MSefi.com read only forum (Jan.15,2018)

I have a MS-II v3.0 Rev. 2.90500. I am running TunerStudio MS Lite v.2.0.6. I have also attached my MSQ. I am using a FAST 4150 style throttle body, the very same one they supply with their EZ-EFI systems. The IAC valve in question is GM #17113598. I have not started the motor yet.

I am trying to figure out the full range of my stepper motor using the method described here: http://www.megamanual.com/ms2/IAC.htm. I am THOROUGHLY confused about how this thing is supposed to work. The first time around I was getting some very inconsistent results. I since figured out that I had the plug wired in reverse (I wired it according to the 2nd example (http://www.megamanual.com/ms2/ewIAC.gif), only as if I was looking at the open end of the plug facing me, not facing the plug socket of the IAC). So, last night, I released the terminals from the plug, put some heat shrink around them to prevent shorts, and plugged them into the IAC as the second example (http://www.megamanual.com/ms2/ewIAC.gif) depicts just to test the operation before I reconfigured the plug. I got the same type of inconsistent results. I have no idea if I reversed the previous operation of the motor or not.

As I said, I used the method outlined on the IAC page. I would assign a number to "Start Value (retract)", click "burn", turn the key to the "off" position to kill power to the ECU, then turn the key back to the "run" position. I can watch the pintle extend to a position, then retract a little and stop. The problem I have, is it is not consistent. I would try a "Start Value (retract)" of 200 and get a measurement (arbitrary position, just a spot I could repeat) of 0.25". Then I would set "Start Value (retract)" to 180 and get a measurement of 0.125". Then I would set "Start Value (retract)" at 210 and get a measurement of 0.25". Then I would set "Start Value (retract)" at 180 and get a measurement totally different from the last time I had it set at 180. The reason the numbers I tried were so high is because it didn't seem like the pintle was retracting fully, so I kept going higher.

I might also add that I cannot turn the pintle with my fingers. I have ejected it twice now, and each time I have had to hold pressure against it, change the "Start Value (retract)" number and HOPE that it will tell the motor to retract the pintle and get it threaded back into the motor.

At that point, I realized I wasn't getting consistent movement and I decided to get a little more methodical. Below are the "Start Value (retract)" numbers I tried, and their corresponding measurements:
1 - 0.38"
15 - 0.44"
30 - 0.53"
45 - 0.59"
60 - 0.66"
75 - 0.69"
90 - 0.72"
105 - ejected the pintle
180 - able to get the pintle threaded back into the motor

At that point I got frustrated, quit, and headed to the computer to search for an answer. I have still not found one...

I set "Cranking Position (extend)(steps)" at 300 in an attempt to keep it from having an effect. The highest number on my "Idle Steps" table is 160.

From the instructions(http://www.megamanual.com/ms2/IAC.htm), I understood that the "Start Value (retract)" number should be how many steps the motor retracts the pintle to be fully open, and allow the maximum amount of air to be allowed into the engine. But that doesn't seem to be the case with mine. And even though it looks like my pintle extended a little further every time I raised the "Start Value (retract)", it really wasn't that consistent, when I entered 180 it went as small as 1/8". With the wiring flipped the other way, its the same type of inconsistent behavior.

So, any clarification would be greatly appreciated. IF WIRED http://www.megamanual.com/ms2/ewIAC.gif; Should the "Start Value (retract)" seat the pintle, or retract it? Is there any other parameter that affects it when I'm bench testing like this?

Sorry if this is confusing, I am absolutely baffled. To me, as I increase the "Start Value (retract)" number, the pintle should either retract or extend (depending on how it's wired) consistently, end of story. I can't determine anything consistent about the operation I'm seeing, so it's hard to make any of this make any sense.

Thanks in advance for any help.

Alright, gonna try something this afternoon maybe. I'll post it here in the hopes that somebody will let me know if it's a waste of time...

From what I understand, the motor fully retracts at key-on. After that is where I'm hazy. The way I comprehend it, some of what I read suggests that the motor fires with the valve completely open, and some suggests that it closes to a value dictated by the IAC Step Table. Being that there is a "Cranking Position" value that one can use to override the position commanded by the IAC Step Table (per the MegaManual) to give a larger opening of the IAC at startup, it follows that; at key-on, the motor fully retracts/opens, then extends/closes to the position the IAC Step Table or the Cranking Position dictates, whichever is open furthest all before the motor runs.

SO, I figure the inconsistency that I'm seeing is because of the difference in the steps I'm commanding to fully open the valve, and the steps the IAC Step Table is commanding to close it based on the temperature. My plan is to set all my table values to 0, that way they won't indicate to close the valve at all from it's full-open position. That way, I can figure out what "Start Value (retract)" value fully opens the valve. Hopefully then I'll be able to tell how many steps fully strokes my IAC.

Part of my problem might be that since I built my harness in the truck before I ever tested the valve, I can't switch the key on and watch the valve at the same time. By the time I get my eyes on the valve after I turn the key on, it's already done moving. I'm not sure.

Hopefully this will work for me. I would appreciate any clarification on the above, if it's even clear enough to come up with clarification...

Thanks!

Problem solved!

I did as I said I would, set all the table steps to zero, then continued to cycle the ignition switch on and off until the pintle opened/retracted completely. Then, to figure out how many steps it took to seat the pintle to close the airway off, I pulled up the IAC Step Table and raised the number of steps on either side(same # of steps on both) of the temperature reported by my ECU until the pintle was seating. What made it even more convenient is that the pintle would actually extend without cycling the power on and off. All I had to do was raise the value on the table and burn it, and the pintle would extend by the number of steps I added or subtracted. My stepper came out to 235 steps for full range.

I don't know if people commonly have problems setting this up or not. Now that I understand how it all works I feel a little dumb. But I look back at how many times I read over the information I had available, and I really think the MegaManual is a little vague on how all this fits together. Just for the record, the pintle fully retracts, then extends by the number of steps on the IAC Step Table or the "Cranking Position", whichever is smaller(open the most), all before the motor cranks over. Either way, hopefully my little struggle will help somebody down the line when they are searching!

Thanks for posting your findings on this issue. I'm just a few steps behind you on doing a FAST ez efi conversion as well, so this should help me a bunch.

Could you post a .msq when you have it running good. I'd like to see how some of your settings compare to mine for the EZ-EFI . Thanks......JP

I can do that. I keep inching closer and closer to having this thing on the road, but realistically it will probably be a month or so.

I'm going to try and let it autotune first, see how far that gets me. Glad my info could help somebody else. Good luck with yours!

I had exactly the same issues a while back when I tried to get my IAC working; I eventually worked it out in a similar way.

1) I connected the IAC up to the MS but not installed on the car. (In my case the IAC and the IAC Body are separate from the engine)[/size]2)
2) I set the Cranking Position value to 0 and the Table values to 0
3) Set starting position to 260 (i.e. retract by 260 steps – just a guess - as I didn’t know how many it would take to bring it all the way open).
4) I powered the IAC, and watched that it retracted the pintle all the way open
5) I slowly starting increasing the table values until I got to the point where it was closed. I verified it by blowing into the inlet opening of the IAC body. I took about 250 steps to close it.
6) I reset my Start position to 252 steps - regardless of the pintle’s position when the motor was last running, it should always come back fully open if the start value is just over the fully extended value.

The rest is all pretty straight forward.

One thing I noticed is that in the fully close position; there is still some very minor air leakage around the pintle. It seemed air tight when I blew into it, but since I installed it the engine is now
idling 4 or 5 kPa higher than it did without the IAC. It’s only a little bit and I'm not worried, but I'm curious to see if anyone else’s does too