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931 MegaSquirt Questions
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rcarson25  



Joined: 14 Dec 2020
Posts: 45
Location: Middle TN

PostPosted: Mon Jul 26, 2021 11:36 pm    Post subject: 931 MegaSquirt Questions Reply with quote

Okay, so let me start off by saying I have spent countless hours researching and have a couple of questions for those in the know. I am just about at the end of my rope with the CIS system and want to ditch it and go Megasquirt II.

For my 1981 931:

Do I need to move to EDIS or similar ignition system or can I get megasquirt II to work with the distributor?

Which fuel rail and injectors work best to clear the stock turbo intake tube?

What is the best TPS modification people have found?

Any other recommendations to make the job easier? I am looking at DIYAutoTune for most of my components unless someone has a better option.

Thanks in advance.
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924RACR  



Joined: 29 Jul 2001
Posts: 8794
Location: Royal Oak, MI, USA

PostPosted: Tue Jul 27, 2021 4:02 am    Post subject: Re: 931 MegaSquirt Questions Reply with quote

rcarson25 wrote:
Okay, so let me start off by saying I have spent countless hours researching and have a couple of questions for those in the know. I am just about at the end of my rope with the CIS system and want to ditch it and go Megasquirt II.

For my 1981 931:

Do I need to move to EDIS or similar ignition system or can I get megasquirt II to work with the distributor?


No. I wired in the stock igniter (small unit on the fender) to my Microsquirt when I first converted. Saved a little time and money to get up and running. BUT - it still had some ignition issues carried over from the pre-conversion components and wiring. I subsequently switched over to the VW 4-tower coil, direct fire, which required only the coil, plug with pigtail, and new Jetta plug wires, and it runs wonderfully now, like a modern car. Well worth a small increase in cost, cheaper than the EDIS setup IMO.

rcarson25 wrote:

What is the best TPS modification people have found?


I used a Volvo TPS, because it was very cheap, but I did have to cut my throttle shaft and make an intermediate mounting plate - which gets close to the intake underneath the throttle body.

I've heard the 944 TPS is much more a bolt-in answer, but the downside is a substantially more expensive part.

rcarson25 wrote:

Any other recommendations to make the job easier? I am looking at DIYAutoTune for most of my components unless someone has a better option.

Thanks in advance.


I found the Microsquirt with included pigtail to be wonderful for doing all the wiring; great quantity of wire, enough to spare to splice and tee off things like injector power while maintaining the wiring color standard.

Bolt-in coolant TPS sensor is the Facet p/n 12-62-1-747-281, got mine from ECS Tuning, BMW 3-series fitment in place of stock thermo-time switch.

The other key sensors (MAP and IAT) I used generic GM type stuff, since I was welding up new intake ducts turbo to IC to TB...

Stock fuel hose fitting sizes are M14 x 1.5 on the return line, M16 x 1.5 on the delivery side, to figure out your AN adapter fittings. Fragola had good options there, I went with -8 hoses.
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Vaughan Scott
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rcarson25  



Joined: 14 Dec 2020
Posts: 45
Location: Middle TN

PostPosted: Tue Jul 27, 2021 9:55 pm    Post subject: Reply with quote

Thanks so much for the clear info. Would you recommend the micro squirt vs the megasquirt 2? I like the idea of the smaller packaging and lower cost. I am just looking to swap out cis for EFI. If the microsquirt will do this just as well as the megasquirt2 I would be all about simplifying the process.
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924RACR  



Joined: 29 Jul 2001
Posts: 8794
Location: Royal Oak, MI, USA

PostPosted: Tue Jul 27, 2021 10:28 pm    Post subject: Reply with quote

I'm less familiar with the differences between the two - perhaps others can comment...

I only plan IC and added boost (already have those), mildly tweaked turbo, nothing more exotic, and am not aware of any limitations on the Microsquirt that impact me with this setup...
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Vaughan Scott
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rcarson25  



Joined: 14 Dec 2020
Posts: 45
Location: Middle TN

PostPosted: Tue Jul 27, 2021 10:58 pm    Post subject: Reply with quote

Sounds good, I have been doing more research as well and best I can tell would be minus a few "features" I would never use and expandability I should be good.

Do you know if the 944 TPS sensor is from an early model or a late model 944? I think they changed in '86.
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rcarson25  



Joined: 14 Dec 2020
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Location: Middle TN

PostPosted: Wed Aug 04, 2021 1:20 am    Post subject: Reply with quote

So, I got the 034 Motorsport cis to efi injector adapters and they are smaller than stock. I was told these are the only cis to efi adapters they have. Are others who have used these adapters using epoxy or some other method to get them to work?
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924RACR  



Joined: 29 Jul 2001
Posts: 8794
Location: Royal Oak, MI, USA

PostPosted: Wed Aug 04, 2021 10:00 pm    Post subject: Reply with quote

Yeah, no, those aren't right.

I used VW p/n 058 133 555, $6 at ECS Tuning, and shaved the top flange off them IIRC to convert to the right sized hole for EFI.
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rcarson25  



Joined: 14 Dec 2020
Posts: 45
Location: Middle TN

PostPosted: Thu Aug 05, 2021 9:45 am    Post subject: Reply with quote

Thanks so much for all of the great info. I really appreciate it. I wish I would have found this out before I spent way too much on inserts that don’t work for this car.

Did you use a different than stock set of spark plugs with the VW ignition setup? I feel like the normal 924 plugs are too short to engage the VW wire set.
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924RACR  



Joined: 29 Jul 2001
Posts: 8794
Location: Royal Oak, MI, USA

PostPosted: Thu Aug 05, 2021 10:21 pm    Post subject: Reply with quote

No, stock plugs, just swapped out the wires.

Any other parts you still need to source, before you grab the wrong stuff?

Hell, here's a dump of my spreadsheet... of course the formatting is jacked, but here's at least the raw info... note that I have a few different options shown (EDIS vs. VW coil setup), or stuff NLA from Ideola...

Description Mfgr part # Source Source P/N price Qty Ordered/Rec'd Notes
Microsquirt with 8' pigtail DIYAutotune Amazon 399 1 399 X
Ford EDIS coil pack 1 0 X
Ford EDIS coil pack pigtail 1 0 X
VW coil pack Bosch 032905106F FCP Euro 50 1 X 2011-2014 Jetta/Golf fitment
connector for VW coil pack (w/ pigtail) 1J0973724 Amazon 13 1 X 2011-2014 Jetta/Golf fitment
wires for VW coil pack Amazon 19 1 X 2011-2014 Jetta/Golf fitment
0
Sensors 0
Crank position sensor - Hall effect Ideola 1 0 X Similar available from DIYAutoTune
crank trigger wheel - 36-1 Ideola Ideola 1 0 X Similar available from DIYAutoTune
water pump pulley spacer Ideola Ideola 1 0 X to adjust alignment for crank trigger wheel install
Coolant temp sensor Facet 12-62-1-747-281 ECS Tuning 1 0 X BMW 3-series fitment
air intake temp sensor with pigtail AC Delco 213-190 Amazon 1 0 X GM style; can use original 931 part with different cal
MAP sensor with pigtail AC Delco 12223861 Amazon 1 0 X GM 3-bar
Throttle Position sensor Bosch 280 122 001 FCP Euro 27 1 27 X Volvo fitment - requires spacer/offset plate and shortening throttle blade shaft


Fuel system
fuel rail Ideola 1 0 X
EFI injector Bosch 0 280 158 123 FCP Euro 68 4 272 X
Injector bung insert VW 058 133 555 ECS Tuning 6 4 24 X trim flange to fit
M14 x 1.5 Female to -8 AN adapter Fragola 491982-BL JEGS 17 1 17 O fuel return line - could do in -6?
M16 x 1.5 Male to -8 AN adapter Fragola 460816-BL JEGS 16.5 1 16.5 O fuel delivery line - 491983-BL is female version
fuel pressure regulator - alternate AEM 25-302BK JEGS 128 1 128 -
plug fitting -8AN JEGS 555-110353 JEGS 3 1 3 O plug end of fuel rail
Adapter 3/8NPT to -8AN to hose flare JEGS 555-110163 JEGS 6 3 18 O FPR port adapters
hose end -8AN JEGS 555-110002 JEGS 8 1 8 O straight
hose end -8AN 90 degree JEGS 555-110022 JEGS 13 5 65 O 90 degree
hose end -8AN 120 degree Vibrant 231-21208 JEGS 23 1 23 O 120 degree
Startlite hose -8AN Aeroquip FCU0806 JEGS 50 1 50 O 6' length
adjustable fuel pressure regulator Holley 510-12-886 JEGS 65 1 65 O
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Vaughan Scott
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'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype
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rcarson25  



Joined: 14 Dec 2020
Posts: 45
Location: Middle TN

PostPosted: Thu Aug 05, 2021 11:44 pm    Post subject: Reply with quote

Thanks for the list, thankfully it seems the injector bungs are my only miss order so far.

What crank/tach signal did you use for the VW ignition setup? I think that is the only thing I am not sure of looking at everything I have now.
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924RACR  



Joined: 29 Jul 2001
Posts: 8794
Location: Royal Oak, MI, USA

PostPosted: Fri Aug 06, 2021 12:24 am    Post subject: Reply with quote

Ah! Good point!

Yeah, switching over to using the VW coil or I think maybe also the EDIS coil means you don't have a coil-level signal to run the stock tach - which I retained, and would imagine most would prefer to use vs. a whole new dash or tach that could use the MS output tach signal.

I see this kind of thing from MS directly:
https://www.diyautotune.com/product/axm-100-high-voltage-tach-adapter/

For myself, don't recall where I got pointed to it, but slightly cheaper used this stuck behind the tach in the harness:
https://www.ebay.com/itm/TACH-TACHOMETER-SIGNAL-BOOSTER-3-16V-In-48-63V-Out-compare-to-MSD-8920/142171581596

Quite easy to install, just power and ground, ECU signal in (from MS) and signal out to the stock tach. Worked perfectly on first install, haven't thought about it since, definitely recommend.
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Vaughan Scott
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'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype
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rcarson25  



Joined: 14 Dec 2020
Posts: 45
Location: Middle TN

PostPosted: Sun Aug 08, 2021 6:04 am    Post subject: Reply with quote

Did you build an additional circuit to run the VW coil or did you just run switched power, ground and ignition out 1 and 2 to the coil?

I saw something about building an additional circuit to run this coil.
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924RACR  



Joined: 29 Jul 2001
Posts: 8794
Location: Royal Oak, MI, USA

PostPosted: Sun Aug 08, 2021 7:59 pm    Post subject: Reply with quote

I did effectively build an "additional" circuit - which was really just a power lead (from my switched new additional fuseblock). Control wires already in the MS harness, and then run a ground.
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Vaughan Scott
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'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype
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rcarson25  



Joined: 14 Dec 2020
Posts: 45
Location: Middle TN

PostPosted: Mon Aug 23, 2021 10:59 pm    Post subject: Reply with quote

I've got most everything wired up, but I have one question on injector wiring. I have looked at too many wire diagrams and I have seen the injectors wire two different ways:

option 1. injectors 1&2 on green wire injectors 3&4 on blue wire

option 2. injectors 1&3 on green wire injectors 2&4 on blue wire

Which is correct for our setup?
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924RACR  



Joined: 29 Jul 2001
Posts: 8794
Location: Royal Oak, MI, USA

PostPosted: Tue Aug 24, 2021 4:03 am    Post subject: Reply with quote

Damn, I had to look that up!

According to my notes, I've got it wired up with 1 and 4 together and 2 and 3 together.
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Vaughan Scott
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'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype
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