Low boost

Manute · 07-21-2005, 10:20 AM

Hi guys! It´s been a long time, how are you doing? I´ve been quite busy working and studying.

Well, I need your help a bit, I just came driving and I have observed low performance in my 951, not accelerating as usual...when I checked the boost gauge, it won´t go over 1,2 bar or so.

It´s just the worst moment for me, cause i´m a bit short of money, what could it be? Would it be costly?I hope not.

Well, thank you in advance, see ya!

carsonmx114 · 07-21-2005, 04:37 PM

there's a big difference between 1 and 2 bar. if your boost seems low check for intake leaks. these cars are old and old rubber dries out and cracks. if you can swing it get a aftermarket boost gauge. this way you'll know how much boost your car is making. the stock gauge doesn't tell you anything you can't feel in the seat of your pants.

Lawrence Coppari · 07-21-2005, 04:45 PM

Check blow off valve. It probably has a broken diaphragm or there is a vacuum/pressure leak in the line that goes to the nipple on the blow off valve. Most of the time this is the problem.

BananaClip · 07-21-2005, 05:04 PM

Quote:

Originally posted by carsonmx114
there's a big difference between 1 and 2 bar. if your boost seems low check for intake leaks. these cars are old and old rubber dries out and cracks. if you can swing it get a aftermarket boost gauge. this way you'll know how much boost your car is making. the stock gauge doesn't tell you anything you can't feel in the seat of your pants.

1,2 = 1.2

Zero10 · 07-21-2005, 09:06 PM

Yep, madrid, spain, they use commas's instead of decimals...

Anyhoo, wish I could help, but I'm chasing a similar problem. I can make and hold 21-22psi of boost at 3500RPM, but by 5000RPM I'm down to 7psi, and by redline it's atmospheric. Best of luck in sorting this out!

SoCal Driver · SoCal Driver's Garage

If they use commas then why is it called a decimal system?

Manute · 07-21-2005, 11:23 PM

Yep, I meant 1.2 bar sorry....my gauge may be it´s not very reliable, but I always attained 1.7-1.8 very clearly.

Quote:

Originally posted by Zero10
Yep, madrid, spain, they use commas's instead of decimals...

Anyhoo, wish I could help, but I'm chasing a similar problem. I can make and hold 21-22psi of boost at 3500RPM, but by 5000RPM I'm down to 7psi, and by redline it's atmospheric. Best of luck in sorting this out!

Well, as far as I know, maximun boost is reached at 3k rpm, then it should decrease...but not below 1.5 bar.

My absolute value now, is 1.2 bar...not more,not less.It has been a suddenly change, so I´m with you thinking about the blow off valve (aka wastegate?)

One more thing....is it that valve the thing just over the cylinder head, with two pipes on it?

If this is my problem....it´s not very expensive, isn´t it? Just a new valve and all solved? (I´m crossing my fingers)

Lawrence Coppari · 07-22-2005, 07:10 AM

Before replacing the valve, I'd check it. The nipple should hold vacuum. If it does not hold vacuum, replace.

Check the "Y" just upstream of the BOV line. It is near the fuel damper.

carsonmx114 · 07-22-2005, 10:17 AM

the blow off valve and the wastegate are two different things. the blow off valve lawrence is talking about is in front of the trottle body on the intake boot. it's job is to protect the turbo from damage when you close the trottle under boost. if the valve is damaged it won't seal off and your boost bleeds off to the intake side of the turbo instead of going into in intake of the engine.

Zero10 · 07-22-2005, 04:25 PM

Stupid question, but isn't 1.2bar what it hits when you're in the over-boost protection mode?

Lawrence Coppari · 07-23-2005, 02:10 PM

1.2 bar absolute is only 0.2 bar boost. Gauge on dash reads in absolute. If you turn on ignition switch and do not start engine, it reads 1.0 bar.

Manute · 07-25-2005, 10:49 AM

Let´s see If I understood...Blow off valve is to protect the engine when releasing throttle under boost, it´s near the throttle body and it´s black with a little pipe just above it (I think I know where it is)...Well, I better upload a pic:

Is it that thing?
And the wastegate....where it is?

And how can I do to know if the diaphragm or the entire vale iis wrong?

I don´t see leaks, I think one of this two valves may be the responsible.

Lawrence Coppari · 11:08 AM

What you have circled is the blow off valve. If the diaphragm inside is bad, the whole valve is bad. Never heard of anyone replacing the diaphragm. Attach a piece of hose on nipple of valve. If you can blow through it, it is bad and replace valve. The diaphragm is a dead end. It must hold positive pressure or vacuum. Diaphragm holds valve closed under boost. If diaphragm is ruptured, boost pressure will open valve and you won't get any more boost than about 1.2 on your gauge.

Wastegate is on other side of engine below it (passenger side). Follow the headers. They will lead you to it after they join up under car.

Lawrence Coppari · 07-25-2005, 11:09 AM

Hopefully, your problem is either this valve or a vacuum/pressure line in the circuit. Wastegates are expensive. This is not.

Manute · 07-26-2005, 12:08 AM

Thanks Lawrence, I´ll check it later in the car.

I hope the problem is what you say, because I was just curious and checked wastegate prizes and are about 2.000$ or more!

But I´m scared because I´m cursed and I usually have the most expensive problem possible.

Well,i´ll tell you what I see.

Manute · 07-27-2005, 10:14 AM

OK, I´ve just checked the car, and I have good news and bad news:

Bad news are that it was impossible to blow through the blow off valve, so it must be OK.

Good news are that the damn problem fixed itself! I love this car, it fixes himself!!

The only answer I have is that I entered that "overboost safe mode", and after driving it again a few days later I just made a reset somehow.

Well, God bless the Porsche engineering; my advice to people with the same problem: just try the "computer method": reset it

And thanks to all for your help, I now know a safe mode exists.