Question on o2 Sensors...

[GTA_V6_Mustang]

Ok well my mileage has been very poor... I drive pretty much 90% highway. And I have new plugs, cap/rotor, air filter I have cleaned the IAT sensor and the MAF sensor, I have even done a throttle body service and used combustion chamber cleaner. when i am conservative my mileage is 15mpg or so and when I am hard on it its 14mpg not much of a difference... The car seems to run fine I dont feel any loss in power and I have all my air pump hoses hooked up. Also my check engine light is not on and it does work. I was wondering if my o2's could have gone south? If they have how can I check?

 

[GTA_V6_Mustang]

Any suggestions?

 

[extremetrek]

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!

 

[HISSIN50]

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. )

 

[MI95Cobra]

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....

 

[MustangGT95]

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]

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...

 

[HISSIN50]

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...

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.

 

[GTA_V6_Mustang]

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.

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?

 

[MustangGT95]

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.

 

[HISSIN50]

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?

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.

 

[GTA_V6_Mustang]

Follow-Up

Follow-Up

Ok well I just replaced both o2's. Turns out they where the originals, hehe. Just got some bosch oe type and put them right in, the old ones where white as hell and had some type of crud on them I am assuming from the 3 bottles of combustion chamber cleaner I had poured down the throttle body when I first bought the car. Well seems to be running better. Wont find out if gas mileage is better untill I drive to kendall this weekend. But it definatly has some power back. Thanks for all the help. One more question though... I wanted to know if you guys have suggestions on anything else I should replace. So far I have put in new...

Spark plugs
Cap/Rotor
PCV Valve
PCV Valve Grommet
Mostly all vacuum lines
Air Filter
Fuel Filter
Crankcase Breather
Differential Fluid (Full Syn 75-140)
Of course oil & filter 4 times in the past 4000 (trying to makes sure the engine is clean)
Thermostat
Radiator
Cleaned MAF Sensor
Cleaned IAT Sensor
Both o2 sensor's

Any other suggestions?

 

[GTA_V6_Mustang]

Nothing else I could replace?

 

[mo_dingo]

If your plug wires are original, I would replace them. Not that the ones you have are bad, but they do wear out.

After you replaced the O2 sensors, did you reset the computer? You need to so the computer can relearn the new o2's.
Scott

 

[GTA_V6_Mustang]

Yeah, i guess... Lol I just unhooked the battery for 5 minutes than turned the key in ignition a cuple of times to drain power from the PCM and started her right up. But yea I do want to replace the wires. Was thinking about going with some ford racing 9mm's

 

[sade04]

Follow-Up

Ok well I just replaced both o2's. Turns out they where the originals, hehe. Just got some bosch oe type and put them right in, the old ones where white as hell and had some type of crud on them I am assuming from the 3 bottles of combustion chamber cleaner I had poured down the throttle body when I first bought the car. Well seems to be running better. Wont find out if gas mileage is better untill I drive to kendall this weekend. But it definatly has some power back. Thanks for all the help.

hey man im in the same boat as you with the crappy-esque gas mileage. I was just wondering...how many miles do you get to the tank in the summer time?
I can usually get 220 easily and 230 if im lucky but in the winter it drops to like 170a tank.

And 50miles per tank is ALOT imo.

So after doing a complete tune up and not really noticing a difference, i decided that winter just affects our cars more than other cars in general.

Things like letting the car warm up for 10 minutes every morning leaving for school, then on the way back, starting her up and only running for about 1min before i drive off (its been in the 10s lately) would cause it run richer. I guess that adds up

Ohh yeah one more thing...do they have like a different formula for gas in the winters??

 

[HISSIN50]

Sade, correct about the warm-up hurting milage (you have run time, but no milage).
And right again about the fuel. At least around here, we have gasahol in the winter. It admittedly wipes out a MPG or two, as I recall.

 

[GTA_V6_Mustang]

The thing is that I live here in southern florida. I am pretty sure there is no change of gas formula in winter. But anyway I was getting averagly 200 miles for a full tank which was like 15 mpg and I only drive highway. Only highway, and I dont take her over 65-70mph and keep the windows up. But now I cant check my mileage because I broke the odometer gear. But now that I replaced the o2's it seems like its better. I am going to go ahead and just replace the IAT anyway and fix my odometer gear to check my mileage because I have a long trip coming up and will be able to see what my highway mileage truly is.

 

[go-stang5.0]

After reading this thread I decided to get some o2's. Rock auto online has denso o2's for $35 plus shipping. You can get both shipped for like 77 bux.

 

[The Green GT]

I plan on changing mine soon. Ill let you know how my mileage goes. I have thrown a few CEL's from them too. Sometimes back to back.