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Discussion Starter · #1 ·
I'm starting to get the boosting bug and I'm a really big fiddler so I need to mess some more.

I've put an MBC on my 2000 DBW APU 1.8T and its fine up to around 1 bar but the N75 seems to start getting in the way and messing everything up.

I'm going to take the N75 out and just use the MBC with a very accurate boost gauge but my question is:

On the APU engine I've read it can fuel happily up to 1bar with the standard 210cc injectors as it can use a long injector duty cycle (21ms+) but where is the limp mode? Is it much higher than 1bar? Can the APU fuel ok much above 1bar?

I know I need to use VAG-COM to check I'm not going lean. I will do this when I really start cranking but things are starting to confuse me like when I turn the MBC up slightly too much it just cuts the boost right down until I back off a bit then it will boost ok again but if I do this too much I will have to turn the MBC right down, drive for a bit then start turning it back up. Never get any check engine lights etc. so it doesn't seem to be in limp. I really need a chip but I can't find a reasonable supplier yet and I reckon I'm not far off what a chip would boost anyway.

Any comments are always appreciated.
 

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I think you're running into the "problem" of the DBW cars having a boost sensor. If you want to go higher boost, you need to diode the boost sensor.

And please do this recklessly, adding huge quantities of boost all at once w/o appropriate logging, and film it for us, OK? ;)
 

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Discussion Starter · #5 ·
I think you're running into the "problem" of the DBW cars having a boost sensor. If you want to go higher boost, you need to diode the boost sensor.

And please do this recklessly, adding huge quantities of boost all at once w/o appropriate logging, and film it for us, OK? ;)
;) So you're saying I should be happy with 1 bar while being a cheapskate and not chipping it?

Next question then - With the 210cc injectors whats the most boost I can hope for from a K03 when chippped? Would a 5bar FPR help? I can't quite stretch to a K04 just yet. a FMIC may be on the cards though. Any reason why I can't just use the SMIC in series with the FMIC? Should I stop asking so many questions all together? :)
 

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Part of the problem would be the boost sensor, once it sees more the 18-19psi is steady it throws the car in to limb mode.
 

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Discussion Starter · #7 ·
Hmm, 18-19 PSI... I'm not sure I'm anywhere near that.

I'll report back when I have an accurate boost gauge.
 

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That's when it throws the car into Limp mode. I'm sure the ECU is seeing 13-14psi and thinking, "Odd. I should only be boosting 9-11psi. Time to turn things down..." without panicking totally.

As they've said, confuddle that boost sensor, and that will help things until you make enough money to buy a chip.
 

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Discussion Starter · #9 ·
Aha interesting. Does anyone have any more info on where the boost sensor is located and which diode to put in there?
 

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That's when it throws the car into Limp mode. I'm sure the ECU is seeing 13-14psi and thinking, "Odd. I should only be boosting 9-11psi. Time to turn things down..." without panicking totally.

As they've said, confuddle that boost sensor, and that will help things until you make enough money to buy a chip.
The boost sensor can get you a couple different ways. The overboost limit is 21.5psi, so if you hit that it will put you into limp. It could also limp if you get large deviations between requested and actual boost, I believe its approx 300-350mbar that will trip it. This would be because the ecu is still asking for stock boost but the setting of the MBC is a t a level that exceeds the stock value by enough to trigger the deviation. At 1 bar setting on the MBC, you're probably going to see problems, like you are. Or, if you bypass the N75, you can get two new conditions. First, your boost is more likely to be like a light switch and you'll lose the curve you get with N75 control. Second, boost can still be bled off via the N249 valve which is triggered if actual load values exceed requested load values by more than a certain margin. The boost sensor input is ignored because the N75 is out of the loop, so then the ecu looks to the next level of safety which is the N249.
 

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I've been playing with an MBC too, including a diode to truncate the voltage level seen by the ECU i.e. let the ECU think boost is at a certain level (depending on the zener voltage level). You'll get codes with only an MBC anyway because part throttle boost will be too high. Positive deviation code will be stored no matter how low you set the MBC.

The N249 is a safety between intake manifold/vacuum canister and the DV. If the ECU thinks its in danger it switches the N249 to let the vacuum canister open the DV (DV is vacuum operated, not boost) and boost levels will decrease. In normal operation the DV control line is connected through th N249 to the intake manifold.
 

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The boost sensor can get you a couple different ways. The overboost limit is 21.5psi, so if you hit that it will put you into limp. It could also limp if you get large deviations between requested and actual boost, I believe its approx 300-350mbar that will trip it. This would be because the ecu is still asking for stock boost but the setting of the MBC is a t a level that exceeds the stock value by enough to trigger the deviation. At 1 bar setting on the MBC, you're probably going to see problems, like you are. Or, if you bypass the N75, you can get two new conditions. First, your boost is more likely to be like a light switch and you'll lose the curve you get with N75 control. Second, boost can still be bled off via the N249 valve which is triggered if actual load values exceed requested load values by more than a certain margin. The boost sensor input is ignored because the N75 is out of the loop, so then the ecu looks to the next level of safety which is the N249.
What he said. I have a MBC in my 02 AWM for the last 10K miles and the throttle response can be very abrupt. You either boost or you don't. This is most apparent under part throttle acceleration. With WOT, it's great. Either way, I am getting chipped.
 

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Discussion Starter · #14 ·
Chipped it is then.

I've read about the 1bar and 1.1bar chips. Whats the max people have heard of on a K03 with stock FPR and injectors?
 

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I have a 1.0Bar Wetterauer chip and all of my engine components are stock...no problems in 67K miles (chipped at 5K). '03 1.8T 5 spd...boost is 16-17psi Max.
 

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Chipped it is then.

I've read about the 1bar and 1.1bar chips. Whats the max people have heard of on a K03 with stock FPR and injectors?

look man, once you chip, your car you will be in a different world. you just need to get it to explain. then you can really tinker for extra power. by the way, don't go nuts and try to hold like 22 psi's with a k03. you'll kill your engine. 18 sustain psi's is the max you want o hold, or at least that's my thought. after circa 16 psi's your turbo loses efficiency, and it's not worth injuring your car for that because you can mod it out other ways to achieive more power without compromising engine integrity----good luck:thumbup:
 

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Discussion Starter · #18 · (Edited)
look man, once you chip, your car you will be in a different world. you just need to get it to explain. then you can really tinker for extra power. by the way, don't go nuts and try to hold like 22 psi's with a k03. you'll kill your engine. 18 sustain psi's is the max you want o hold, or at least that's my thought. after circa 16 psi's your turbo loses efficiency, and it's not worth injuring your car for that because you can mod it out other ways to achieive more power without compromising engine integrity----good luck:thumbup:
Thanks :) I'm a little under the thumb so I can't spend too much on the car. ;) I am saving up for a chip though.
 
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