Odd CIS Problem

I'm experiencing the following strange symptoms on my '78 SC, despite 3 trips to the shop:

1. The car will start fine from cold, and idle well at around 1,200rpm's for approximately 2 minutes, after which it starts to nearly stall, speed up, nearly stall, etc. I notice a heavy fuel odor coming from the exhaust during this process.
2. After an hour or so drive, if the car is turned off for a few minutes, it's difficult to restart, and when it does start, it idles low and runs poorly until driven for 10-15 minutes.

I don't know if this is related, but the fuel pump sounds like one of those key-in-the-ignition buzzers found on the older VW Beetles. My mechanic, who says all the system pressures are within spec, said this is normal.

I'm a little discouraged at this point, so any input would be most appreciated.......

Ask you mechanic if he measured control pressures with the engine running during the cold start process. You get different numbers with the engine running and with it not running, because the WUR has vacuum connections. Also ask him if he checked the proper operation of the vacuum thermovalve (small plastic disc located under the heater blower motor). If it's stuck closed, your mixture will be too rich. It is supposed to be closed on cold start and then opens up after a short time.

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Bill Krause
'79 911SC Euro

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[This message has been edited by wckrause (edited 03-06-2001).]

Hi,

I have/have had similar fuel pump noises. I was told that it signals the impending death of the pump, but that the actual timing is difficult to determine. I am not sure if you have replaced the fuel filter, but the noise decreased dramatically when I had this done.

cheers

Neil

81SC

Thanks!

According to my mechanic, the pressures were tested on, off, at start-up, and during the warm-up process. He said the warm-up regulator was not getting proper pressure, but he corrected that anomaly.

I'm not able to locate the vacuum thermovalve that was referred to, even though the heater blower assembly is not in the car at this time.

'78 911SC Euro

If you follow the vacuum lines from the WUR. The bottom one will take you to the thermovalve. The Haynes manual has the proper vacuum diagram (the Bentley manual does not).

It's part 17A in this diagram
http://www.pelicanparts.com/911/911_Parts/1978-83/1-7-2.JPG

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Bill Krause
'79 911SC Euro

Thanks again!

Is there an "at-home" way to test this device?

The thermovalve is just a little vacuum switch, like the aux air regulator. It should be closed when cold, and open when warmed up. I took mine out, and stuck it in the freezer for about 15 minutes, and then tried blowing through it. You can then hook it back up, run the car for a bit (a couple of minutes at most), and then check to see that it opened up.

Mine was gunked up from excess oil that got sucked into the CIS when the PO overfilled the oil (I swear I didn't do it).

If your mechanic checked control pressures with the engine running, then that should have shown any problem with the thermovalve. If it's stuck open, your initial (cold) control pressure would not be low enough, and if it is stuck closed, your final (warm) control pressure would be too low.

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Bill Krause
'79 911SC Euro