# Meguasquirt piggyback system on an OBD2 ABA?



## notso2slo (May 1, 2006)

I'm looking at trying to set up Megasquirt for my 1996 Volkswagen GTI. Has anyone tried to keep all the Motronic system intact and just let the Megasquirt take over fuel and spark?
I'd like to try out the new Megasquirt 3, since it would support my current MAF sensor.
I was thinking about just making a harness adaptor that would fit between the engine harness and main harness, to avoid having to hack anything. The only other connections I'd need to hack is the coilpack and MAF. I need to be able to disable the system for competition in my local autocross, but still want to mess with all my maps.
I'd have to parallel connections to all the sensors, and solder in some sort of resistor to the injectors and coil to convince the Motronic that it's still connected to them.
My questions include the following:
Would the Motronic system freak out and throw a CEL if the Megasquirt was tuned way more aggressive than the Motronic?
Would the MAF be better for driveability, or would it just be better to use MS2 and a MAP?
And does anyone know which plugs on the OBD2 Throttle Body do what? I need to know what's TPS and what's IAC.


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## ValveCoverGasket (Mar 20, 2002)

*Re: Meguasquirt piggyback system on an OBD2 ABA? (notso2slo)*

its likely that the OBD2 would catch onto the fact that its not in control and at the very least set a CEL for some kind of unresponsive 02 sensor when it tries to adjust fueling (to compensate your MS maps changes) and doesnt see an appropriate response in 02 voltage.
this might work on an older setup with more primative OBD...
still worth a shot though, and resistors in the injector spots may help avoid the CEL while the engine is stationary...
any reason you cant just make a harness to temporarily install MS completely - then leaving you the option to plug the factory stuff back in when youre done, or when you sell the car, etc...
i see no reason to run the MAF unless youre interested in experimenting with the MS3 code as it gets updated to include MAF stuff... otherwise id just run one of the older variants with a MAP sensor.


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## need_a_VR6 (May 19, 1999)

*FV-QR*

If you need to easily remove it, and go back to stock, your best bet would be to build a plug and play type harness using a stock ECU connector. The best thing is the Motronic wouldn't even know what's going on in that case, as it won't be connected. Sharing sensors, especially the crank sensor can get tricky. 
You don't need to use the MAF at all with any version of MS but MS3 supports it via the spare ADC's (2nd ego, ext map, etc) if you really want. I've used it before for logging but that's about it.
The bigger black/white are the idle valve, 4,5,7 are the tps but I can't remember what's what off the top of my head.


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## notso2slo (May 1, 2006)

*Re: Meguasquirt piggyback system on an OBD2 ABA? (ValveCoverGasket)*

If it's gonna throw codes no matter what, then I might as well just get over it and take out the CEL bulb.
And yeah, I was planning for a total plug and play, via the harness connector on the side of the block, plus a few others. 
And what is so difficult about the crank sensor? Just because it's a VR? I'm guessing hooking up more than one wire to it messes with your resistance signals. Do any of the other sensors have a similar problem? I'd like to leave things like the coolant temp sensor and tach all hooked up so I don't have to mess with any of that wiring, would those be easy enough to share?
And I guess my other question would be oxygen sensors. Will the stock ones be sufficient for daily driving on megasquirt, or should I spend the money on a wideband? I have friends with megasquirt that could loan me a wideband for tuning purposes. I'd like to get one, but it's all budget permitting.


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## need_a_VR6 (May 19, 1999)

*FV-QR*

If you totally unplug the stock ECU there's no codes to throw and you can use the CEL as a shift light








Yes, a VR sensor is sensitive to what it's interfaced with. The coolant and air intake temp sensors will take some extra circuitry to share as well.
If you want to learn how to tune the car and really learn, just get a wideband at the get-go and leave it in the car. 
I still don't recommend piggbacking, just build the MS with all the stuff you need to replace the stocker when you don't want to use it (IAC driver, tach circuit, etc). Cut up a stock ecu for the connector and make it real simple. I did that with my car for a long time and it took all of 5 minutes to go from MS to stock ecu. Just swap the connectors over and flip a switch from the WB02 output back to narrowband simulate.


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## ValveCoverGasket (Mar 20, 2002)

*Re: Meguasquirt piggyback system on an OBD2 ABA? (notso2slo)*


_Quote, originally posted by *notso2slo* »_If it's gonna throw codes no matter what, then I might as well just get over it and take out the CEL bulb.


at that point id just run a full MS install with connectors on the harness at the main ecu plug that would allow you to swap back and forth between the stock ECU and the MS.


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## Withidlehands (Nov 29, 2007)

*FV-QR*

go to http://www.fireandfueltuning.com/ he has plug and play ms for mk3. he hooked me up on the mk4 project of mine. MS is awesome!
Also the ms3 board seems kinda lame on a few things. Id just go ms2 vs.3.0 and be happy with all the features.


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## ValveCoverGasket (Mar 20, 2002)

*Re: FV-QR (Withidlehands)*


_Quote, originally posted by *Withidlehands* »_
Also the ms3 board seems kinda lame on a few things.

such as?


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## mack73 (Jan 2, 2002)

*Re: FV-QR (Withidlehands)*


_Quote, originally posted by *Withidlehands* »_go to http://www.fireandfueltuning.com/ he has plug and play ms for mk3. he hooked me up on the mk4 project of mine. MS is awesome!


WOW nice setup http://****************.com/smile/emthup.gif If I wasn't going carbs on the rally car that would be an awesome solution. MS craps out - slap in a stock ECU and keep racing http://****************.com/smile/emthup.gif


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## need_a_VR6 (May 19, 1999)

*FV-QR*


_Quote, originally posted by *ValveCoverGasket* »_
such as?


Seriously, MS3 is pretty rad.
I can do PnP setups as well, but most folks are trying to save $$ and/or want to delete/mod their stock wiring anyway.


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## notso2slo (May 1, 2006)

*Re: FV-QR (need_a_VR6)*

That PnP is a pretty cool setup, which leads me to another question... I run in SCCA style autocross, in a street touring class. It doesn't allow standalone, which is why I wanted to be able to unplug it. However, here's how the rules read...
1. Reprogrammed ECU (via hardware and/or software) may be used *in the standard housing.* Traction control parameters may not be altered. Altered engine controllers may not alter boost levels in forced induction engines. Alternate software maps which violate these restrictions may not be present during competition, regard- less of activation.
2. Electronic components may be installed in-line between an en- gine’s sensors and ECU. These components may alter the signal coming from the sensor in order to affect the ECU’s operation of engine management system. Example: fuel controllers that modify the signal coming from an airflow sensor.
3. Fuel pressure regulators may be replaced in lieu of electronic al- terations to the fuel system. It is not permitted to electronically modify the fuel system AND replace a fuel pressure regulator.
4. Ignition timing may be set at any point on factory adjustable dis- tributor ignition systems.
5. VTEC controllers and other devices may be used which alter the timing of factory standard electronic variable valve timing sys- tems.
6. All vehicles must comply with the EPA tailpipe emissions test re- quirements as a minimum. 
So in other words, by reprogramming the engine control unit via the hardware and software of megasquirt, and leaving it in the standard ECU housing, might I be able to interpret the rules such that this would be legal?


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## need_a_VR6 (May 19, 1999)

*FV-QR*

Totally legal, the IT road racers have been doing similar things for a while. BUT I have a vague recollection that the std V2.2/3 boards are too long to fit in the stock case. One of DIY's new PnP ones might fit, though I've never checked.


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## ValveCoverGasket (Mar 20, 2002)

*Re: FV-QR (notso2slo)*


_Quote, originally posted by *notso2slo* »_So in other words, by reprogramming the engine control unit via the hardware and software of megasquirt, and leaving it in the standard ECU housing, might I be able to interpret the rules such that this would be legal?

yeah, i know guys whove been doing this for a while in the local autox scene.
and as paul said, ms3 is the bees knees... 
my view on the plug and play setups - having done a couple on miatas and an ae86 - is that you shouldnt have ecu failures like that. if youve got the engine tuned up right and youre using some wild cams, or turbo or something, and your ms fails (which if built and installed properly it very likely wont do) then plugging in your stock ecu and trying to drive it home/finish the race is going to probably cause you engine damage anyway.
better IMO to cut the harness and build it specifically for MS, and then carry a spare MS if youre concerned about random ecu failures. which again, ill stress happen very rarely, and theres almost always an underlying issue on the car side to cause a working ecu to suddenly stop working.


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## need_a_VR6 (May 19, 1999)

*FV-QR*

I only do it because I'm inherently lazy and like to do back to back dynos on strange things


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## Prof315 (Jan 5, 2009)

*Re: FV-QR (Withidlehands)*

MS3 is the absolute sh*t. It is rapidly approaching the capabilties of a Motec M800 at 10% of the cost. My ABA rado running in basic upgrade mode on MS3 (no sequential or COP) is knocking down close to 40 mpg at 70-75mph and idles at 850 rpm pulling 19-20 in/hg vacuum with a mild cam in it. And my top speed is over 125MPH! What's not to like?










_Modified by Prof315 at 5:06 PM 4-29-2010_


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## need_a_VR6 (May 19, 1999)

*FV-QR*

Hrm.. you did say it was a Corrado...


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## Prof315 (Jan 5, 2009)

*Re: FV-QR (need_a_VR6)*

Yeah I did







. And it's your spark map, Paul, that got me the 40 MPG!


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## notso2slo (May 1, 2006)

*Re: FV-QR (Prof315)*

Does anyone know who's done this? I'd like to talk to them about any problems they had squishing it into the MK3 ECU.
And I'm still confused about all the MS's.. are you talking about the new Megasquirt 3 or the Megasquirt 3 PCB?
So people who do this, is there a method of running a MAF on Megasquirt 1 or 2? I don't think running an extra sensor for MAP in is technically kosher... 
And I'm also confused about knock sensors and Megasquirt. My friend says he doesn't use them, but I figure they're a somewhat important safety feature.... 
And how much of the emission controls will the Megasquirt control? I don't have an EGR or a SAI to worry about.
I'm currently pouring over the wiring harness diagrams and labeling all the pins on the ECU.


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## Prof315 (Jan 5, 2009)

*Re: FV-QR (notso2slo)*


_Quote, originally posted by *notso2slo* »_Does anyone know who's done this? I'd like to talk to them about any problems they had squishing it into the MK3 ECU.
And I'm still confused about all the MS's.. are you talking about the new Megasquirt 3 or the Megasquirt 3 PCB?
So people who do this, is there a method of running a MAF on Megasquirt 1 or 2? I don't think running an extra sensor for MAP in is technically kosher... 
And I'm also confused about knock sensors and Megasquirt. My friend says he doesn't use them, but I figure they're a somewhat important safety feature.... 
And how much of the emission controls will the Megasquirt control? I don't have an EGR or a SAI to worry about.
I'm currently pouring over the wiring harness diagrams and labeling all the pins on the ECU.

I don't know anybody who has put an MS in a MK3 case. I think it might be too small to fit and if it was'nt it would be a serious project between the soldering and hacking the case for the DB9 serial port.
There are now 3 Megasquirt chips 1, 2, and 3. Paul and I are both beta testing Megasquirt3. Paul was 1st round, I got mine in phase 2.
I think there is some beta code in MS2/Extra that supports MAF but SCCA club racing IT rules allow addition of a MAP sensor for sure.
A Megasquirt can easily be modified to accept a Knock sensor and they are a nice protection feature but the are not essential even on a turbo motor. Yes you can easily kill an engine with a poorly tuned standalone sytem but even a knock sensor doesn't stop it most of the time. A wideband AFR sensor is MUCH more important to have.
MS can do IAC, O2 sensor, (wide band or narrow band, wide band being the best), cooling fan control, simple canister purge and it would be easy to do as well. SAI would be easy, EGR could be fairly easy to impossible, basic VVT is easy.


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## notso2slo (May 1, 2006)

*Re: FV-QR (Prof315)*


_Quote, originally posted by *Prof315* »_
I don't know anybody who has put an MS in a MK3 case. I think it might be too small to fit and if it was'nt it would be a serious project between the soldering and hacking the case for the DB9 serial port.
There are now 3 Megasquirt chips 1, 2, and 3. Paul and I are both beta testing Megasquirt3. Paul was 1st round, I got mine in phase 2.
I think there is some beta code in MS2/Extra that supports MAF but SCCA club racing IT rules allow addition of a MAP sensor for sure.
A Megasquirt can easily be modified to accept a Knock sensor and they are a nice protection feature but the are not essential even on a turbo motor. Yes you can easily kill an engine with a poorly tuned standalone sytem but even a knock sensor doesn't stop it most of the time. A wideband AFR sensor is MUCH more important to have.
MS can do IAC, O2 sensor, (wide band or narrow band, wide band being the best), cooling fan control, simple canister purge and it would be easy to do as well. SAI would be easy, EGR could be fairly easy to impossible, basic VVT is easy.

So there are 3 versions of PCB, and 3 versions of processors?
And I'd like to know if it could be done, squishing it into a mk3 case. The mk3 case IS the largest of any A platform, as far as I know. And wiring's gonna be a bitch no matter what I do, so why not?
And this Street Touring, not Street Prepared. I don't get IT rules. I'll have to ask about adding an extra oxygen sensor and map sensor.
And I was planning on upgrading to a MK4 exhaust manifold, which would give me an extra O2 port. That would allow me to wire everything in so I could swap back to my stock ECU without even messing with the oxygen sensors.
And I don't think I have much more than a canister purge valve, I wrote out all the connections from the wiring diagram. There's just a few I couldn't figure out (still trying to figure out how to read some parts of the diagrams








)
So if anyone knows anyone who has squished a Megasquirt into a mk3 ECU box, please let me know?


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## ValveCoverGasket (Mar 20, 2002)

*Re: FV-QR (notso2slo)*


_Quote, originally posted by *notso2slo* »_
So there are 3 versions of PCB, and 3 versions of processors?


2 pcb versions, 3 processors, though MS3 uses its own case... but still sits on a v3 board


_Modified by ValveCoverGasket at 8:05 AM 4-30-2010_


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## Prof315 (Jan 5, 2009)

*Re: FV-QR (ValveCoverGasket)*


_Quote, originally posted by *ValveCoverGasket* »_
2 pcb versions, 3 processors.

Actually there are 3 PCBs V2.2 V3.0 and V3.57 although 3.0 and 3.57 are pretty much functionally identical.


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## ValveCoverGasket (Mar 20, 2002)

*Re: FV-QR (Prof315)*


_Quote, originally posted by *Prof315* »_
Actually there are 3 PCBs V2.2 V3.0 and V3.57 although 3.0 and 3.57 are pretty much functionally identical.

ah, youre right








i never use the 3.57, so its totally off my radar


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## need_a_VR6 (May 19, 1999)

*FV-QR*

There's a 1.01 as well... I had one







Not too many of those though. 
I used my MAF for datalogging on MS1, I know the code is there to use it. MS2 didn't have it for a bit but I think it's finally added in one of the newer versions of the code. 
I don't use knock sensors, ever. 
You won't have to add an O2 either, just use the wideband all the time. The Innovate has narrow and wideband outputs, I had mine on a switch to go back to stock ECU. The MAP sensor on the MS is 'onboard' you'd just need a case hole to use it. I can't see that being a problem as it's a 'hardware solution in the stock case.'
You could do EGR or VVT off the boost duty map.. if for some reason it's necessary.


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## ValveCoverGasket (Mar 20, 2002)

*Re: FV-QR (need_a_VR6)*


_Quote, originally posted by *need_a_VR6* »_I don't use knock sensors, ever. 


same
tune it once with a good knock sensing system, dial in appropriate spark pulls, and youre set
we built an amplified circuit that filters out ambient noise, stuck a mic on an alligator clip with a long noise suppressing audio cable so we can run it into the cab. makes it real easy to hear knock


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## need_a_VR6 (May 19, 1999)

*FV-QR*

I use an engine ear when I'm worried about that sort of thing and the knock sensor *never* picks up anything useful.
I just checked a Motronic case with a V3 board I had sitting about. The board itself fits both ways. Long ways the end of the board is about even with the plane that the case end is. Sideways, it needs to go from corner to corner to fit, but it fits. I'm not sure if it's possible either way with components.


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## ValveCoverGasket (Mar 20, 2002)

*Re: FV-QR (need_a_VR6)*

i wonder if you soldered wires straight to the db37 pads, if you could get away with cramming it in there...


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## notso2slo (May 1, 2006)

I can always carve out a little as well... the rules say it must be IN the standard case, not that the standard case has to be umodified...
And does megasquirt even do anything with knock sensors? I mean, I'll wire them in if they're there, and don't mind that they really don't do anything. I'll just do it to do it.
And you'd have to make some sort of adaptor to fit to the VW harness, so maybe soldering diorectly would be easier in the end anyway?


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## need_a_VR6 (May 19, 1999)

*FV-QR*

With the board sideways the end cap/connector would fit. You'd have to leave off the DB37 and the DB9 in any case.


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## Prof315 (Jan 5, 2009)

*Re: (notso2slo)*



notso2slo said:


> I
> And does megasquirt even do anything with knock sensors? I mean, I'll wire them in if they're there, and don't mind that they really don't do anything. I'll just do it to do it.
> 
> 
> > MS can accept a knock input but it requires an interface like knocksense or a GM knock module.


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## notso2slo (May 1, 2006)

*Re: (Prof315)*


_Quote, originally posted by *Prof315* »_MS can accept a knock input but it requires an interface like knocksense or a GM knock module.

but will it actually retard the timing, or just show knocking?


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## Prof315 (Jan 5, 2009)

*Re: (notso2slo)*

You set up either or. Just detect the knock or set up timing retard on knock.


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## need_a_VR6 (May 19, 1999)

*FV-QR*

I've used Knocksense and the MS knock circuit before, don't bother.


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## notso2slo (May 1, 2006)

don't bother it doesn't do anything, or don't bother it screws with things?
Cause if it just doesn't do much, I'd still like to do it just cause... I'm that kind of guy.


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## need_a_VR6 (May 19, 1999)

*FV-QR*

In my experience, they're very good at picking up noise and totally missing knock when you really would need it to.


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