Overboost protection? Dont take as being correct, confusing thread.

[stevieyid]

I have just had new coils and new thermostat fitted to try and sort out my misfire which i thought it had. I dont get the misfire now when the engine is hot but on the last leg of my way home today i gave it WOT in 4th at about 30mph to overtake a car. As the boost built up i got huge jolts like overboost protection. The other slight misfire i was getting when hot has now gone but i have got this problem now. It did do it the day before i had the coils and the thermo fitted but i reset the ECU and it was fine. I also went up the strip today and it was fine. It only seems to do it u give it WOT at low revs so the boost pressure builds right up. Do u think this is linked to the other misfire or do u think this is a new problem? I will clean the Maf tomorrow but i was thinking it may have developed a boost leak. If it did have a boost leak though surely it would have affected my run up the strip wouldnt it? Thanks

[stevieyid]

Anybody? Really dont know if this is linked and now after a post on gti thread saying i should get my car checked after my sprint run im starting to think the worst. Anybody got vag-com down south that can read some codes or something? Thanks peeps

[kingos2]

my car has been playing up like this but i've been putting it down to the heat or teperature sender on top of inlet manifold if this help's for ideas

[stevieyid]

Well i reset the codes and cleaned the MAF then i took the car out to see what happens. 20MPH left it in 3rd and gave it WOT, boost built up to 20+ PSI and i had no problems. So i guess this rules out a boost leak. So now im thinking this has to be due to a temp problem. Now im thinking it could be the POS or the inlet temp sensor. What do u lot think? Would any of these give out a fault code? Also what the prices for a new inlet temp sensor and POS

[stevieyid]

Just been talking to a mate about this and he says possibly the intercooler is playing up? Whats your thoughts on this?

[newsh]

Mine does this sometimes, its just as you describe, when you have fairly low revs, build some boost, maybe lift off just slightly then floor it. Just when you'd expect to get maximum boost maximum torque it just goes into overboost protection and the ecu shuts it down, really annoying as its usually when you'r trying to pull off a cheeky overtake..
It happens quite rarely and it ALWAYS is cured by cleaning the WGFV. It never happens when you are really driving the car hard through the gears and revving it properly, always when I've just been pootling along and suddenly floor it.
My theory is that the WGFV gets sticky and allows too much boost, maybe it does this when its hot, don't know, but it definitely happens at the point when the ECU takes over from the WG spring and the WGFV starts turning up the boost, it just seems to turn it up too high sometimes.

[newsh]

Just been talking to a mate about this and he says possibly the intercooler is playing up? Whats your thoughts on this?

Does he mean the IC might be leaking? I don't see how an intercooler can "play up", a boost leak might cause the same symptoms though.

[newsh]

Steve. Have you done the Mark H Mod?

[stevieyid]

No i have got the bits but i have not fitted it yet. Yeah i think he did mean leaking. Just seems strange it dirves fine and evrything was fine on the strip but after a long drive home i floored it in 4th at about 30mph boost started to build and then i got the violent jolts which i take it was overboost protection. Once it has done that it will kepp doing until u take the motor fuse and reset the ECU so i guess it is giving out a code.

[newsh]

DanB will be coming down again soon to fit his MHM and some Samcos, you could come over and do yours at the same time if you like, we'd have 3 S2s and a ur in one place, almost a meet

[stevieyid]

Yeah that would be good mate. Do u know when?

[mojogoes]

My belief of whats happening is this , i don't believe like Newsh has pointed out but rather the oposite in that the spring and the diaphragm of the actuator are not strong enough to keep the wastegate closed , so when you hit wot from/at low rpm's there's high loads/pressure are acting upon the wastegate unlike even drag racing from standing start situations like from 1st gear , so then the wastegate creeps open too soon which in turn makes the turbo not spin up as fast as it should do so that the requested boost level/s are not been met in accordance with the boost maps so the ecu goes into limp the same as if it were overspeeding and was making more boost than requested.



Steve.

[stevieyid]

So basically change the WGFV and it should be fine?

[newsh]

Dunno about that, but thats an interesting thought, maybe, I can see my boost go quite high sometimes, anyway my setup runs a 1 Bar spring so I dont think its creeping. Difficult to repeat the problem it happens so rarely, but yes it happens at maximum load always, right on the steepest part of the torque curve. Thinking about it, I used to get a lot more problems like this before I changed to the Samco MAF hose.

I've also heard this called a MAF cutout.

My belief of whats happening is this , i don't believe like Newsh has pointed out but rather the oposite in that the spring and the diaphragm of the actuator are not strong enough to keep the wastegate closed , so when you hit wot from/at low rpm's there's high loads/pressure are acting upon the wastegate unlike even drag racing from standing start situations like from 1st gear , so then the wastegate creeps open too soon which in turn makes the turbo not spin up as fast as it should do so that the requested boost level/s are not been met in accordance with the boost maps so the ecu goes into limp the same as if it were overspeeding and was making more boost than requested.



Steve.

[mojogoes]

Yeh......the thing is i don't know what boost pressures you guys are using and what up grades you have , but i feel if any more than and including a remap would give this situation.

If say your running 1 bar boost and your car has been chipped with no boost controller the minimum the actuator spring tension should be is 1 bar , if your running 1 bar and a boost controller you can get away with either a .5 to .7 bar actuator and so on .

I'm running or trying to run 2 bar constant boost or there abouts so with out any boost controller i would need an actuator that has a diaphagm and spring to match that gave/gives 2 bar or slightly more just so the ecu boost maps were adhered to , or a 1.5 bar actuator along with a gated boost controller to give the same effect.