Car starts to miss after warmup!

Everyone,

I'm very new to the 928 owners scene and for the past few days, My 83 US starts to miss and loose power after the cars warms up. When cold the cars runs great and just finished the norm, New Timing Belt, Water pump (two months ago). Thermostat and Catalytic converter yesterday but no change.

Any suggestions would be greatly appreciated.

Thanks,
David

Sounds as if it's leaning out the fuel too much when warm or you're losing vacuum somewhere. My 79 euro is a completely different beast, but it was running decent cold and spitting when warm. I needed to check my fuel pressures.

One possible cause for your problem night be a faulty Temp II sensor. You can check the resistance of the sensors with an Ohmmeter (there are two sensors in the one housing). On top front of the intake, near where the radiator hose connects, find a harness going into a small rectangular sensor. Pull the harness - there should be two pins inside the sensor. Check from each pin to ground, not from pin to pin - these are two separate sensors. At room temp, there should be 1.4 KOhms to 3.6 KOhms; at 104 deg F, 0.9 KOhms to 1.3 KOhms; at 175 deg F, there should be 250 - 390 Ohms.

Wally Plumley
Charter Member
928 Specialists
www.928gt.com

Thanks for the advice, the Temp II was bad. Once I replaced it the car runs great again.

Many 1980 to 1984 Porsche 928 owners of cars with L-Jetronic injection have not set the base CO (air/fuel ratio) setting. When set properly, the Lambda regulation can manage the air/fuel ratio properly. The proper CO% setting is 0.8% plus/minus 0.2 (measured ahead of catalytic converter and oxygen sensor disconnected). The setting change is done by turning a screw at the air flow sensor.

After the CO% setting, set the idle RPM to 650 plus/minus 50. Double check CO% following idle setting.

Rich
'93 928 GTS "Cover Girl"
'87 928 S4
'79 928 5-speed rescue
'79 928 5-liter track beast