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Join Date: May 2007
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Partly Cloudy Porsche - Bad Injector?

As I put more miles on my 911, I've noticed an occasional thin, white cloud following me around. The car has a rebuilt 2.7 with CIS. It doesn't happen all the time, but is especially evident in the following situations:

1. A cold start - the car runs rough for a few seconds right after it catches. This rough running is accompanied by a fairly large white cloud.

2. Acceleration from a longish period of idling - if I sit idling at a stop light for a minute or so and then pull away, I will notice a wisp of white cloud coming from the exhaust. It is much smaller than in #1, and it doesn't last for long. Just a puff and then it goes away. The car seems to run fine.

3. Hot starts - I'm driving for a while, and the car gets up to operating temperature. Then I stop and run into the bank or to get a sandwich or whatever. I come out a few minutes later, and the car starts fine but seems to be way down on power and feels sluggish. In cases like this the cloud is pretty big. After I get back on the road and run up through the gears the sluggishness and the cloud goes away.

In every case, the cloud is white and smells like gas. I've long suspected that the car runs rich at times, and this seems to confirm.

Is trouble like this indicative of malfunctioning injectors? Is there one component of the CIS system that I should check before others? Any other opinions? I bought a book this weekend on repairing and tuning Bosch injection systems and a couple Bosch technical manuals, but thought I'd solicit the copious experience here as I begin reading.
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Luke
1977 Porsche 911S
Guards Red/Cork, no sunroof, no flares!
Old 06-11-2007, 07:43 AM
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Still too early to know for sure, but a likely candidate is the WUR (Warm Up Regulator). If you search this, you will see that quite often a bad, clogged or out of spec WUR seems to cause most of the start/run problems in CIS cars.

To best check this, a fuel pressure gauge for CIS is needed. JC Whitney has it for around $60.
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Last edited by Paulporsche; 06-11-2007 at 10:33 AM..
Old 06-11-2007, 10:30 AM
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2. Acceleration from a longish period of idling - if I sit idling at a stop light for a minute or so and then pull away, I will notice a wisp of white cloud coming from the exhaust. It is much smaller than in #1, and it doesn't last for long. Just a puff and then it goes away. The car seems to run fine.

My 3.2 '87 has the same problem.

It also used to put out a lot of white smoke but without the smell of gas at start (smooth running). the problem improved a lot after I run it at idle for 30+ seconds before shut down.

My guess is that the 3 symptoms/signs you described may result from different faults.
smell of gas in smoke --> clogged fule injector or fouled/misfiring spark plugs
white smoke --> condensation or valve guide/piston ring if with high oil consumption.
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Old 06-13-2007, 05:39 PM
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