biturbomax

Hi i'm from italy near Venice.
i have a porsche 928 S4 '87 M28/41 manual transmission.
which it is the correct operation of the air pump diverter valve.
the valve is always opened?
the pump of the air through this valve sendes always additional air in the exhaust system?
when the valve would have to be closed and not send air in the exhaust system?
if I measure the value lambda probe to the end of the exhaust system measure approximately 1.2 like if the carburation were too much lean but if I detach the depression tube on diverter valve the value returns approximately to 1.0
thanks.
greestings.
Massimo.

ZEUS+

If your system is functioning properly, air is pumped to the exh. manifold with throttle open. With throttle closed air is diverted to the air cleaner.

biturbomax

Thanks ZEUS+
my air is always diverted to exhaust manifold.
which it can be the cause of the defect?
the position of the gas throttle can be mistaken?
it can be that the throttle housing it has need of being cleaned up?
it could be that it must regulate the idlee speed through the cable of the accelerator?
MASSIMO (ITALY)

biturbomax

someone can help me?

the flyin' scotsman

The diverter valve is operated by vacuum. Check the vac. connection and test the valve with a vacuum pump.

I understand the valves can go bad as I sold mine when I removed the air pump and associated plumbing.

fabric

Specifically, it's operated by ported vacuum - as revs increase, vacuum increases. So in addition to checking that the valve works when applying vacuum, you'll wanat to test the connection from the throttle to verify that you are getting no vacuum at idle, and vacuum when you give it revs.

Edit: I'm sorry, I probably have this wrong, I was looking at the vapor recovery vacuum system. The vacuum may be manifold for this, in which case the opposite of what I explained. Something I need to add to my idle/troubleshooting section on vacuum.

Still, you'll want to check that the valve works, and that you're getting some kind of vacuum from the throttle body.

biturbomax

the air is always diverted to exhaust manifold at the idlee and when revs increase.
if i detach the vacum connection on the diverter valve the air go to the air filter.

fabric

It sounds like it's working, but that perhaps constant vacuum is being supplied, since the valve switches when you remove the connection. You're vacuum hoses may not be routed correctly. This diagram shows all of the vacuum connections:

http://members.rennlist.com/fabric/vacuum-diagram.JPG
http://members.rennlist.com/fabric/v...gram-index.JPG

The 2nd link is the index, and we're refeering to "I". I can't tell where the vacuum goes, but it looks like it has it's own connection of the throttle body. If the line to I runs to the 5 way or 4 way splittlers, it's definitely wrong.

Here's the actual exhaust control diagram from the WSM, and it pretty much shows the same thing - that the valve goes to the throttle body. I suspect that it's no vacuum at idle, vacuum at throttle, but your valve is not connected correctly:

biturbomax

I have controlled the connection of the vacum tube.
the conection is right.
the tube connected to the diverter valve is that white tube who comes from the low side of the trhottle body.
MASSIMO

Richard S

Greetings Massimo....The valve is opened with vacuum. Therefore, at idle, with vacuum, the valve is open and sending air to the exhaust. When cruising at a steady speed, with the vacuum constant, the valve is open, sending air to the exhaust. When you accelerate quickly, you temporarily lose/reduce vacuum, the valve closes and air is diverted to the airbox above it. Why does it do this? I really don't know.

By the way, I visited Venice 2 years ago, it was incredible!! Very expensive for me as a tourist, but definitely worth it. We then rented a car and drove to Florence, Siena, Orvieto, Naples, and Rome. I enjoyed Venice and Orvieto the most.

biturbomax

greetings Richard.
Are you sure that the valve functions in that way?
I have had other types of answers.
ZEUS+ has said to me that the valve divert the air in air filter only at the idlee therefore the vacum is not present at the idle but is present when the revs go up.
which it is the operation of the valve?
who is sure to 100%?
also I have been to Orvieto.Orvieto is very beautiful.
To Orvieto I have made a Maserati meeting I have one Maserati Biturbo SI '87.
The italian version of MASERATI BITURBO SI is 2000cc and have 225cv.
Massimo.

Richard S

This is how mine works too. If you increase the revs fast enough, the vacuum will drop quickly, closing the diverter valve until the vacuum catches back up. For example, remove airbox, start engine, and feel that there is no air coming out of the hose to the airbox. Now have someone rev the engine quickly (or reach over and do it yourself with the throttle cable) while you check that hose....air should be diverted until vacuum goes back up.

Orvieto was great, very relaxed place. I actually crunched the rental car there, trying to go around a very narrow corner I put a big dent and scratch along the passenger side. Luckily the rental office never even looked at it.

I've always liked the Bi-turbo, however it has a reputation as a maintenance nightmare here in the U.S. What's been your experience?

Rich

ZEUS+

The diverter valve is operated with manifold vacuum. When decelerating or when throttle is closed no air should go to exh manifold. The additional air under these richer conditions will cause popping and backfire. That is one reason why check valve #23 is used. Failure of the diverter valve is the other. This is a basic design for all vehicles with this type of A.I.R. system. They may have different components or controls but the purpose and function is the same. Edit vacuum supply.
http://jenniskens.livedsl.nl/Technic...0/MyTip062.htm
http://www.familycar.com/Classroom/emission.htm

marton

if possible in your country, I would just throw the air pump away.
I tried that here in switzerland but when I had the regular Government inspection they made me put it back.
Without the air pump it ran fine and passed all the Swiss exhaust gas tests.

Marton

Richard S

Ok, just read those two links and it makes more sense now. With little or no vacuum, air is diverted. When vacuum increases/stabilizes air is sent to exhaust. If valve malfunctions and is always sending air to exhaust, popping will occur. Now I'm curious and will have to check my valve again (just played with it last week before the smog test).

Rich