Hi there,

Got a UK 00MY running a boost controller at 1.15bar. Since increasing boost I have had a problem hitting the overboost cut-out when shifting between gears.

I`ve put this down to the Dump Valve - not opening quickly enough or opening but not flowing enough air when the throttle is closed.....

Anyone had a similar problem or confirm/trash my dump valve theory?

 

Don't have similar problem but think your theory is in tact.

I have just fitted a forge dump valve as I suspected mine was releasing at too low a pressure, which meant, I could have been dumping charge when feathering the throttle.

the forge seems to dump charge much more quickly, or at least sounds like it does, perhaps that is an option.

 

James,

When you say "between gears", do you mean you get cut out when you've just changed gear, and then floor it.

I could be wrong, but I'm not certain how a dump valve would cause overboost. If anything, if it wasn't dumping the air, it would be more likely to stall the turbo.

Mark.

 

I more or less got the same problem with my standard dump valve after fitting a K&N 57i filter.It sounded like it was sucking in too much air for the dump valve to cope so I took it off and it is back to normal.

 

James

Sounds like your peak boost is too high - a boost guage will show what pressure you're getting on gearchange....as Mark says, should be none if the dump valve is opening.

Richard

 

Thanks All...

To clarify I have boost gauges fitted both A-pillar and electronically through the APEX AVC-R.

Peak boost is around 16.5PSi. Boost cut is being hit on gear shifting ie the moment the throttle is closed.....

You lift closing the throttle, this creates a pressure delta accross the dump valve causing it to open and release the now trapped air back through the intake system. Now if the the valve can`t respond quickly enough to the pressure delta then you`d get a boost spike alternatively it is opening but can`t flow enough air hence a boost spike again!!

Also the steady state boost is fluctuating somewhat, again suggesting that the dump valve is leaking slightly.

Any other comments?

 

James

I once had a my99 with a sticky dump-valve (it exagerated the 2.5-3k hesitancy) - took it off and cleaned with wd40 so that it's action was smooth again.

May be worth a try for you too - or borrow a friend's one, it's a 10 minute job to remove. At least then you can rule it out

Richard

 

Dowser
did you have the part throttle 2-3k hesitation or the full throttle surging variety?
I'm desperate to cure part throttle hesitation ASAP (sooooooo annoying) so might try cleaning the dump valve.

Nick

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by dowser:
<B>James

I once had a my99 with a sticky dump-valve (it exagerated the 2.5-3k hesitancy) - took it off and cleaned with wd40 so that it's action was smooth again.

May be worth a try for you too - or borrow a friend's one, it's a 10 minute job to remove. At least then you can rule it out

Richard[/quote]

 

I didn't have any such problems when I blanked my dump valve off... ie. I removed the BOV from the equasion.

Are you remembering to lift off the throttle as you declutch? If you keep your foot down the engine may rev higher with no load and (_unlikely_ as load removed from engine) generate a quick boost spike.

I prefer Mr A's idea... boost spike as the engine is put under load again after you re-engage the clutch.

 

James

The MAP sensor which detects the overboost should be plumbed to the inlet manifold.As soon as you take your foot of the throttle the inlet manifold pressure WILL drop immediately .There is no way the pressure can rise causing overboost.

However on the intercooler side of the throttle the pressure does rise for a split second until the dump valve has time to open.This should not cause a problem no matter what size the dump valve is (because the closed throttle is in the way).

Are you sure your MAP sensor has not been accidentally connected to the intercooler side of the throttle for example when the AVC was fitted as this would cause an overboost cut when the throttle was lifted

By the way the dump valve is opened by inlet manifold vacuum in the main but is assisted by the pressure drop across it.

Your boost gauges should also show a vacuum when you are at idle,they should not read zero.

If they read zero they are incorrectly connected to the intercooler side of the throttle rather than the inlet manifold side

Andy

 

Its just hitting the boost cut, nothing to do with the dump valve which only needs to crack open to kill/reduce boost. You will have to adjust your boost controller downwards, is your gauge accurate btw ? the ecu could be seeing higher boost than you think if its not.

 

Thanks to all.......yes the APEXi is installed correctly - pipe wise. Had another look under the bonnet and yes boost sensor is after throttle plate so that rules BoV out!!

I suspect it may be a leak in the boost controller circuit....otherwise it would appear that the APEXi AVC-R is unable to control the boost charateristics of a std 00MY UK turbo!!!! I feel this is unlikely....so any other suggestions?

 

Nick

Yep - it was the part throttle hesitancy variety

I cleaned the dump valve (*very* sticky), the boost solenoid and all related hoses. Made things much, much better.....but was still there until warm

Richard