Replaced O2 sensor, dead spot at top of throttle now.

[Maleficio]

O2 sensor has been disconnected since I bought the car in April. Hooked it up last week, car ran all screwed up. Replaced sensor, car runs so much better, but ECU running in closed loop induced a dead spot at the top of the throttle, wasn't there before.

Maybe the AFM needs some massaging? Not sure how to approach this gripe.

[JK McDonald]

Hey Maleficio, What year 928 are we diagnosing - Can you ask the previous owner about the issue ? Does the car seem to run OK in the open loop mode without the Oxygen sensor ? How do the plugs look, performance, fuel mileage, etc..... Are you saying that the problem only occurs at the top end of the performance curve - how often are you up there ?

Have the local police added you to their watch list yet ? There is one policeman in my area that always seems to be on duty when I feel the need for speed.

Michael

[Opelotus]

Did you install a universal sensor or an original style one? If original, how much was it?

[Maleficio]

I installed the only sensor available, single wire from NAPA, same as what Pelican sells.

Plugs are brand new, factory Bosch, car runs fine with sensor disconnected, but gives bad gas mileage. Plugged in, car seems to run better, pulls a little harder, smoother, but during warmup when just barely pushing the throttle, severe lack of power, like fuel cannot be delivered properly. After long warmup, problem seems to go away.

I wonder if a coolant temp sensor is malfunctioning?

82 auto.

[JK McDonald]

Hey Maleficiom The long warm-up period and poor initial operation (even with the new oxygen sensor) could possibly be improved by installing a three wire oxygen sensor. A three wire unit has the square wave output signal from the oxygen sensor lead to the lambda computer and the other two connections are simply a hard wired +12 power / Ground for it’s heater element. The heating element allows the control of the fuel mixture earlier from a cold start. Although initially the 82 Porsche 928 did not use a three wire oxygen sensor - I have added them to some of the K-jetronic/lambda cars for improved performance during the warm-up cycle.

The key is to make sure there are no false air leaks in the intake area. Once the exhaust has reached the correct operating temperature - even a single wire oxygen sensor normally controls things just fine. Do not forget to also eliminate some of the basics - verify that your warm up regulator is controlling the cold to warm engine fuel pressures properly and that the auxiliary air valve is open when cold and closed once the engine warms up.

Good Luck, Michael

[Maleficio]

Originally Posted by JK McDonald

Hey Maleficiom The long warm-up period and poor initial operation (even with the new oxygen sensor) could possibly be improved by installing a three wire oxygen sensor. A three wire unit has the square wave output signal from the oxygen sensor lead to the lambda computer and the other two connections are simply a hard wired +12 power / Ground for it’s heater element. The heating element allows the control of the fuel mixture earlier from a cold start. Although initially the 82 Porsche 928 did not use a three wire oxygen sensor - I have added them to some of the K-jetronic/lambda cars for improved performance during the warm-up cycle.

The key is to make sure there are no false air leaks in the intake area. Once the exhaust has reached the correct operating temperature - even a single wire oxygen sensor normally controls things just fine. Do not forget to also eliminate some of the basics - verify that your warm up regulator is controlling the cold to warm engine fuel pressures properly and that the auxiliary air valve is open when cold and closed once the engine warms up.

Good Luck, Michael

Thanks, Michael.

[Maleficio]

My initial problem of the dead spot is long gone.

I figure the car's been running in open loop for very many years, and now having the active circuits turn on may have exposed a weakness in the ECU. I figure the ECU may have needed some burn-in time just like a brand new would.

I just left it alone and backed off the air/fuel mix as lean as I could. Horrible exhaust vapors have subsided, and the car's running very smoothly.

All is good now, and the car's running better than ever.

[Danglerb]

O2 sensor isn't used past about 2/3 throttle, once that wot switch clicks the afr is from tables.

[Maleficio]

Maybe I'm saying it wrong: the throttle had a huge dead spot from idle. Once the pedal was mashed about 1/3 in, the car would roar. Now that problem is gone, I didn't do anything but drive it, so I figure the ECU needed some burn-in time after being semi-shutdown for probably fifteen years.

[Danglerb]

Kinda sounds like the idle switch, but gone is gone.

Common description might be hesitation.