it seems like my boost leak is related to Mass Air Flow...
06-03-2003, 10:06 AM
#1
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it seems like my boost leak is related to Mass Air Flow...
... at 140g/s.
Here are two more graphs of data runs.
<img src="http://www3.sympatico.ca/kirkgj/images/maf_data_chipped.gif">
<img src="http://www3.sympatico.ca/kirkgj/images/maf_data_stock.gif">
I tried hooking the by-pass valve up to the intake manifold directly (like it is on 99.5 and older 1.8T) and there was no change in result. Car still went into limp mode like before and there was no change in the way the car felt either. This rules out the by-pass valve control solenoid (N249) and I think, any sort vacuum leak to the rest of the system (like the secondary air system, vacuum brake booster, leak detection system, vacuum reservoir)... but who knows at this point.
Its interesting that in stock mode there is no drop in boost or in intake air at 5400 rpms. I then thought well what happens at 150g/s on the MAF... well in unchipped mode it never gets that much air flow. There is a drop in MAF reading around 140g/s but this is way up in the rpm range (you're driving around 170km/h in 4th gear to get this much air flow) and it was hard to get this data more than once really.
So what now. It seems like at 140g/s unchipped the car hesitated for a bit. I didn't know if I hit the rev limiter or not... but then it went again. Its like something let go and then caught again. You can see the MAF data drop here and then go back up.
So it seems the leak is not rpm related but more related to air flow at 140g/s. At 140g/s unchipped the N75 is only about 65% command (makes sense for stock) and this results in the air being pushed into the intake being at less pressure. At 140g/s chipped, the N75 is full at 95% and this results in the air being pushed into the intake being at a higher pressure.
Whatever is leaking likes to leak at that amount of air flow but in unchipped mode, once the pressure is released for a period of time, the leak closes while in chipped mode, once the leak happens, it stays open under the higher pressure.
One of the other things that has me curious in all of this is the fact that the boost leak results in lower MAF readings. To me, it means that the loss of air in the pressure side of the intake air track is being put back into the low pressure side of the intake. The only thing that can do this is the by-pass valve.
I guess its time to try a hyperboost valve and see if it helps me figure this out. Anyone have a spare hyperboost laying around I can borrow.
Other than that, I'm out of ideas.
Kirk
Here are two more graphs of data runs.
<img src="http://www3.sympatico.ca/kirkgj/images/maf_data_chipped.gif">
<img src="http://www3.sympatico.ca/kirkgj/images/maf_data_stock.gif">
I tried hooking the by-pass valve up to the intake manifold directly (like it is on 99.5 and older 1.8T) and there was no change in result. Car still went into limp mode like before and there was no change in the way the car felt either. This rules out the by-pass valve control solenoid (N249) and I think, any sort vacuum leak to the rest of the system (like the secondary air system, vacuum brake booster, leak detection system, vacuum reservoir)... but who knows at this point.
Its interesting that in stock mode there is no drop in boost or in intake air at 5400 rpms. I then thought well what happens at 150g/s on the MAF... well in unchipped mode it never gets that much air flow. There is a drop in MAF reading around 140g/s but this is way up in the rpm range (you're driving around 170km/h in 4th gear to get this much air flow) and it was hard to get this data more than once really.
So what now. It seems like at 140g/s unchipped the car hesitated for a bit. I didn't know if I hit the rev limiter or not... but then it went again. Its like something let go and then caught again. You can see the MAF data drop here and then go back up.
So it seems the leak is not rpm related but more related to air flow at 140g/s. At 140g/s unchipped the N75 is only about 65% command (makes sense for stock) and this results in the air being pushed into the intake being at less pressure. At 140g/s chipped, the N75 is full at 95% and this results in the air being pushed into the intake being at a higher pressure.
Whatever is leaking likes to leak at that amount of air flow but in unchipped mode, once the pressure is released for a period of time, the leak closes while in chipped mode, once the leak happens, it stays open under the higher pressure.
One of the other things that has me curious in all of this is the fact that the boost leak results in lower MAF readings. To me, it means that the loss of air in the pressure side of the intake air track is being put back into the low pressure side of the intake. The only thing that can do this is the by-pass valve.
I guess its time to try a hyperboost valve and see if it helps me figure this out. Anyone have a spare hyperboost laying around I can borrow.
Other than that, I'm out of ideas.
Kirk
06-03-2003, 10:31 AM
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Could it just be a maf sensor that is going out.
Your maf readings should be much higher then that with a aftermarket chip. Our 2001 x-chip even hits 170+ g/s and the maf's have a max OEM reading of 215 g/s. Have you looked to see what your g/s are at just idle and what your block 032 is set at? BTW if you have a leak or pressure drop caused by a FMIC or your stock SMIC the boost sensor will put the car into limp. I had this exact issue when we were doing R&D testing with the EVO fmic and GIAC custom software, the car would go into limp right around 5400-5500 rpms only in 3rd gear or higher.
06-03-2003, 02:29 PM
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How is the bypass valve oriented?
Maybe try swapping it around to see if that helps.
There is a bentley test to check the MAF. Watch your g/s while holding a high idle of 2500 RPM's. The MAF should read between 7-9 g/s. When mine was dead it would only show 6 g/s at 2500 and would only peak at 160 during WOT. Now that I have a new MAF it peaks at 215 (the limit of the MAF) and my high idle numbers are right on the money.
There is a bentley test to check the MAF. Watch your g/s while holding a high idle of 2500 RPM's. The MAF should read between 7-9 g/s. When mine was dead it would only show 6 g/s at 2500 and would only peak at 160 during WOT. Now that I have a new MAF it peaks at 215 (the limit of the MAF) and my high idle numbers are right on the money.
06-03-2003, 06:55 PM
#4
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I've done the MAF test from bentley...
... the numbers are within spec. Is there a way to see the max MAF numbers. I think it might be dead and only peaking at 140g/s or so.
My bpv is oriented in the stock way. I'm trying to figure out if a hyperboost is worth a try or not.
I might try and build some home made boost leak kit to test if the intercooler is leaking.
Thanks Audi2ptzero and Brent,
Kirk
My bpv is oriented in the stock way. I'm trying to figure out if a hyperboost is worth a try or not.
I might try and build some home made boost leak kit to test if the intercooler is leaking.
Thanks Audi2ptzero and Brent,
Kirk
06-03-2003, 10:41 PM
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Actually Brent V had that exact problem.
No matter what we did to his car, the maf would only go to 125 g/s and then stop or drop off. This was with a K04, he thought it was a bad K04 so he put a stage 3 kit in and the issue was still there. He then put a new one in and the problem was solved.
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06-04-2003, 01:30 PM
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What exactly were your MAF values?
and what test did you perform? When my MAF was bad it showed it clearly on the bentley tests. Even at idle where the maf should read around 3.0g/s mine was reading 2.
06-04-2003, 01:52 PM
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Is this on a stock K03 and stock maf housing?
2.9 at idle seems a bit low, with the PES kit it ran about that. With the K03 setup and stock maf it should be around mid 4's. With my K04, stock maf on my 2 liter I got 5-6 g/s just at idle.
Low readings at idle are a big sign of a maf going bad. It might still work but it the readings are going to be off, which means when you go wot your car is going to be off for fuel and is always going to be toward the lean side. Block 032 also tells you when your maf is going bad, since it will start moving closer to zero since both readings should be on the - side.
Low readings at idle are a big sign of a maf going bad. It might still work but it the readings are going to be off, which means when you go wot your car is going to be off for fuel and is always going to be toward the lean side. Block 032 also tells you when your maf is going bad, since it will start moving closer to zero since both readings should be on the - side.