IACV routing on turbo setup???

[fastcougar]

Do you see any reason why the IACV tube needs to be on the pressure side of the turbo (currently just before the throttle body). Is there any reason why I shouldn't place the tube pre-compressor, just after the MAF? Your thoughts? I suspect that having it after the turbine is causing the sensor to see boost it isn't designed for and thus it has failed prematurely (high sticking idle).

 

[SicSE]

Do you see any reason why the IACV tube needs to be on the pressure side of the turbo (currently just before the throttle body). Is there any reason why I shouldn't place the tube pre-compressor, just after the MAF? Your thoughts? I suspect that having it after the turbine is causing the sensor to see boost it isn't designed for and thus it has failed prematurely (high sticking idle).

I would leave it the way it is since the IAC should not be boost sensative. Plus, I think moving it to between the MAF & turbo could possibly create tip-in driveability issues. If you rerouted it as you are contemplating, at closed throttle, the air mass between the turbo & TB will be still, (unless your throttle plate has a hole in it). Upon cracking the throttle, that mass of air will be set in motion but the information the PCM gets at that exact time from the MAFS may not be accurate for what is actually entering the engine.

 

[Swazo]

The IAC routing on my turbo setup had the same routing idea (slightly different for the UIM I used, but would have the same result)

 

[fastcougar]

The IAC routing on my turbo setup had the same routing idea (slightly different for the UIM I used, but would have the same result)

Thanks Swazo ... here is my rational:

The IACV has two sides ... behind the throttle body and before. The IACV itself is simply a plunger with a spring behind it to keep it seated (closed). The plunger is attached to a solenoid that retracts when 5v is applied, overpowering the spring and opening the orifice. The "sprung side" is behind the throttle body. So, under boost, the valve is forced closed regardless as the solenoid isn't powerfull enough to overcome the boost. Beside, that would NEVER happen because in order for the IACV to activate, the TPS sensor signals that the throttle body is closed, which means no boost anyways.

Now the the "before" side (before the throttle body), that supplies the idle air, that can be either fed with boosted air or N/A. What I suspect is happening is that the boost fed IACV is opening under boost (throttle wide open) and it's weakening the spring and solenoid because it's operating twice as much now ... at idle and under boost. Make sense?

I'm definitely moving the connection pre-compressor.

 

[striker2]

with the IAC pulling air post compressor, it will have the same boost pressure on both sides of the plunger. the 2 pressures cancel out and your back to just the pressure of the spring holding the plunger closed.

 

[fastcougar]

I thought the same thing, but not exactly true. While the throttle blade is closing, there is a pressure difference in favor of the pre-throttle side. Also, due to the routing to the IACV passeges, while the engine is creating boost, the pre-throttle side will see boost a split second sooner than the post-throttle side. Regardless of the severity, I'm relocating for routing issues more so than mechanical ones.

 

[SicSE]

I'm definitely moving the connection pre-compressor.

Thinking about this farther, I just realized that if you do this, you're going to leak boost out of your IAC inlet. The valve is commanded full-open at WOT to act as a dashpot so the car doesn't stall from dropping to idle too quickly. That's gonna be one mean-ass boost leak... let us know how it sounds. :help:

 

[fastcougar]

Thinking about this farther, I just realized that if you do this, you're going to leak boost out of your IAC inlet. The valve is commanded full-open at WOT to act as a dashpot so the car doesn't stall from dropping to idle too quickly. That's gonna be one mean-ass boost leak... let us know how it sounds. :help:

I would suspect ANY amount of boost would create more force to close the valve than the solenoid could generate to open it :shrug:

 

[SicSE]

The plunger is attached to a solenoid that retracts when 5v is applied, overpowering the spring and opening the orifice.

Incorrect. The spring forces the valve open. This is how it defaults to open when the key is off or if the solenoid fails. The solenoid works against the spring to close the valve, and pushes it against it's seat to do so. Also, the voltage supplied to the valve is between 3-11.5 volts depending on desired valve position.

So, under boost, the valve is forced closed

Also incorrect. With your current setup, the pressure is close enough to even on both sides of the valve to allow valve position to be exactly where the PCM wants it to be. If you reroute as you are proposing, pressure will be greater on the intake side so both the spring and boost pressure will be pushing against the valve when the PCM wants to close it. Though that won't matter too much because the valve is almost always open at least a little.

Make sense?

Literally, yes. Factually, no.

 

[fastcougar]

Fair enough ... just looking for an explination. Thanks!

 

[Swazo]

I'm sorry, I should have added a little more info to clarify what I meant.

I ran an aluminum 3L UIM (the IAC normally mounts to the top of the UIM, just after the TB. That looked like crap IMO, AND there would be hood clearance issues if it remained there) and also had a water to air intercooler. I tapped the ports of the IAC, added brass barbed hose fittings, 1/2" or maybe 5/8" braided hose, ran the inlet inbetween the intercooler and the TB. The outlet ran to one of the many nipples after the TB.

I had no issues with the IAC at all.