i just got a 96 eddie bauer 2wd with the 300 inline six in it and a 5 speed trans. i got a check engine light but it never ran any different than without the light. i took it to autozone and had them scan the code and the guy says it is either an o2 sensor or the catalytic converter but he cant tell me which one or if it is the pre or post cat o2 sensor. i also have a small exhaust tick that you only hear when you accelerate. i heard somewhere that the tick may be the cat and if so, would a new cat solve the light and the tick? any suggestions? sorry for the long post...

 

Hmm, I suggest that the odds with the code are on a failed O2 sensor - hear a lot more about those failing as compared to the cat. My only experience with a failed cat was where it was plugged solid with no code posted, but I've replaced many O2 sensors that have coded. As for the tick - recommend to do more investigating before replacing anything. I use a mechanic's stethoscope or a short piece of garden hose to my ear to determine where the noise is coming from. I had an exhaust tick on my 5.0, turns out the exhaust manifold had a hairline crack in it.

 

how do i tell if the problem is caused by the pre cat o2 sensor or the one after the cat? the sensors are about 50.00 each at autozone and i would rather not replace the wrong one.

 

The straight 6's have a problem with the manifolds cracking. I would replace the 02's before replacing the cats too.

 

It would seem logical that Ford would have programmed a code for each O2 sensor, and that there should be an analyzer out there to read it - hmm, and perhaps a person sharp enough to correctly read the analyzer (sorry, just never been real impressed with the technical know-how of most AutoZone employees).

If not and if the sensors are identical, I guess you're stuck replacing one, and if the code doesn't clear, then change the other one out - hoping that you don't damage the new and the working sensors in the process. Based on my experience, you've got a 50/50 chance of being right the first time - which means you have a 75% chance of being wrong :-) Perhaps NGM will have some additional suggestions when he logs on.

 

Due to age I would replace both of them just for maintenance. It can result in better fuel mileage too believe it or not.

 

well, i just went ahead and replaced both sensors, i also broke one of autozone's rental o2 sensor sockets but they gave me my deposit back without any hassle.

 

after i replaced both of the sensors, i cleared the codes and within about 30 miles, the check engine light was back on, i took it back to autozone to recheck the codes =same ones (po171 & po174) so i just wasted $105 on sensors for nothing at all. any ideas on what to do next?

 

It wasnt for nothing. They needed to be replaced due to the age of the vehicle. 105.00 for sensors is CHEAP. Some of the ones we sell are 400.00-500.00. Now lets get down to the codes...

Since both codes are lean codes and not oxygen sensor codes. I would look for a vacuum leak.
P0171 is System (adaptive fuel) too lean bank 1
P0174 is System (adaptive fuel) too lean bank 2
This means both banks are running lean. I would check for a vacuum leak. Check the fuel filter to make sure its not clogged up.

 

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