I have an 03 Ranger with the 3.0, I received recently in a trade with a CEL for running rich. All sensors look to be working and the only things I haven’t checked are the injectors or ecm. I just noticed the tach was jumping around while driving and generally runs a bit high but there is no actual surge in rpms so I’m guessing it’s gonna be an electrical issue or faulty ecm. Does anyone know where the ecm gets the rpm signal? Or how to check ecm for failure?

 

Welcome to the forum

Crank sensor, at the front of the engine, is "tach" signal, its also the only sensor that can cause a no start or stall the engine, so its fine if you can start and drive the vehicle
Tach jumping is more likely to be the gauge/cluster

What was the exact "Rich code"?

No, there is no way to test a Ford PCM(ecm)
You can do "sanity tests", i.e. unplug a sensor like the TPS and start engine, and see if PCM sets a code for TPS circuit failure

Full list of Ford codes seen here: https://www.therangerstation.com/tec...II_codes.shtml

There are many codes for the same sensor or issue, so EXACT code number is important
Never just "google" a code number, look it up on a full list so you can see the codes the PCM did NOT use, it can make more sense for the one it did use

 

Thank you.

I’m getting codes P0172 and P0175. Both banks running rich at upstream O2 sensors. Both O2 sensors are new, as well as MAF and PCV. I don’t remember the number but I also had the code pop for downstream O2 running rich and that disappeared on its own after a about 50 miles of driving. Injectors also aren’t leaking, or at least they didn’t when I put it in mode to clear a flood.

 

Then I would check fuel pressure, 55psi is expected, there is a fuel pressure regulator in the gas tank, if its stuck closed you could be run above 65psi which will cause Rich Codes

Lean and Rich codes do not mean engine is running lean or rich

The computer calculates how long to open each injector based on engine size, air weight(MAF), throttle position(TPS), RPMs, injector size and fuel pressure

This calculation is called Short term fuel trim(STFT) and it starts as 0, and lets say that calculation is to open each injector for 100ms(milliseconds)
So computer opens injectors for 100ms
It then looks at O2 sensor voltage, .1v is lean, .9v is rich
If O2 is at .9 then computer changes STFT to -2, so injectors are now only opening for 98ms
If O2 is still at .9 then STFT goes to -4, then -6 then -8, then -10, injectors opening for 90ms
If it gets to STFT -16 then computer will set a Rich code to notify the driver there is a problem with its calculations
But computer will keep going to -30 if needed to get O2 sensors to shows .4/.5v, the sweet spot
All this take about 2 seconds of run time, so engine is never running Rich or Lean
If you were blowing out black/grey smoke from tail pipe then that would indicate RICH running, lol

Same happens for Lean, but its STFT +2, +4, +6 ect..............

So the codes mean that there is something wrong with the calculations, a variable is incorrect
The computer is programmed for factory injector size, and for 55psi fuel pressure, there is no fuel pressure sensor
So computer knows exactly how much gasoline will flow out of that size injector with 55psi pressure if its open for 100ms

Now if you put in larger injectors(like flex fuel size) then computer calculations would be off, Rich, because more fuel is flowing out than calculated
If fuel pressure was too high then more fuel would flow out than calculated
In either of these cases the computer would have to go into negative STFT to compensate for the higher fuel flow rate