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  #1  
Old 10-17-2011, 02:53 PM
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Vacuum leak and the IRIS valve

From what I have read, the IRIS valve opens at 4000 RPMs. Below this, the two halves of the intake manifold are isolated. If the vacuum line between the pressure regulator and the nipple on the right/passenger side of the intake manifold were to leak, would that cause the air/fuel ratio to be too high on that bank and only on that bank (below 4000 RPMs) and the ECU to adjust fuel trim up to compensate?

What other vacuum lines are connected in a way that could cause an imbalance between the banks when the IRIS is closed?
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1996 Subaru SVX LSi, 152,XXX miles, Redline D4 ATF, Redline 75W90 gear oil, K&N HP-4001 Oil Filter, Mobil 1 5W50 FS (3qt) and 5W30 High Mileage (4qt) Oil Blend, Motul RBF600 Brake Fluid, AC Delco A975C Air Filter, NGK BKR6EIX-11 plugs, Centric Rotors, Akebono ProACT Brake Pads
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Last edited by Huskymaniac; 10-17-2011 at 02:59 PM.
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Old 10-17-2011, 07:13 PM
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Re: Vacuum leak and the IRIS valve

i don't get this either...how can that valve increase air flow when both the sides are coming from the same intake!
if it acted like a 6 cylinder (6 different timings for 6 cylinders) it would matter but on a double 3 cylinder it won't
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Old 10-17-2011, 07:50 PM
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Re: Vacuum leak and the IRIS valve

Quote:
Originally Posted by david_12121 View Post
i don't get this either...how can that valve increase air flow when both the sides are coming from the same intake!
if it acted like a 6 cylinder (6 different timings for 6 cylinders) it would matter but on a double 3 cylinder it won't
Hint: all of the intake valves are not open at the same time.....
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Old 10-17-2011, 08:14 PM
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Re: Vacuum leak and the IRIS valve

Quote:
Originally Posted by Huskymaniac View Post
From what I have read, the IRIS valve opens at 4000 RPMs. Below this, the two halves of the intake manifold are isolated. If the vacuum line between the pressure regulator and the nipple on the right/passenger side of the intake manifold were to leak, would that cause the air/fuel ratio to be too high on that bank and only on that bank (below 4000 RPMs) and the ECU to adjust fuel trim up to compensate?

What other vacuum lines are connected in a way that could cause an imbalance between the banks when the IRIS is closed?
If the fuel pressure regulator's sensor pipe has a leak in it ,then the fuel pressure will be higher, to all cylinders. The O2 sensors will then reduce the pulse width to reduce the fuel within its available range.

The IRIS opening will have no effect on the vacuum level that they work from.

Quote:
Originally Posted by david_12121 View Post
i don't get this either...how can that valve increase air flow when both the sides are coming from the same intake!
if it acted like a 6 cylinder (6 different timings for 6 cylinders) it would matter but on a double 3 cylinder it won't
. The system has been perfected to utilize the length of the tract from the face of the throttle bodies to the end of the log section that the three tracts run off. This section acts as a Helmholtz chamber that develops an oscillating air pressure wave that is generated by the three cylinders sucking air in turns, one after the other 240* apart.

As the piston in the first cylinder starts from a standstill at the top of the cylinder, accelerates to maximum speed about half way down, to slow to a stop at the bottom. It accelerates the air in the chamber to produce a sine wave of pressure to force the air into the cylinder as the pistol is rising on the compression stroke. The inlet valve is then closed as the pressure is at its max to force more air into the cylinder, virtually supercharging the cylinder. The pressure in the chamber then reduces, but then the next cylinder valve opens to start the air acceleration process again.

This then has the air in the chamber pulsing back and forwards at a rate that is set by the length and volume of the chamber, and the frequency of the inductions. In the EG33 this peaks at about 3000 rpm. If we try to increase the effect by lengthing the chamber, it will reduce the rpm that it maxes at. If we try to increase the engine rpm that it occurs at, we have to reduce the length of the chamber, and that will reduce the mass of air and the developed pressure. If we try to increase the inlet duration by even 10*, it will mean that when the pressure is acting on the first cylinder to force the air in before the valve closes, the next cylinder’s inlet valve will open 10* before it closes, to rob the air pressure from the first cylinder that would fill it. Even the lift and the valve size are chosen to maximize the air velocity at this rpm, which produces the good combustion that it has now at that speed.


Harvey.
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  #5  
Old 10-17-2011, 10:57 PM
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Re: Vacuum leak and the IRIS valve

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Originally Posted by oab_au View Post
If the fuel pressure regulator's sensor pipe has a leak in it ,then the fuel pressure will be higher, to all cylinders. The O2 sensors will then reduce the pulse width to reduce the fuel within its available range.

The IRIS opening will have no effect on the vacuum level that they work from.

Harvey.
What I was thinking was that a leak in the line to this nipple (the bend is quite harsh so it would be a candidate for a leak as the hose get dry and hard) would cause extra air to get sucked into the right side of the manifold. That extra air would eventually be detected downstream by the O2 sensor. Consequently, the ECU would increase the amount of fuel injected by the right side injectors (fuel trim) to maintain the desired ratio.

At high RPMs, the IRIS would be open and the extra air being sucked in through this leak would be divided by both banks. That should result in the fuel trim being increased on both banks but by a lesser amount. At low RPMs, the extra air would stay confined to the right side so only the right bank fuel trim would be increased.

The IRIS keeps the left side and right side of the intake manifold isolated at low RPMs, correct? If so, any air leak on either side should result in an increased fuel trim for that side only, at low RPMs. So the main question really is, where could there be a leak that would be isolated to either side at low RPMs?
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Old 10-18-2011, 09:35 AM
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Re: Vacuum leak and the IRIS valve

It looks like there may be another vacuum line that goes from the "filter" to the right side of the intake manifold. Attached is the vacuum diagram.

Attached Images
File Type: jpg Vacuum System.jpg (81.5 KB, 5344 views)
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1996 Subaru SVX LSi, 152,XXX miles, Redline D4 ATF, Redline 75W90 gear oil, K&N HP-4001 Oil Filter, Mobil 1 5W50 FS (3qt) and 5W30 High Mileage (4qt) Oil Blend, Motul RBF600 Brake Fluid, AC Delco A975C Air Filter, NGK BKR6EIX-11 plugs, Centric Rotors, Akebono ProACT Brake Pads
2005 Acura RL, 142,XXX miles, Redline D4 ATF with Lubegard Black Protectant, Mobil 1 5W20 High Mileage Extended Performance Oil
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Old 10-18-2011, 07:14 PM
oab_au oab_au is offline
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Re: Vacuum leak and the IRIS valve

Quote:
Originally Posted by Huskymaniac View Post
What I was thinking was that a leak in the line to this nipple (the bend is quite harsh so it would be a candidate for a leak as the hose get dry and hard) would cause extra air to get sucked into the right side of the manifold. That extra air would eventually be detected downstream by the O2 sensor. Consequently, the ECU would increase the amount of fuel injected by the right side injectors (fuel trim) to maintain the desired ratio.

At high RPMs, the IRIS would be open and the extra air being sucked in through this leak would be divided by both banks. That should result in the fuel trim being increased on both banks but by a lesser amount. At low RPMs, the extra air would stay confined to the right side so only the right bank fuel trim would be increased.

The IRIS keeps the left side and right side of the intake manifold isolated at low RPMs, correct? If so, any air leak on either side should result in an increased fuel trim for that side only, at low RPMs. So the main question really is, where could there be a leak that would be isolated to either side at low RPMs?
No mate you are missing the point here, you are looking at a diagram, instead of looking at the manifold.

A leak in that hose will cause the fuel pressure regulator to increase the fuel pressure to both sides, the ECU won't know the leak is on one side, just that the engine is running too rich. It will then reduce the pulse width to both sides to compensate.
The air leak will be insignificant. The manifold has a few channels that join the vacuum from both sides together, like the EGR channel.

Harvey.
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Old 10-18-2011, 09:39 PM
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Re: Vacuum leak and the IRIS valve

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Originally Posted by oab_au View Post
No mate you are missing the point here, you are looking at a diagram, instead of looking at the manifold.

Harvey.
Doesn't the iris act in the same (or similar) capacity as Porsche's Varioram? Adjusting the resonance chamber size according to engine RPM to optimize airflow?
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Old 10-19-2011, 04:51 PM
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Re: Vacuum leak and the IRIS valve

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Originally Posted by dbarnblatt View Post
Doesn't the iris act in the same (or similar) capacity as Porsche's Varioram? Adjusting the resonance chamber size according to engine RPM to optimize airflow?
The Porsche Varioram does use a dual inlet system, but it is not the same as the IRIS. They have two inlet tracts of different lengths. The long tract works as a low speed ram, with a low speed resonate length that works up to about 5000. The other one is a short high speed resonate tract,

The main difference is that it does not use the Helmholtz principle in the low speed system, to boost the inlet pressure, like the SVX system. You have to have three cylinders, and 240* inlet duration, to get it to work. So it will only be used on 3,6,9,12, cylinder engines.

Harvey.
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  #10  
Old 10-20-2011, 02:49 PM
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Re: Vacuum leak and the IRIS valve

two things:
1.- The iris valve is not a completelly sealed valve. It does not completelly isolate both chambers
2. the fuel injection pulse at iddle is not controlled by the O2 sensors; it's preprogramed on the ECU. That is why you have unstable idle when you realese the gas pedal and have a leak of vacuum.
Recomendation: replace all the vacuum hoses and the IRIS valve shaft's O'ring.
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