Oppiefive

Have a 2004 996TT, and although I get boosts anywhere from .2-.6 on acceleration, the boost does not seem to remain..it will go up and then drop back to zero. Is this normal??

Thanks

Peter

"02996ttx50

no.

Tuxiemama

Is it going to zero when you are WOT ?

rmc1148

Start with looking for leaks/hose connections.

Oppiefive

Will try WOT, not sure if it goes to zero..What is it supposed to do at WOT?

Oppiefive

What is the easiest way to check for boost leaks?

RugRunner

Sounds like your boost level is a bit low, too.

Macster

If you keep your foot hard on the gas pedal as RPMs rise the boost drops. IIRC the lowest I've observed with my 03 Turbo is 0.4 bar. (Or maybe 0.3 bar. I"m not sure now, but I'm sure it was not 0.2 (or lower) nor was 0.5 or higher.)

Depending upon the degree of throttle you are using boost can range from well, no boost to 0.7 bar, normally. Just giving the engine a bit of gas on a flat stretch of road can have the boost climb from 0.0 bar to 0.1 bar maybe even 0.2 bar.

On my work commute I climb a bit of mountain grade and the boost can reach and remain at 0.2 bar for a distance up the steepest part of the grade.

At WOT if you are seeing under 0.7 bar the most likely explanation is the engine controller doesn't believe any more boost is necessary to satisfy the torque demand signaled by the gas pedal.

You have to really mash the pedal and conditions have to be rather optimum. Once in a while all I have managed to see is 0.6 bar boost.

But at other times, driving at higher elevations, I have seen the boost reach 0.8 bar, even 0.9 bar and remain there long enough for me to know it was not a "glitch".

If boost is truly dropping to 0.0 bar and you are not subconsciously lifting off the gas pedal -- under hard acceleration these cars obtain ballistic speed and unless one has the right spot for this lifting is a form of self-preservation -- there is something wrong.

Perhaps the DME is detecting detonation and limiting boost? How are the plugs? The gas? The engine's overall "health"?

Kevinmacd

What I have observed is WOT in third gear gets me a peak boost of .7 as the car gets up to more speed then drops to .6 and stays there quit awhile.

Dock

If you have any hills (even small ones) in your area, approach one of them in a higher gear (3rd or 4th) and lower RPM (~2000 RPM). As you start up the hill go WOT. Boost should rise to a steady 0.6-0.7 and remain there for a couple thousand RPM or more (or until you come off the throttle).

Ridin Dirty

It's supposed to go to full boost, stay there, and you should be holding on for dear life If it's any sustained period of time.
Has to be a boost leak somewhere surprised it's not throwing the CEL

ReidN

Crazy mine boosts to 1.0 and 1.1. Sounds like you need a tune.

up4speed

I'm almost positive that you have a boost leak. I had a leak and the symptoms were exactly the same. Under steady throttle, the boost built up, then steadily dropped off even though I was still under load with the throttle.
The best way to check it is to pressurize the intake with 10 to 15 PSI. First take off the air filter assembly, then use a tool (that you make out of Home Depot parts) that clamps onto the intake rubber hose. Once pressurized, just listen for leaks. If you can't see them, try spraying soapy water on all the connections until it's obvious. I had trouble finding mine, but I eventually found it buried under the blowoff valves (it was the V-pipe). A few things to know:
1. Never over pressurize it, you may cause a new problem (you may finish off a hose that is on it's last legs...not sure if this is good or bad though)
2. You may need to lower the engine a little to really get in there and find the leak, or possibly to fix it. Not that difficult, and I had to do that on mine.
3. Make sure ALL of the hose clamps are tight before you begin.
4. Put a heavy blanket in the engine compartment around the plug. If it shoots out, it has some force. It will not only scare you, it may hurt you or the car if it shoots out if you skip this step.
5. After you make the plug, wrap some duct tape over the end that gets clamped so there is more traction on it, plus it has a better fit so it doesn't shoot out. (mine shot out, but it was from the other side of the rubber bellows, my tool stayed clamped in place)
6. Proceed at your own risk, have a pro do it if you are not comfortable.
See attached photo of the tool that I made. I used standard PVC plumbing parts (it was a bushing (I think 3" to 2 1/2"), short piece of pipe and a cap). I then drilled a 1/2" hole and screwed in the air hose fitting. I put some epoxy on the threads just to make sure it was secure and it didn't leak. Lastly, I wrapped the part that was going to get clamped into the rubber bellow with Gorrilla tape.

Good luck, let us know how it works out for you.

ReidN

Pretty slick little tool. Great advise.

up4speed

Thanks!