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another iac ms question

aussyvolvo

aussyvolvo

Will stalk for money
Joined
Jul 12, 2007
Location
South Australia
I considered just using the relay option for a 2 wire lh2.4, but I'd rather my ms2 v2.2 deal with it (yes I finally got the upgrade). But I'm having a little trouble understanding this diagram http://www.msextra.com/doc/ms2extra/MS2-Extra_Hardware.htm#Fidle

pwm-tip120.jpg


The right side is what looks to be the Q5 transistor, but the left side looks like..... I don't know.... is that just another version of the v2.2 circuit board? Do I only follow the right side?

and is it safe to put that 12v through x14 or something?
 
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You are using the older V2.2 board. On the newer V3 board the idle air valve control transistor is Q4 and the transistor supplied with the board (and replaced by the TIP 122) is a ZTX450 and looks like the transistor on the left side of the diagram. This is not relevant to your installation. I have never seen a V2.2 MS Board; but, they appear to be set up to use a 2N2222 transistor which is typically a TO 18 'can' style of package. You should use the diagram on the right if you have a 'can' style transistor.

Make sure that you mount the TIP 122 on a heat sink and use an electrical insulator between the transistor's metal tab and the heat sink. The transistor gets hot.

I am not sure what your reference to x14 is. Are you talking wire size or pin number?
 
Those 2 diagrams show how the larger transistor replaces either of the 2 styles of native transistors.

Pick the one that applies to your board.

When I do this I use the schematic and a data sheet for the device to ID the pins.
I never know if the pictograms are drawn from the top or bottom.....
 
142 guy said:
You are using the older V2.2 board. On the newer V3 board the idle air valve control transistor is Q4 and the transistor supplied with the board (and replaced by the TIP 122) is a ZTX450 and looks like the transistor on the left side of the diagram. This is not relevant to your installation. I have never seen a V2.2 MS Board; but, they appear to be set up to use a 2N2222 transistor which is typically a TO 18 'can' style of package. You should use the diagram on the right if you have a 'can' style transistor.

Make sure that you mount the TIP 122 on a heat sink and use an electrical insulator between the transistor's metal tab and the heat sink. The transistor gets hot.

I am not sure what your reference to x14 is. Are you talking wire size or pin number?
Click to expand...

X14 is a free header pin that pops out on the db-37. I would think running 12v in that way would be safe, I don't know what kind of draw that's going to have though. I've always been able to get em to work fairly well without the diode, but I doubt it hurts things
 
That's a recirculation or flyback diode. It allows the current going through the IAC coil to recirculate and die off more slowly when the drive current from the transistor shuts off. I've seen mixed reports on if it usually helps IAC tunability or not. Doesn't hurt either way.

The +12v ign is just 12volts somewhere on the MS board (close to the connector is better). It doesn't need it's own new wire.
 
On the V2.2 board, the collector of Q5 is already connected to Pin #30 on the db-37 connector (the idl output). If they wire the TIP 122 in to the Q5 position as shown, the output automatically comes out on pin #30. No need to use the X14 jumper pad. I have been running my Bosch 2 wire idle air valve through pin #30 for a couple of years now with no problem.

Also, the V2.2 schematics diagrams

http://www.bgsoflex.com/v22/megasquirt_ShemV2.2.pdf

indicate that Q5 already has a 1n4001 recirculation diode installed on the Q5 collector position (diode D9). As such, it is not clear to me why that diagram from MSExtra.com indicates the addition of a 1n4001 recirculation diode unless there were later changes to the board. The version 3.0 board use a more elaborate driver for the idle air solenoid including a current limiting feedback control and a zener to clamp the output voltage on Q4. If you do the TIP122 modification on a V3.0 board you definitely need to add the 1N4001 recirculation diode.

If the OP has not acquired the idle air valve already, I would recommend the Bosch 3 wire over the 2 wire valve. The position of the pintel in the 2 wire valve is sensitive to the supply voltage and that position sensitivity needs to be programmed in to MSExtra for correct operation. The restraining torque on the 3 wire valve is supplied by a 2nd winding (rather than a spring) which eliminates the change in position of the pintel with the change in supply voltage. The voltage sensitivity is a significant issue if the voltage drops significantly during cranking of the motor. If you program the PW to operate with a normal voltage of around 13.8 and the voltage drops to 10 volts during cranking, the opening on a 2 wire valve may be more than 20% less at 10 volts than 13.8 volts.
 
bobxyz said:
That's a recirculation or flyback diode. It allows the current going through the IAC coil to recirculate and die off more slowly when the drive current from the transistor shuts off. I've seen mixed reports on if it usually helps IAC tunability or not. Doesn't hurt either way.

The +12v ign is just 12volts somewhere on the MS board (close to the connector is better). It doesn't need it's own new wire.
Click to expand...

The recirculation diode is there to protect the control transistor by clamping (effectively shorting it) the reverse voltage that occurs across the idle air valve coil when the current is shut off. I doubt that it helps tune ability, unless you view survivability of the transistor as a prerequisite for tune ability :).

The TIP 122 has a rated Vce of 100 volts and is rated to tolerate an inductive stored energy of 50 mjoules without the use of a clamping circuit. I haven't measured the inductance on a Bosch 2 wire valve so I have no way of saying whether its within or would exceed the ratings of the TIP 122. The cost on a 1n4001 is around $ 0.10 ($0.03 if you can find 3000 other friends who want one). Cheap insurance, particularly since the v2.2 board already seems to have one.
 
^^^ oops, you're right, my mistake. I must have been thinking of the drive transistor for the boost solenoid. I wonder why they recommend two different parts and circuits for similar air valves?
 
I wasn't concerned about prices, or why the diode was there haha just confused. Bobxyz, you say that I can get 12v from inside the box? I'm looking, and can't seem to find this information.

There is 1 last thing, what relays do you find work best, I need a "main relay," and "fuel pump relay". I want cheap, it doesn't need to be fancy (it's just for a track car), but not flimsy.
 
Check your circuit board. If it is a V2.2 board and you have D9 installed and you use IDL output (db-37 pin #30) to connect the idle air valve, you already have a 1n4001 connected to +12 v.

If you don't want to use the IDL output and want to install a separate 1n4001 diode, you could pick 12 v off of the board from one side of the D9 diode location (use the schematics linked previously to figure out which side).
 
142 guy said:
Check your circuit board. If it is a V2.2 board and you have D9 installed and you use IDL output (db-37 pin #30) to connect the idle air valve, you already have a 1n4001 connected to +12 v.

If you don't want to use the IDL output and want to install a separate 1n4001 diode, you could pick 12 v off of the board from one side of the D9 diode location (use the schematics linked previously to figure out which side).
Click to expand...

there is a D9, I can't quite read what's on it though, but it might be as you stated, the pcb also lignes it up to the right pin, are you saying that all I need to do is put the transistor in, and I'm done?
 
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