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Discussion Starter #1
I just dropped a '92 1.6L rebuild into my '90 Miata (after the '90 timing gear failed @ crank horn; '92 has a more-robust crank horn at timing gear), added a KW kit with Rotrex SC; "fuel management system," which is a secondary, vacuum-actuated fuel restrictor; new fuel gilter, and the kit's stronger fuel pump. I've got all-new electrical and sensor components on the engine, but am re-using the manifolds (intake and exhaust) and throttle body. The TB Position Sensor is new, but I'm re-using the original ECU, and '90 engine's idle-speed control valve (mounted @ bottom of TB) and air valve (mounted on side of intake; heat from coolant lines control it). All these re-used components worked fine on the old engine.
The new engine with the SC started no problem after install, and timing is set at factory 10 degrees. But I'm having a few problems with this new configuration:
First, the idle drifts up and down. I've gone through the long idle-setting routine described at miata.net. If I set it at 750, idle drifts up and down and the engine often dies at stops. I can set it to approx. 1100, where it's almost stable, but that's annoyingly high.
Second, the engine guzzles gas (10 MPG); acceleration often feels compromised (but boosting seems to work at 4K-5K RPM), and I can't get the tach past 6K RPM (the factory ECU redline is set to cut spark at 7.5K), the engine sputters and struggles at 6K RPM and goes no higher. It also throws a 17 code (O2 sensor).
I've researched the richness problem ad infinitum and tried all the recommended remedies; swapped out the O2 sensor, thermosensor (near firewall), AFM, and thermostat with known-good parts. Runs the same, same problems, guzzles gas (other forums suggest that I should be getting maybe 5 MPG less than factory, e.g. 23 MPG), won't idle, continues to throw code 17 (even after clearing codes with battery disconnect/brake-pedal routine).
Kraftwerks claims that this kit is plug-and-play, but it's not working out that way. The kit included a part that wasn't mentioned in the '90 install instructions and that I didnt need, and now I wonder if I received the correct fuel injectors in the kit.
The car constantly runs as if the ECU can't or won't change from cold-start to engine-operating-temp mode.
Any opinions on a remedy, other than removing a $3K SC kit and returning to factory naturally-aspirated config, or worse, gambling on the ideat that sn $800 MegaSquirt ECU is necessary to fix (if at all) these issues?
Note that for early Miatas, the SC kit does not include a "SuperCard" for the ECU; I suspect that these OBD1 systems' ECUs have no card slots, but instead, all the chips are soldered to the motherboard.
Maybe a Kraftwerks rep will weigh in on this thread...
 

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Discussion Starter #3
Thanks, Bronto, for your likely sage (until attempted) advice.

My question remains (as one unfamiliar with these mods, but not unfamiliar with having rebuild an engine using factory specs):

1) Do I need an after-market engine-management system such as MegaSquirt? I suspect that something in the factory brainbox can't understand sensor data (increased O2 input from supercharger), and all the torrent of computational confusion the factory ECU experiences.

2) Can the factory ECY comprehend the data from a wideband 02 sensor, or is a custom engine-management ECU required to decipher the supercharged air/fuel data?

I'm resigning myself to the understanding that yes, Kraftwerks was correct in that the engine will RUN with the SC installed per their kit instructions (with AFM--the install even shows and explains how to re-locate the AFM), but not optimally, and KW doesn't include a wideband in the rather pricey SC kit, nor do they suggest installing a wideband. Nor do they suggest installing an aftermarket ECU. Nor do they include a SuperCard, which likely can't be installed in a '90 ECU, given that no slots are available in an ECU that's all hardwired/soldered to the motherboard.
 

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remove SC, see if anything changes. Sounds like, if I read this correctly, it ran fine prior to the rebuild but now runs like puupuu after the rebuild. Someone may have done gufed.

You don't need the ECU to understand anything about the wideband. it's there to tell what the AFR is.
 

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If you don't have a wideband you should park your car until you get one.
+1

Thanks, Bronto, for your likely sage (until attempted) advice.

My question remains (as one unfamiliar with these mods, but not unfamiliar with having rebuild an engine using factory specs):

1) Do I need an after-market engine-management system such as MegaSquirt? I suspect that something in the factory brainbox can't understand sensor data (increased O2 input from supercharger), and all the torrent of computational confusion the factory ECU experiences.

2) Can the factory ECY comprehend the data from a wideband 02 sensor, or is a custom engine-management ECU required to decipher the supercharged air/fuel data?

I'm resigning myself to the understanding that yes, Kraftwerks was correct in that the engine will RUN with the SC installed per their kit instructions (with AFM--the install even shows and explains how to re-locate the AFM), but not optimally, and KW doesn't include a wideband in the rather pricey SC kit, nor do they suggest installing a wideband. Nor do they suggest installing an aftermarket ECU. Nor do they include a SuperCard, which likely can't be installed in a '90 ECU, given that no slots are available in an ECU that's all hardwired/soldered to the motherboard.
1)Whether or not you need a Megasquirt (and don't try to reinvent the wheel with AEM or Adaptronic) depends on your expectations of how you want the car to run. The fuel cards, when done properly, can be made to work but you leave a lot on the table and it will always have less than ideal settings for the car. A large majority of cars I've come across with fuel cards of some sort never have the transient response that a well tuned Megasquirt can provide. With a Rotrex the transient throttle response is part of what you are paying for, nothing else comes close to it.

2)Widebands such as the AEM UEGO have a narrow band emulation function but the stock ECU does not read this properly in my experience. A customer installed an AEM into their 92 and set it to narrow band mode, however, the car ran VERY rich. That tells me the ECU defaulted into a fail safe mode because it is not receiving an o2 signal. If you install the wideband while running the stock ECU add a bung and run it as a standalone.

My advice is to save your money and buy a PNP Megasquirt to realize the potential of the supercharger kit. There is no reason to use a bandaid tuning approach these days unless you have to for smog.
 

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^i agree with what was stated above except i prefer aem. I use the aem ems4 on my set up and it screams. But a wide band is a necessity to see what's going on. And a standalone keeps your car alive longer.
 

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Were the injector o-rings replaced during that engine's rebuild?
Could that be part of the idle and mileage problem, or is this all down to the lack of a MSPnP?
 

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Were the injector o-rings replaced during that engine's rebuild?
Could that be part of the idle and mileage problem, or is this all down to the lack of a MSPnP?
Doesn't matter. OP's car is running rich, not lean. Leaky o-rings would actually help OP's situation.

I suspect the FPR isn't working correctly or is incorrectly referenced. Furthermore I am confused as all **** as to why Kraftwerks thought this was an acceptable solution.

If I was in the OP's place I would ditch all that garbage (except for the fuel pump, although that is pretty worthless as well), buy a Megasquirt of some sort and some RX8 injectors and go to town.

I am not exaggerating when I say park your car. You could easily be running so rich that it actually becomes an issue (cylinder wall wash, etc).
 

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Discussion Starter #11
Bronto, yes, I appreciate your advice. I'm likely to keep it parked while until a MSPnP arrives in the mail. I have plenty to do in the meantime; install a new shifter boot, seats (newER, from a later model Miata), and heater core (ripping out the dash should be fun -- not). Thanks for the engine-damage warning. I've put about 235 mi. (two tanks of gas) on the car so far, so hopefully haven't messed up too much on this new engine install.
 

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Discussion Starter #12
I suspect the FPR isn't working correctly or is incorrectly referenced. Furthermore I am confused as all **** as to why Kraftwerks thought this was an acceptable solution.
The Kraftwerks kit comes to the with a "fuel-management" system, which is just a FPR mounted to the firewall and connected to the stock FPR (which I installed new).
The instructions that came with the kit are locate here, FPR install starts on p. 12:
http://www.good-win-racing.com/manuals/90-93-Miata-Supercharger-Instructions.pdf
 

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Your car is obdI so no o2 sensor post cat like a obdII to tell the ecu if the catalytic converter is working properly and running rich will kill a catalytic converter quicker than just about anything else.
 

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Discussion Starter #15
I suspect the FPR isn't working correctly or is incorrectly referenced. Furthermore I am confused as all **** as to why Kraftwerks thought this was an acceptable solution.
The Kraftwerks kit comes to the with a "fuel-management" system, which is just a FPR mounted to the firewall and connected to the stock FPR (which I installed new) via vac. hoses and fuel lines.
The instructions that came with the kit are located here, FPR install starts on p. 12:
http://www.good-win-racing.com/manuals/90-93-Miata-Supercharger-Instructions.pdf
 

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Discussion Starter #16
Your car is obdI so no o2 sensor post cat like a obdII to tell the ecu if the catalytic converter is working properly and running rich will kill a catalytic converter quicker than just about anything else.
Well... I'll likely get a MSPnP, the ECU isn't dealing with the forced air and all those other SC-changed parameters. Question is, am I advised to install a wideband in place of the factory o2 sensor?
And what's meant by "standalone?"
 

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It is BETTER to install a second bung and install the wideband sensor so in the event you need to run the stock ecu then it is there but if that isn't likely then sure you can replace the factory o2 sensor with the wideband sensor.

Standalone ecu is just a term used for an aftermarket ecu that can be used/tuned independently and w/o the stock ecu, which is what a Megasquirt is/does.
 

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Discussion Starter #18
Update:
I caved and bought a MSPnP, wow, complex user interface! $800.
Got it professionally tuned, another $800.
The '90 Miata with a reman '92 rebuilt long block & Rotrex supercharger now produces just under 170 HP. Astonishing difference over the former factory performance I drove for decades.
With Yonaka coilover shocks, the whole project ran about &11K, still far cheaper than a new 2016 @ $30K.
Thanks for your input, everyone. Feel free to ask questions if you're looking into doing a similar mod.
 
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