Ky944TurboNewbie

I think I might be the only person in the world that would want to do this. I don't even know why I am asking this question as I have enough things I am trying to chase down to make everything work like it should. But.... while researching my problems and learning more about the Turbo system, I may have found a safety switch should I ever decide to loan this car to my son.

I believe when the cycling valve fails, it fails in open position and everything is directed to the wastegate. With a stock setup, that would mean you can only get about 1.2 bar. Can I make the leap that unplugging the wires from the CV will fail the valve to open position and limit boost? Are my assumptions correct?

I know I shouldn't let him drive the car if I don't think he can handle it properly. However, I trust he can handle it. Limiting boost would simply give me a little more peace of mind. Would this is a non-destructive and effective way to limit boost?

lart951

I dont think that's quite right, if the cv valve is bad usually you hit overboost protection. Because the cv is what controls your boost level, is not wise to use your wastegate as boost controller if that be the case why mbc's and ebc's are used? why not used a predetermined rate spring on your wastegate to set boost? okay the stock wastegate starts to open at 4 psi. not sure if you can have the boost spike to a higher level

Ky944TurboNewbie

I had my open and closed mixed up. This is what I was thinking about (from clarks-garage) "If the cycling valve fails, loses power, or a problem occurs in the KLR unit, the cycling valve will fail fully closed. In this mode boost is limited to approximately 1.2 bar. This is essentially the boost at which the force of the exhaust pressure will overcome the wastegate diaphragm spring pressure. "

lart951

Iam not an expert but the risk of boost spikes may exist

Oddjob

If you unplug a functioning CV in a fully stock/working boost control system, the car will run no boost (about 1.1 to 1.2 bar abs) and the KLR might pick it up as a diagnostic failure and go into limp mode, which will also retard the timing.

The CV is a solenoid that when energized blocks the airflow to the WG and directs it to the intake. When not energized, the CV allows the intake pressure to go directly to the WG diaphragm, so it opens the WG.

FRporscheman

Be careful with the cycling valve, they get so brittle, it's pretty much impossible to touch it without breaking of of the nipples off.

If you want an easy way to reduce the car's power for when you loan it to your son, how about a manual boost controller? Or even a chip or piggyback with a lower-power setting. Whatever you do, if your son is determined and knows his way around cars, he'll defeat it.

Rogue_Ant

Yes, you are correct.

No, the KLR will not go into limp from too low of boost.


You could run one of the CV wires to a keyed switch, the have an easy "secure" way of turning on or off the CV...

Ky944TurboNewbie

Very nice. I have a relatively new CV, so it shouldn't be too brittle yet. The keyed switch sounds like an interesting idea. Thank you for your answers.

Oddjob

Diagnostic blink code 3-1, can find the explanation and possible causes in either the FSM or the DME/KLR tech bulletin.

Rogue_Ant

It might throw a blink code, but it will not go into 'limp-mode' and pull timing.

pettybird

would it limit boost because of it? I THOUGHT I read that...

Rogue_Ant

If you are not controlling boost by other means (MBC or EBC) - then yes, disconnecting the CV will lower boost pressure.

Oddjob

Any dianostic fault that the KLR identifies and displays a blink code, will trigger the limp mode. I have found this to be true (KLR will operate in limp mode if the KLR is giving a blink code fault) and factory documentation supports that. If in doubt - unplug the TPS, read the blink code, and see how much boost a stock car will make.

Page 28-30 of the Turbo supplement:

"The knock/charging pressure system includes a self-monitoring system, which can output a recognized defect w/ the help of a test adapter...output is in the form of a blink code. If a defect has been found, the engine will operate on a safety system (basic charging pressure up to approx 0.3 bar overpressure and 6 deg later ignition)..."

Code 3-1 indicates boost pressure too low. And possible causes listed the DME/KLR Test Plan include "plug has fallen off of timing valve... Wire break... Break in pressure hose to KLR control unit." etc.

No guarantee that the KLR will actually identify low boost as a fault (its not a very robust/reliable diagnostic system, e.g. I have never seen the KLR identify excessive boost, nor knock sensor failure even if its unplugged). But according to documentation, a low boost fault check does exist in the system parameters, and if detected, it is supposed to generate the blink code and trigger the limp mode.

Rogue_Ant

Interesting - I will do some testing to see if I can reproduce that (timing reduction if boost pressure is too low). I have not seen the timing reduction happen, but I suppose it is worth taking a more in-depth look at... I am still quite doubtful, as the the turbo responds different depending on gear / road / altitude / ect, so I'm not sure how the KLR would determine that there is not enough boost.

lart951

back in 1994 one of my first 951's had a blown head gasket, took it to the mechanic and had him replaced, I picked the car around 5pm on my way home to Chino, I saw a nice M3 and decided to show him what 951's are good at and floored my car, I did smoked him, literally I blow another HG, took it back to the mechanic, didn't know much about 951's back them, but my mechanic found a bad/craked Cycling valve, I am just saying maybe experience is better than theory, sometimes?