Ford PWM IAC and Boost

hardline · Post by **hardline** » Wed Jun 24, 2009 4:58 pm

Seem to be running into an issue where the Idle Valve is being blown open under boost. Is anyone else running into this.

Matt Cramer · Post by **Matt Cramer** » Thu Jun 25, 2009 4:16 am

Where is the inlet of the IAC valve plumbed up? Is it running to a point downstream of the turbo?

Cuz · Post by **Cuz** » Sat Jun 27, 2009 11:43 pm

Yeah, i've been thinking about this one too. I have mine hooked up to have one side of the valve going to the plenum and the other side going to the cooler piping after the turbo. I have a 1-way valve on the line between the IAC and the plenum (so air can only be sucked into the plenum from the plenum side and not forced back into the IAC from the plenum side when the plenum is pressurized under boost). For the line between the cooler piping and the IAC I think another valve is needed. This one, however, needs to be able to be sucked through from the IAC side but not blown through from the cooler piping side. Does such a valve exist?

hardline · Post by **hardline** » Mon Jun 29, 2009 8:12 pm

The IAC is running to atmosphere since I cannot weld aluminum. I am using the IAC off of a Ford Crown Vic, which has a 5/8" fitting on one end for a hose, and that is running to a breather filter. The valve seems to be being blown open, acting like a blowoff valve at boost above 10 PSI. Perhaps I am incorrect on this assumption, but it is the only thing I can come up with since once it hits 10 PSI, the Boost Gauge begins oscillating between 8-13 PSI and the AFR between 10 and 13.5 until I let off of it. If I set the boost control to keep it under 10 PSI, it doesnt happen.

Matt Cramer · Post by **Matt Cramer** » Tue Jun 30, 2009 5:42 am

hardline wrote:The IAC is running to atmosphere since I cannot weld aluminum.

That could very well be your problem. See if there's any way - even if it takes JB Weld - to plumb it to boost instead.

devastator · Post by **devastator** » Thu Jul 02, 2009 7:28 am

Matt Cramer wrote:See if there's any way - even if it takes JB Weld

There are similar, 2-part welding materials designed just for aluminum. Look in McMaster Carr online. Here is one of the types available, but there are others as well. :http://www.mcmaster.com/#catalog/115/3347/=2kkjdc

hardline · Post by **hardline** » Sat Jul 04, 2009 11:29 am

OK, i figured it out. The Idle Valve is not closing off idle. When I unplug it, it does not leak all the way to 45 PSI (tested on shop air). I'm thinking i need to look closer at the idle settings. I might have it in open loop......

Cuz · Post by **Cuz** » Mon Jul 06, 2009 6:29 am

does the IAC code close the valve when it is not in idle? assuming this is what the "closed dc" value is

Cuz · Post by **Cuz** » Sun Aug 02, 2009 8:25 am

anyone?

Matt Cramer · Post by **Matt Cramer** » Mon Aug 03, 2009 5:04 am

It depends on your settings - and on the particular car. Some will work best if the IAC is set partially open. I would plumb it so the IAC inlet sees boost.

Cuz · Post by **Cuz** » Tue Aug 04, 2009 7:50 am

right, but assuming you set the "closed dc" value to something which will close the valve (ie 0), the value will stay closed every time it was not in idle?

Matt Cramer · Post by **Matt Cramer** » Tue Aug 04, 2009 8:56 am

Not necessarily - check your data logs and see what the DC is going to. Also, a DC value that's closed at idle may not be closed under boost.

Cuz · Post by **Cuz** » Tue Aug 11, 2009 5:36 am

Matt Cramer wrote: Also, a DC value that's closed at idle may not be closed under boost.

ahhh i see. could you expand on this please?

Matt Cramer · Post by **Matt Cramer** » Tue Aug 11, 2009 8:58 am

Cuz wrote:
Matt Cramer wrote: Also, a DC value that's closed at idle may not be closed under boost.
ahhh i see. could you expand on this please?

The IAC valve is not designed to see positive pressure, and if you've plumbed it incorrectly, the boost can force it open even at a duty cycle where it would normally be closed. The IAC normally balances the force of the solenoid against a spring tension; adding boost changes the balance between the two forces.

Cuz · Post by **Cuz** » Wed Aug 12, 2009 1:14 am

Matt Cramer wrote:The IAC valve is not designed to see positive pressure, and if you've plumbed it incorrectly, the boost can force it open even at a duty cycle where it would normally be closed. The IAC normally balances the force of the solenoid against a spring tension; adding boost changes the balance between the two forces.

Yep, cool. But as per the post further up in this thread, this valve does not leak all the way to 45 PSI (tested on shop air), with this in mind setting the closed DC value to 0 should mean that it is 100% closed and as long as boost does not exceed 45psi it will work as intended?

xr2wishy · Post by **xr2wishy** » Fri Sep 04, 2009 1:56 am

you need to fit the feed for the valve off a boost pipe, this will equalise pressure on both sides of the valve and therefore the spring isn't under stain.
i run the same valve in my project and have no issues.

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