Help me solve this CIS problem -

ZCAT3 · 03-13-2005, 09:42 AM

My 930 cuts the fuel when you shift while on moderate or higher boost. I have determined that if I disconnect the green plug (see pictures below) on the back of the fuel meter the problem stops (but then the pumps run non-stop). I have been told that this plug is a roll over protection switch that is supposed to cut off fuel should the car go on its side or roof. I have the engine out right now and pulled off the venturi and fuel head to clean this system. The green plug is attached by a screw from the underside that runs through a rectangular metal strip under the metering plate. Anyone have any ideas how to fix this?

john walker's workshop · 03-13-2005, 10:40 AM

unplug and ground the white wire to the over-boost swith, or find one that cuts off at a higher pressure.

ZCAT3 · 03-13-2005, 10:51 AM

John - I am running a Kokeln IC with a Apexi AVCR boost controller. I seem to recall that the overboost switch is already disconnected?? Where exactly is this located?

ZCAT3 · 03-13-2005, 11:55 AM

John - I went through my shop manual and as far as I can tell the overboost switch is now plugged directly into the IC. Is it the black thing in the first picture below? If so, then the white wire connects to the white connector in the second picture. So you are saying to leave the wire from the switch on the IC disconnected and then ground the wire with the white connector on the left side of the bay?

john walker's workshop · 03-13-2005, 02:29 PM

the white wire comes out of the the engine wire loom, in the vicinity of the left side of the intake, above #2 and #3. do you still have the stock loom?

beepbeep · 03-13-2005, 02:52 PM

Hmm...As far as I remember, 930 CIS incorporates switch that turns on the pump the moment flapper goes down (thus when engine starts inhaling the air). This switch is there to prevent pumps running when ignition is on but engine is not turning.

So it might be some corrosion on that switch or overboost switch that is causing cut-out.

I would be very careful with disconnecting overboost-switch. It's the "last resort" protecting you from grenading the engine.

If problems occur only when you shift, you might have problems with pressure-peaks mounting in the intercooler when lifting of the throttle. Is BOV fitted and working properly?

Even if you have moderate boost, faulty or non-existant BOV (recirculating or not) will lead to spinning turbo trying to force air into closed throttle, raising the pressure in intercooler and thus tripping the overboost switch. You will also run higher risk of damaging impeller when it starts surging w/o BOV.

So there are two things to check:

1. Corrosion/bad contact at run-switch (CIS flapper)
2. Faulty or non existant BOV -> boost spikes in intercooler -> tripped overboost protection

ZCAT3 · 03-13-2005, 03:00 PM

I just had the top of the air meter off and went through everything with a friend that is a mechanic. Everything there looks to be fine. It is odd that unplugging the green wire makes the problem go away - which of course leads me to believe that the problem lies either in the air metering system or with the wiring from that green plug.

Goran - how would I test "1. Corrosion/bad contact at run-switch (CIS flapper)"?

The boost is quite steady as the boost controller does a nice job with that.

beepbeep · 03-13-2005, 03:08 PM

Boost can be perfectly steady but boost-controller cannot affect the pressure inside the intercooler when you lift-off the throttle. Is there any BOV-valve fitted to system?

(with BOV-valve I mean Blow-Off valve, recirculating valve etc. The thing that opens and releases air trapped between turbo and close throttle, either by venting to atmosphere or sending it back into turbo-intake)

ZCAT3 · 03-13-2005, 03:32 PM

John - I found the white wire you are referring to and it is already ground to the fan housing.

Goran - the Kokeln IC is a bolt on kit that replaces the stock IC. Does the stock IC have a BOV on it? If so, where do I look to find this (what does it look like)? My mechanic friend suggested the same thing as you as he has seen this problem in a 993TT and the problem was the BOV.

beepbeep · 03-13-2005, 03:55 PM

No intercooler itself has dump-valve/BOV installed. It's external thing. You can see OEM 930 dump-valve (another name for it) on this picture:

I don't know how you engine looks like, as you have another intercooler. Dump-valve might be missing. As dump-valve is only being used at lift-off, some shops never install it. Unfortunately, it can lead to this kind of problems, or even worse: blown intercooler pipes when using plastic intercooler (Audi cars), damaged impeller blades etc.

ZCAT3 · 03-13-2005, 04:09 PM

Which piece is the BOV? I know the orange piece is the boost sensor.

ZCAT3 · 03-13-2005, 04:19 PM

Hi Goran - I do have a BOV - it is Bosch 0 280 142 108 (you can see it discussed on this page: http://wwwrsphysse.anu.edu.au/~amh110/Technical_pages/blow_off_valve.htm )

Is it possible that this valve is not functioning correctly?

ZCAT3 · 03-13-2005, 05:11 PM

What about this product - it seems that this describes the problem I am having -

http://www.************************/ProductPage.aspx?ProductName=Surge+Filter&productid=106020&producttype=20