Help - Boost problem!

[OllieH]

Right, had a previous thread on here about this and was just gonna update it, but can't find it when searching. Anyway, originally I had a coilpack issue, with the engine misfiring when trying to accelerate. Replaced the coilpack and the plugs which sorted the coilpack problem, but then noticed a boost problem that wasn't there before. My S3 has a custom code stage 1 remap and when I used to accelerate I could hear the sucky/whistle noise of the turbo boosting up and the car used to accelerate hard from 2.5k revs. Now though, I can still hear the turbo boosting up at the same revs, but the car does not accelerate until 3+k revs, at which point it suddenly kicks it. The boost is definately there as if I go to change gear at say just short of 3k revs I get the normal DV noise where it is dumping the boost.

Trying to trace this problem I have done the following:

change the split-r DV for a 007P.

checked the pcv system for leaks, found a split hose and replaced it, but have since removed the pcv system altogether.

removed the front bumper and lights and traced each boost hose looking for leaks, and found nothing.

Cleaned the MAF sensor.

Not sure what to do now?? Could it be a MAF problem? At £60 ish I don't want to change it just for the sake of it.

I've got VAGCOM now so will try and log the engine later today. From reading a similar thread I'm gonna log the following:

Log 1:- 020 Timing pull, 031 Fuelling, 115 Boost.
Log 2:- 115 Boost, 002 Airflow, 031 fuelling.

Anything else I should log?

Just to add, I only changed the coilpacks for cylinders 3 and 4, so 1 and 2 are still old, but don't think my symptoms suggest coilpacks, plus when I last checked there were no faults on VAGCOM to suggest that.

Any help will be greatly appreciated with this as I'm starting to clutch at straws now, and just want it fixed.

 

[Westy]

My mate had boost issue on his S3 and all was fixed with a new N75 valve. I think a new valve is around £60, I was thinking about getting myself a new one because I get some inconsistant boosting quite regularly.

 

[OllieH]

Was thinking about this as when I first had the problem I logged requested vs actual boost, and actual was lagging requested by about 500 revs, but now I'm not so sure as I'm still hearing the boosting noise and it still dumps on gear changes...?

Here is the graph I made up from the original log:

Problem is I don't have a log to compare this against of when the car was working ok.

 

[<tuffty/>]

Logging those blocks is a good start... make sure the engine is fully warm first though (90 deg)

Once you have done your runs and saved the logs, check block 032 too... these are the ECU adaption values.. do this parked up and with the engine idling..

Post up screen shots of the results of the runs....

Airflow wise you should be seeing 200+ g/s on a stage 1 with a decent MAF, any lower than that then it could well be on its way out... pretty sure I am due another one as well... that will be my third in 15 months...

<tuffty/>

 

[Westy]

Dont worry too much about the requested boost with regards to revs mate. My map requests impossible boost out of a K04 revs wise but it matches it on boost pressure which is what really matters.

 

[OllieH]

Problem is, with regards to airflow g/s, once it starts accelerating it seems to go just as hard as it used to, but just 500 revs later than it did, so I'm thinking the max g/s will be the same?? Should I do the logs in 2nd or 3rd gear?

 

[OllieH]

Dont worry too much about the requested boost with regards to revs mate. My map requests impossible boost out of a K04 revs wise but it matches it on boost pressure which is what really matters.

Ok, so you are saying the graph above could be quite normal, as the K04 will struggle to make the boost as quick as the map is asking for it, but will get to the max boost eventually?

 

[Westy]

You could do with checking the N75 cycle rates on block 118 or if you know someone nearby who has a newish N75 valve you could try running with that.

Also have you tried driving the car with the MAF unplugged?

 

[OllieH]

You could do with checking the N75 cycle rates on block 118 or if you know someone nearby who has a newish N75 valve you could try running with that.

Also have you tried driving the car with the MAF unplugged?

Unfortunately, don't know anyone near me with an S3. Think I tried running with the MAF unplugged when I first had the problem but made no difference. Will give it another go today though.

 

[<tuffty/>]

Problem is, with regards to airflow g/s, once it starts accelerating it seems to go just as hard as it used to, but just 500 revs later than it did, so I'm thinking the max g/s will be the same?? Should I do the logs in 2nd or 3rd gear?

3rd

<tuffty/>

 

[Westy]

Ok, so you are saying the graph above could be quite normal, as the K04 will struggle to make the boost as quick as the map is asking for it, but will get to the max boost eventually?

Yep spot on. My map requests boost that a K04 cant physically achieve at the revs its asking for.

It does sound very similar to my mates N75 issues but he would also get some over boosting and sometimes hit soft limp mode because of it.

 

[OllieH]

Well, looking at the above graph it does go over the max requested by quite abit, as you can see the flat line at the top where it has gone past the 1.55 bar readable level of the MAP sensor. I have never hit limp mode though, although I have been driving like a granny ever since I had this problem just incase I was causing any damage.

 

[Westy]

Dont worry about that too much, mine smashes the requested boost by 4psi!:

Also just had another thought. The N249 valve opperates the DV if it detects an overboost. I gained 2 psi by tearing out the N249 valve and vac chamber.

 

[OllieH]

Forgot to add that I'd done the N249 bypass aswell . If nothing obvious appears when I log later, I might have to bite the bullet and get a new N75 and MAF, and also replace the coilpacks from cylinders 1 and 2. That's probably £160 worth there!

 

[Westy]

Coilpacks shouldn't effect your boost mate not in the way you describe. Your engine will hesitate, stutter if the coilpacks are faulty and you should also get VAGCOM errors.

If I was you i'd start with the N75 if your car runs the same with the MAF unplugged it probably wont be the MAF at fault.

 

[OllieH]

Right then, have done some logs. Here are the screen shots:

this next one is block 118, N75 cycle rate. Not sure what to make of this:

Tuffty, looked at 032 like you said whilst sat at idle. The left hand column said -0.9% and the right hand column said -3.9%. I'm assuming this is good as I've read somewhere that anything over +5% means the ECU is adding fuel, which means a vacuum leak??

Any suggestions on the above logs?

Thanks.

 

[<tuffty/>]

Boost request is early enough but spool seems slow and getting a lot of timing pull. What fuel you using at the moment?

Airflow is a little down.

Difficult to know what to suggest atm....

<tuffty/>

 

[OllieH]

Normally use V Power but had to put £20 worth of ordinary 95 ron in the other day. Not sure whether it's connected, but when starting from cold I can hear what maybe a very slight blow from the exhaust. A little raspy sound, but goes when warmed up. I can't see any cracks in the exhaust or anything.

 

[<tuffty/>]

Gaskets will split (turbo to mani and turbo to DP) and the gaps expand when warm, could be why this is happening. Doubt you will see the cracks as they tend to happen where the turbo meets the mani and are only visible when apart... not much to worry about at this stage though and I doubt that is contributing to your current issues..

Assuming you put £20 of 95 ron into an empty tank then yes, the timing pull will most likely be due to that. This will have a knock on effect to the rest of the performance too.

Get a tank of Tesco 99 or V Power through the engine then log again...

Can't explain the late spool as yet...

<tuffty/>

 

[OllieH]

Yes, £20 went into an empty tank. Will log again like you said when I next top up. Where are you looking to see a late spool? Block 115 with the requested vs actual pressure? Do you think this could be the N75 valve?

 

[<tuffty/>]

The 95 ron fuel is why the timing pull is so bad so 98/99 ron fuel will sort that out.

Looking at your second log, ECU is requesting around 1.3bar at about 2.3k rpm but actual boost doesn't start getting close until about 3k... is this the symptom you are on about?

I never really logged my car that much while I was still using a K04 so not really got enough background to comment on this but I am sure Bill or someone else will... Not having driven a K04 powered car for a while I only know where my boost comes in these days and its not too far behind yours lol...

What mileage is your car and is there anything in its previous history to suggest any engine work being carried out? Trying to establish if the turbo may be worn.

The rest looks ok, doubt its the N75 tbh... Its controlling boost ok looking at req vs actual once there is boost present. Best bet would be to borrow one if you can as I think they are around the £50 mark new... lot of cash to blow if its not right... money better spent on decent fuel ;P

One last thing, have you checked the actual charge pipe system for boost leaks? I know you have checked for vac leaks... re-tighten the jubilee clips on the hoses of the charge system (boost pipes). If you get the click of death from over tightening though, replace the offending clip... preferably with a hi-torque one like the ones from Forge.

<tuffty/>

 

[OllieH]

Looking at your second log, ECU is requesting around 1.3bar at about 2.3k rpm but actual boost doesn't start getting close until about 3k... is this the symptom you are on about?

Yes, this is the exact symptom I'm on about. Definately used to come in at 2.5k rather than the current 3k.

What mileage is your car and is there anything in its previous history to suggest any engine work being carried out? Trying to establish if the turbo may be worn.

It's a 2003 car on 77k miles and have full history, with no engine work that I know of. Used to be Andy-S3's car on here, and he looked after it very well. Was weird how it only started happening after I got the misfire and took it to AMD in Essex to get diagnosed?! Literally in the space of 2 days.

One last thing, have you checked the actual charge pipe system for boost leaks? I know you have checked for vac leaks... re-tighten the jubilee clips on the hoses of the charge system (boost pipes). If you get the click of death from over tightening though, replace the offending clip... preferably with a hi-torque one like the ones from Forge.

Yes, had the charge pipe off, then took off the whole front end inc. lights and traced the boost pipes to and from intercoolers etc, but found nothing. Had someone revving the car whilst looking to get some boost pressure in there. All jubilees seem tight aswell. Gonna try a DIY pressure test at some point using some acetal plastic and a tyre valve, then some smoke in a can.

 

[OllieH]

Hi, just an update to this as I've still got the delayed boost problem!!

Since the last post I've tried a known working N75 valve which didn't change anything. I've also changed all coilpacks, and recently a new MAF sensor. I've also fitted a silicon TIP, checking the turbo for any play when the oem one was off, and all is good there. Since the MAF sensor change I've cleared all Vagcom faults and aligned the throttle body. I can't find any boost leaks, and the one vacuum leak I had is now gone as I've removed the pcv system. My ECU fuelling adaptation values (Block 032) confirm this.

I've had it that long now I'm not sure whether it's just me, or whether there really is a problem. Can anyone tell me when you should hear the K04 start spooling up, and when you should actually get the shove in the back?? At the moment I hear the spooling at 2.5k rpm but dont get the shove till 3,200-3,500 rpm. I'm pretty sure before I had the initial coilpack problem the two used to coincide together.

Just to add, my idle is still lumpy even after all new coilpacks, plugs, MAF, throttlebody alignment, no vacuum leaks. What is going on??!!

Here's some fresh logs (with Shell V-Power in the tank). Maybe some of the experts on here (Tuffty? Bill? ) can see something I'm missing

 

[finesse]

2500rpm onwards shove it back

can hear it from about 2000rpm.....

hope you get to the bottom of this issue, really unsettling when you don't know what the cause is

 

[Broken Byzan]

As you have already noticed you are spooling late, if you are hearing a slight blow of exhaust , i guess it's poosibly the wastgate flap is not sealing as it should. The blow could maybe indicate a crack, although they usually crack internally and not to atmosphere.

 

[OllieH]

As you have already noticed you are spooling late, if you are hearing a slight blow of exhaust , i guess it's poosibly the wastgate flap is not sealing as it should. The blow could maybe indicate a crack, although they usually crack internally and not to atmosphere.

I'm assuming this isn't easily fixable?