Problem with Ford IAC

EFIDart · Post by **EFIDart** » Fri Nov 18, 2005 6:27 pm

Ive been having some problems lately with my Ford IAC valve with my MS II.
I bought my MS from diyautotune.com with the Ford IAC mod installed.

Testing the PWM on my stim I find when I adjust the PWM of my IAC the LED dims or brightens which is right. But when I hook up my IAC valve it doesnt want to work, I can connect or disconnect it and it does nothing even when adjusting the pwm for warmup.

I removed the relay from my relay board and jumpered the DB37 source where the relay used to sit to the Fidle pin (2 & 4 I believe).
I also put a diode between the + (comes from the fuel pump lead) and the Fidle wire, like the documentation says.
The valve used to fast idle when I connected it but it was stuck open it seemed.. but wouldnt come down..

Any ideas??

i8dirt · Post by **i8dirt** » Fri Nov 18, 2005 10:05 pm

Hi,

Just incase you already did not do this:

Did you do the PWM modification in step 62 in the assembly manual. http://www.megasquirt.info/ms2/V3assemble.htm

Is Q4 a ZTX450 transistor or did you do the PWM modification with a TIP121.

The original Q4 cannot take the current to drive a PWM, so a TIP121 must be used in its place.

Not being a MS expert this is the best I can suggest for now:

After you used the MS in the car and the IAC "failed" did you try to see if the MS worked properly on the stim again. If it is bad on the stim now, I would check the components on the board for failure.

If you did the TIP121 mod on Q4 and the MS works on the stim, then I would start to troubleshoot the wiring.

Good luck,
Mark

EFIDart · Post by **EFIDart** » Mon Nov 21, 2005 11:40 am

I would assume that is all done the mod I had done is "a 1/4w 620ohm resistor to replace R19 and a ZTX688b to replace Q4".

I did check it with the stim after and it fades the LED like it should for the pwm.

I have a diode between the 2 IAC wires... and even with the PWM at 0 or 100% it still shows the fast idle light.. when on the stim it actually goes off. Im wondering if the Diode is screwing something up??

FoundSoul · Post by **FoundSoul** » Mon Nov 21, 2005 12:29 pm

The 620o and ZTX688 mod dates to Ryanpzz's research as recorded here: http://www.msefi.com/viewtopic.php?t=11301&highlight=

Ryan knows his stuff and noone has noted any issues with this setup that I'm aware of at all. I'm not aware of any docs directing use of a diode as a part of this though...

Post by **jsmcortina** » Mon Nov 21, 2005 1:26 pm

FoundSoul wrote:I'm not aware of any docs directing use of a diode as a part of this though...

The stock V3 circuit has a Zener diode as protection. According to Bruce, this could overheat if used with a PWM valve and should be removed and a 1N4001 fitted like on the V2.2 board or directly across the valve.

James

Bossman · Post by **Bossman** » Mon Feb 27, 2006 5:47 pm

YOu know what, this mod has been out for awhile now, yet NO ONE has changed the stupid assembly manual to reflect this.
You see, a person has to go hunt down these posts so they can verify whether OLD SCHOOL directions still apply. This particularly makes me mad because there is a huge section in the instructions dedicated to all this jumpering and replacement parts when the above MOD has proven to be effective.
Update the stinking instructions to reflect recent findings instead of the long winded work arounds that were first tried.

Bossman · Post by **Bossman** » Mon Feb 27, 2006 6:06 pm

I'm building a MSI v3. Both instructions you listed don't show anything about the mod kit.
So now people are left wondering, "well do I do the mod kit and some of those jumpers and diodes, or is the mod kit fine and dandy?"

racingmini_mtl · Post by **racingmini_mtl** » Mon Feb 27, 2006 6:53 pm

Lance,

I believe that this "mod kit" is something from DIYAutoTune. So Bossman (and anyone using those) should talk to Jerry if they have any question.

I think that Jerry (aka FoundSoul) should make it clearer on his site and/or when he ships those kits what needs to be done. You shouldn't have to deal with any vendor specific issues and you certainly do not deserve the language used above.

Regards,
Jean