Porsche-O-Phile

Well, the new J-boot showed up today. I VERY CAREFULLY installed it, making sure there were NO leaks, missing hoses, missing clamps, etc. Everything was nicely bolted down and hooked up. In anticipation of breaking the 1.2 bar barrier on what has become known as the world's only 951 n/a, I backed it out of the garage, let it warm up and climbed in. I rounded the corner and eased onto the throttle - nothing. 1.2 bar max.

Okay, fine. I pulled it back into the garage, yanked the CV-to-wastegate line off and plugged it solidly with a bolt. Just to be sure, I CLAMPED the hose onto the bolt and then clamped a vicegrip on the line. No air getting in THAT line. Okay, now I repeated the same process, carefully increasing throttle - mindful that the overboost protection would not work. STILL only 1.2 bar. WTF?!?!?!

I then went back and pulled the bolt out and stuck my hand vaccum pump on the line and stuck about 25psi worth of vaccum into the wastegate line to FORCE the wastegate spring closed. STILL only 1.2 bar of boost when driven.

Needless to say, I'm getting royally pissed off at pulling the entire induction and exhaust system apart on this damn car every weekend. Anyone have any thoughts on something I HAVEN'T either checked or replaced? I'm officially giving up at this point until someone suggests something I either haven't tried or looked into.

Bri Bro

Did you check the recirculation (Pop off) valve?

Porsche-O-Phile

It seems okay to me. When I try to blow through it (after wiping it clean, of course), it doesn't have any blow-by or leakage. Should I be testing it some other way?

AlexE

Only one other thing. Your turbo is shot. Did you check to see that the fins are not bent (stray bolt) etc.

Porsche-O-Phile

Well I just recently replaced the turbo. My old one had some foreign material go through it so I'm SURE that one was shot (there are ugly pics of it on here somewhere). The replacement was the one off Danno's car before he upgraded and worked fine for him. I can hear it spool and the shaft turns fine and there's no play. Can't figure out why it'd be that. . .

Someone mentioned something about the throttle position sensor. . . does this make any sense?

Laust Pedersen

Have you looked for a blocked exhaust? Cracked ceramic in the cat, folded inner skin on the cat-pipe (the zig-zag pipe from the down-pipe to the cat) or otherwise.

Bri Bro

There is a good test for the TSP in the manual, don't think that is it but...
Did you check the intercooler for free-flow of air?
BTW, does the car buck at 1.2 boost?

Mike S

Does it seem slow to build rpm even with the low boost? Sound a little quieter or different than normal? I'm leaning towards a collapsed cat or collapsed down pipe.

NZ951

KLR?

Porsche-O-Phile

Well, I had the cat pipe off when I pulled the wastegate last weekend; it appeared fine. Of course there's no way to be 100% certain without either cutting the pipe open (which would destroy it) or with a boroscope, but I did look in both ends (looked fine) and pulled the plug out of the bottom of the cat and peeked in - everything looked fine / intact / not melted / etc. I'm reasonably certain it's not that.

The down pipe looked fine from below (where the cat pipe bolts onto it) and a month or two ago when I replaced the turbo it also looked fine, so I've ruled that one out.

The boost never really "worked" in this car so I have no idea how fast "normal" is - I have no basis for comparison. It seems to build up reasonably fast to 1.1 - 1.2 and then it just stops dead in its tracks. The turbo sounds fine (no whining or howling that would indicate bad blades). I looked at it just tonight when I had the J-boot off - nothing looked out of place.

If the KLR was bad, my understanding is the cycling valve would dump pressurized air directly to the wastegate to force the valve open, limiting boost to 1.2 bar maximum. Since I had the wastegate line off (disconnected) and plugged, the KLR is effectively removed from the loop anyhow, so I doubt it's that.

I suppose it could be a collapsed crossover pipe, but the part of the interior that I could see from the wastegate connection looked fine to me also. This one has me totally stumped.

The intercooler flows freely (I can blow into one end and feel it coming out the other end with no apparent resistance). There is no bucking when the car hits the 1.2 bar limit, it just continues to accelerate as if it were an n/a car. The engine runs great and smooth, just no "oomph". Very weird. I've got to be missing something simple here. . .

Rich Sandor

your symptons sound just like mine did. instead of pinching off the line, simply disconnect the wg hose from the cv. just leave it loose.

try it.

then go out and really open her up.

Rich Sandor

PS, why would we be worried so muc habout overboost when we know that a stock wastegate, hell even a shimmed wastegate, can barely hold 12-15psi???

PorscheDoc

Start by updating your vacuum lines under the manifold and get rid of the venturi tube/Cycling valve, and add a manual boost controller. And i am talking about the big lines, not the little 5/32 lines.

Porsche-O-Phile

I have been driving around with the wastegate line loose for a while - nothing. Still 1.2 bar of boost.

How would I "update" the lines? AFAIK this would result in loss of the overboost protection as well as the idle stabilizer. I'm unsure how deleting all that would help me.

mochman

did you check your fuel pressure? what's the driveability like when you're not trying to make boost, what's the mileage like? at 90k on one of my cars the cat collapsed even though it still looked good and it made no power.