Hi folks, this is my first time posting here after a lot of lurking. I could use some help interpreting the results of a CIS pressure test on my 1980 Euro 911sc. (I bought the car last year from a former Pelicaner, so some people may recognize it - pic below). It runs pretty rough when it's cold - hesitating, low idle, and backfiring at times - and then it smooths out and runs really well when it's at full operating temperature. The gas mileage is not great (around 15), and after a long drive there's always a thin layer of soot on the back end. All this leads me to believe that the WUR is not functioning properly. I checked for vacuum leaks and didn't find anything, so I got the CIS pressure gauge from our host and tested it. Here are the numbers I got (in bar):
Control pressure cold 1.65
Control pressure warm (engine not running) 2.75
System pressure 4.8
Control pressure with engine running, warm 3.2
The right numbers for this car, according to Jim Williams' CIS primer site at Rennlist, are
Cold pressure 1.8
warm pressure 3.0
system pressure 4.5 - 5.2
warm pressure with vac connected 3.4
So, the long and short of it is the system pressure is within spec, but the cold and warm pressure numbers are low. I'm fudging it with temperatures as I don't have a thermometer.
My question is, before I go spending money on a new WUR, should I be looking at other possible sources for the problem? Do these numbers fit the pattern for malfunctioning WURs? I did give it a tune up recently - adjusted valves, set timing, changed the plugs, wires, rotor, cap, etc. Also a Porsche mechanic set the fuel mixture last spring, after a backfire blew out the pop-off valve. That helped with the idle but didn't solve the other issues. (I'm guessing that the mixture had been tweaked to compensate for the bad WUR). I'm working on the assumption that you have to get the CIS pressure sorted out before you can address any other issues. But on the other hand I don't want to get into a wild goose chase replacing this part and that.
Thanks a million for any help, Danny.
here she is:
