Broken AOS
#16
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One thing to point out. Okay, two things. First, if air is moving through a pipe, and the pipe has a hole in it, it will create a venturi affect, which is a vacuum at that hole. So it will suck in air. Second, the AFM is a resistor, meaning it will create a pressure drop across it to make air flow. That means the pressure behind it is less than the pressure in front of it. That's another source for vacuum at that leak. So it will probably suck in a little unmetered air.
Actually, I have a third point. In closed loop, the O2 sensor will correct those leaks anyway.
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And you are also correct... with an exception... a major boost leak at the fuel pressure regulator. I learned the hard way on an old turbo car I had. Vac line split at FPR and car went extremely lean while under full boost in a long 4th gear pull (non Porsche motor)... well ended up with holes in the top of #2 and 3 pistons...
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Okay, so I've deduced that "AOS" means something in addition to open diff S2 trans. I'm guessing that's not what y'all are talking about. So what is an AOS in this situation?
One thing to point out. Okay, two things. First, if air is moving through a pipe, and the pipe has a hole in it, it will create a venturi affect, which is a vacuum at that hole. So it will suck in air. Second, the AFM is a resistor, meaning it will create a pressure drop across it to make air flow. That means the pressure behind it is less than the pressure in front of it. That's another source for vacuum at that leak. So it will probably suck in a little unmetered air.
Actually, I have a third point. In closed loop, the O2 sensor will correct those leaks anyway.
One thing to point out. Okay, two things. First, if air is moving through a pipe, and the pipe has a hole in it, it will create a venturi affect, which is a vacuum at that hole. So it will suck in air. Second, the AFM is a resistor, meaning it will create a pressure drop across it to make air flow. That means the pressure behind it is less than the pressure in front of it. That's another source for vacuum at that leak. So it will probably suck in a little unmetered air.
Actually, I have a third point. In closed loop, the O2 sensor will correct those leaks anyway.
Im not sure how the O2 sensor setups in our cars work, but for most vehicles this is only true within a very small window based on the design of the O2 sensor (narrowband). And under full boost or WOT (when the mixture richens) the computer ignores the O2 sensor input showing a rich condition....so in essence, no it will not correct for the leaks...
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And you are also correct... with an exception... a major boost leak at the fuel pressure regulator. I learned the hard way on an old turbo car I had. Vac line split at FPR and car went extremely lean while under full boost in a long 4th gear pull (non Porsche motor)... well ended up with holes in the top of #2 and 3 pistons...
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Okay, wait a minute!
My AOS is totally separated at the top of the cylinder. THAT is a lot of air going to an open hole. Next, that hole is before the turbo inlet, (via a smaller hose) so the AFM signal is significantly different from the amount of air actually entering the turbo.
NOW, how does that ACTUALLY affect the DME's fuel flow decision?
I'm running way rich. My boost hits at 4k on a 26/6. I have chased EVERY vac leak and exhaust leak.
We're down to a very few veriables!
I'm thinking that my trashed AOS os causing a HUGE leak of air.
I would love some real ideas on this...not that the discussion isn't great, but it keeps going in opposite directions...too me anyway.
My AOS is totally separated at the top of the cylinder. THAT is a lot of air going to an open hole. Next, that hole is before the turbo inlet, (via a smaller hose) so the AFM signal is significantly different from the amount of air actually entering the turbo.
NOW, how does that ACTUALLY affect the DME's fuel flow decision?
I'm running way rich. My boost hits at 4k on a 26/6. I have chased EVERY vac leak and exhaust leak.
We're down to a very few veriables!
I'm thinking that my trashed AOS os causing a HUGE leak of air.
I would love some real ideas on this...not that the discussion isn't great, but it keeps going in opposite directions...too me anyway.
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So, MORE air is being read at the meter, than is ACTUALLY entering the turbo.
That should mean more fuel for less air, IF the fuel is being metered based on the AFM's air load...YES?
Bottom line is that there is more "metered air" than is actually entering the system. The meter is not reading ACTUAL air entering the turbo. It's reading the air it THINKS is entering the turbo.
Right?
Last edited by ehall; 04-12-2011 at 04:40 AM. Reason: properly edited
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Okay, wait a minute!
My AOS is totally separated at the top of the cylinder. THAT is a lot of air going to an open hole. Next, that hole is before the turbo inlet, (via a smaller hose) so the AFM signal is significantly different from the amount of air actually entering the turbo.
NOW, how does that ACTUALLY affect the DME's fuel flow decision?
I'm running way rich. My boost hits at 4k on a 26/6. I have chased EVERY vac leak and exhaust leak.
We're down to a very few veriables!
I'm thinking that my trashed AOS os causing a HUGE leak of air.
I would love some real ideas on this...not that the discussion isn't great, but it keeps going in opposite directions...too me anyway.
My AOS is totally separated at the top of the cylinder. THAT is a lot of air going to an open hole. Next, that hole is before the turbo inlet, (via a smaller hose) so the AFM signal is significantly different from the amount of air actually entering the turbo.
NOW, how does that ACTUALLY affect the DME's fuel flow decision?
I'm running way rich. My boost hits at 4k on a 26/6. I have chased EVERY vac leak and exhaust leak.
We're down to a very few veriables!
I'm thinking that my trashed AOS os causing a HUGE leak of air.
I would love some real ideas on this...not that the discussion isn't great, but it keeps going in opposite directions...too me anyway.
If you find out why the turbo lags so much, id really like to know.
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Here's the thing. I just put on a head that has Larger intake valves, and is otherwise totally new, with no other mods, so I should actually be seeing EARLIER spool than I was. I used to spool at about 3100, HARD. Now it's 3900 to 4100. That doesn't add up. Somewhere I've got a hole in my engine.
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Here's the thing. I just put on a head that has Larger intake valves, and is otherwise totally new, with no other mods, so I should actually be seeing EARLIER spool than I was. I used to spool at about 3100, HARD. Now it's 3900 to 4100. That doesn't add up. Somewhere I've got a hole in my engine.
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nope. It was after replacing the Head and the HG. I've checked every vac hose ane reconnected. I ran seafoam through to check exhaust leaks. I used ether to check vac leaks...AGAIN!...I'm down to a few Ideas.
1. I KNOW that the entire top of the AOS can be lifted rigt off the cylinder without any effort...it's just laying there!
2. Timing was set a tooth or two retarded,
3.FQS switch is set too rich for the 3", no cat exhaust and better flowing head, than before I changed them.
All changes were made at same time.
1. I KNOW that the entire top of the AOS can be lifted rigt off the cylinder without any effort...it's just laying there!
2. Timing was set a tooth or two retarded,
3.FQS switch is set too rich for the 3", no cat exhaust and better flowing head, than before I changed them.
All changes were made at same time.
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okay, NO! The leak is AFTER the AFM and the meter. The hose to the AOS is near the rear of the J boot ASFAIK., but before the turbo.
So, MORE air is being read at the meter, than is ACTUALLY entering the turbo.Are you reading this... c'mon pal, a fifth grader could catch this... air leak POST AFM and PRE turbo, means air getting in that is unmetered and therefore means that less air is being pulled in through the meter for a given load. meaning a lean condition
That should mean more fuel for less air, IF the fuel is being metered based on the AFM's air load...YES? No... less air=less fuel because the computer is seeing less air flow through the meter and a leak post meter is allowing air that is not metered to get into the system. The same amount of air is going into the motor, just a portion of it is not known by the DME because the leak is after the AFM and not getting measured
Bottom line is that there is more "metered air" than is actually entering the system. The meter is not reading ACTUAL air entering the turbo. It's reading the air it THINKS is entering the turbo.
Right? Sort of... it's reading what it thinks is making it to the turbo, which is less than what it should be, and therefore the fuel is cut making it run lean under part throttle conditions
So, MORE air is being read at the meter, than is ACTUALLY entering the turbo.Are you reading this... c'mon pal, a fifth grader could catch this... air leak POST AFM and PRE turbo, means air getting in that is unmetered and therefore means that less air is being pulled in through the meter for a given load. meaning a lean condition
That should mean more fuel for less air, IF the fuel is being metered based on the AFM's air load...YES? No... less air=less fuel because the computer is seeing less air flow through the meter and a leak post meter is allowing air that is not metered to get into the system. The same amount of air is going into the motor, just a portion of it is not known by the DME because the leak is after the AFM and not getting measured
Bottom line is that there is more "metered air" than is actually entering the system. The meter is not reading ACTUAL air entering the turbo. It's reading the air it THINKS is entering the turbo.
Right? Sort of... it's reading what it thinks is making it to the turbo, which is less than what it should be, and therefore the fuel is cut making it run lean under part throttle conditions
This does not explain why you are running rich... that, I have no idea without knowing exactly what has gone on with your car. We can sit here and guess all day, but without seeing what is going on is like looking for a needle in a stack of needles... its all guessing..
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Either way, I wish it would have only been a blown headgasket in mine...
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ok no, I'm not certain either. What I'm reading is that you are saying that more air is entering the turbo than is being read at the AFm. The hole to the AOS is after the AFM but before the turbo, so why would you think that more is getting to the turbo? The air is bleeding out of the tube towards the aos and not getting to the turbo. Are you saying that the turbo is pulling air from the AOS? If so, from where? Why would that affect the fuel load? HOW would that affect the fuel load? What part of the computer is going to read that and adjust for it?
A wide open AOS is a gaping no-pressure hole, venting air away from the turbo inlet....is it not? It's a path of least resistance.
Are you saying that the turbo is creating a venturi effect across that orifice?
There is ZERO question that I'm running rich, BTW. WAY rich!
A wide open AOS is a gaping no-pressure hole, venting air away from the turbo inlet....is it not? It's a path of least resistance.
Are you saying that the turbo is creating a venturi effect across that orifice?
There is ZERO question that I'm running rich, BTW. WAY rich!