Question on o2 Sensors...

Well, i'm not the most knowledgeable but I am willing to reply:

When my o2s were bad it wouldn't throw a check engine light, however, when I ran the OBD I test it would come up with an HEGO system lean code, I ended up replacing them both, cost about $60 each.

Testing the O2 sensors involves probing the sensor leads underneath your car, be careful its hot down there, on our cars it is a 4 hole sensor with the following arrangement:

GND B+Volt
SIG HTD GND

Allow the car to warm up to operating temp and then probe between the GND and SIG, this should produce a varying signal voltage between 0.1 and 0.9 volts once the car is at normal operating temperature.

You can also test the O2 sensor heater by probing the B+volt and HTR GND, this requires assistance as the signal is only sent for ~3s have someone turn the key to the "on" position and obseve the voltmeter you should observe some change in voltage.

If either of these tests fail you car is most likely running in an open loop mode, wherein the O2 sensors are being completely bypassed and air/fuel mixtures are being calculated based upon preprogrammed values.

I'm curious what you're original fuel mileage was, as it seems to me that even with the O2s in the open loop mode gas mileage shouldn't be down THAT much. I guess its possible, and like I said I don't know too much about it. I'd say if you have the money, swap 'em out, its not too hard and I am sure you are getting up there in miles to where its not a bad idea.

I'd also check all of the fuel lines for leaks, I had a clogged up fuel filter as well and that was a quick and cheap job. Could be dirty/clogged fuel injectors and so on and so forth...its a treasure hunt.

Hope this helps a little...best of luck!

It can take the O2's being nearly completely toast to trigger the CEL. You can put a DMM on each O2's signal wire and watch the reading. It should fluctuate from ~0.05 to 0.95 Volts a couple times a second. If the sensor signals have lost amplitude or frequency, that's an indication that they have seen better days.

Good luck.

EDIT: Great stuff from John above! When I loaded the page, his post hadn't hit the thread yet, hence the repetitive-redundancy. )

when my 02 sensors went out after driving around a block or so i would come up to a red light and my car would take off sluggishly until i was driving in 2nd then everything would be fine, but my check engine light would come on...i hope this helped....

I think I may need to change mine also. I am in the same boat as you. I get 170-180 miles per tank regardless of how I drive.

GTA_V6_Mustang said:

Yep thats exactly whats going on here. But I had the instructor of the Ford program at my school take a look at it and he hooked up the scanner and it gave an evap canister purge code. Dont know if that would effect mileage that bad though...

Click to expand...

The EVAP purge solenoid injects vapor stored in the charcoal cannister. This happens at idle and cruise but the change in mileage is super negligible. I would not look at it as a cause.

I found 02's at autozone for 50$ each. Alittle cheaper than I found elsewhere. I just bought some heads lol...my priorities changed I guess.

GTA_V6_Mustang said:

See the instructor for the Ford program has tried and keeps trying to get me into his program but because of things I see like this is why I am in the CAP program my chrysler instructors seem to be able to figure out much more than both the Ford instructors at my school. So should I just replace both o2's when I get my income tax return?

Also what effect would the EVAP canister purge problem have on my car?

Click to expand...

If the O2's are old, it's not a bad idea. They say the lifespan of them is about 60K if you're lucky.

FWIW, the EVAP set-up on these cars is fairly ubiquitious to many Makes. When venting the gas tanks to Atomosphere was deemed uncool, a cannister to store vapor and a means of venting it were needed. It's one device that doesnt have bad side effects and actually richens things up at times.

The EVAP cannister code should have no effect on your car. This is backed up by the 20K guys on here who deleted theirs. For some reason, you solenoid probably is not opening (you can test it real quick if you want. It is that black thing hangin from two vac lines and an E-connector on the passenger firewall). If you're familiar with OBD-II EVAP systems, ours is super simple in comparison.

I understand about you going with your discipline due to the resources available - that's smart. This Ford stuff is not too hard to understand anyhow.

Good luck.