Please Explain Overboost Cut-Out
 

Still sorting my "new" 89 Turbo and learning the mysterious ways of "The Boost." Going up through the gears, car pulls like a bandit in 2nd and 3rd...but on sustained acceleration I get a total loss of fire in 4th, it seems between 4K and 5K rpm on the boost. Feels like fuel starvation as opposed to an electronic interruption of ignition.

My OE boost guage has been known to reach 2.0 but I'm haven't ever had my eyes on the gauge when the cut out occurs...too busy making sure I don't overrun some wobbling ricer on the freeway :) FYI, car cruises all day at 100+ no problem, just stumbles under extended acceleration.

Owner Number Two (of five, counting me) appears to have taken the CV out of the system and was using a boost controller that is not present. There is a capped hose coming off the intercooler tube and an open one coming up from the waste gate that is open. I'm assuming the PO's boost controller was once hooked up in line between these two hoses. There is an aftermarket Tial wastegate on the car of unknown specifications. Owners Three and Four clearly used the car quite sparingly and didn't spend much time at the upper end of its capability, leaving me to uncover this interesting circumstance.

When I woke up this morning I was assuming that my first investigation should be to swap in the adjustable fuel pressure regulator from the NA racer to check and see if I the car was just asking for more fuel tham the OE FPR is allowing....BUT reading here this morning about overboost cut out led me to recall the 2.0 bar readings I occasionally see on the guage.

Sooooo, who can give me the skinny of overboost cut out in 25 words or less? What is the diagnostic for same in a non-CV environment? Who knows the meaning of life? Why is there air? Is Elvis really dead?

Yep - that's an easy one. You can't leave the wastegate line disconnected. You will get maximun boost permitted by wastegate spring with exhaust only pressure - which could anything with the Tial.

With that tial, you should get a black knob and an sftermarket boost guage. Not too expensive, and nothing you will have to redo if you modify it more.

I had a overboost problem when I bought my car. the stock gauge innside the car would go up to 2bar, mounted a aftermarket boost gauge and the car was in fact running 1,4 and sometimes even 1,6 bar of boost .. The result could be viewed in my "need advice on cylinder score" thread.

You could buy a boostcontroler to put in . Without a pressure to control the WG, think it would open at lowest setting.
I`m more worried about the other end of the hose, the one coming from the IC tube.
Is there a hose coming up from the top of WG that is connected with hose from IC tube?

To my knowlege, there is no current connection between the hose from the WG and the hose from the IC tube. The IC tube hose is closed off with an allen bolt secured with the small hose clamp. The hose coming up from the WG is open to the atmosphere. I am assuming that the boost controller was in-line between these two hoses.

Yes, it was.

Soooo, if you were me (I know, I know, you'd be the lucky owner of nice Turbo S with 65K miles and a full 968 M030 suspension upgrade, tee hee)....and you wanted to address this cut out, would you bother with swapping out the FPR with a billet adjustable or would you go straight to reinstalling a boost controller?

no control on the wastegate is the NUMBER ONE priority. This is wrong - especially since you don't know what spring is in it.
If you get ant ADFPR, get the paragon billet - there is nothing that compares to it.

If I where you, I would put in a boost controler and get someone with a WBO2 to log the car..

I`m not familiar with the Tial but should not the WG get boost signal from the banjo bolt in the ic to turbo pipe regardless of if there where a boost controler or not..

BTW , found this from an earlier thread

http://img.photobucket.com/albums/v2...modified-2.jpg

Hmmmm, this is making some sense. First, yes, I do have the Paragon billet ADFPR, sweet piece, made a world of positive difference on my NA track car! Second, I'm hearin' ya on the issue of getting some boost feedback system hooked up to the WG. What would happen, if as a test, I unplugged the IC line and simply reconnected it to the open WG hose without a controller in the line?

Something else to think about.... if you are running higher than normal boost
you should have chips mapped for the setup your running. Other wise, you stand the chance of going lean under hard acceleration.

Wow - so far everything on this thread is good info - must be a friggin record.

I`m not a turbo guru here , but I`l definity think you`ll be seeing some overboost issues..

The reason why i adviced you to get a WBO2 or go to someone with a WBO2 , is that it`s much better to know if there are any issues, than wondering if there could be any.
You allready have a ADFPR so you are capable of making some adjustment..

All good, agreed. Don't know if I'm running high boost for sure or not, having only the factory gauge to judge by...and this mysterious loss of fire under sustained boost. But I do know that lean is bad :)

The car was delivered to Owner Four with two aftermarket chips that have since been removed and replaced with the OE chips stored in a little zip lock in the owners manual. I still have the aftermarket chips in the glove compartment. I will get them and ID them for the group later today. Owner Four suffered from very rich condition and heavy smell of fuel with aftermarket chips, and felt that the car improved in tractability with OE chip reinstall.

Uhhh, yeah, 'splain WB02 pleeze :)

Wideband Oxygen sensor - they are so cheap now, anyone with a modded 951 should have one.