Sensors

[Peter73]

Hi,

I have a question about the sensors in the exhaust pipes. I have a EG33 engine from a 1991 JDM SVX. In the exhaust pipe are 2 sensors ( 1 left and 1 right), these are the "lambda" sensors or o2 sensors. 20 cm further there are another 2 sensors in a sort of small muffler left and right. What are these sensors and what are they for?

Thanks,

Peter

[Suby Fan]

those are your four O2 sensors the to front ones are for calculating air/fuel ratio and the back ones are for monitoring catalytic converter efficiency

[Peter73]

Originally Posted by Suby Fan

those are your four O2 sensors the to front ones are for calculating air/fuel ratio and the back ones are for monitoring catalytic converter efficiency

What happens when the back ones aren't mounted?

[Suby Fan]

it will throw a catalist efficiency code and run the same

[b3lha]

I have a 1991 JDM SVX and I'm pretty sure it only has two sensors - one each side. The wiring diagram only shows two and I don't see "Catalyst Efficiency" on the list of Trouble Codes. AFAIK the later modeIs have three O2 sensors, but I've never heard of an SVX having four O2 sensors. It's going in for MOT tomorrow, so I'll have look underneath and see what you are referring to. Are you sure it is the original exhaust? Are the sensors connected to anything?

[Suby Fan]

see sadly enough i havent been under my own car in long enough to remember but if it does have 4 O2 then the backs are for monitoring the cat... if there is only 2 then it is just for Air/fuel stuff

[curly2k3]

as stated in your other thread your car has 2 sensors, they are right before the precats on the Y-pipe, as stated its monitoring and calculating basically. put them both in if you dont want to throw a code

[b3lha]

Turns out that Peter73 and Subyfan were right. Both my SVXes have four sensors in the exhaust. The attached diagram from the USDM service manual shows the O2 sensors in the catalytic converters. It also shows an unlabelled hole in the pipe between the cat and the manifold.

On my cars, the O2 sensors are fitted into the unlabelled holes and there are also sensors in the cats themselves. The sensors in the cats have metallic heatproof sleeving on the wires and a different plug to the O2 sensors. Is this different to US models?

[Earthworm]

Originally Posted by b3lha

On my cars, the O2 sensors are fitted into the unlabelled holes and there are also sensors in the cats themselves. The sensors in the cats have metallic heatproof sleeving on the wires and a different plug to the O2 sensors. Is this different to US models?

Yes, the 2 O2 sensors on ours are in fron of the pre-cats and the 96/97 models have a 3rd sensor in the centre cat.

[b3lha]

Originally Posted by Earthworm

Yes, the 2 O2 sensors on ours are in fron of the pre-cats and the 96/97 models have a 3rd sensor in the centre cat.

I *think* the two front sensors (in the pipes) are the O2 sensors and the two back sensors (in the cats) are catalyst temperature sensors.

Are you really reading every post that happened while you were away?

[svxistentialist]

Reading them, but not reading through them.

Speed reading only works for stories.

[svxistentialist]

Originally Posted by b3lha

I *think* the two front sensors (in the pipes) are the O2 sensors and the two back sensors (in the cats) are catalyst temperature sensors.

Are you really reading every post that happened while you were away?

Phil, the Twin Turbo silver Legacy I had in JAE '05, it had a light on the dash for exhaust temperature.

I think it is a more critical issue for turbos. They may be a situation where the turbo engine fuels so rich to avoid detonation, it can send a lot of unburnt fuel down the exhaust, and possibly damage the catalyst metal coating.

Do you think the cat temp sensors in our cars use the same sensors and sites as the turbo cars?
Is it the case that the information from these temp sensors never lights a warning light for us, but instead informs the injection fuelling circuitry to run more lean or rich as required?

Joe

[b3lha]

Originally Posted by svxistentialist

Phil, the Twin Turbo silver Legacy I had in JAE '05, it had a light on the dash for exhaust temperature.

I think it is a more critical issue for turbos. They may be a situation where the turbo engine fuels so rich to avoid detonation, it can send a lot of unburnt fuel down the exhaust, and possibly damage the catalyst metal coating.

Do you think the cat temp sensors in our cars use the same sensors and sites as the turbo cars?
Is it the case that the information from these temp sensors never lights a warning light for us, but instead informs the injection fuelling circuitry to run more lean or rich as required?

Joe

I haven't yet done enough research in the ECU to say what it does with the cat temp signals.

Darren made a posting a while back saying that the light at the top left of the dash, next to the 4WS light, is for Catalyst Temperature warning. It looks like a box with flames on top. I originally thought it had something to do with the transmission.

[Earthworm]

Originally Posted by b3lha

Are you really reading every post that happened while you were away?

Yup...just wait until I get to General SVX Babble!

[svxistentialist]

Missed us a lot, huh?