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LEON CR fluttering boost problem
- Thread starter martin CR
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- boost fluttering leon problem
As I understand it, a J valve will increase the overboost/overshoot compared to an F valve and that's what you're feeling - the boost overshoots, the wastegate opens, boost falls, the wastegate closes again, the boost overshoots, which is the fluctuation/surging that you're feeling.
I think there's a maximum value over requested boost that the ECU will allow, then it'll drop into limp (which you've not said yours is doing), it'll throw a code when it does this.
On the logs sportbilly has sent me (and that he used to create the graphs he posted) his requested boost is lower than I see on mine, but the actual is pretty good, apart from the fact that you can see the ECU trying to bring the boost back down to match requested, then it overshoots, brings it down etc.
I think in sportbilly's case, the surging is a symptom of something else, with the requested being lower than I usually see on mine. A couple of people (heroes and very, very nice men) that know a lot more about this than me are looking over those logs for us. hopefully they can suggest why his requested is low, if in fact it is low (mine might be high
)I have to say though - sportbillang's symptoms are different to yours; he's getting a surge at full throttle.
One way round the surging on full throttle might be to turn the boost up! To me, that way the requested boost will be higher, the N75 won't cut boost so and there will be no surging. And you'll be having fun as well
If you do this though, you'll need to keep an eye on inlet temps, timing etc.Scotty - are you still running standard Revo settings with your Imolavirus? That might be your problem - we all saw how eager to make boost Sie's was.
I'm fairly sure that most LCRs have faint surge on gentle throttle when chipped, mine always has, but some cars might be more pronnounced than others - individual N75's perhaps. Again, cordobabrendy reposted an adjustment procedure the other day, might be worth a try if your desperate, but I would log actual boost before playing and be prepared to replace the N75 after it's been "adjusted" (read "buggered about with").
HTH
Mine fluctuates on full throttle and doesn't always hit full boost. Seems fine when weather is good though, only occasional fluctuation.
Finally managed to view this, didnt work from home! Yes this is what I am seeing, it does settle eventually on mine which I can't tell on the video as its not long enough.
I've not read throught all the this thread so some of you might have already tried them, but is it the DV fluctuating and if so have you tried running it off intake manifold pressure to rule out the N249 valves?
if i could get a good enough video of mine id post it but its a little difficult whilst driving. plus, my phone doesnt like the backlight of my boost guage at night...too bright
ill try my best, but mine isnt like the video
ill try my best, but mine isnt like the video
I've had the N249 tried and last friday i changed the DV to cold side which made no difference.
I changed my DV back to Hot side, removed the TIP and checked all pipes and connections and they all look fine.
I had a chat with one of the "heroes and very nice men" earlier. The conclusion was that spivboomerang's requested boost isn't low, it's "fine". SB's is a 225, mine's a 210, maybe that's the difference
So, maybe SB's is just overboosting, which would be a similar cause to Scotty's (with the hybrid) and the N75 can't smooth it out. One thing I've suggested is that he just turns the boost right up and sees what happens. It might smooth it out, it might make it worse, it might make something go pop.
SB's going to do some more logging tonight and try a few things.
Again, I think you're not all having the same problem - I think part throttle surging on K03S cars is fairly common? Try a search on the other forums, vwvortex, audi-sport, briskoda? Someone will have had it before.
So, maybe SB's is just overboosting, which would be a similar cause to Scotty's (with the hybrid) and the N75 can't smooth it out. One thing I've suggested is that he just turns the boost right up and sees what happens. It might smooth it out, it might make it worse, it might make something go pop.
SB's going to do some more logging tonight and try a few things.
Again, I think you're not all having the same problem - I think part throttle surging on K03S cars is fairly common? Try a search on the other forums, vwvortex, audi-sport, briskoda? Someone will have had it before.
beezasport
Sold the car to buy a....
OK, after doing quite a few logs and getting them checked over by the 'specialists' (thanks guys!) it seems that what I was seeing was overboosting - now this seems to have come out of nowhere as it just started happening one day after no changes to the engine
As a last resort after searching numerous times for leaks (did find split hose but it wasnt causing this problem!) I decided after some advice to have a go at altering the N75 to turn the boost down so to speak - now although this might only be masking the problem if it fixes it I can't see an issue - afterall smooth underboosting had got to be better than any king of overboost!
So.. I turned the N75 clockwise 1/8th of a turn, went for a run - no difference, so one more try I though, another 1/8th of a turn (so in total from 12o'clock to 3o'clock) - went for a run - wow! seems to have cured it.
I then did some logs of which you can see the graph below and it seems to be ok just simply not getting requested boost which is what I expected but it is obviously handling this much better than before. Now the boost I am getting is fine with me and more or less what it was settling at once it finished 'bouncing'
I have since been out in the car and I am pretty shocked how much smoother it is when booting it without the fluctuating boost - pretty damn amazed actually after putting up with it for 10k miles!
Here are before and after video's for your viewing to show exactly what I was getting. Now this only happens at full throttle from say 3500RPM, if you floor it more conservatively from 4500RPM for example the boost will be pretty smooth but you would expect that as you sort of controlling it with your foot - which you dont want to have to do really
Before
After
Hope this helps, just a note playing with the N75 could kill it so alter at your own will, I looked down every avenue and did this as a last option - at the end of the day the decision is yours.
My N75 screw was very stiff to move, I had to use a larger screwdrive with a bit end which just fit to move without knackering the head of the screw.
As a last resort after searching numerous times for leaks (did find split hose but it wasnt causing this problem!) I decided after some advice to have a go at altering the N75 to turn the boost down so to speak - now although this might only be masking the problem if it fixes it I can't see an issue - afterall smooth underboosting had got to be better than any king of overboost!
So.. I turned the N75 clockwise 1/8th of a turn, went for a run - no difference, so one more try I though, another 1/8th of a turn (so in total from 12o'clock to 3o'clock) - went for a run - wow! seems to have cured it.
I then did some logs of which you can see the graph below and it seems to be ok just simply not getting requested boost which is what I expected but it is obviously handling this much better than before. Now the boost I am getting is fine with me and more or less what it was settling at once it finished 'bouncing'
I have since been out in the car and I am pretty shocked how much smoother it is when booting it without the fluctuating boost - pretty damn amazed actually after putting up with it for 10k miles!
Here are before and after video's for your viewing to show exactly what I was getting. Now this only happens at full throttle from say 3500RPM, if you floor it more conservatively from 4500RPM for example the boost will be pretty smooth but you would expect that as you sort of controlling it with your foot - which you dont want to have to do really
Before
After
Hope this helps, just a note playing with the N75 could kill it so alter at your own will, I looked down every avenue and did this as a last option - at the end of the day the decision is yours.
My N75 screw was very stiff to move, I had to use a larger screwdrive with a bit end which just fit to move without knackering the head of the screw.
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I'd Turn it back 1/16 of a turn
If you don't have EXACTLY the same issue as SB had (i.e full throttle boost surging), I wouldn't start tinkering with the N75.
Hey its fine for me, not going to go fiddling!
As Feel states, I wouldn't go altering the N75 unless you have exactly the same problem - which is why I have posted video and an explanation.
I went through 3 N75's trying to solve this and knowing a new one did nothing thats when I thought altering was the only option.
that confusses me even more as i have changed the n75 to a j and had the local dealer do it and im sure the valve was turned 180 degrees and solved the problem briefley [only two weeks]
what i might do is get some srew clips rather than the one's seat use and see if there is a way off having the valve the same position as before
what i might do is get some srew clips rather than the one's seat use and see if there is a way off having the valve the same position as before
I altered slightly back to see if I can get a just right but when I drove the car I got the fluctuation back, moved back to the 1/4 turn position and seemed ok but will test again today ... bloody cars.
Trouble is with these car is that they relly on a fairly simple control loop to controll boost against airflow. The gain may work perfectly on most cars, but simple changes to the system, like air intakes, exhausts etc can effect the turbo response.
Slight differences in n75's, and mafs can throw it out, as can minor vac or boost leaks.
The boost control on mine was perfect with less than 2 psi of overboost, then holding bang on 26psi. When it was tuned it had a vac leak. Fixed the vac leak, and the boost control is not quite as good with minor 1/2psi fluctuations when in boost, especialy in lower gears. 1/2 psi in 26 makes bugger all diference, so I don't worry about it. Demonstrates how tiny differences can make a difference though.
THe lower the boost level though the easier it is.
Slight differences in n75's, and mafs can throw it out, as can minor vac or boost leaks.
The boost control on mine was perfect with less than 2 psi of overboost, then holding bang on 26psi. When it was tuned it had a vac leak. Fixed the vac leak, and the boost control is not quite as good with minor 1/2psi fluctuations when in boost, especialy in lower gears. 1/2 psi in 26 makes bugger all diference, so I don't worry about it. Demonstrates how tiny differences can make a difference though.
THe lower the boost level though the easier it is.
I'll say it one more time! I think you have a different problem. SB's was surging on everything other than light throttle, all the way through the revs.
I would leave the stock clips alone, they're acutally pretty good on small hoses, better than small hose clips anyway (and with small hose clips it's very easy to overtighten them and cut the hose). Have you ever tried running yours with the MAF unplugged? Does it do it then?
I'll say it one more time! I think you have a different problem. SB's was surging on everything other than light throttle, all the way through the revs.
I would leave the stock clips alone, they're acutally pretty good on small hoses, better than small hose clips anyway (and with small hose clips it's very easy to overtighten them and cut the hose). Have you ever tried running yours with the MAF unplugged? Does it do it then?
ok i got that but it was just a thought as the postion was different!
anyway i think ill try this as its a possibility it could tell me something.
so unplugging maf would be ok to then start or unplug while running?
i would have thought the first was the right choice
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