Quote:
Originally Posted by 801coppertop
911sc 1982 - CIS + Lamda
Recently Rebuilt - JE 9.8 compression, headers, 2in 2 out GT3 muffler; everything else stock
WUR pn - 090 Fuel Distributor pn 0 438 100 077
Vacuum test results - No leaks
Compression all w/in 3psi
WUR & AAV voltage correct - Both working as expected with about 3-4 minutes to heat bi-metalic strip
Decel Valve - Performed TSB and closed by 1mm
Fuel pump volume- Over spec
System Pressure - 4.9
Control Pressure Cold - 2bar - (@17.2c)
Control Pressure Warm - 3.5bar
Pressure after 20 mins - 1.9bar
Air Sensor Plate set at .5m below venuri line
All injectors have great spray pattern and are injecting within 5% volume of each other
Lambda System -
W 15 deg grounded - 65 Duty Cycle
Lean stop 02 Grounded - 90 Duty Cycle
Rich stop - 13.4 Duty Cycle
35 deg grounded - enrichment occurs for 2 seconds to 75 Duty cycle for 2 seconds
New O2 sensor verified working and in spec; even have tried to use my MTX-AL wideband as a narrowband emulator and had more or less same results
Lambda system seems to functioning as it should.
Ignition -
MSD with MSD blaster coil - Clewett Engineering 8mm wires - New Cap & Rotor - New Bosche Trigger wire (Wired correctly, verified by Oscilloscope)
AFR set to 14.3-14.4ish while
Here is the issue as best as I can define/pinpoint it.
Engine runs well as it is warming up. Even into closed loop (a bit of oscillating idle but runs ok)
Once engine is fully warm/heat soaked engine runs lean, starts to backfire a bit off idle.
Runs well at speed and under load, with the occasional stumble.
The main lean off idle has been happening in varying degrees since I can remember. It seemed to get worse after a recent rain storm where
fuel went very lean (o2 sensor had taken water in) I was able to drive home in Open loop with o2 sensor unplugged. Recently the car has driven its best
with the o2 sensor unplugged and a bit rich.
Need some CIS wizards advice, to this point I have studied and read many of the available books on the subject, including
Porsche Fuel injection manual; Probst - Fuel injection and Engine Management: Watson - How to tune & modify Bosch fuel injection - and many many many responses to others CIS woes...
Im having a hard time seeing what has changed to make the engine running characteristics different once fully warm.
Control pressure stays the same - No leaks (Even smoke tested while hot) - Lambda seems to be functioning as it should..; the level of patience I have for continuing to mess with CIS is dawning.
|
The O2 sensor voltage (too positive) is causing the Lambda unit to lean the mixture too much. For testing only, you can always disconnect the Lambda unit and
richen the mixture. You'll have hard starting when cold, and a little flat accel when warm. If you still have the problem, it's not Lambda electronics related.