I'm new to this forum thing so if I format anything incorrectly, I'm sorry haha.

So I have 1994 Miata 1.8 with a FM Turbo Kit. When I bought the car there was a Voodoo Box Piggyback ECU on the car. The car is running extremely rich, idling at around 11-12, cruising at about 12.5. Basically just burning my gas for no reason. After a lot of reading and research I decided to buy the Megasquirt 2 PNP for my car because the Voodoo box seems like it's not tuneable. I've called pretty much every shop around where I live and no one will touch the car to tune it because there's nowhere to plug into the ECU. Anyways, the MegaSquirt came in and I took the car to a friend to help me get it set up and dial it in. Upon installing the MegaSquirt, we discovered the previous owner had actually tapped into the wire harness to install the Voodoo Box. So the MegaSquirt wont start the car because the Voodoo Box is still trying to control the stock ecu. I guess my question is, is there a way to make the MegaSquirt ignore the voodoo box? Or am I gonna have to cut the voodoo box out and re-splice the wire harness wires back together? If so, can anyone direct me because Im really worried about messing up the wire harness trying to get this piggyback out and I dont want to have to buy a whole new wire harness to fix this.

Thanks,
Cody

 

You will want to remove the DooDoo box and get wiring back to stock, you can't successfully tune the Megasquirt if the piggyback is also making adjustments. I would not expect the piggyback to keep the Megasquirt from starting, so may there's another issue? I would look up the VooDoo instructions and grab a wiring diagram and try to get it back to stock. Don't cut corners on your splices, the last thing you want is to chase down issues because of wire joints failing. Make good contacts (whether solder or crimp, I prefer crimp), use heat shrink with glue, then make sure the wire can't dangle and put strain on the joint (zip tie where need be to alleviate this). Look into running a composite log with the Megasquirt, then you can see if the cam/crank signals are coming in successfully, this is the first way to diagnose a no-start issue.

 

I'm probably gonna end up crimping it. Makes me feel a little better knowing someone else would resplice the wires instead of buying a new harness. Can I buy heat shrink with glue already in it? (probably a dumb question)

Once I get the piggyback off I'm gonna run some logs to see if there was another reason the car wouldnt start other than the piggyback.

Thanks

 

The voodoo should be completely passive until its pressure sensor sees positive boost. Tapping into the wiring harness is also the normal installation method for the voodoo box, so that should not be surprising. All the voodoo box does is measure pressure, and when boost begins to rise from vacuum, it sends voltage down the injector wires to hold the injectors open longer than the stock ecu would. With more boost pressure, it holds them open longer. But it doesn't talk to the stock ecu in any way, you just have two devices holding the injectors open, and the voodoo can hold them open under boost when the stock ecu normally shuts off voltage and would have closed them, since it isn't tuned to account for boost. The injectors don't care which computer the voltage is coming from, they just stay open as long as there is voltage.

You should definitely cut the voodoo out eventually, but I agree it shouldn't be preventing the car from starting. If it will start with the stock ecu, it should start with a properly configured megasquirt.

 

Interesting. I'm new to the tuning thing completely. I actually bought the car with the turbo and voodoo already on it, so Ive read a lot of people saying buy a MegaSquirt, learn to tune, and then go turbo as advice, and unfortunately I have to work backwards in a sense.

Maybe you could link me to a good thread to tune? Or would you recommend to find someone else who knows what they're doing, as I would only really be following instructions online.

 

Also, if it makes any difference, the MegaSquirt turns on, and the car turns over, but then dies right away. I should've been less vague.

 

This forum is just about the best place for megasquirt info, but it leans toward the self-help side. Have you followed the DIYautotune's install guide? Have you connected the vacuum line to the MSPNP, or did you just plug it in? If no, you probably need to either spend some time digging on your own before looking for troubleshooting assistance, or finding a tuner. If you have followed the install guide, I also ran into a problem with my '94 after initial install where it would start but immediately die. I could keep it running by giving it throttle, but it wouldn't idle. I needed to open the idle air control adjuster screw on the throttle body up a bit before it would idle.

 

I have read a lot and followed the install guide, it's just the install guide doesn't tell me what to do in the situation that I am in with having a piggyback on a MS. And I can't find much info on it either. Obviously the Voodoo box needs to come off, I'm just asking questions like this now because if the car should still start even with the Voodoo on it, I'm obviously not seeing something or doing something wrong.

Actually, now that I think about it. The Voodoo Box had a vacumn line running to it already, so I just took it off the Voodoo and ran it to the MegaSquirt instead, but if the Voodoo Box is still trying to operate, maybe the car's not staying on because there's not a vacumn line on both ECU's, just the MS?

 

If you pulled the vacuum line off the voodoo box, it might think you're on the verge of building boost, and could be holding the injectors open. I don't think you can be sure you're not getting interference until you remove the voodoo box. Of course, at that point, there is nothing to add more fuel under boost if you drive the car with the oem ecu, so you would go lean and damage your engine unless you get the megasquirt working.

 

Your best bet may actually be to remove the VooDoo, wire the wastegate open (disconnect wastegate and wire it open so the flapper can't hit the turbine wheel, this way it makes 0psi of boost), then make sure the car runs with the stock ECU. This will validate that your splice job went well. Then install Megasquirt and learn to tune. Then install injectors and learn to tune larger injectors. Then reinstall wastegate and start to tune for boost. It's a lot safer to learn how to tune on a stock motor than boosted.

 

Ace hit it right on the head.

 

I will give this a try. Thank you

 

Yeah, I'm just gonna cut the Voodoo box out and resplice the wires back to how it would be stock, and go from there

 

It might be easier to just buy a new engine harness. I wouldn't wanna trust a cut and spliced together haphazardly harness with unknown history.

 

Buddy of mine suggested the same thing. I'm just not sure where to find one, I cant find one for my car year on ebay or anything

 

Join the Parts Miata group (link HERE) and make a post. You'll find one in no time...Since you're native to Florida, I buy a lot of used miata parts from Ben, somebody who parts out Miatas, on Facebook as well. You can find Ben's facebook below.

=68.ARB4e7GsmxC7C5mZSFNnHggMVIxvgdKnN5o1ax5T7YA1f6 Y8OUOuRz7fp0uJ9aHp5RZsh91btk_uuxrNMHK6N020yBd6PI0F x0Bo-oNZaot314fWWqtupfDSJMyqwae3lWyLZtlhuobLQglN3Y27A2M qvo2pkSEMlmo1rcsl7Y38jYHgq4PLiPs1ZQHijYsTbJUWmon33 xIq1aP7cxYeXrUmUoM27YS76WG2Mxa24dLUB1FS-wIOPj-Aj7y2fBmN4dQ10IBy1b4v7ZfRkD0Wzw2XCEWPaQIzdQHIrfN41 CFsDwaRTKyolqKCps0UGwI_cdfiziB7eQTvUeSdhvU7]https://www.facebook.com/Bensmiataparts/?__tn__=kCH-R&eid=ARB_D0-EcVnFbWtlc-5QrlDcbKLxK58JvT97e1quwLKTqIXTuParVU4FRspm9sesgtRy 0KVja8R7fG19&hc_ref=ARS1rx6mmVH3OQFC2RjF2XgeZzDJII-_zJ3adZn_YoSWA68673seeLDOOKURF58Rtns&fref=nf&__xts __[0]=68.ARB4e7GsmxC7C5mZSFNnHggMVIxvgdKnN5o1ax5T7YA1f6 Y8OUOuRz7fp0uJ9aHp5RZsh91btk_uuxrNMHK6N020yBd6PI0F x0Bo-oNZaot314fWWqtupfDSJMyqwae3lWyLZtlhuobLQglN3Y27A2M qvo2pkSEMlmo1rcsl7Y38jYHgq4PLiPs1ZQHijYsTbJUWmon33 xIq1aP7cxYeXrUmUoM27YS76WG2Mxa24dLUB1FS-wIOPj-Aj7y2fBmN4dQ10IBy1b4v7ZfRkD0Wzw2XCEWPaQIzdQHIrfN41 CFsDwaRTKyolqKCps0UGwI_cdfiziB7eQTvUeSdhvU7

 

What tuning have you done on the megasquirt?

Or you just opened the box with a new megasquirt, plugged it into the car and expect the car to start?

 

So this is something I thought I had said already, but I took it to a local guy who does street tunes to get it tuned. He's tuned numerous miatas owned by people I know who recommended him to me. Basically he loaded up a base map on the MS and the car would turn over but wouldn't start. Like I've said, I know close to nothing about these cars and how to tune, etc. I'm trying to learn as I go. But he had concluded that the Voodoo box had something to do with the car not staying on. Maybe he doesn't know enough about tuning to be able to work around it, maybe he's right and the VooDoo box is interfering, or maybe he just did something wrong when trying to get it tuned that wouldn't let the car start. I'm not sure, that's why I'm here trying to find some sort of answer/direction to take.

 

Thank you, I'll definitely look into it