Initial Setup of TBI, TPI and MPFI systems. Min Air Adjust, TPS set and Fuel Pressure

[JeepsAndGuns]

Ahh, good to know.

[88ragtop]

This article explains pretty well how the various types work: http://www.megamanual.com/ms2/IAC.htm. Just read around the megasquirt configuration stuff that you dont care about :)

- Frank

[1project2many]

A stepper motor like the IAC need to have power and ground applied to different terminals to make the armature turn a complete revolution. Look at the gm wiring diagram for your system and you'll see two connections for coil A and coil B. Each of these needs to be connected to 12V in turn on order to make the IAC move. When the ECM shows IAC counts, that's how many times the ecm has applied power to one or the other coils to make the IAC move. I have an old tool made by Thexton but I couldn't find it in their current tool lineup. Here's a thread that gives a homegrown way to check the IAC: http://www.chevytalk.org/fusionbb/sh...96c4b37436442/ There's also a mention of an OTC3320 IAC tester but I really think those old tools are only going to show up in Ebay auctions or swap meets now.

[EagleMark]

You sure it's 12 volt? I wasn't... then read the IAC procedure .pdf and it says do not apply 12 volt... ?

[Mastiff]

I tried this procedure and when the A/B pins were shorted the IAC made noise and never stopped. Just kept sort of buzzing. Well, I didn't wait forever, but 30 seconds or so. Should it take a long time to bottom out, or is something wrong with my IAC?

Also, you specifically said to have almost no pressure on the return line. Why is that important? I've never checked it, but I am using a section of my original 1/4" steel return line, which may be on the thin side.

[EagleMark]

Yes when it's buzzing it is completly closed and ready to pull the connector.

Any pressure on return line directly increases pressure on feed line. Remember when you pinched your return line?

[Mastiff]

Any pressure on return line directly increases pressure on feed line. Remember when you pinched your return line?

Yeah, I understand that, but if there were, say, 5 PSI due to backpressure from the return line, it doesn't seem like it would make any difference. If I'm keeping 11 PSI at idle, when the least fuel is being used at the injectors, I think I'd be okay everywhere else. In other words, if I don't go over pressure at idle I shouldn't have trouble off-idle when more fuel is being used.

But if there's more to it I'd like to know. It wouldn't be too difficult to used 3/8" line all the way back if I really needed to.

[EagleMark]

I don't think that is your issue. If it were you would be over 11-13 PSI. Read other thread.