Da Groj

So around 2 years ago, Loren parted out a Miata he had picked up. It was supercharged (JacksonRacing - probably an M45), had a wideband and some other gauges, timing controller, fuel card, a couple other gizmos. I bought all that junk, with the intention of putting it in my car. It wasn't a 100% kinda thing, for me anyway, as the stuff was on an NB (second gen) Miata, and mine is an NA. Both 1.8s, but, well, you know. Biggest question was whether the "dummy" throttle body would fit. Anyway, being how I roll, the parts sat while I did other stuffs. Some of that stuffs included searching the interwebz to try to find out if an NB supercharger kit would fit on an NA. No clear answer, but the signs collectively pointed to yes.

Soon, opportunity knocked, and a plan was concocted to git'r'done while codriving the Fastiva while Ben was away on walkabout. Well, that came and went...although I did eventually test-fit the dummy throttle body, and it is a match, so, full-speed-ahead. Well, half-speed anyway. I think Ben got back over the summer at some point. I've lost track. But the Fastiva is fun...

Well, after a few discussions and some eavesdropping and more reading, I figured the way to go was to ditch all the electronic gadgets and just go Megasquirt. Even just saying that is intimidating. So the plan became to revert the electronics and stuff in my car (modded ecu, timing controller, timing advance) back to stock, put in the wideband, get the Megasquirt, tune it without the supercharger, then put on the 'charger and then retune it from there.

I got the wideband, boost gauge, and voltmeter in this weekend, put back the stock ECU, removed the Bipes timing controller, and reset base timing, to stock 10 btdc (for now).
Yeah, big deal - gauges in a Miata. But I'm pleased. Electrics is my weak point, I'm a crappy solderer, but I managed, all the joints are heatshrinkwrapped, and it all worked at the first turn of the key (and kept working). And, good vacuum and the charging system is healthy. No surprises on AFRs with the stock ecu.

So, here's what for me is a challenge: My '94 Miata is OBD1, but it has a 4 wire o2 sensor. I've got the narrowband output of the wideband o2 sensor spliced into the stock signal wire to the ecu (so the computer gets it's narrowband afr info and the car runs nicely). The other 3 wires I left connected to the old narrowband, which is wiretied under the hood. I understand that the old o2 sensor has a heater (even though it's OBD1), and if I cut those heater wires, at best I'll get a CEL (which I don't want to deal with). The internet says I can get two 50w-100ohm resistors in parallel between the heater wires to trick the ECU, and cut out the old o2 sensor. BUT, it doesn't heat up. Even after a decent drive, whereas it shoulda been several hundred degrees...nothing. Would a dead o2 sensor not heat up? I guess I need to shave a little insulation off the heater wires and see if there's current in them? Once I get the Megasquirt, it's not an issue at all, but I'm learning, and this has me curious. (edit: just read a bit more, and just 'cuz it's OBD1 it still - obviously - can have a heated o2 sensor).

Anyway, gotta order the Megasquirt, learn how to datalog, and keep up my momentum before another 2 years goes by...

You're going MS, anyway. The car is running. O2 is working. CEL is not currently on. Don't stress about it! Drive it until you're ready for the next step.

When you get the MS, you install it. Wire the WB output of your O2 controller to the MS. Be happy. At that point, you can do what you want with the NB sensor. Leave it in there to plug the hole that it occupies.

You're worrying about stuff you really don't need to worry about, right?

Not worrying - curious. Most of this stuff is new to me. And there's only one sensor bung, so either I have to pull the header to get another bung done, or remove the stock sensor.

Wait... didn't you already remove the stock sensor?

I guess I didn't understand your question. Too many words.

Okay, so you're saying that it's a 4-wire O2, and the OBD1 is going to choke on no heater in the circuit? That doesn't sound right. OBD1 shouldn't be that sophisticated. I'm not saying it's not, it might be... in my mind, it shouldn't be. But, Mazda did do some weird stuff with the 94-95 model years. If that's the case (you've installed the WB, wired in the simulated NB input, and you're getting a code due to no heater in the circuit)...

The simple solution: Hijack the stock O2 SIGNAL wire and run the WBO2 simulated NB output to it. Plug the NB sensor into the stock harness so that the heater itself is actually in the circuit! Use a piece of wire or something to tie the NB sensor someplace safe (like to the exhaust... that heater WILL make it hot).

With that, the ECU will see the heater that it wants to see. But, the SIGNAL is coming from the WB that's in your manifold, rather than the NB that's hanging in free air.

Make sense? You could wire in some resistors to simulate the heater, but just using the stock O2 sensor means you don't have to source those resistors!

My guess is that even without the heater connected, it probably won't throw a code. What probably WOULD throw the code would be when the ECU detects that it's taking too long for the O2 signal to read a correct value. In other words, it's probably not looking at the fact that the heater circuit is good (as an OBD2 would), but IS looking at the RESULT of the heater functioning. No heater = O2 signal voltage out of range for longer than expected.

From here: https://www.miata.net/garage/faultcodes.html

The only two codes related to O2 are:
15 Heated oxygen sensor (inactivation)
17 Heated oxygen sensor (inversion)

Translation:
15 = No signal... dead or unplugged O2 sensor
17 = Signal connected backwards (unless inversion of the signal is a failure mode that I'm unaware of)

But, nothing about the actual heater circuit. Shouldn't set a code for that at all as far as I can tell. OBD1 = Dumb as a box of rocks. VERY basic diagnostics.

Loren wrote:The simple solution: Hijack the stock O2 SIGNAL wire and run the WBO2 simulated NB output to it. Plug the NB sensor into the stock harness so that the heater itself is actually in the circuit! Use a piece of wire or something to tie the NB sensor someplace safe

^^^THAT is exactly what I did. I guess I didn't explain it well in my first post.
What's got me scratching my head is that the stock sensor, now just tied up under the hood and connected (except for the signal) does not get hot. It's really not an issue - I know I could leave it as is, until I get the Megasquirt, at which point it all gets pulled. But I'm curious. It should heat up: dead sensor? OBD1 funky wiring leads to nowhere? I hadn't thought of looking up potential CEL codes, so thank you for that - good to know it seems that if I should decide to remove it before 'squirting that it probably won't make a CEL. But that still leaves me wondering why it doesn't heat Next time I fuss with it I may expose a heater wire and break out the voltmeter to see if there's powah...

Yeah, you can check for power to satisfy your curiosity. It's either got no power or the heater is dead. Really doesn't matter, you're not going to use the sensor OR that power source. You don't have enough time as it is, focus on the stuff that matters!

You could also check the resistance of the heater on the sensor itself. It's just a coil of wire that heats up. If it reads infinity, it's open. If it reads something in the hundreds, it's probably fine. If it reads zero ohms or close to it, it's somehow shorted and has probably blown a fuse.

But, again... you're wasting your precious time.

always check the spark plug bearings first.

Wait...what?!
Heh. No bearings on my sparkplugs - I upgraded to bearingless years ago. I highly recommend it.

Good for you Steve. I paid a mechanic just to change a flasher switch after cutting my arm and wrenching my back trying to get at the damned thing two different ways. You are fighting the great fight against old timers disease. There is something to be said for not trying to keep a car stock. So much easier to work on when it's ugly.

lol thanks Doug.

Still haven't put together the scratch to purchase the Megasquirt. So I got started replacing the top. New fancy pvc/rubber rain rail. Lightly used top on a frame I picked up (from Andy) a good while back. Didn't finish that, either...

You need to tow it to a performance shop, smoke up some BBQ and drink Margaritas on your pool deck until you get the call, "Mr. Frank, your car is ready". Hell I would even be willing to give up a few weekends to help you make the BBQ and Margiritas.

Race cars don't need no soft top. Matt finally got his megasquirt figured out on his turbo. Boosted is boosted, right?

Solar wrote:You need to tow it to a performance shop, smoke up some BBQ and drink Margaritas on your pool deck until you get the call, "Mr. Frank, your car is ready". Hell I would even be willing to give up a few weekends to help you make the BBQ and Margiritas.

Let's make it happen!

twistedwankel wrote:Race cars don't need no soft top. Matt finally got his megasquirt figured out on his turbo. Boosted is boosted, right?

Lol - Matt lives life on 2 hours sleep a night. He's The Man!

So let him sleep over.

Top's done. New rain rail has no compost in it, and thus the car smells a LOT better! I figured it was the upholstery...
Found a heater hose on the way out. Two steps forward...

And just as an observation, stock ECU keeps AFRs in the 10-11 range at WOT at higher rpm. Figured it was rich, but not quite that much.

Yeah, the stock ECU is stupid rich at WOT. That's why you can get away with a 10% overclock on the ECU. It leans it out by 10%... and it's STILL rich!

So the new heater hose is sitting on the shelf in the garage. Whole helluvalotta good that does...
And I've ordered the Megasquirt! Happy birthday/tax refund to me!!

Nothing to see here...