Was having a chat with a mate of mine the other day (yes I do have some friends) and we were on about testing O2 sensors - don't for the life of me ask why as I have no idea why we were on about that.

Anyways, I read somewhere that you can read the voltage coming out of the O2 sensors to see if it's reading around the right sort of level, but we wondered what would happen if you just disconnected one of the O2 sensors, or the sensor in the air intake.

Would the ECU just kill the engine as it wouldn't have any reliable figures to work out how much fuel needs injecting or would it just go to a failsafe rich map and just push in too much fuel to stop it leaning out?

I haven't been brave enough to try it but just wondered if any of you knew so we could settle our argument

Thanks in advance!

OK just found out I can do it with the MAF - what about the other O2 sensors, anyone know?

No idea mate but you looked lonely without anyone answering, then talking to yourself and answering your own questions.

Hello Aido.

I thought the o2 sensor was a squarewave output?

Erm....

(Cue sound of something rushing over my head).............

Not sure to be honest mate!

How are you doing dude?

Nice to see you posting a bit more regulary on LOC and LOC. Hope you are well and we want pics of your latest mods to your Aristo

Not sure on the answer to your question, but on my BMW (that uses a MAF) if the sensor is unplugged the car just steps back and runs on a safely map - this is not limp home mode, the car still works pretty well. Thats the way to check if the MAF sensor is working, because if you unplug the MAF and the car runs better the you know your MAF sensor is faulty. I hope that makes sense - I don't know if this applies AT ALL to the Aristo however.

To test a O2 sensor use a scope on the output, should see a sine wave. Make the air/fuel rich or lean and you should see an instant reaction to the output. This is an easy way to see if the sensor is producing the wrong output or is lazy.

If you disconnect a sensor the ECU will either run rich to compensate or go into limp mode. Either way you will get a CEL. Once the sensor is put back it will take three cycles of ignition/engine start for the error to clear, or use an ODBII tool to clear,

hello gents, hope you're all well

Thanks for the replies, I'm gonna have a chat with my mate and let him know!

As a matter of interest how do you connect the meter to the sensor, is it inline or does it work when not connected to the vehicle for power?

Anees, will have to catch up with you at some point, fitted an FMIC and SSQV at Steves, it looks pretty angry now!

Ok I just tried disconnecting the maf when the car was running and it immediately cut out - tried starting and it would turn over and cut out.

I'm going to clean the MAF tomorrow so will see if that affects my idle

Actually just realised my car has a MAP sensor, not a MAF, oops!

doh..

I think its the UK/US spec Supras that have MAF sensors, the J-Spec Supras and Aristos have MAP.

Cheers Colin. Had a feeling it wasn't a straight DC voltage. Be careful when measuring it with a normal multi meter then Aido the results will be incorrect. As Colin says, use a scope if possible.



Have you seen those handheld scopes? Used one the other day and they're brill. a scope and a multimeter all in one. Was simply measuring a power supply and although the voltage was right, you should have seen the spikes and stuff on the line. Feel free to start a "Get Geoffers a scope meter" fund.

you can test your O2 sensors with a digital volatage meter, they don't need to be disconected as they need to be in and the engine running whilst you check em.

First you will have 4 wires on the sensor, 2 the same colour are for the heating element so don't try them. Not a problem if you do it won't do any harm..

Get the other 2 coloured wires and fire the engine up and plug yer voltage meter in, can and must do it without disconecting them.
Whilst engine ticking over you should get a reading of and about .01v to 0.09v. if you do that means the sensor is doing its job and this is called cycling. Also means it is working OK. If the voltage is not cycling then it is U/S..

hope it helps old boy

what probs you having aido, we have the smae engines, and i got a full set of workshop manuals. i also have been testing my stock o2 sensor

Just have a dodgy idle at the moment mate, varies in rpm just ever so slightly - we're talking no more than 100 - 200rpm here...

I've got new spark plugs, cam breather pipes and coil pack connectors all waiting to go on but to be honest looking at this stuff is just to see if I can improve the MPG much so I can stop Shell bending me over and bumming me so much

How's things with you dude - enjoying the Supe? Absolute animals aren't they these engines - when I had the new FMIC fitted I was gobsmacked how quick this thing goes up thru the speedo and I've got 300Kgs on you

Dunno what LOC & LOC are though Anees ? Sounds like a Solicitor man & wife team

Anyway great to see the big guy back on


No way, you'd lost weight last time I saw you !!
Anyway you had better be coming down to the WIM meet Sunday 13th July.
Hitch a lift with Gord/Geoffers to stop a Shell bumming

Bouncing an old one as I got that wrong - it's a MAF as I've cleaned it today