Does your 930 click?

logician · 10-10-2002, 11:10 PM

Hi,

So is your 930 sluggish? Does it click when you blip the gas? Then the gasket in your bypass valve may need to be replaced.

The bypass valve recirculates compressed air back to the turbo during vacuum conditions. The recirculation allows the turbo to keep spinning when you let up on the throttle. In my case, the gasket that seals against the piston when the valve is shut was disintegrated, and that presumably caused a loss in compressed air, i.e. poor performance. The symptom of the problem (other than poor perfornace) is that the bypass valve clicks when you blip the throttle at idle.

My mechanic had been trying to convince me to replace the gasket for a while now. Well tonight I finally opened the valve, and sure enough the gasket was completely broken and useless. Actually, it probably was allowing some unmetered air into the system, as well as bypassing some of the compressed air.

Replacing the gasket involves removing the intercooler and the left hand heater duct, and then removing 4 nuts that hold the end cover on. It's not too hard to fix!

-Juan

hobieboy · 10-11-2002, 06:12 AM

Hi Juan,
What do you mean by "click when you blip the gas"?

thanks...

cstreit · cstreit's Garage

You'll know it when you hear it, it's a loud click when you blib the throttle, comes from the rear.... mine is doing it too... Shoot, just placed and order... Juan, you have the pelican part # for this?

cstreit · cstreit's Garage

So what is it that's clicking then?

88911coupe · 10-11-2002, 08:18 AM

My friend's 88 930 does this...what are the possible ramifications of not fixing it?

cstreit · cstreit's Garage

Well I removed my cover, and mine fell into 10 pieces as well...

Now to find the proper part #!

logician · 10-11-2002, 09:16 AM

Hi,

> What do you mean by "click when you blip the gas"?

Well, maybe it's more of a clack. It's a sounds like you rapped two pieces of metal together and a little hollow. It doesn't sound like the engine is in any danger of destroying itself.

> Now to find the proper part #!

Look on page 31 of the "Parts and Technical Reference Catalog". There is a diagram on the lower right of the page labeled "Pop-off valve". It is the part identified as 42. The part is listed as 930.110.149.00. It's an amber rubber ring, about 2" in diameter, and 1/4" thick. I don't know if Pelican has it, as I ordered it through my mechanic (Alan/Charles at The Stable in San Francisco).

> So what is it that's clicking then?

There is a piston who's position is controlled by manifold pressure. The clacking is the piston hitting the metal plate at the end of it's travel. Normally, the piston would hit the gasket first instead of the metal end plate.

-Juan

beepbeep · 10-11-2002, 09:20 AM

Been there, done that, snapped some pictures:

Changing 930 dump-gaskets, pictures galore

logician · 10-11-2002, 09:42 AM

Hi Beepbeep,

Thanks for the detailed write-up and great pictures! Actually, I choose not to remove the whole bypass manifold, and simply remove the bottom end plate -- the one that the piston rests against when it's closed. In order to do this, I had to remove the air duct on the left of the alternator/fan. Don't know which procedure is easier, although with my procedure, I could not check the gasket on the other side of the valve. Question: did you find that both gaskets were bad, or was it just the one at the rest position of the piston?

Another thing that I had forgotten to mention is that the top of my piston has two grooves cut in it. I think those are intended to allow a little air to bypass under the piston. I think the orientation of the piston may be important so that those grooves are lined up with the passages on each side. Unfortunately, I did not note the orientation of the piston when I took the assembly apart. Did you note this, and do you know what should be the correct orientation of the piston? Hey Chris, did you notice the orientation of your piston when you pulled yours apart yesterday?

-Juan

cstreit · cstreit's Garage

I could see a notch in the piston top. Mine was at the top...

logician · 10-11-2002, 11:37 AM

Hi,

> I could see a notch in the piston top. Mine was at the top...

So my piston had two notches opposite each other on the top of the piston.

-Juan

beepbeep · 10-11-2002, 11:40 AM

Logician:

Both gaskets were completly and utterly gone. As far as i understand, one gasket is just for preventing "clunk" and other is for sealing things, so i chances are you fixed "clunk"-issue but didn't rectify potential air-leak.

Also, there are lot's of hoses that get sloppy there and need to be checked/retightened so i suggest doing things my way instead of quick way. I checked all hoses and retightened some sloppy ones that were hard to reach (left that way by dealer mechanic, go figure) and my previously >1200RPM hunting cold-idle become rock steady 950RPM warm or cold engine regardless.

I didn't check for the grooves, but dump works perfectly so i probably managed to put it back correctly by sheer luck...thanx for a hint!

Cheers!