In my truck, I have no O2 sensor. I installed a set of headers, and just left the O2 sensor unplugged. The truck is running fine, but I was considering some other mods. I have a camshaft on the brain, along with larger injectors. I want to know, will the computer be able to adjust to these mods, ar even realize that there is a change in the case of the injectors, without the 02 sensor?
Also, how does this system measure air flow? There is no MAF. is everything calibrated based on whats going out the back?

 

your engine makes calibrations to the air fuel ratio based on input from the O2 sensor. Without the input, the computer automatically gives a full rich signal to the injectors. Your truck also uses a manifold absolute pressure sensor, intake air temp, and some other sensors.

 

so you should get that sensor back on your rig. any muffler shop can weld a bung for the sensor to bolt into.

 

Actually, the computer just relies on the O2 sensor for feedback. Fuel/air calculations are made in these trucks based on manifold vacuum and throttle position, trimmed with air temp input and water temp input. The computer monitors the accuracy of its calculations with the O2 sensor. It is important, and I'd get it back in the exhaust. Bigger injectors will not be any help with an unmodified engine. Stock injectors can flow enough fuel for right around 300 horsepower. If the amount of air entering the engine hasn't changed by a lot, larger injectors will still only need to inject the same amount of fuel as the stock injectors. You can swap cams, but it has to be one that's designed for speed density (MAP) fuel injection.

 

Actually, these trucks use the O2 to change the fuel ratio. How will the engine know what to do if it doesn't have a clue about the oxygen content in the exhaust? The PCM commands a rich signal with no O2 present to prevent detonation. The PCM can't control air fuel ratioh without knowing whats happening in the exhaust. It does use the MAP and air temp along with throttle position when running at partial to moderate throttle position. Water temp is only used for cold start up and does not affect the calculations once the vehicle is warm. The O2 feedback is the backbone of the air/fuel delivery. Without the O2 sensor the vehicle computer will stay in open loop and will continue to operate on the PCM set startup calculations for air and fuel. The O2 only enters closed loop with the O2 sensor signal. Only then does it use the MAP, intake air temp, water temp, etc... to make calculations for air fuel ratios. Without an O2 the vehicle will have increased fuel consumption and if left alone will destroy the cats prematurely.

 

Actually that is not the case. By your logic, how does the computer run the engine at all in open loop? The O2 sensor is only there to give feedback to the computer about the air/fuel ratio, and the computer can adjust things based on what it is seeing. If there is no O2 sensor, it will run in open loop, just using the MAP sensor and TPS for main fuel trim calculations. Depending on how good Ford got the fuel maps in the ECU, it should be pretty close to 14.7:1, not rich. The computer uses the MAP and TP and temp sensors all the time, open loop or closed loop. Think about this: the truck runs in open loop at every cold start up. Sure the mixture is richened up, but that is because the engine is cold. If you don't believe me, either read up on http://fordfuelinjection.com or Charles D. Probst's book Ford Fuel Injection and Electronic Engine Control.

 

TPS and MAP are only used when throttle is applied. The engine will run rich in open loop because there are only a limited number of programmed fuel maps designed for cold starts that the PCM contains. There are no "calculations" made during open loop. The PCM picks the best map that it contains for the given MAP TPS inputs. Calculations can only be made in closed loop and the O2 is required for this. The engine will run rich like a carb with the choke closed. Continuously running the vehicle this way will cause cat and other engine damage.

 

No. If that's so, then why do cam swaps mess up the idle?

It might run rich, it might not - depends on the health of all the sensors. If everything is functioning correctly, it should run at stoich - 14.7:1. The only difference between open loop and closed loop is that the computer fine tunes fuel trim when in closed loop by taking readings from the O2 sensor. The computer calculates air/fuel ratio at all times, regardless of closed loop or open loop - otherwise it would not know what the engine was doing and could not run it at all. Please read what I recommended in my last post, they will tell you the same thing. Also add this to your list to read: http://www.austincc.edu/cloud/efi/eectch98.pdf .

 

Thanks for all the advice. At this point, I still have no O2 sensor.

The truck is running a little rough. The main symptoms are a slight miss under mid to full acceleration, and an idle that bounces around.

This is a typical example of pulling up to a red light after driving for a bit and the engine is warm:

At an idle, the truck will run at about 1000 for maybe 20 sec. then drop fast to about 600, and then jump back to about 800 and idle, continously bouncing around from 700 to 900, up and down.

I just replaced the frame mounted fuel pump, and filter.

I am wondering if the tank pump is failing and the pressure is bouncing around, or if it might be something else?

I have cleaned, but not replaced the IAC valve.
The idle acts the same with the IAC plugged in or unplugged.

 

might need to change out the tps sensor

 

Would that give it the funny idle?

 

Not having an O2 sensor could cause that to happen as well.

 

The computer goes into fail-safe mode if it looses any fuel system sensor, like the O2s. Basically, what happens is the computer just uses the base fuel maps that are programmed into it, to keep the engine running. The O2s provides a level of refinement to this. The engine will run without it, but you will have decreased performance (not enough fuel or too much fuel) because the computer is forced to take a stab in the dark at the mixture.
With any speed/density system, if you do anything more than a mild cam swap, the computer must be reprogrammed. This is especially true for injector swaps, as the computer is programmed so that a certain pulse width equals a certain amount of fuel into the engine. Increasing the amount of fuel will cause a major rich condition.
I know for a fact that Meineke will weld in an O2s ring for about $50. I know, I have installed several.

 

Thanks for the response fordsix, but that doesn't explain the funny idle. The truck runs good going down the highway, but idles stupid at a red light. The response when I first step on the gas, even between shifts, seems to lag. Maybe the TPS is bad right at the idle position. I think I have another at home I can try. Any other info or ideas would be appriciated, but I don't want to just start changing sensors at random as this can get very expensive.

 

Put the O2 sensor back in it. Get the O2 sensor back in before you start looking for problems elsewhere.