Ok so good news, check engine light came back on! so I did my KOEO test again and go some interesting results.

so for the hard codes I got the same two codes.
31- EGR valve position (EVP) out of range (low)
67- Neutral drive switch open

so those codes shouldn't affect my issue, next I got the Continuous memory codes
31- EGR valve position (EVP) out of range (low)
41- No heated oxygen sensor switch detected, right side
66- Mass airflow sensor circuit out of range (low)

So those two last codes would definitely explain the poor running conditions I have, now I just need to solve those issues.. so to me I think I should start my triple checking my wiring for those two sensors, I doubt I have a faulty o2 sensor but I could just take the sensors out and swap them, if the code pops up again telling me the o2 sensor is on the left side that is fauly then I will know one of them is bad. again, I doubt thats the case so I think wiring is my primary suspect. As for the mass airflow sensor, I'm not sure what would cause it to be out of range other than it not being the right type of sensor, Im not sure if my air filter being too close would cause it to trip a code like that? anyways the fact that the computer is getting a reading from the sensor tells me the wiring is probably ok on that side although I can also check that as well

 

If you are using tweecer or similar the slot style MAF can work provided you use the correct MAF curve and the physical placement is correct.

 

The fact that it's not the type of MAF the ECU expects is why it's out of range. Filter placement can effect it as well but in this case, the primary cause is MAF type being wrong. The "fooler" device they sent along is intended to fix this, apparently. If it was a stock MAF with a filter right on it then I'd blame it on filter location.

The o2 sensor code says it's not switching (not switching between above/below 14.7:1 as it does when running in closed loop), not that it's out of range or faulty.

 

I'm not sure how I would be able to replace the MAF sensor with a stock sensor, as far as I know depending on what type of fuel injectors I use, the MAF needs to be calibrated for that. So if I buy a stock MAF, install it, best case it works problem solved. But then when I switch to my 351W motor, it has 32lb injectors (I believe stock is 19lbs) and so then I would run into more issues unless I kept the air adjuster or bought another MAF sensor that is calibrated for 32lb injectors?

So for the o2 sensor I'm not sure I understand what you mean by it running in closed loop or switching

 

I didn't say to buy a stock one per say, I was just saying that's why it's out of range.

The whole MAF being "calibrated" for a certain injector size is a marketing ploy to make it sound more complicated than it is. There is no calibration being done to make a certain MAF expect to be used with a certain injector size. They just say if the injectors are 50% larger than stock and the MAF is 50% larger than stock then it's "calibrated" when in reality, it's just a 50% larger MAF and any 50% larger MAF is "calibrated" by their definition when in reality the calibration (the relationship between MAF size and injector size) is determined by the ECU and never changes unless you have a way to tune the ECU.

The flaw in this process is that load calculations done by the ECU are based on the air mass the engine is ingesting under varying conditions (as measured by the MAF). When you use a larger than stock MAF, these load calculations are no longer accurate which throws off everything load based in the ECU calibration (the most important being where on the timing advance table it's running at under varying conditions and therefore timing advance no longer lines up with where it should be according to Ford's ECU calibration). If you've got a way to tune the ECU then it's not a big deal as you just adjust the timing table accordingly. If you don't have a way to tune it though, you're just stuck with the "wrong" timing.

So in your current scenario, you've got a stock Mustang ECU so it expects to use stock Mustang sized injectors and a stock Mustang MAF, or any "calibrated" set of larger injectors/MAF. So if you're still hoping to figure out what's going on with this particular combination of parts but want it future proof for your next engine, you'd get injectors large enough to support the 351w and a MAF that is the same % larger than stock as the injectors are.

With a tunable Speed Density system, all of this added complication goes away. There is no matching injectors to MAF size or worrying about what MAF or injectors the ECU expects you to run or anything like that.

 

So if that's the case, then what is going on with the o2 sensor? is that caused by something else like having the wrong MAF or is that something that is not hooked up correctly or a broken part?

 

Stock MAF sensors when used in closed loop operation (where the ECU is making fueling changes based on o2 sensor feedback) cycle back and forth between richer than 14.7 and leaner than 14.7:1 so the average is 14.7:1 but they aren't actually sitting at that value. If it's not switching then it's not running in closed loop (which isn't surprising as engines have to be running properly, have to be warmed up, etc. for that to happen). So I'd actually not spend too much time trying to figure that out until the MAF deal is sorted as fixing that may fix the o2 problem.

 

I would have to say “yes” that stock MAF for the Mustang computer would most likely solve that problem. I’d think you would need a MAF sensor calibrated for 32# injectors when you get to that point. I would not use something to fool the computer.

The truck seems to always be running lean so the oxygen sensor never momentarily switches to rich. Ideally the sensor is constantly switches between lean and rich as it controls fuel flow.

 

+1, the MAF sensor mismatch is screwing up the whole system, the computer has to dial fueling requirements into a pretty narrow range before the O2 will start switching back an forth between slightly rich and slightly lean and it needs accurate air mass data to do that.

 

Ok so if I were to go the route to replace the MAF sensor back to stock, how to I find the correct MAF? As in I know I need one for a mustang, but what year? I would also like to call the IST tech, just want to know why they would include a MAF sensor that doesn't even belong to this truck, maybe they can send me over the right one so I don't have to buy a new one.

 

87-93 Mustang V8/5.0 is the application for the sensor.

I'm pretty sure we have one in our box of removed MAF's if you want me to check our storage area.

 

Yeah if it's not too much trouble. I was looking on summit racing and found this: looks like the MAF I have now and aparently it's compatible with a 1993 mustang so I am a it confused
https://www.summitracing.com/int/par.../model/mustang

 

Every MAF in existence (including the one in the link above) is compatible with an 87-93 Mustang if you've got a way to tune the ECU for it. For this reason there are tons of MAF's listed for that application. This does not mean they are a direct replacement for the stock sensor with no other changes.

As an example, I've got a 2014 Mustang MAF sensor in my 2006 Mustang and I'm using it as a blow thru sensor (after the turbo) even though it was originally used as draw thru. How? With a tuner to modify the calibration on the ECU.

 

Alright but one that came in that era Mustang is what was pictured in post #84

 

SPE Are you able to send me your email via PM?