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View Full Version : T4 won't boost past 0.7bar... help please!



Al115
Monday 11th August 2008, 12:52
OK, this is bugging me... any suggestions please guys?

1999 S40 T4, hasn't been boosting right for a while. Trying to get it back to 1.0bar stock boost.

Originally was boosting to just 0.4bar, suspected the boost control solenoid so replaced with a Blitz dual-spec R boost controller (good for 2+bar) that I had lying around. Now we get 0.7bar but no more, even with the Blitz wound right up to 100% (a bit scary trying THAT!)

The car spools up nicely to 0.7bar but then will just hold 0.7 and dump the excess boost to atmosphere. Quite an abrupt effect, I could believe that the Blitz was cutting in early but can't see any evidence for this.

Checked for the usual air leaks etc, nothing found. Wastegate actuator feels reasonably tight, not sloppy.

Currently has an atmospheric DV AND the standard recirc, which might be causing the issue? I'm blanking off the recirc valve later this week to see if that might help...

What else can we think of?

PNuT
Monday 11th August 2008, 15:02
what is the recuirc valve connected too? if nothing then thats most probably your problem as they require boost pressure to hold them shut....

Al115
Monday 11th August 2008, 15:09
It's connected to the intake manifold...

Stevie-Boy
Monday 11th August 2008, 16:31
What does your vac read at when the car is idle?

Alan M
Monday 11th August 2008, 16:37
Could there be a blockage in the exhaust system? I remember someone on this site having a problem with a blocked cat tha resulted in no more than 0.8 bar of boost and it worked fine up until that figure.

Al115
Monday 11th August 2008, 17:19
What does your vac read at when the car is idle?

0.7ish from memory, but I don't recall the units :D

What could I tell from this?

Al115
Monday 11th August 2008, 17:20
Could there be a blockage in the exhaust system? I remember someone on this site having a problem with a blocked cat tha resulted in no more than 0.8 bar of boost and it worked fine up until that figure.

hehee, my first T5 came with a collapsed cat and that prevented ANY boost! Great fun once we'd sorted THAT!

I think the exhaust should be fine as it's only a year old (through from the turbo back).

Thanks though!

CONDYBOY
Monday 11th August 2008, 17:31
Recirc valve is the most probable cause imo. blanking plate required.

Al115
Monday 11th August 2008, 20:17
Recirc valve is the most probable cause imo. blanking plate required.

Weird if the stock recirc can handle a bar of boost... unless it's having issues working in tandem with the atmospheric dv? Quite possible I suppose...

Stevie-Boy
Monday 11th August 2008, 21:53
So your vac is at 10psi when the car is idling then. That sounds alright really, a dodgy vac value could point to a boost leak.

Just thinking, if you're boosting to 10psi and the standard boost is 13psi(?) then it's probably going to end up being something like a minor boost leak or that recirc as it's not a massive drop in boost. Be interesting to see what does happen when you blank that off.

Ross9
Tuesday 12th August 2008, 01:43
have you tried running a straight vac hose from the inlet to the actuator?

this will at least let you know at which point the actuator pops open and bleeds off

Ross

Al115
Tuesday 12th August 2008, 09:07
have you tried running a straight vac hose from the inlet to the actuator?

this will at least let you know at which point the actuator pops open and bleeds off

Ross

No I haven't and maybe I should! Good idea thanks. Can try it tonight...

Any risks involved in doing this that I should be aware of? :D

PNuT
Tuesday 12th August 2008, 10:10
have you checked for any hidden codes?

Al115
Tuesday 12th August 2008, 10:31
Good point and no I haven't, will have a crack at that too.

Al115
Wednesday 20th August 2008, 18:40
Update... not too positive... :(

No DTCs stored.

Blanked the recirc valve off and retested... no change whatsoever (apart from more noise...)

It feels to me like something is dumping boost at 0.7bar, but I can't blame the Blitz as the same thing was happening when the stock BCS was fitted!

Guess it might be time to hunt for holes in hoses, but I've been through that once... any pointers? Suggestions? Words of encouragement? :D

Cheers guys...

jimka
Wednesday 20th August 2008, 18:48
Wastegate actuator diaphragm split?

PNuT
Wednesday 20th August 2008, 20:27
Wastegate actuator diaphragm split?

that would stop the wastegate opening.... i would expect more boost than 0.7bar even with the leak via the diaphragm