960 1994 Oxygen sensor

Kappy5003 · Post by **Kappy5003** » 14 Feb 2010, 07:12

Hi
Recently aquired a 94 960 sedan and just love it, drives and handles well.

There are a few small issues mainly fuel economy, no matter what I do I can't get any better than 24 mpg (UK gallons that is)highway cycle and around 18mpg city cycle.

I was talking with a friend who seems to think that a faulty O2 sensor can affect fuel economy without causing a hard code, I've checked and have no codes. Can this be confirmed and secondly how hard is it to replace.

My next issue is when I turn on the igition I hear what sounds like a creaking sound that last approx 3 to 4 seconds then goes away, also a shorter sound that occurs on turning off.

Hope someone can help.

Cheers

Post by **billofdurham** » 14 Feb 2010, 12:45

O2 sensors that are badly degraded can continue to work well enough not to set a fault code, but not well enough to prevent an increase in emissions and fuel consumption. The absence of a fault code or warning lamp, therefore, does not mean the O2 sensor is functioning properly. The sensor may be lazy, or biased rich or lean.

They are easy to change but you do need a wrench like this one to get over the wire.

The noises you are hearing are probably the car groaning at the thought of going out again and a sigh of relief when you get back. Seriously, I can't help with this unless you can be more precise about where the noise is coming from - inside the car, under the dash, in the engine compartment?

Bill.

Post by **JDS60R** » 14 Feb 2010, 16:06

I agree
The normal culprits are the coolant temp sensor , the 02 sensor and the MAF.

I think a UK gallon is aprox 1.2 US gallons so your UK 24 mpg highway would be equal to about 20mpg US . So I agree with you - thats bad mpg.

The creaking to me sounds like the metals reaction to all of the extra exhaust heat. In order to get rid of all of the petrol with the bad mpg the engine has to run too rich. This causes extra heat as the unburned gas enters the exhaust. Your car is going to be much ahppier when you get this resolved.

I figured you already changed spark plug and air filter.

Best of everything

Kappy5003 · Post by **Kappy5003** » 14 Feb 2010, 16:57

Thanks everyone.

The creaking noise seems to be coming from the middle of the dash, approx behind the centre vents, more so when I turn on the ignition less so when turning off... I did notice the noise dissapear after turning the ignition on and off about 3 time in succession without actually starting, puzzling.

With regards the O2 sensor is that a most likely suspect to start with or does one go to the expense of doing all 3 mentioned.

Plugs and filter seem to be fine.

Kappy5003 · Post by **Kappy5003** » 16 Feb 2010, 19:42

Hi
I've been making inquiries into obtaining a new sensor, seems my 960 is late 94 nearly 95 and it's been suggested there was a change in around august 94. Its been suggested that they are either 3 wire or 4 wire, I don't know the difference.

The genuine article is over AUD $250 and as low as $197 ouch

I have discovered a Ebay shop in oz who has the for a around $60 he says a 3 wire would do the job but I had a look at the convertor and there seems as though there are 4 wires.

Can anyone enlighten me in this regard.

Cheers

danr960 · Post by **danr960** » 17 Feb 2010, 12:13

I too have a '94, and I believe the difference is that a 2nd ground was added for the heating element. My original was a three wire and have used a four wire in the past because they are much cheaper here. Just grounding the 2nd wire to the engine block.

I have also used one from a Ford Mustang of the same vintage, the plug has to be replaced but did get about 100k miles out of that one. But requires soldering of the wires.

DanR '94 964 348,000 miles (114,000 on the new engine)

Post by **billofdurham** » 17 Feb 2010, 12:35

On a 3 wire one wire carries the signal and two wires are used to supply a voltage to the internal heater. Signal earth (ground) return is achieved through the vehicle body. This is a case earthed sensor.

On a 4 wire one wire is the sensor signal, one is the isolated sensor signal earth and the remaining two are used to supply a voltage to the internal heater. This is an isolated earth sensor.

It is not recommended to replace isolated ground sensors with case ground types.

The 4 wire sensor usually has one plug with all the wires in it. A 3 wire often has 2 plugs, one for the signal and the other for the heater. 960s fitted with only one sensor, at the front of the cat, are 3 wire and those with two sensors, one in front and one in rear of cat, are 4 wire.

Bill.

Kappy5003 · Post by **Kappy5003** » 17 Feb 2010, 15:56

I'm a little confused.

I had a look under the car and there appears only to be one sensor with 4 wires. This is near the front of the Cat. So I guess I should use a 4 wire one even though most of the books say it should be 3 wires.

Apparently one school of thought is that the type sensor in Australia was change in August 1994.

As the original sensors are so expensive the supplier I have found provides a type that you join to the original wires.

In this case the 4 wire is dearer than the 3 wire.