tink89 said:
I recently bought an 89 XJ, 4.0 Renix MPI engin that promply failed it's emissions. A freind of the family took it to his automotive tech school and has recently told me that IF it is nessary to replace the O2 sensor the part will be near $500. He explained that the Renix system use a "special" O2 sensor that was used in only a few jeeps and Toyotas and that explained the cost. IT is suposedly a nominaly "on" switch instead of an nominaly "off" one and operated at a difrent voltage than a "normal" O2 sensor.
Since I have caught the guy talking out of his ass about other automotive things I am suspicious of this situation. Has any one heard of this exotic O2 sensor or am I getting a hosed?
Thanks
Tink89
The RENIX HEGO sensor is different (but he's wrong as to why.)
The typical "Titania" HEGO sensor used in most vehicles generates a variable voltage, between 0 and +1VDC, with +.5VDC being a "normal" reading, or "lambda = 1." Under .5VDC, as I recall, indicates a "lean" condition, and over .5VDC indicates a "rich" condition.
The "Zirconia" sensor used in RENIX (and limited other vehicles,) is a "variable resistance" which is fed a +5VDC "reference" voltage by the ECU. The Zirconia HEGO sensor then works as a voltage divider, and a return signal of +2.5VDC is "normal" - with lower voltages indicating "lean" and higher indicating "rich" (again, as I recall. I may have those voltage signals reversed, but the idea is still there.)
This is why you see a lot of posts by me telling people
not to use "universal" HEGO sensors in their RENIX rigs - the universal is a Titania type, and is incompatible with the RENIX system. Since the Zirconia only costs a few bucks more, generally, why not just get one that works?
The
only HEGO sensors I've seen run anywhere
near $500 (and they're more like $300!) are the "Wideband" HEGO sensors used with AFR meters. The conventional HEGO sensor responds on a "knuckle" - you get a linear signal within a very narrow range of AFR (say, 14.0:1 to 15.5:1) and then it's just a flat "rich" or "lean" beyond that. These are typically referred to as "narrowband" or "knuckle" HEGO sensors - I usually call them NHEGO (Narrowband Heated Exhaust Gas Oxygen) when I'm talking about both of them.
Wideband (WHEGO) sensors will give a quantifiable response from, say, 5.0:1 to 25.5:1 AFR, and can therefore quantify just
how "rich" or "lean" an engine is running. They're typically used as tuning tools.
Side note - you can change a HEGO sensor yourself on RENIX in about a half-hour - use a HEGO sensor socket if you have one, a 7/8" wrench if you don't. Pull with the engine still warm, it will be easier.
Get a replacement from Borg/Warner, ACDelco, or Bosch - I've had good luck with all three. Make sure there is never-seez on the threads - apply it if not present. Use a socket to reinstall, torque to 21 pound-feet.
Connect the electrics, and have a beer - you're done!
