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does anyone run their car without a power transistor?

biglady112

Proven Member
1,725
267
May 20, 2004
Commerce City, Colorado
I am getting a little tired of dealing with these things flaking out, the connectors corroding as often as they do and just about everything about them. It sure would be nice to be able to clean things up and get rid of it. Does anyone run without the power transistor (ptu) on a stock ecu? Can the ecu handle it?

I want to go straight from the ecu, to the arc ignition, to the new motorcycle coils a have.

Anyone see a problem.?
 

dexterholland04

Proven Member
756
104
Jan 1, 2007
Rush, New_York
I am getting a little tired of dealing with these things flaking out, the connectors corroding as often as they do and just about everything about them. It sure would be nice to be able to clean things up and get rid of it. Does anyone run without the power transistor (ptu) on a stock ecu? Can the ecu handle it?

I want to go straight from the ecu, to the arc ignition, to the new motorcycle coils a have.

Anyone see a problem.?

Yes, this would be a bad idea. The ECU requires a PTU because it cannot drive the current to the stock coil necessary to maintain a proper dwell time. With the CDI system, the PTU is still required because the capacitor (which stores the spark energy) requires a large amount of current to charge in a very small period of time. Now, you could drive the CDI directly from the ECU, but I would be interested in what kind of RPM you would get out of it...since you would be limited to how fast the tiny driver in the ECU can push current to charge the CDI.

Hope this makes sense.

-Will
 

serviceguy

Proven Member
571
35
May 11, 2002
Clifton, New_Jersey
I may be wrong but I believe the CDI would draw current directly from the battery while using the ECU signal only to determine when to fire the spark.
 

biglady112

Proven Member
1,725
267
May 20, 2004
Commerce City, Colorado
I am seeing a ton of diagrams out there that do not show a resistor. They likely are not Mitsubishi specific. I am just wondering if there is any ill effect to the ecu in removing it. My friend was going to dive into the Mitsubishi schematics at work and see if there is something special about the transistor. I am sure the cdican handle it, just not sure if and how long the ecu could.
 

dexterholland04

Proven Member
756
104
Jan 1, 2007
Rush, New_York
I am seeing a ton of diagrams out there that do not show a resistor. They likely are not Mitsubishi specific. I am just wondering if there is any ill effect to the ecu in removing it. My friend was going to dive into the Mitsubishi schematics at work and see if there is something special about the transistor. I am sure the cdican handle it, just not sure if and how long the ecu could.

See my first answer. The attached diagram shows why. The red line represents the high current sink for charging the coils inductively (stock), with a CDI, or with whatever you want to use. The red line shows a low current sink, where the ECU (pale green) merely provides ground to turn the PTU on and off. Also, you'll lose your tachometer signal, as well, because you lose the XNOR logic to generate the tachometer pulses.

Original:

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Color-coded:
upload_2016-5-9_14-42-45.png
 

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biglady112

Proven Member
1,725
267
May 20, 2004
Commerce City, Colorado
This car runs no dash and uses and aftermarket tach. That is not a concern. I was told the ecu could not run without an mpi relay and I have made it happen one four different cars now. I am sure this is possible in some way.
 
Last edited:

serviceguy

Proven Member
571
35
May 11, 2002
Clifton, New_Jersey
You are, see my posts.

If anything your posts seem to confirm what I said. The CDI does the work of the PTU using the trigger signal from the ECU. The ECU outputs are not the one sinking the current. I never implied you could control the coils using the logic outputs of the ECU without a CDI in place of the PTU.
 

brads

DSM Wiseman
840
73
Oct 24, 2002
Alta Loma, California
Quite a few people run the ARC-2 without a power transistor. Both DSM guys, and Evo guys. I don't recommend it because of the additional wiring to get everything working. But it sounds as if your wiring is already cut up, so no worries there.

Adding the PTU in between the ECU and ARC-2 also adds a level of noise isolation between the 2, since it is like a predriver stage.

Aside from that, it will work. The trigger signal for firing will be inverted, but the ARC-2 is designed so that you can select which edge to fire on. You won't need the tach adapter from the ARC-2, since that is designed to fool the PTU. Instead you will have to hardwire the tach output from the ARC-2 into the tach wiring. So you are probably better off using a universal install harness at that point.
 

biglady112

Proven Member
1,725
267
May 20, 2004
Commerce City, Colorado
This car already had had stand alone, aftermarket tachometer working and installed. This is a race car. There is nothing more than an engine harness that I extremely thin and had nothing more than what it needs to run the engine. The arc box and wiring is a universal unit in this car. I witrd everything in to my liking already.

So on paper I can wire it like I want, flip the little switch and I should be ready to go back to the dyno, no?

What makes or causes the signal to need to be inverted?
 

bastarddsm

Proven Member
5,342
1,146
Aug 26, 2003
Mendota, Illinois
I run my dynatech straight from the ecu, when I run it.

I don't necessarily think that the ptu adds noise isolation. The input too the PTU is high impedance, so I'm not sure how driving the high impedance dynateck, from a low impedance source, triggered off a low impedance input is any better than triggering the dynatech right off the ecu.

Ditching the ptu and stupid tach adaptor is well worth it.

the two trigger wires from the ecu goto the dyna trigger wires, tach signal from the dyna goes to the tach signal wire at the ptu, and that's about the only changes. easy as pie. If you have a plug from an old MAFT around you can make an easy plug and play!.
 

brads

DSM Wiseman
840
73
Oct 24, 2002
Alta Loma, California
This car already had had stand alone, aftermarket tachometer working and installed. This is a race car. There is nothing more than an engine harness that I extremely thin and had nothing more than what it needs to run the engine. The arc box and wiring is a universal unit in this car. I witrd everything in to my liking already.

So on paper I can wire it like I want, flip the little switch and I should be ready to go back to the dyno, no?

What makes or causes the signal to need to be inverted?

Most all transistorized ignitions(like the stock DSM one) work by supplying 12V to one side of the coil, and then switching the other side(coil -) to ground. When coil - is grounded, current flows through the coil and it charges. When coil - is disconnected from ground, that is when the spark occurs. The voltage at coil - goes from nearly 0V to way over 12V, usually 200V or so. So the coil is firing when that coil - signal transitions from low to high.

However, the signal from the ECU to the PTU is high to tell it to ground the coil -, and low to tell it to disconnect the ground. So the coil fires when the signal transitions from high to low. This ECU to PTU signal is inverted mainly because electrically it is the simplest way to control the PTU.

The fact that the coil - wire is firing on a low to high transition is nearly universal, so you know if you hook a CDI up right before the coil, it is always this way. Most CDI boxes are designed to fire on the low to high transition.

Newer vehicles with COP that have transistors built into the coil are hiding that coil - wire inside the coil so you can't access it. Instead the wire going to the coil is the ECU to PTU signal. So a lot of times if you are looking at the coil signal on those cars, you have to view that signal wire going to the coil as inverted.

The ARC-2 and some other CDIs allow you to select it to trigger on the low to high, or the high to low transition. This trigger point is what it treats as the firing point of the stock ignition. So you can adjust it to work with a signal from either location.
 

brads

DSM Wiseman
840
73
Oct 24, 2002
Alta Loma, California
I don't necessarily think that the ptu adds noise isolation. The input too the PTU is high impedance, so I'm not sure how driving the high impedance dynateck, from a low impedance source, triggered off a low impedance input is any better than triggering the dynatech right off the ecu.

Ditching the ptu and stupid tach adaptor is well worth it.

You shouldn't run into a problem wiring it like that, we designed the thing to be pretty well idiot proof :) It's just not ideal. Wiring things correctly in the first place helps avoid problems down the road. But I see people wiring it in by extending the wiring, moving it in the cabin, putting the output wires close to other wires, running the 12V battery wires close to other noise sensitive wiring, and still not having problems. Doesn't mean I would start recommending any of those.
 

biglady112

Proven Member
1,725
267
May 20, 2004
Commerce City, Colorado
Rewired the car tonight. This ended up working out without any issues. First trip around the block the car was down a cylinder (the reason why this fiasco started). Did some more poking around and ended up finding three injectors with rust coming out of the pintles. Cleaned all the injectors and back to your cylinders. A trip around the block again and we are back to normal. Now I can go back to the dyno and clean the tune up a little more and work on adjusting the cam gears on the dyno some more. We might just make our race next month yet.

It was worth doing this as if this thing had not started acting up I would not have found the corroded connector until it was too late on the road at a race somewhere. I would rather simplify things anyway and be reliant on less parts. So far so good. We will see how she acts on the dyno with the transistor missing and the new motorcycle coils. Hopefully it can get back to kicking some ass.
 
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