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Old 02-21-2012, 09:30 AM   #1
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megasquirt PWM and jumper question.

Ok I purchased the megasquirt 2 with pcb3. I have been soldering it using the directions for the ms-extra. Now I just found "how to megasquirt your mustang" and started reading over that and noticed a few differences.

For the PWMIAC in the mustang directions it has you use a tip 120 soldered to Q4 via the diagram. Or do I use the MS-Extra where you have 2 wires go to Q4 one to r43 and a diode to s12?

Also for some of the jumper wires the mustang directions have XG1-XG2, Optoin-Tachselect, Tsel-Optoout. VS the MS-Extra Optoout-Tsel, Tachselect-Xg1, And 2 others depending on 5v or 12v (which one for a mustang?)

So my question is should I continue doing the Ms-extra build, or go back and just follow the mustang build.? The car is in the garage so there is no hurry, If I have to backtrack and follow the mustang specific that is fine with me.

My build is a 89 mustang..
351W
10.5:1 CR
Performer RPM heads with port work
Custom cam 542/563lift 282/290duration
50lb injectors,
msd 6al
gt40 intake, extrude holed lower
nos

Future plans .. I have a D1 procharger waiting to go in, new super victor intake, elbow and probably bigger injectors..

I need to rebuild the motor to drop the CR for the procharger so I figured I would do the megasquirt first (if i screw up and melt a piston at least it's a piston I'm pulling out anyway..)
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Old 02-21-2012, 11:00 AM   #2
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Quote:
Originally Posted by dbldrew View Post
Ok I purchased the megasquirt 2 with pcb3. I have been soldering it using the directions for the ms-extra. Now I just found "how to megasquirt your mustang" and started reading over that and noticed a few differences.

For the PWMIAC in the mustang directions it has you use a tip 120 soldered to Q4 via the diagram. Or do I use the MS-Extra where you have 2 wires go to Q4 one to r43 and a diode to s12?

Also for some of the jumper wires the mustang directions have XG1-XG2, Optoin-Tachselect, Tsel-Optoout. VS the MS-Extra Optoout-Tsel, Tachselect-Xg1, And 2 others depending on 5v or 12v (which one for a mustang?)

So my question is should I continue doing the Ms-extra build, or go back and just follow the mustang build.? The car is in the garage so there is no hurry, If I have to backtrack and follow the mustang specific that is fine with me.

My build is a 89 mustang..
351W
10.5:1 CR
Performer RPM heads with port work
Custom cam 542/563lift 282/290duration
50lb injectors,
msd 6al
gt40 intake, extrude holed lower
nos

Future plans .. I have a D1 procharger waiting to go in, new super victor intake, elbow and probably bigger injectors..

I need to rebuild the motor to drop the CR for the procharger so I figured I would do the megasquirt first (if i screw up and melt a piston at least it's a piston I'm pulling out anyway..)
Can you put up some links and reference to step #'s so that we can be sure we're on the same page.

At a quick glance, you mention a TIP120 in place of Q4. That's in the Megasquirt 1 instructions, not megasquirt 2?
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T56 w/ AJE xmember, McLeod street twin, MM/Bilstein '03 IRS, JRi Agent47 SLA
Megasquirt

Last edited by seijirou; 02-21-2012 at 11:52 AM.
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Old 02-21-2012, 02:18 PM   #3
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Either set of directions can work.
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Old 02-21-2012, 02:20 PM   #4
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Quote:
Originally Posted by seijirou View Post
Can you put up some links and reference to step #'s so that we can be sure we're on the same page.

At a quick glance, you mention a TIP120 in place of Q4. That's in the Megasquirt 1 instructions, not megasquirt 2?
How to MegaSquirt your Ford Mustang 5.0

1/2 down the page it has MS-II PCBv3.0 istructions
step 59 on that page talkes about the mk-PWMIAC mod and a link to it here..
PCBv3 -- PWM IAC Valve Control (TIP120) &#39Mod-Kit&#39 DIYAutoTune.com

that link shows the TIP120 going into Q4 on a PCB3.0.

Also step 62 in the mustang build, referances doing step 62 in the mega manual for the blue box, which is the same diagram..

Assembly Guide - MegaSquirt<sup>®</sup> V3.0 Main Board


Thanks for the help
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Old 02-21-2012, 02:43 PM   #5
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Quote:
Originally Posted by Matt Cramer View Post
Either set of directions can work.
ok thanks, is one set of instructions better for my build? should I stick with the ms-extra or do the mustang specific? I've noticed a few other variations. The MS-extra said not to use R12, the mustang specific said to put in R12, and i'm sure there are other examples as well if I keep looking. I really don't care which one I use as long as it's the best option for my car..

Thanks
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Old 02-22-2012, 08:59 AM   #6
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In the case of R12, they both end up with a similar total amount of resistance. Just pick one set of directions and stay with it.
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Old 02-22-2012, 12:39 PM   #7
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Note: All of the following could be wrong but I think it's right. Any clarifications/corrections would be cool.

IAC thing. It's kind of hard to follow as I can't find complete diagrams of either setup but with some imagination I think I can see why they're the same difference.

I was able to find the diagram for the standard megasquirt idle control here. It's a little more than halfway down and to the right.

Looking at that, for the "mustang" way, you can cut Q20 and D8 out. R39 is not a resistor so imagine that as just a straight line to ground.

So basically you've got a transistor that I believe is acting like a switch. The Collector (top of Q4 in that diagram) goes to "idl", which is pin 30 on the db37 (if you scroll down that page a little more you'll find the DB37) and connects to the IAC. The Emitter goes directly to ground. I'm guessing then the Base goes to the cpu then ("Idle-1") through r19 so that when the Base is energized, the Emitter and Collector become connected, effectively pulling the Collector to ground. Assuming the other wire to the IAC is just +12 from ignition, we're using Q4 as an on/off switch for the ground side of the IAC.
The last bit of the "mustang" instructions is to install a diode with the cathode (striped end) on the +12, and the other end (Anode) on the "lead that goes to megasquirt", which is that same pin 30 on the db37 that goes directly to the Collector of Q4.

So it looks like the MSnE way connects the Base in the same manner.
The Collector is wired the same way.
The Emitter is different in that it goes to R43. I did some digging and found that R43 also goes to ground, so it's really not effectively different than going to R39, especially since the MSnE have no resistor at R43.

So, our wiring of the transistor is functionally identical.

Now look at the diode. Basically instead of having it up at the IAC valve, it's down here by the transistor. The Cathode is going to the s12 pad which I found out gives +12, and the Anode goes to the Collector of Q4. On the "mustang" way the Anode goes to the wire, that in turn connects to the Collector of Q4. So it's essentially the same thing, just on a different spot along the wire.

So the only real difference I see is that in the mustang way, the +12 for the flyback diode comes from the +12 wire going directly to the IAC, where the MSnE way gets the +12 from the s12 pad.

I don't know if one is more ideal than the other.

I'll try to make sense of the other jumpers you asked about when I get more time.
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393w, Vic Jr 60cc, XE282HR, Victor 5.8 EFI, 42# injectors, Hooker LT 1 3/4 to 3", Borla proXS
T56 w/ AJE xmember, McLeod street twin, MM/Bilstein '03 IRS, JRi Agent47 SLA
Megasquirt

Last edited by seijirou; 02-22-2012 at 12:47 PM.
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Old 02-23-2012, 11:32 AM   #8
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Quote:
Originally Posted by Matt Cramer View Post
In the case of R12, they both end up with a similar total amount of resistance. Just pick one set of directions and stay with it.
I decided because I have a stang.. might as well go with the mustang directions..

Thanks for all the help
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