Car starts to miss after warmup!

More
08 Sep 2014 20:09 #17588 by novellmd
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

Please Log in or Create an account to join the conversation.

More
09 Sep 2014 07:24 #17592 by he_mech_usmc
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.

You can be a mechanic or technician...The choice is in HOW you fix it, not THAT you fix it.

Please Log in or Create an account to join the conversation.

More
10 Sep 2014 08:15 #17596 by wallyp
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

Wally Plumley
928 Specialists
www.928gt.com

Please Log in or Create an account to join the conversation.

More
10 Sep 2014 19:02 #17601 by novellmd
Thanks for the advice, the Temp II was bad. Once I replaced it the car runs great again.

Please Log in or Create an account to join the conversation.

More
14 Sep 2014 14:11 #17613 by Rich928
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

Rich
Membership Chairman
Charter Member
1993 928 GTS Cover Girl
1987 928 S4
1979 928 5-speed rescue
1979 928 5-liter track beast

Please Log in or Create an account to join the conversation.

Moderators: Rich928mm928billvvOC

Don't have an account yet? Register Now!