2.0 JTS O2 sensor voltage - Alfa Romeo Forum
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(Post Link) post #1 of 4 Old 18-03-18 Thread Starter
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2.0 JTS O2 sensor voltage

I'm trying to decide if there is an issue.
To give background, I did a major overhaul on engine 9k miles ago due to gasket failure. Head was skimmed, decoked along with injector cleaning. Obviously I did the usual Goetze piston rings with deglaze, bottom end shells etc whilst doing so. I have since fitted new Bosch pre-cat O2 sensors. Engine runs 10W/60 which is still fairly clean.

When warm, O2 sensor voltage is 2.25 at idle. It drops to 1.45 at fast idle or on road at speed. Voltage is steady at steady throttle.

Fuel trims are 4.6 & 8.4 (both positive values).
Post cat O2 sensors feed back 0.7 volts (+/- 0.05) but this reduces to 0.3 volts at 3750 rpm in 5th which is also fairly steady if throttle and speed are steady.

On the face of it, it seems a bit rich but fuel trims and post cat sensor do not necessarily agree.

Thoughts please....
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(Post Link) post #2 of 4 Old 18-03-18 Thread Starter
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Perhaps I should have mentioned, the thermostat is recent. Coolant temp diagnostically reads about 90 degrees.
MAF sensor reads up to 465 kg/hr which I believe is good.

Post cat 02 sensor values do fluctuate a bit but the average values are as I described. The can read between 0.1-0.85 volts.

Highest reading from pre-cat sensors after I lift off is 4.15 volts.

Cats are standard. Centre section is a stainless pipe. Rear box is a TS Remus of slightly smaller diameter which should not be restrictive.

Airbox and filter is standard.
Plugs and air filter are due imminent change as car has done over 190k km/110k miles. In any case, an occasional misfire can be detected, so worn plugs are clearly needing plenty voltage (which no.1 coil is not willing to supply). It will be rectified soon though.

Last edited by Fruity; 18-03-18 at 15:58.
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Are these Bosch lambdas? If they are NTK they are the wrong ohm rating .. had one in my TS for a couple of years and it was a pita ... swapped it for a bosch universal and car was much better afterwards.
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(Post Link) post #4 of 4 Old 23-03-18 Thread Starter
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Yes, they are genuine Bosch.
With regard to TS O2 sensors, I was told years ago that it was the switching speed which was too slow. Using the graph function on diagnostic equipment, I've seen a number of times that Bosch ones do switch faster.
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