, in this car. I just HAD to have the tach working...
Vague plan is to call you-know-who tomorrow and whine and beg for a schematic and any idea as to what I probably fried, then shove the computer to a guy we know who repairs electronics.
And if that doesn't work, I wonder how fast I can put struts in my Volvo and run in Prepared Front. With tires that are... umm... in Evan's basement two hours away.
Would a 99-00 ms2 help you out?
What I need is a time machine so I can go back and kick myself in the nuts before I try to mess with it.
Vince (our electronics guy) is Da Man. If anything can be fixed, he can do it. But first we have to identify what failed. I see nothing visually and can only ID a vague electronicky odor in the case. None of the transistors look popped.
When I fried the flyback transistor in my 1.01 box, it was definitely something diagnosable by eye. Blackened the circuit board for a few mm.
clearly it's time you switched over to the dark and simple side....e30 ;)
j/k though....wish I could help out here, but definitely not in my expertise. Out of curiosity I don't really get the need for a tach, whether you can hear the engine or not. Maybe his car has short gearing or something, but I generally launch and shift to 2nd when it bangs off the limiter a few times, and don't touch the shifter again for the rest of the run (barring a stupid spinout like at GLDivs last year, of course). Did you expect to need to be shifting a lot in the Miata?
Did you SEE the runs I posted to YouTube? 1st gear was insta-spin, 2nd gear was insta-spin when the boost came up, 3rd gear you could actually drive instead of just keeping the tail behind the front but corners were still kinda sketchy under power...
IIRC the limiter is set at only 6500. The car is a frickin' beast even at only 8psi.
Adding insult to injury: Just broke the cork on my bottle of Elijah Craig. ARE YOU DONE SCREWING WITH ME, WORLD??
edit: fixed the cork. video evidence of beastitude: https://www.youtube.com/watch?v=kdSV-b91isw
also https://www.youtube.com/watch?v=JeqwJMKIFYs for maximum Initial D styles
Knurled,
Just so you feel a little better, I fried my MS3 once trying to get the stock tach to work in my old SVO. Turned out I fried a transistor and the crank position sensor. Felt like such an idiot. I fixed it, but it took a lot of time and energy to figure it all out. It was a big huge reminder that if it ain't broke, don't fix it. It sucked. Sorry man.
Jcamper
irish44j wrote:
Out of curiosity I don't really get the need for a tach, whether you can hear the engine or not. Maybe his car has short gearing or something, but I generally launch and shift to 2nd when it bangs off the limiter a few times, and don't touch the shifter again for the rest of the run.
Yea, I agree with you (which is why I never really got around to fixing it). On a normal course with rally tires it doesn't need to come out of second, at least the way I drive it.
RossD
PowerDork
8/5/15 7:34 a.m.
Texas Instruments LM2907 takes the signal from the VR sensor and outputs voltage. If you look starting at page 9, they use this chip for tachs. My thought would be to use one of these and a single LED for redline.
Added this thread to my watchlist. Let me know if there i$ any help that I can provide; overnighting parts from japan, etc.
If I don't hear from MSM by noon then I'm going to do what I can to prep the Volvo. Noon is the bogey time for information.
Let me know the verdict, I can throw the rally tires in ZB's truck.
By MSM you mean DIY autotune?
Only a slightly unrelated note, I watched those vids. That little thing is beast status! Is it just the stock Torsen rear end? How is that thing holding up? Good luck with your issue man, hope you get it resolved!
It is a clutch-type LSD from a non-turbo FC RX-7. When I got it the diff was pretty much open but I shimmed the clutch plates and it has been fine since.
kylini
HalfDork
8/5/15 12:59 p.m.
Good luck. I have nothing to add since I don't know how cars work.
I'm 99% that it's the transistors, but he doesn't want to take a guess and would want the exact part number. Which he won't have. So no Miata at Nats.
Well it's already dead...what harm can guessing at the transistors cause?
That was my attitude but he didn't want to touch it.
Should be able to look up the specs of any transistor just based on the number on it. They get another very similar transistor from another manufacturer or whatever. We used to have to do it all the time in college EE classes...
Got any numbers on those bad boys? I'll try to help but you might be out of time.
New plan: Evan gets a MS3Pro or something, because his car needs rotational idle and bang-bang and other turbo awesomeness (it's at ten now, it needs to go to Eleven) and I drive one of his other cars at Nationals on someone else's rally tires.
One of these days I'll get to drive my own car again at a rallycross 
On the bright side, I get to transit in a car with A/C and a kickass stereo to bump all sorts of weird metal/J-pop fusion crap for twenty hours.
When you run bang-bang antilag at an autocross it is amazing how easy it is to swap ends until your brain gets used to it. Also corner workers cover their ears a lot. It is fun.
It kinda does both of those things now...
Well, in its current state pre-failure. Which pisses me off to no end on a personal level. I'm going to grouse about it for a very long time. Breaking my own E36 M3 is one thing, but it bothers me greatly when I break other people's E36 M3.
I never really understood the idea of driving someone else's car hard because you're not responsible for it. Well, no, you ARE responsible for it, and you morally have to repair what you break, only you don't get to reap the longterm benefits of said repairing other than a general warm feeling in the scruples region of the brain.
Which is probably why Evan is letting me drive his Subaru. I just am not allowed to WORK on it 
It'll be okay, I have a lot of 2.5RS experience. Step 1 is trust in the steering. Step 2 is check the oil level Every. Frickin. Run. That is also steps 3 through 8.
The regiment elects to have it repaired!
At least I didn't break the Subaru. Except for putting the GRM stickers on wrong.
