So the shop I took the Miata too says it needs a new PCM. After a quick Google, it looks like this is a different term for ECM or ECU. Mazda said the OEM replacement part is $1300! First off I'm blown away by the price. Are these things really that expensive? What other choices do I have? Junk yard diving, Ebay, or upgrade I suppose. What would you guys recommend?
The engine and electrical system is hosed. transplant LSx immediately!!
Megasquirt (with a turbo) is the only solution.
http://www.flyinmiata.com/salvage/search.php
Second page of results shows multiple ECUs.
Grtechguy wrote: The engine and electrical system is hosed. transplant LSx immediately!!
Tommy Suddard said: Megasquirt (with a turbo) is the only solution.
You guys gonna come help me do it?? 
....Wait! Megasquirt turbo on an LSx! It's the most complicated Miata project.............
in the world!
....Wait! Twin Megasquirt with two sets of sequential turbochargers on an LSx! It's the most complicated Miata project.............
in the world!
Fixed that for ya.
Though i'd be more tempted to twincharge one using (in part) the supercharger they nestle into the valley on those newer Vettes.
You forgot to add nitrous.
how about one of those turbos all the way at the end of the exhaust too?
And under body neons!
Uh...sorry, that slipped out.
Anyways, I'm looking for a used PCM now, and planning on doing this myself.
What about a Megasquirt PnP? Sure, you're going to have to tune up, but it's going to be a fraction cheaper than the new OEM unit, and you have room to grow.
Derick Freese wrote: What about a Megasquirt PnP? Sure, you're going to have to tune up, but it's going to be a fraction cheaper than the new OEM unit, and you have room to grow.
It should give you a little more power through AFM removal and waaaay better full throttle tuning. Better mpg too!
What would the PNP do to emmisions?
Depends on how it's tuned.
Shops love to diagnose the ECU/PCM/whatever as a problem if they don't understand what's happening. But it very rarely is. I'd do a lot more troubleshooting first. Give us a call.
I would maybe believe a bad ECU on a 20-25 year old japanese car, the caps DO give out.
But on yours? Which i think is a.... 97? No. Shop is likely dumb. Call Keith.
<3, HalfTrac 
HT, it's a 2001.
Well according to the shop, Mazda says its the PCM. They said the problem is it's incorrectly reading the position of the cam, making it think the timing is super retarded. The shop said they checked the cam, sensor, and valves which all worked correctly. Apparently Mazda has even put out a bulletin about this.
But on the up side, the shop said nothing else is wrong, and the PCM isn't changing any timing or doing any damage. It's just going to keep saying there's a problem.
I'm against going aftermarket, but the problem is complexity. I don't know much about Megasquirt, but what I do know are horror stories. I know it's probably a case people don't talk about it when it works right. But if it's really PnP, I could get in on that.
If you needed one from a 94-95, I'd be your hookup.
Somebody else has one, though. Good luck!
For a 2001, you have a lot fewer options for aftermarket. Most of them can't control the intake cam. I think there's a beta setup for doing it with MS, but it would not be plug and play. The Hydra can certainly do it.
I have seen a 2001 develop a problem reading the cam position. There's a toothed wheel (well, two teeth if I remember correctly) pressed on to the cam that can slip. If you do that, obviously it'll read all wrong. If the PCM reads the cam position wrong, it won't control the VVT properly.
I'd do more research or go to a different shop. There's no way the car is 1) reading the cam position incorrectly and 2) not changing something in response. See if you can find that Mazda bulletin.
Drewsifer wrote: super retarded.
I think you meant wicked.
Find a friendly Miata head locally w/ a 2001 ECU they'll let you try.
Swap it in - see if the problem goes away.
Check the CAS again...
Keith wrote: For a 2001, you have a lot fewer options for aftermarket. Most of them can't control the intake cam. I think there's a beta setup for doing it with MS, but it would not be plug and play. The Hydra can certainly do it. I have seen a 2001 develop a problem reading the cam position. There's a toothed wheel (well, two teeth if I remember correctly) pressed on to the cam that can slip. If you do that, obviously it'll read all wrong. If the PCM reads the cam position wrong, it won't control the VVT properly. I'd do more research or go to a different shop. There's no way the car is 1) reading the cam position incorrectly and 2) not changing something in response. See if you can find that Mazda bulletin.
This is the 4th shop I've had this car at, at it doesn't sound like I'm any closer to fixing whats wrong. I'm just at my wits end, and honestly taking it to ANOTHER shop just doesn't sound like it's gonna help. I still owe $5600 on the loan for this car, and I don't think I could even get that much for it right now.
Also, I'm really, really, REALLY bad at buying cars.
Swapping ECUs on a 2001 isn't an easy thing - they're mated to the immobilizer for this exact reason, to mess with people trying to fix them 
Drewsifier, what are your actual symptoms? What's wrong with the car?
Drewsifer wrote: Also, I'm really, really, REALLY bad at buying cars.
If it helps I also seem to be a member of this not very exclusive club...
Keith, IIRC drewsifer's Miata kept throwing check engine lights on a regular basis that none of the garages that looked at it could trace. But I might have missed an update or three.
Keith,
Sit awhile, but don't take your boots off. This could take a minute.
Bought the car 3 months ago in El Paso. Immediately started throwing codes. Dealer changed the oil, replaced the O2 sensors and Catayltic converter. Still throwing P0300 and P0420 codes. Took it to another shop that said the catalytic converter was not OBD II compliant. Replaced CC, problem went away for a little bit. CEL came back on. I've replaced the plugs, wires, ignition coil, and gas cap. Now it's at the shop and they say it needs a new PCM.
The car stumbles really badly when it's warming up, like almost dies. Before it's fully warm it feels like there's a stumble or hesitation when accelareting. And it smells like unburned fuel while driving.
Here's what the manual says.
P0300 (random misfire)
- CKP sensor (crank position, I think)
- CMP sensor (camshaft position)
- ignition coil
- plug wires
- MAF sensor contaminated
- "excess air suction in intake-air system" between MAF and dynamic chamber
- fuel pressure
- fuel line clogged
- fuel filter clogged
- fuel leak
- purge control solenoid valve
- PCV valve
- EGR valve
- vacuum hoses
- connectors, terminals, wiring, etc.
There are 22 steps to checking this out, the last of which is "replace PCM". That's always the last step 
Compression check comes before that.
P0420 is usually a result of the misfires. Sadly, that unburnt fuel likes to kill cats. Here's what the manual says.
- cat deterioration
- exhaust leak
- loose O2 sensor
- front O2 sensor malfunction
I'd dig into that P0300 cause, checking fuel pressure and a few other bits. Leave the P0420 until after, although it's possible the cat is dead by now. A Mazda dealer should be able to plug their magic tool in and check the condition of all the sensor inputs. If there's one out of range (such as the cam position), then fix that. As I mentioned, the trigger wheel has been known to come adrift.
(edited to overcome the retarded formatting of the GRM forum)
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