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My A/F gauge will call you out on that, until the truck goes into closed loop, it runs in the 12-13 fuel in open loop, at 4 miles after running, temp gauge says, its warm, you can see it go into closed loop, and A/F shows 13,8-14.9.
So its is rucher than running with a O2, than not. I can take video, or pic, of it doing it.
I tell you what, when the weather warms up, I will disconnect both of my O2 sensors and send a picture of my A/F gauge.
But in the mean time, the picture below shows what my factory coding on my 5.8l MAF/EEC-IV/OIL2 strategy. it's only at/above half load that the fuel mixture is richer than 14:1. Yes, different computer have different settings and I'm not saying you are wrong, I'm just showing you I'm not wrong.
feedback control is so that mathematical calculations can be trimmed (fuel trim) up or down to maximise the potential of the fuel and the air coming into the engine. if you have mechanical differences in the hardware on each bank, so like injectors with debris on a cylinder somewhere , or porous casting in the intake runners on one side but polished on the other , or coked up spark plugs, burned valve on a cylinder, worn cam lobe.. you name it.. the computer CANNOT account for those on their own or as a stacked effect.
So mathematically, it knows the amount of air coming in and it should have a fairly consistent and predictable fuel delivery , so feedback side-to-side seems almost extra work for no gain. but suddenly you got miles on an engine or parts variability from factory it makes sense why we have it.
Now , lets say you dont have your O2 sensors anymore. okay, well now the engine cant know what it is for sure feedback wise, so its going to run calculations but not be able to adjust them, it will have tables for enrichment for engine speed and load, and it will have a meager knock sensor thats not even integrated to the engine running if its a 300 and 302, but pulls timing at its only helpful role.
Thats with MAF presumed, all i just wrote. Now, we have a reality. MAF arent perfect on their own and they also arent the best replacement for a MAP sensor , sadly ford decided only boosted 3.8 or maybe a car based 5.8 needed to have both. maybe late explorer, not sure tho.So a skewed MAF sensor which can be from intake leaks after the sensor, or from air flow ducting poorly routed, mismatched sizes etc. can be from contaminated wires which insulate the wire from the air flow and thus dont cool it fast enough.
so now your engine isnt going to have the right amount of air measured under all circumstances . The temp sensors both play a role in fueling and probably timing too. So skewed or incorrect temp sensors also will play with things here.
Then evap system, it needs to purge fuel vapors. if its going to richen the AF ratio predictably if it works right. if it doesnt, thats partly how your computer is either diagnosing that system or knows how to use those vapors to the best efficiency and usefulness.
The egr system, its going to predictably affect part throttle work, so thats how to diag those or know what to do for timing and mix then too.
if you mess with vacuum system too, that can affect it a lot. so big leak because of the recirc motor like every truck damn near by now has had break. leans out.
all that I went over, thats why feedback is important. imagine if we just mathematically tuned it with no way to adjust, then a vacuum leak could spell the end of life for an engine quick.
A stuck injector could cause your oil to have so much gas i nit your ring lands and rings get worn because of all the oil that gets washed off the cylinder walls
My engine has maf and eec-v it will stay in open loop because it cant go into closed loop without at least one oxygen sensor. ive noticed if one sensor works, then the other bank will be tied to the bank that has the better result/ not sure if this is in EEC-IV or not, but figured to mention it.
Also there is Open Loop - Enrichment which is for accelerating, its deliberately richer than the open loop idling
and engine that needs fuel added not pulled when o2 suddenly work will probably make the expected result different in your disagreement
Crazy part is some computers, like mine, do not use an O2 sensor for operation. I tell it what I want The table to be. The O2 is only used when I want it to self tune, which is almost never these days.
Then evap system, it needs to purge fuel vapors. if its going to richen the AF ratio predictably if it works right. if it doesnt, thats partly how your computer is either diagnosing that system or knows how to use those vapors to the best efficiency and usefulness.
I've been down this path before and I have learned the hard way, although when the purge system is working, it typically causes the engine to run rich, but not always. If there is no fuel vapors in the canister, then the mixture will be leaner. I suspect, Ford knows this and allows a certain amount of change when the purge is in operation. I've seen purge problems that caused lean and rich codes, although rich codes are far more prevalent.
FYI, the Federal Emissions testing does not go above a certain RPM. I do know in the late 80's, the emissions testing stopped at 3,750 rpm. I know of one manufacture that turned off their EGR operation at 3,800rpm. I asked why and they told me that was the answer. It made sense because they have to have a limit and I suspect all engine had a higher redline than 3,750rpm. I also know, there is no emissions testing above a certain load too. That is one reason why engines can run at a rich mixture without being flagged.
Crazy part is some computers, like mine, do not use an O2 sensor for operation. I tell it what I want The table to be. The O2 is only used when I want it to self tune, which is almost never these days.
What system are you describing, OEM or aftermarket?
...when the weather warms up, I will disconnect both of my O2 sensors and send a picture of my A/F gauge.
But in the mean time, the picture below shows what my factory coding on my 5.8l MAF/EEC-IV/OIL2 strategy. it's only at/above half load that the fuel mixture is richer than 14:1. Yes, different computer have different settings and I'm not saying you are wrong, I'm just showing you I'm not wrong.
Then why did you post NOT TRUE?
Are you describing an unmodified OEM SETUP or something that has been modified in some way or another? Why an A/F gauge??
Are you describing an unmodified OEM SETUP or something that has been modified in some way or another? Why an A/F gauge??
I have a Kenne-Bell supercharger on basically a stock 95 5.8l MAF engine. After 20 years with this set up, I finally have the time and money [mostly time] to dive into the tuning rabbit hole. I purchased a Tweecer and wanting to change the settings, it's probably best I have an A/F ratio gauge to let me know what is happening. That is why I have a gauge. The adjustments I have made are on loads higher than .500. Most of the adjustments I have made have been leaner, not richer. Looking at the factory tune, I feel there is no reason any fuel mixture needs to be 11, even 12 is too rich for me.
Why did I post not true? Because it's not true. When the O2 sensor is off line, the fuel mixture is kept at the proper value Ford [or the tuner] wanted. As you can see with the chart I posted, Ford does not tune the engine as rich as you mentioned. It tunes it to around 14. One other thing that all manufacturers do is allow the O2 sensor make adjustments to a certain amount. After that, the check engine light comes on. Usually it's +/- 25% [see chart below]. What I have seen is that the typical adjustment the O2 sensor has is about +/- .02. That is how well the factory has tuned the base setting. That is why, disconnecting the O2 sensor will most likely not change much more than .02%.
I can only share my experience of what I have seen. I live at sea level in the PNW, maybe your area is different which would explain why your experience is different.
The first chart I posted is the stock fuel map. None of those values were changed. I can post what I have on my tune, but that is not what we are discussing. It's my understanding that we are discussing OEM tunes. If we are discussing aftermarket tunes, then anyone can do anything they want.
Last edited by 1Butcher; Mar 26, 2026 at 10:32 AM.
Again, you are correct again, but the factory settings that I have posted are relevant to the topic at hand. They show that the settings are around 14:1 until the load gets to .5.
So, if the O2 sensors are offline, the fuel mixture should not go to 12-13 that was posted above. The fuel mixture would be calculated to match the chart. If the A/F changes that much with the O2 sensors disconnected, something is not correct.
If that was the case the Short and Long term trim numbers would be way off and probably set a code indicating the fuel mixture is too rich [or lean]. In a perfect world, the O2 sensor should report back information for the computer to make slight corrections in the mixture, not severe adjustments which would indicate there is a problem.
I just recently added the Tweecer so I can see what those settings are and modify them. I could post the changes, but that would be way off topic. We are dealing with factory tuning specs.
I have a Kenne-Bell supercharger on basically a stock 95 5.8l MAF engine. After 20 years with this set up, I finally have the time and money [mostly time] to dive into the tuning rabbit hole. I purchased a Tweecer and wanting to change the settings, it's probably best I have an A/F ratio gauge to let me know what is happening. That is why I have a gauge. The adjustments I have made are on loads higher than .500. Most of the adjustments I have made have been leaner, not richer. Looking at the factory tune, I feel there is no reason any fuel mixture needs to be 11, even 12 is too rich for me.
Why did I post not true? Because it's not true. When the O2 sensor is off line, the fuel mixture is kept at the proper value Ford [or the tuner] wanted. As you can see with the chart I posted, Ford does not tune the engine as rich as you mentioned. It tunes it to around 14. One other thing that all manufacturers do is allow the O2 sensor make adjustments to a certain amount. After that, the check engine light comes on. Usually it's +/- 25% [see chart below]. What I have seen is that the typical adjustment the O2 sensor has is about +/- .02. That is how well the factory has tuned the base setting. That is why, disconnecting the O2 sensor will most likely not change much more than .02%.
I can only share my experience of what I have seen. I live at sea level in the PNW, maybe your area is different which would explain why your experience is different.
The first chart I posted is the stock fuel map. None of those values were changed. I can post what I have on my tune, but that is not what we are discussing. It's my understanding that we are discussing OEM tunes. If we are discussing aftermarket tunes, then anyone can do anything they want.
do you use a MAP sensor of some kind, since MAF isnt the best at huge quick changes to throttle etc etc
Having a MAP with the functionality to read the boost pressures (idk how many bar that is) is helpful to my understanding
Update for anyone searching similar issues: Definitely is leaking injectors. Pulled two plugs and both were fouled pretty bad with gas. Fuel pressure drops quick after key off, like within 10 seconds back to zero. Guess I'm pulling that upper intake plenum off after all. Possibly bad FPR too but I get no gas from it when I disconnect vacuum. But might as well change it while I'm in there. Also removing plenum gives me a chance to clean out the throttle body as well. I don't use it as a daily driver so it can wait a few weeks until I can get to it.
As far all the talk about A/F ratios: I don't understand half of all that, but I would assume the O2 sensor (mine only has 1) tells the ECM the state of exhaust and ECM makes changes based on that input. Without the O2 sensor, it's going to default to something and I assume rich? I have a new O2 sensor but haven't bothered to replace it yet because I don't think mine is bad. Or if it is, that's not my main problem right now. FWIW, my truck is 100% stock. When I rebuilt it I wanted to keep it all original as much as possible so no EGR deletes or ECM tunes or anything like that.
