Possibly an o2 sensor issue?

As some of you know, i have an overfueling problem in my Thunderbird. Ive noticed in the past (last year, just remembered) that according to my Norrowband gauge (yeah I know) the o2 sensor would quit switching once in a while twards the top end of the stoich lights. At that time, the CEL would light, and I'd get two codes: O2 sensor not switching, and RICH.

Ive since installed a wideband sensor and have been monitoring the output. I noticed that my wideband was pegging rich under boost (mid 9's) and I ended up taking about 4 lbs of fuel pressure out of it to make it run relatively normal. Even while my wideband was telling me PIG RICH, the narrowband only ever lit up to the high end of stoich, or mabey 1 light into RICH. I looked at the stock sensor when we had the Turbo out this spring, and the entire sensor tip was bone WHITE. According to the narrowband, it switches like it should... mabey a hair slower than normal. there has to be a sensor telling the car that it is running too lean, thereby making the ecu dump too much fuel somewhere in the car. I seem to remember getting a lean code at one point too, but I cant remember when.


The o2 sensor is one of the few parts that have NOT been changed out on this car. Is it possible that the sensor is reporting that the car is running too lean and making the ecu dump fuel? If it dumps a lot of fuel, this would explain why the wideband is telling me RICh when the narrowband is telling me normal? Since I subtracted fuel pressure, the drivability has improved, but its still running pig rich. I know that a narrowband gauge is a fucking joke, but it should read RICH when the mixture is obviously PIG RICH, right?


Does it sound like i am on the right track?

Have you EVER ran leaded race gas in your car?

If you have, then the o2 sensor is shot.

If not, how many miles since the last time it was changed?

Furthermore..... the o2 sensor is a key player in telling the computer what the mixture is.

Yes, a narrowband reading will still show what the mix is doing, just not as precisely, obviously. My ScanMaster
in my Buick only reads off the stock o2, a narrowband reading, but it's surprisingly accurate for what it is.

might be but under WOT the o2 does nothing.

Does the wideband say its rich while at a steady cruise? It is possible that the 02 is getting a false signal thinking it is lean and then adding fuel to make it run richer than stoich.

1twisted6 wrote:

Have you EVER ran leaded race gas in your car?

If you have, then the o2 sensor is shot.

If not, how many miles since the last time it was changed?

Furthermore..... the o2 sensor is a key player in telling the computer what the mixture is.

Ummm.... yeah.... I know that is a no-no. I ran 110 Leaded from a place in Waunakee last year and the year before..... usually about 5 gallons of that mixed with 15 of 93 no corn. I only did that maybe 3 times in a two year stretch. Essentially it was 1-3 ratio leaded-unleaded. The sensor has not been changed since then. The sensor was changed over 50K ago last time I remember. The tip of the sensor was white.... suggesting silicone contamination. Another thing that might be worth mentioning..... i think my buddie aaron used some ultra copper when we put the down flange on the turbo the first time. We did NOT use any when re-assembling the turbo this last time after machining flanges. The sensor went through that as well.


The Wideband says that the car is cruising near 14.7, so it seems right. it idles around 14.7 as well. When you get into boost, it rapidly dips to the 10's, and then into the low 10's and 9's as you reach full boost. The Narrowband under cruise is switching like it should.

If you ran leaded gas i would replace your O2 sensors

Yeah, the only one that had leaded ran past it was the one that is hooked to the ECU.... and at 40 bucks, its a no brainer.... even if it isnt the cause of the issues I'm seeing.

I'd be installing a new o2 pronto.

What little leaded you ran thru it is minor, but that combined with 50,000 miles.... I'd change it out.

just swap the sensor. They dont cost that much.

yes change it but under WOT it is not doing anything so that has nothing to do with your WOT tune.

Here's another thought that just ran thru my pea-brain.

Do you have a fuel pressure gauge? I mean one in the car, not just one that hooks to the fuel rail to check static pressure.

If so, are you getting fuel pressure rise with boost. It should go up pound-for-pound. If not, maybe the computer is seeing a lack of fuel, and trying to dump as much as possible to compensate.

Yep, i did that Twisted. It does rise 1 for 1 with the boost, and there is no fluctuation.


Brngrhd- So what would cause the overfueling up top? The air meter is pegged, so it basically ignores that, if it doesnt read the O2 at WOT, how does it correct mixture? If i'm thinking right, there should be a WOT fuel table that it would run off of...... but shouldnt there still be a sensor that gives its input so it adjusts?


I was also thinking about the other sensors that I havnt replaced. The Air Charge Temp Sensor, the Knock sensor (unplugged so irrelevent) the BP sensor (it reads correct with a frequency meter) ...... there has to be something telling the computer to dump a TON of fuel.... and it almost has to be a sensor that the ECU uses to increase or decrease the injector pulsewidth.

At wide open throttle your car should run off of a set WOT map. Kind of like when your car goes in limp mode, but the opposite. Im sort of thinking you need your WOT map adjusted, not sure how easy that is on your car. I know its near impossible on my truck. Ford OBDI FTL

LOl I hear ya on that. I'm running a J3 Chip from moates.net, but I havnt really messed with the stock tune at all. The only things I have done are to lower the fan turn on temp very slightly and change the air meter samples from 1 to 3 so it will average the signal. i can take my chip out and it still acts the same.



Stock setup 2.3T computers are known for going pig rich at boost onset. Fuel tables target 11.5~11.1:1 over 3000rpm. IIRC, this should end up at low 11s, high 10s 3-4krpm, leaning out as the revs increase. its not leaning out at the top end at all.

I think if you have a way to do it, its time to start messing with the tune, specifically at WOT. Correct me if im wrong, but if it acts the same without the chip arnt you driving untuned with mods? Thats a no no

it will read sensors like the mass and tps when it see wot it will look at the mass air to see how much air is coming in and look at rpm. os sensors are only for cruise idle and light throttle wot they do not look at them

He still should replace the O2 sensors if he ran leaded gas through the system.

That what I thought. Since the VAM (air meter) is pegged at WOT, thats why it is supposed to lean out as the rpms get higher at a set boost pressure. It doesnt do that for some reason.



And yeah, its pretty much untuned with the Mods that are done to it. What I dont get is that there are people who run the exact same setup that I have, running STRONG untuned. The stock fuel system, air meter, and ECU tune are good to 300 HP or so. After that its time for bigger injectors and a tune. I really shouldnt need more than small tweaks ( fuel pressure and ignition/cam timing in order to run the Mods I have on the car now.



The O2 sensor is going to be replaced on Friday. O'riellys has the bosch sensor I need for 39.99, so its going in.

Is there a way you can lean it out as the rpm's increase manually via the tune? might be the fix for you even if others dont have to do it

Blackout wrote:

That what I thought. Since the VAM (air meter) is pegged at WOT, thats why it is supposed to lean out as the rpms get higher at a set boost pressure. It doesnt do that for some reason.

no it will/should not lean out as rpm goes up. if your VAM is pegged then it looks at RPM and from every step in rpm (could be 200, 400, 600rpm steps it looks at its table and injects X amount of fuel. you tune those tables to get youtr tune done. on the cars i have tuned there is a table of like 12 X 12 and one is rpm the other is load.

brngrhd wrote:

no it will/should not lean out as rpm goes up.

Huh? explain this to me?

like i said they program the computer with how much air is being moved at WOT under pcm controlled boost set to say 5psi they know that as rpm goes up so does the need for fuel so it add the proper amount of fuel. if he upped hte boost it would lean out but it should do it all the way across the board

I know that part, ive got lots of drivability notes on the subject, but the sentence i quoted makes no sense to me

Well, the fuel is boost dependant until you reach Full boost. So say Im running 30 PSI of fuel pressure base, and I boost it 15 PSI. My reading at 15PSI should be 45 PSI on the gauge. The computer should adjust the pulsewidth wider as the rpms go up, but it should lean out a bit considering there is only much that the ecu can increase the duty cycle.


As the injector duty cycle increases, its my understanding that it can only go so much..... causing it to lean out twards the upper limits. After all, its still at the same 45PSI fuel pressure.

LLcoolJames wrote:

brngrhd wrote:

no it will/should not lean out as rpm goes up.

Huh? explain this to me?

it was a "it will not or should not lean out as rpm goes up" sorry if that was written bad.