Ok so i hooked a fairly advanced scan tool the hooks to my phone through bluetooth to my odb2 port. When i used it to check the air/fuel mix from the truck it was reading a mix of 9.3:1. This seems extremly rich to me. Is there any way to get this down to a reasonable mix without taking it to a shop?

 

Welcome to the forum

Assume a 4cyl engine but what model year?

Shop can't do anything about air/fuel mix, that is something that is controlled by the engine computer.

And the air/fuel mix you are looking at is not the actual air/fuel mix...........it is the calculated air/fuel mix based on computers input/output data

Fuel injection computers have a few "assumptions", things they can not check but just assume to be correct.
One is the air flow coming into the engine, it "assumes" ALL the air coming in is going thru the MAF(mass air flow) sensor, so no air or vacuum leaks in the system
It also "assumes" a stable fuel pressure at the injectors, if pressure is lower than assumed, then computer has to open the fuel injectors longer to get the same amount of fuel into the engine if it was at higher pressure.

What you want to look at is STFT(short term fuel trim)
Computer calculates 0 STFT on the fly, this is based on RPM, Throttle position, and MAF data
Computer "knows" it is running a 2.5 LITER engine(for example), so it knows how much air a 2.5 LITER engine will pull in at any RPM or throttle position, and uses the MAF data to fine tune that air flow.
It then uses the 14.7:1 air:fuel ratio to calculate how much gasoline to add to that amount of air
And that is 0 STFT
After this 0 STFT mix is burned in the engine the computer looks at the upstream O2 sensor, O2 sensors "see" Oxygen, not gasoline, too much oxygen in exhaust means Lean burn, too little oxygen mean Rich burn

If 0 STFT mix produces a Lean burn then computer changes to +1 STFT, adds more gasoline, then looks at O2 sensors again, if still Lean then computer changes to +2 STFT
And so it goes until O2 reports "good" burn

If 0 STFT Burn was Rich then computer adds less gasoline, -1 STFT, -2 STFT, -3 STFT, ect.....

If STFT gets to more than -15 or +15 computer will turn on the CEL(check engine light) to notify driver that there is a problem with the calculations
All this "trimming" of the air:fuel mix is done in milliseconds, so engine is never actually running Lean or Rich, these are just the terms used
If an engine is actually running Lean it will ping and knock
If it is actually running Rich it will blow black/grey smoke and MPG will be in the toilet

-5 to +5 is normal STFT and it SHOULD change up and down, needs to to keep Cat converters working(HOT)
At idle +10 is not unusual, idle needs to be Rich


Computer also has two operating modes
Open Loop and Closed Loop

O2 sensors don't work when cold, they need to be above 600degF in order to read oxygen levels in exhaust
Which is why they are heated, and why there is Open Loop

When you start a cold engine the computer runs factory air:fuel mix tables based on RPM and throttle position
After a few minutes of warm up the O2 sensors start to work and computer switches to Closed loop.

So if you have any engine problems it is very important to ID if problem happens cold or warm, Open Loop or Closed Loop.

Also watch engine temp, ECT sensor data, engines should run with coolant above 185degF, under that and they have to run Rich


Yes, 9.3:1 is Rich mix data but if you had low fuel pressure or an air leak then that data would be the result of that, not actually running Rich.
If you have black/grey smoke coming out the exhaust and/or big MPG drop then engine is actually running Rich

Upstream O2 sensor should be replaced every 100k miles, they use a chemical reaction to read oxygen levels so use up the chemical and wear out
Downstream O2 sensor(after Cat converters) last longer, so 300K miles