fast951

Jimbo, You have not said anything to explain why a bad/leaky CV causes low boost (not limp mode).. Think about it, you got it backward.. Whatever!

I agree a leaky CV should be replaced, but it does not cause low boost (it might cause no boost or 4psi when not connected/elictrical problem) or lots of boost when leaking and not sending pressure to the WG.

smokey

I had a problem of going into limp-home mode because one of the spigots on the CV was cracked, and opened up and leaked even though the standard "test" of hearing the click indicated that the CV was ok. We didn't see the crack until after removing the cv. You're getting partial boost, so it's not the same problem, but I'd replace the cv to see what happens.

jimbo1111

Ok. Does anybody know why there is a 3rd connection going to the j boot?
I will answer my own ? When the electrical circuit drops out the plunger will not close when under boost even though it's spring loaded. Also the boost that is built up will remain in the waste gate line and not allow the waste gate to close again if it's not vented. The j boot connection is under negative pressure at all times. By way of plumbing this allows the plunger to drop even when the valve body is under pressure. It also allows the venting of the wastegate lines trapped gases. If the cv is cracked or defective you could loose boost internally by routing pressurized air into the intake. No external leak will be seen but yet you could still be loosing boost. The cv works almost like a bov with the exception that it is power driven and a bov is vacuum driven. The vacuum is still there to allow for proper plunger function and venting.

hosrom_951

Tommy: Before i replaced all the vacuum hoses and lines under the intake, i got 1.9bar on the factory boost gauge. After i replaced everything, including a new cycling valve (thanks Rob!) since one of the nipple connectors on the old one broke off, the factory boost gauge read 1.8bar.

Now, what i suspect from you're case (and mine) is that maybe one (or two) of the hoses on the cycling valve were leaking a bit, thus causing slightly more air to be drawn and cause the gauge to read higher. Or it could be due to a difference vaccum hose that was slightly drawing in more air.

fast951

Jimbo, sorry but not buying this theory, too many holes in it!! Even if the CV is routing all of the pressurized air (not likely) to the J-boot instead of the WG, the car will overboost... No need to beat a dead horse, you know what you know and I know what I know!

jimbo1111

too many holes in it!! I agree. change the cv and see what happens.

tommye

Ok - thanks a lot for all the answers and concern - this forum is really great !!!

I will put the old CV back in,(w/o lifting the manifold again if possible) and I'll let you know whether boost goes up or down......
BTW the CV leak is at the electrical contacts feedthrough.

And, as soon as everything is sorted out, I'll put in those Vitesse chips that are still waiting on the shelf......

Tommy

fast951

Tommy, With the vitesse chips you do not need the CV. Use a MBC (ball&spring or check valve style) instead!

tommye

Well, I was planning to run as much stock and stock looking as possible. Only chips and a black painted LBE well hidden under the manifold.
Besides, the CV quickly vents out pressure from the WG-line back into the J-boot during gearshifts allowing for quick boost buildup in the next gear, right ? It seems to me to be a better solution than a tiny little bleed hole that can get clogged that some MBC:s use.
And while we're at the subject, why hasen't any of the tuners messed around with the CV-control circuitry/maps in the KLR ? This seems to me to be the obvious thing to do since it controls both boost build-up speed and max. boost pressure......I'm obviously missing something here!!!

Tommy

smokey

The Milledge chip kit involves drilling the cv in a specific way.

jimbo1111

When bypassing the cv it is best to go to a dp waste gate. The stock cv is needed for proper single port function. Notice how some peoples boost curve drops like a brick when they bypass the cv in favor of a boost controller. Most think it's the WG spring going bad. The vac is needed to keep it closed and vent it.

tommye

This is a great day - sunny and warm and the 951 cab is at last running perfectly!!!!
I lifted the manifold again this morning to put the old CV back - that was it !
My brand new, expensive genuine Porsche CV not only leaked, but also limited boost to 1.6 bar...................
Now I have 1.8 bar again, and much better response as well!!!
Vacuum at idle is 13-14 in.Hg cold and 15-16 hot.
Did 7-8 WOT runs in 3:rd and 4:rth, and no signs of the old overboost cut-outs
Back home again, checked the plugs, and they look really good, light brown.
Before fixing all the vacuum leaks, they were often black.

Thanks again for all the suggestions !!!

Now I start to look more seriously at those Vitesse chips on my garage shelf. I did not want to put them in before the car ran 100%.
Boost is now 1.8 up to 5000 rpm, then falls to 1.6 at redline. Is it worthwhile to shim the wastegate to improve this ??




PS. Anyone want to buy a brand new genuine CV, real cheap? I know somebody who might have one for sale.... I think it's even the new improved traffic safety and longer engine life version !

hosrom_951

tommye: Good to know things are running better for you, congratulations!

Shiming the wastegate would help, but would be "wise" with chips. Better yet, a new wastegate from SFR, MySwiss or Lindsey Racing would do the job (all are dual port) but would need an aftermarket boost gauge and a manual boost controller.

jimbo1111

I'm glad all is well now. Good luck with your ride.

danny951

Isn't a stock car supposed to drop from around 1.8 to 1.6 bar anyway? I'm pretty sure that is listed in the faq and on clarks-garage. Don't assume it's your wastegate, as it may be doing exactly what it's supposed to. I'd try putting in your chips first to see if that changes your redline boost levels.

(i could be totally wrong, I'm a newb, but I know I've read this a couple of places, and some of the guys helping me with my boost issues have told me that too.)