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Wiring it up - My First Megasquirt System

29K views 64 replies 18 participants last post by  need_a_VR6 
#1 ·
I got my MS ecu so its time to get started with my first megasquirt install. I'll have a lot of questions along the way and your feedback is welcome. Since all these wires except maybe 2 are going to the engine compartment anyway, I decided to put the ecu in the rain tray instead of running all those wires from the inside of the car to the engine. There was a already a threaded stud and a post there from the original Digi II ecu bracket mounting, I enlarged the hole in the MS ecu flange for the stud, and then popped a rubber grommet over the post that the original ecu bracket used, and filed that corner of the MS ecu flange down just enough to slide it into the slot in the grommet. I just hate drilling holes when I don't have to. I going to fabricate a small triangular bracket to connect the 2 holes on the other end of the MS ecu to the post that secured the rear of the orginal DigiI I bracket.





Now I'm trying to figure out if I can tap into the wires in this connector that went to the original module, instead of going to the fuse box for fuel pump trigger and power. This is a 91 GTI Digi II car.



So far I've determined that:

Red/White - Heated Oxygen sensor + 12v supply
Red/Yellow - Fuel Pump Relay signal to ECU
Red/Green - Starter cranking signal
Black/Yellow - +12v from digifant relay
Red/Black - ? Main Fusebox Starter Power? (goes to coil)
White/Red - ? maybe for MFA option

Could I just use red/yellow for fuel pump trigger and black/yellow for power ?
 
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#37 ·
the corrado has similar wires but its split into 2 plugs . but i could never get MS to control my FP. i had to wire my FP to just comes on as soon as i have the key turned on. ill have to look again how i have it wired. any help on how it should be.


Three pin connector:
1. R/W goes to the O2 sensor connector.
2. R/Y (smaller one) goes to ECU pin 3, fuel pump relay
3. R/Y (larger one) goes to fuel injector harness

Four pin connector:
1. R/G goes to ECU pin 1 (start)
2. BK/Y goes to ISV and ECU pin 14. (Splits inside the harness)
3. Y goes to ECU pin 20 (check engine light)
4. BK/W goes to ECU pin 23 (ECU relay)
 
#38 ·
Yes I tapped everything into those plugs and just cleaned up some wiring recently. I'll see If I can find my wiring, but definitely trigger my FP directly from one of those connectors. I seem to recall my wire colors being a bit off from the Bentley though.

I do trigger my LM1 wideband via a key switched relay though and didn't run via those connectors (not that you couldn't or shouldn't)

S
 
#39 · (Edited)
Yep, wired purple from MS to Middle pin (#2) of that 3 pin connector. Beware as some descriptions show #3 as Fuel Pump Output. This is actually off of the FP relay (i.e. + power from #87 contact to power injectors)

Also powered MS via T3B2 (pin 2 of 4 pin connector)

Remember that MS will only trigger FP for a sec when you turn on key (enable in TS) and then again when it senses a Crank or Run condition.
 
#40 ·
the problem i had was when i had it wired "correctly" i could not get power to the ecu even. ill look at my wiring today and see what up. i dont have my motor back fro machine shop yet so i have plenty of time to deal with wireing
 
#46 · (Edited)
Wires everywhere but making progress.
Wiring up my Spartan Wideband to make it easier to replace, IF, it ever goes bad. On the power wire used a male / female connector with heat shrink over the connector and on
ground & signal wires heading back to the ECU used a 2 pin weatherpack connector.

spartan wiring where it splits off for power, 2 for the ecu, and ground to engine block



and connector heading to ecu

 
#51 ·
So, still working on this when I have some free time that is. I have my catch can finally installed and my vacuum log/manifold installed.
Will update soon, as I am sure after I get Tuner Studio loaded on my laptop and I'm getting ready to fire it up I will have some questions.
 
#52 ·
Well the engine starts and really sounds good but will not idle, so I've been doing some checks.

Just checked for power with key in the on position at ecu and getting power from the first 6 pins on the bottom row if counting from the left which I think are pin #'s 20 through 25 and also the 10th pin which I think is # 29

Which is odd because my wiring diagram shows pin #6 and #10 as auxillary wires.

Also that would indicate that the TPS sensor #7 and main relay #9 don't get power with the key in the on position.

But I'm trying to figure out how these wires have power with just having the key in the on position
 
#54 ·
Thanks Paul,

Those pin # sound odd as 1-2 and 7-19 are all grounds in a normal ms harness.[/QUOTE

Yes with connector/harness unpluged from the ecu and looking at the connector I'm checking at the connector pins that connect to the ecu and thes are on the botttom row counting left to right.

This was originally a 8v Digi 2 car that I swapped a 16V engine and trans into and I tapped in to original connector you can see pictures of this in the first few pictures in this thread.


In the Bentley it shows that red/yellow wire connects to fuel pump relay termimal 85, which is exactly where my purple MS- terminal 37 wire needs to go. So I just connected to that.

Also the Bentley shows that black/yellow wire connects to Digi control unit relay terminal 87, which is exactly where my red MS 12V+ switched- terminal 28 wire needs to go. So I just connect to that after adding a 2 amp in line fuse,

Do you think this could be part of the problem?


I got this wiring harness from DIY Auto tune, maybe I should pull the sleeve off the harness and make sure the right color wires are going to the right pin location in the conmector.
 
#59 ·
That was a big gap in time there for a while. Just curious what the current state of things is with the car?

I'm currently (barely) running bike carbs on my 8v but am thinking of making the plunge into MS for long-term purposes. I'm eager to hear how it has worked out for you. :thumbup:
 
#60 ·
Well, sometimes its the little things that make such a big difference.

I finally got the engine to idle. It would always start and I could keep my foot on the gas and it and rev it up and and it would sound great, but anything less than about 2500 RPMs it would just turn off.

I was talking to a friend of mine who has a great amount of automotive experience, and we were reviewing things like wiring diagrams, settings and he questioned where did I mount my MAP sensor.

I told him it was inside the Megasquirt ECU and I have a vacuum hose from the ECU to the throttle body.

And he quickly said well that couild very well be your problem, because you need manifold vacuum not port.

And I was thinking could be really be that easy???? So I removed the vacuum line from the the throttle body, put a vacuum cap on it and attached the vacuum line to the back of the intake and statrted it up.

As soon as it started I revved it up to about 2500 and then let off, and it was idling at 1000 rpms in a smooth awesome sounding idle, and all I did was reposition the vacuum hose for the MAP Sensor.

Amazing, this is a project car, a 1991 16v GTI and I started this project in 2004. I bought this car in 2004, drove it home and parkied it in the middle of the garage and took it completely apart and have been working on it in my spare time since.

Complete trans and engine disassembly and reassembly with goodies, and the list goes on and on about what I have done to this car and now I can finally drive it!!!!!!

I am also going to use a T vacuum fitting at that location and attach the vacuum hose from the fuel pressure regulator to the same vacuum source at the back of the 16V manifold.

Amazing. All that time questioning myself and going over wiring diagrams in my head and retracing my steps only to find I need to move a vacuum line from the throttle body to the intake manifold

Many thanks to Spitfire EFI and Paul at KPTuned!!
 
#61 ·
Wow, I have had that happen a handful of times over the years and it is not an easy find. Especially if you think the tb port is on the manifold side! Usually happens with the booster check valves as those see manifold vac but not a great source.

Glad you found the glitch and its smooth sailing!
 
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