After a lot of internet research I have found that most suppliers list for late 1999 - to 2003 XK8 two types of pre-cat air/fuel sensors - Denso 234-9016 and 234-9029 ...the later costs a half price than 234-9016. Are they interchangeable? If not, then why?...

 

Some cars have both an upstream and downstream air/fuel sensor. Could this be the case with your vehicle?

 

Well, I am certainly NOT a Jaguar professional. but the difference in the two sensors is that one is a zirconia sensor used on the AJ26 engine and the other is a "wide band" sensor used on the AJ27 engine. So, no, they are not interchangaqble.

 

Right on the money, Ross! The AJ26 uses zirconium dioxide sensors that output a varying voltage of .1v to .9v. The AJ27 uses "Universal" type for the upstream sensors. They output a varying current signal to the ECM. Absolutely NOT interchangeable.

Cheers,

 

those sensors I mentioned are both listed for AJ27 by the auto parts stores

 

Best I can tell the 9016 IS a wideband sensor, which would mean it would fit your car in the upstream position.

The 9029 sensor appears to 2002 X-Type and 2003 and later 4.2L V8's. That would mean it's no good for you.

Seems no one is very good at stating what the true application is for their parts, upstream or downstream.

Cheers,