Negative Boost Deviation - Any Idea's?

[Craig!]

My friends car recently has been plagued by errors and limp mode, in the 4th and 5th gears at WOT the car throws itself into limp mode every now and then. I did the N249 bypass last week which improved the car slightly, however theres still the negative boost error.

Could this be down to a faulty N75? Is there any chance that if the N75 was incorrectly fitted it could cause it as I know a certain main dealer who I don't trust re-fitted his turbo.

Also his MAF readings seem a little low, but they always have. I wouldnt have thought this would cause negative boost problems, but is it something I have over looked? The plan is to sort the negative boost then asses the state of the MAF.

 

[Simon L]

I get this error occasionally, normally when ive been driving hard for 10-15 mins, usually in 4th or 5th gear at around 4k. (peak torque for me)

I think it's one of the boost hoses collapsing due to heat making it soft.

I've tried multiple N75's and got the error with all of them. MAF always stayed around 150g/s.

 

[Radek]

I've had similar issue . It was caused by N75 . Replaced it with Audi S2 N75

 

[Simon L]

Would that be an N75J?

 

[Radek]

Yes

 

[Simon L]

Thats the one i use most of the time, and i still get the problem occasionally.

 

[Radek]

So there has to be another cause . What's the error no. ?
I wrote my solution for Craig!'s post

 

[Simon L]

Yes. Thats what i said. Read my first post.

 

[bellautos]

This is a common problem with cars that have non standard BIGGER turbos fitted.

What it normaly boils down to is the deviation value in the file inside the ecu software.

The KO3s sometimes take more time to create the requested boost compared to the KO3 ,and the time difference between the two causes negative deviation which causes limp mode.

The problem sometimes occures after the car has had a good pasting , when heat soak etc etc is starting to kick in as the engine and all related components are getting hotter and hotter.

Also to be taken into consideration is the Drop pressure of the new bigger intercooler.

There is a cure for it , alter the deviation value in the file but is not a easyone to find but is possibile with time and testing.

 

[PhilW]

Some basically if your ecu is requestion say 2100mbar at 2k and your turbo is spooling/generating boost and you dont hit anywhere near this figure you get this fault code.

Would it be right to fit a different N75 which brings the boost on quicker in the lower rpm?

 

[Simon L]

Are you getting limp mode at 2k though?

Only happens to me 4k/5k when hoofing it for prolonged periods of time.

 

[bellautos]

yes that is correct, in SOME cases a new N75 may help the problem.

 

[bellautos]

Are you getting limp mode at 2k though?

Only happens to me 4k/5k when hoofing it for prolonged periods of time.

You are not the only one with this problem as 4/5k .
I take it your car has a remap and possibily a new turbo ??

 

[David_smith_909]

i was always under the impression that this error simply meant you had a boost leak of some sort? your actual boost is not meeting your requested boost??

dont slap me

 

[bellautos]

To a certian extent this could be correct. normaly only if it were a standard car.

There are many reasons why you can get a negitive devation, pipe split , leaking hose , weak turbo etc etc the list goes on.

BUT in the case of cars that have had a non standard turbo fitted and big intercooler it is normaly down to the ecu maps.

most people seem to jump to the leaking boost pressure to try and solve the problem, in a tuned big turbod intercooled cars cars this is not normaly the problem.

What do most people who fit big turbos say to there tuner ??
( big boost please )

BUT sometimes requesting/demanding big boost causes non mechanical problems like negitive deviation limp mode.


ALL above is asuming that all N75 and related machanical parts are working correctly.

 

[Simon L]

You are not the only one with this problem as 4/5k .
I take it your car has a remap and possibily a new turbo ??

StarPerformance remap, forge DV, standard everything else.

 

[bellautos]

StarPerformance remap, forge DV, standard everything else.

it could be just a simple adjustment needed.

have you made a log of boost actual and requested @ this rpm ?

 

[ibizacupra]

matching request to physical actual (possible) but you cant ignore the chance of leaks from the multitude of vac lines which some of the ibiza's will be having now. (cloth covered rubber hose which is inevitably gone hard and splitting, and not visible under the cloth covering)

change of n75 and its internal restriction will alter the control be it faster or slower, which may well plug the gap in the request vs actual boost scenario

 

[bellautos]

I agree it is possibile that there could be a leak somewhere or some other part/pipe failure.

As in my last post, i was asuming all is fine with the car mechanically and electronicly with sensors etc.


In the case of craigs friend his car was perfect with the KO3s untill he fitter a bigger intercooler, asuming all the pipework is good.and drop pressure is not to high when heat soak sets in.

The only option left is possibile component failure or a file problem.

 

[ibizacupra]

its very difficult to diagnose via forums... but generaly if the car has previously run fine and then developed a fault its not likely software, and the question of whats been changed recently may well have a baring.