# BAM overboosting



## mimjed (Jan 13, 2014)

ive had a search around and am struggling to find an answer, dont know if anyone has ever had similar issues. its a BAM 225 engine.

the symptoms are, a definite "jolt" as you accelerate anywhere past 1/4 throttle in second gear at 2,800rpm. feels like someone stamps on the brakes (boost is dumped, and im assuming fuel is cut off too). then the same issue in 3rd gear at around 3,800rpm. you can hear the turbo fluttering and dumping boost throughout the rev range. car is not as quick as it should be.

have checked as many boost pipes as i can for leaks, none found. changed N75 valve, full service, maf functioning correctly, checked turbo actuator for function - ok (16mm of thread showing, hasnt been moved for a very long time by the looks of it). everything on the car is standard, intercooler, exhaust, map etc. no fault codes on vagcom.

i have been going through measuring blocks on vagcom and found that the ecu is requesting 26psi from the turbo, the turbo keeps up with this, but it seems the engine cant make use of it, so it is dumping the boost.

anybody have any previous experience or clues where to look? dont want to cook the turbo.

cheers jim


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## L33JSA (Jun 30, 2010)

mimjed said:


> .....found that the ecu is requesting 26psi from the turbo, the turbo keeps up with this...


If the car is standard then I doubt it's requesting 26psi.....have you got any logs you could post up? If it's overboosting then you would potentially get the code 'Charge Pressure Limit Exceeded' logged.


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## mimjed (Jan 13, 2014)

sadly i didn't record the logs. have had a second opinion and a second vag com on it, didn't tell him anything other than symptoms, came up with the same results.

its not my car so odds are on i wont see it again until friday.

i also dont understand why the ecu would be requesting 26psi, i believe around 18psi to be a healthy figure.

no fault codes, no limp mode, only light that comes up is traction control.


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## c4z (Aug 15, 2011)

It has a diverter valve rather than a dump valve.
If you're standard (airbox/diverter valve) then there is little to no 'dump' or turbo sound.
Noise suggests a boost leak.
I suppose your boost pipe could be collapsing causing the stuttering?

Any pics of your set up?


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## L33JSA (Jun 30, 2010)

Did you look at MAF values?


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## kasandrich (Sep 5, 2011)

There will be noise at 26psi

Are you sure this has a std map??


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## c4z (Aug 15, 2011)

Thinking more about it, i'd check all the vacuum pipes under the thottle body. Remove and reclamp all turbo pipes while checking for splits.
Has the car been re-mapped?
Have any mods been added since the re-map?
Is the N75 valve ok?


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## mimjed (Jan 13, 2014)

there is indeed a lot of noise from the turbo, it is definitely pushing hard.

no map on the car what so ever, have read ecu file to see if its been fettled with, but all seems standard.

have tried unplugging maf while running and changes exhaust note, have ran the car with maf unplugged to put on to base values and still the same.

have changed the n75 for a known working one (F revision) no change.

have had a fair amount of the boost pipes off to check the position/function of the actuator on the turbo. vac hoses seem to be in tact too.

its a bog standard s3 bay, with n75, dv and n249 still in place. everything as it was when it left the factory.


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## L33JSA (Jun 30, 2010)

mimjed said:


> have tried unplugging maf while running and changes exhaust note, have ran the car with maf unplugged to put on to base values and still the same.


...but have you actually logged the MAF values?


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## mimjed (Jan 13, 2014)

truthfully no i havent. the assumption was it wouldnt be a factor as running without a maf made no difference to the issues the car is having, which in my head says its not causing the issue.

1.8t's are not an area im fully competent in, i served my forced induction time on g60's and now sadly run diesels.

i will check values when i see the car next, but dont believe this is the key to the problem.

starting to think its the penny in the wastegate.


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## kasandrich (Sep 5, 2011)

a wastegate issue will not cause the ecu to request 26psi


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## L33JSA (Jun 30, 2010)

mimjed said:


> truthfully no i havent. the assumption was it wouldnt be a factor as running without a maf made no difference


It may have made no difference but it would also help in being able to detect if the TIP was collapsing as the MAF figures would probably be all over the shop.



mimjed said:


> ....starting to think its the penny in the wastegate.


In what way? You've said you've checked actuation which is working. If the penny has somehow become jammed (doubtful since the actuator probably wouldnt move) then yes it will overboost - however having a stuck penny would not tell the ECU to request 26psi.

If the penny wasnt shutting properly then it wouldn't make enough boost.


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## mimjed (Jan 13, 2014)

Will get it logged next chance I get.

Should be taking it to a rolling road for further investigation on Friday.

Thinking the penny after reading/seeing videos of them moving on 2 axis rather than just the one. The car came with pretty good history and doesn't seem to have had a turbo on it before. Granted this would not request 26psi, but having only picked the car up last week, I'm not aware of previous owners attempts or lack of attempts to rectify this.


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## steveupton (Mar 23, 2010)

This is a long shot but have heard of Chinese K04 copies giving similar symptoms. When my step sons K04 blew up, he had a genuine one fitted after we read about the problems with the Chinese copies.


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## Wak (May 6, 2002)

steveupton said:


> This is a long shot but have heard of Chinese K04 copies giving similar symptoms. When my step sons K04 blew up, he had a genuine one fitted after we read about the problems with the Chinese copies.


That's a good point clones have been known to have smaller ports under the penny or actuators with little movement!


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## L33JSA (Jun 30, 2010)

Do you get an automatic 26psi boost request when you fit a chinese copy??? :lol: :lol:


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## Wak (May 6, 2002)

L33JSA said:


> Do you get an automatic 26psi boost request when you fit a chinese copy??? :lol: :lol:


Even more than that for a few weeks then it settles down .... way down! :roll:


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## Adam86 (Nov 20, 2013)

mimjed said:


> the symptoms are, a definite "jolt" as you accelerate anywhere past 1/4 throttle in second gear at 2,800rpm. feels like someone stamps on the brakes (boost is dumped, and im assuming fuel is cut off too). then the same issue in 3rd gear at around 3,800rpm. you can hear the turbo fluttering and dumping boost throughout the rev range. car is not as quick as it should
> 
> anybody have any previous experience or clues where to look? dont want to cook the turbo.
> 
> cheers jim


This sounds exactly how my car performed shortly after a remap and it turned out to be the coil packs.

Correct me if im totally wrong as im not really clued up on running logs but as to the requested 26psi is this taking atmostheric pressure into consideration? And in actual fact it's only requesting 16psi?


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## L33JSA (Jun 30, 2010)

If its requesting 26psi absolute this would be around 1792mb.

Which would equate to around 11.5psi positive pressure which would be about right for a standard car.


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## mimjed (Jan 13, 2014)

I hope it is as simple as a bad coil , but fear that's not the case. No warning lights, and didn't notice missing on vagcom.

Going up on the ramps again tomorrow for another round of leak hunting, will try and run some logs on the way over.

On a seperate note, is there any major opinions on deleting n249 and n75. The owner of the car is keen on doing so, but I don't know enough about 1.8t's to give an honest opinion on it being a good idea or not.


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## nilrem (Sep 9, 2011)

mimjed said:


> I hope it is as simple as a bad coil , but fear that's not the case. No warning lights, and didn't notice missing on vagcom.
> 
> Going up on the ramps again tomorrow for another round of leak hunting, will try and run some logs on the way over.
> 
> On a seperate note, is there any major opinions on deleting n249 and n75. The owner of the car is keen on doing so, but I don't know enough about 1.8t's to give an honest opinion on it being a good idea or not.


Wak will advise against the N249 delete :grin:
And as the N75 is the boost controller you'd need to fit a manual one in its place so no point unless your mods require one.

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## c4z (Aug 15, 2011)

My guess is still a vac leak perhaps from the small pipes under the inlet manifold.


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## Adam86 (Nov 20, 2013)

mimjed said:


> I hope it is as simple as a bad coil , but fear that's not the case. No warning lights, and didn't notice missing on vagcom.
> 
> Going up on the ramps again tomorrow for another round of leak hunting, will try and run some logs on the way over.
> 
> On a seperate note, is there any major opinions on deleting n249 and n75. The owner of the car is keen on doing so, but I don't know enough about 1.8t's to give an honest opinion on it being a good idea or not.


I would still deffinatly try the coils, I spent days leak testing, replaced maf, n75, clutch switch, tip, temp sender ect ect and in the end it was the coils, I had no faults logged to indicat a miss fire so it was the last thing I though of checking. And on the plus side it may be entitled to them for free from audi so it must be worth trying....


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## mimjed (Jan 13, 2014)

apologies for the long silence.

got it up to a mates unit with ramps, fitted a manual boost gauge, got vagcom hooked up and on measuring blocks.....made it about 100 yards down the road on full chat in second - loud bang and a smell of oil.

instant panic!!! turned out it had blown the end tank clean off the inter cooler on the near side. we limped it back to the ramps and ripped out the old inter coolers.

we have now fitted a fmic, and got it out for a quick run. no logs though sorry...was a late night getting the bumper to fit over it.

now have a fault code throwing for the egt (exhaust gas temp sensor). not convinced its causing the problems, haven't seen it go over 900 in temp.

still the same as before, if it holds at 20psi it goes like stink, as soon as it spikes to 26psi it jolts and dumps boost. have had off and inspected boost pipes, couldn't find any leaks. will see if we can borrow some known working coils for elimination purposes. starting to get peed off with it now, map sensor on the blink?

have also replaced brake light switch while it was sitting as traction control was intermittent and was pointing to a bad switch on vagcom.


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## L33JSA (Jun 30, 2010)

mimjed said:


> ... fitted a manual boost gauge, got vagcom hooked up
> 
> map sensor on the blink?


When you were logging did the manual boost gauge agree with the vagcom measuring blocks? If so the map sensor is fine.



mimjed said:


> now have a fault code throwing for the egt (exhaust gas temp sensor). not convinced its causing the problems, haven't seen it go over 900 in temp.


This wouldnt cause a boost spike....however it does need changing as chances are it will overfuel if it's intermittantly working.



mimjed said:


> will see if we can borrow some known working coils for elimination purposes


Faulty coils wouldnt cause a boost spike

26 or even 20 psi is far far too high for a standard unmapped car.

What happens if you unplug the N75 valve - what boost do you end up running then?

Really need to see some logs of requested pressure, actual pressure & N75 duty - MAF would be handy too.

I'm putting my money on N75 valve at the moment - I know you said you changed it but what did you change it with? A new one or another used one? Exactly the same part code or not? How do you know it was not knackered too?


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## J•RED (Feb 10, 2013)

You can take a resistance reading on the n75. (Although I don't know if it's the best way of checking it) I believe it's meant to be between 25-35ohms. Don't forget they can also break down when they get warm, so it could be in tolerance when cold and out when it gets a bit of heat into it.

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## mimjed (Jan 13, 2014)

the manual boost gauge confirmed figures on vagcom. -20 on vacuum and 26 when it spikes.

will get those logged when i see the car again. his mrs isnt keen on the amount of time we have spent together recently :lol: so not sure when it will be yet.

n75 was a different part number, later revision F i seem to remember. it was taken off a working car so assumption is its good, will get the resistance measured.

fookin cars.


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## mimjed (Jan 13, 2014)

got some very short logs just now, hard to get anything decent with traffic and his daughter in the car. s3 and s33 are in 4th gear. s32 is in third gear and shows how bad the spiking gets.

hopefully you can make some sense out of it in vag scope.

View attachment s3LOG-01-113-114-115.CSV

View attachment s32LOG-01-113-114-115.CSV

View attachment s33LOG-01-113-114-115.CSV


will try and run some longer logs tonight or tomorrow with any luck.


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## L33JSA (Jun 30, 2010)

Looking at those logs I'd say that the car has been mapped...it's requesting 20-22psi.

However nowhere is it ever hitting 26psi - the highest it sees is 2540mb which equates to around 22psi. But at these points its only requesting around 20psi so it's 2psi over hence why the N249 kicks in and dumps boost to try and lower it back.

Nothing else looks abnormal to be honest - I'm still thinking N75 valve or possible small leak on the actuator/N75 lines.

MAF log would be handy too.

You really need to get rid of child and go find a private runway and do the logs from 1500rpm all the way upto redline for the best results.


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## mimjed (Jan 13, 2014)

Yes completely agree circumstances are not good for testing. It's now hammering it down in leics so not going to get anything done today.

Have had n75 to actuator off and it holds at 5psi.

It's booked in with dynodaze for a diagnostic session on Friday.

Spiking now hits 30psi on the manual boost gauge, Dec getting worse.

Thank you for your input too, good to have decent knowledge on hand.


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## L33JSA (Jun 30, 2010)

I take it you mean you've electronically disconnected the N75 because if you'd pulled the vac line off you'd be running virtually unlimited boost due to the actuator not being told to open

5/6psi is perfect with it unplugged......I still reckon N75.


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## c4z (Aug 15, 2011)

As above and as said previously it looks to have been re-mapped at some point.


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## mimjed (Jan 13, 2014)

Well it turns out the ecu was fried, pretty amazed it still ran at all.

Couldn't get the skc to read off it so had to take it to an independent to get another ecu coded in.

All fixed.

But to add salt to the wounds the power steering rack started pouring out fluid, which apparently is non serviceable. Ball bag.

Any how to's on changing racks that anyone is aware of?


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