Oxygen sensor gone bad? Lean at idle, any ideas?

[twinturbozs]

A buddy of mine used a multimeter using the diagnostic ports OX1 and IG. The reading gave a pretty constant reading of .62-.63V at idle. He says it should flucuate between a much wider range maybe between .3V - .8V. He recommended that i replace the sensor immediately with another OEM unit.


Checking my Vf readings, at idle im pegging 4.8V which means im running lean or the TCCS thinks im running? Is that correct?

Im currently running:

Lexus AFM (screw all the way in)
550 injectors
AFPR (32psi base pressure)
MKIV (recently installed)

Ive been trying to get the TCCS to fall into the 3.0V range at idle with no luck. Increasing the base pressure, drilling out the J-tube restrictor, or adding a MKIV fuel pump hasnt helped. Unfortunately i dont have a wideband hooked up, which will probably be my next purchase.

 

[3p141592654]

[0 volts]
Maximum Lean, reduction of the fuel mixture from the BASIC
FUEL CALCULATION

[1.25 volts]
Minimum Lean, reduction of the fuel mixture from the BASIC
FUEL CALCULATION

[2.5 volts]
No correction at all to BASIC FUEL CALCULATION

[3.75 volts]
Minimum Rich, increasing the fuel mixture above the BASIC
FUEL CALCULATION

[5 volts]
Maximum Rich, increasing the fuel mixture above the initial
calculation


If you're at 5V, then you probably have an air leak after the AFM, or your fuel pressure is too low.

 

[jetjock]

Your friend is right but why would he use IG when testing the O2 sensor?

You first need to verify whether the sensor itself is at fault or if the engine has a problem that's driving it full lean. If your buddy measured correctly (if he used IG he did not) the sensor may indeed be dead, although they don't usually die outputting the voltage you claim. It's why I'm suspicious. Measure it again using either VF and battery negative with the diag jumper in and the engine off idle, or measure it directly using OX. Expect a slow cross count at idle and faster when off idle.

If it isn't counting deliberately make the engine rich and lean to see if the sensor flops full over to each side. Hold the engine at 2000 rpm and pull off the brake line to make it swing full lean. Shoot some propane or carb cleaner into the line to drive it full rich. If the sensor gets driven full over in each case the odds are it's good and the problem lies elsewhere. If it doesn't get driven full over either test it off the car or replace.

A couple of points:

1) The VF can be max and the O2 sensor still cross counting at any rpm. A high Vf doesn't mean the engine is lean, it just means the ECU is adding more fuel to make it right. It *could* be lean if the ECU can't add enough but without measuring the O2 sensor properly you can't tell.

2) Which screw is in the Lex AFM? If it's stock that's likely not going to be enough even if it's all the way in. Block the entire lower chamber of the AFM and see if VF comes down. If it doesn't you probably have (as 3p pointed out) pirate air. It could be several other things too. A bad trim sensor, incorrect fuel pressure, ect.

3) Assuming it actually is why do you care if the engine is slightly lean at idle as long as idle quality is good? Or why do you care if VF isn't dead on there? What is your VF during steady state cruise?

Either way your first job is to verify the O2 sensor to see if it's bad or simply responding to an actual lean condition caused by something else.

 

[twinturbozs]

Ok so testing the O2 directly, i use diag port OX1 and negative battery? what range should i be testing for?
How far should the cross counting range be for?

thanks for the info.

 

[jetjock]

Yes. The sensor outputs 0 to 1 volt so use millivolts or whatever range is closest to that. Read your service manual for more details. Not to be a prick but by dint of reading this you must be connected to the greatest source of information the world has ever known so you could also Google "oxygen sensor". The internet is more than a global pornography network you know...