Hey Scotty,
Can you tell me if my statement below is correct? This is for cars in general so not specific to any one vehicle. Here it goes:
.
A very high percentage, positive fuel trim (%) does not mean I necessarily have an issue with the fuel filter/fuel pump. However, if there is an issue with the fuel filter/fuel pump it will always show as a very high percentage, positive fuel trim (%).
A very high percentage, positive fuel trim (%) does not mean I necessarily have an issue with the fuel filter/fuel pump
correct. A high fuel trims aren't any kind of indicator that you have failed components. The troubleshooting to find cause is up to you.
High FT simply means: computer is adding fuel (usually by increasing fuel injector pulse time)
This can often be because a too lean mixture was detected at the O2 sensors, but not necessarily.
For example FTs will temporarily go high during "power enrichment mode". (that's when you floor it to pass on the highway)
Vacuum leaks also cause lean mixture.
However, if there is an issue with the fuel filter/fuel pump it will always show as a very high percentage, positive fuel trim (%).
not necessarily. for example if you have an intermittent problem, especially if it's only when the engine is cold, then FTs may not show anything. FTs aren't even used until certain conditions are met (coolant temp, O2 heaters, etc.) and fuel metering enters closed loop mode.
But what if the issue is not intermittent, say it’s constant, and my fuel filter/pump is shot? Wouldn’t that for sure result in high fuel trim values?
the most accurate way to diagnose fuel issues is to hook up a pressure gauge. (or some vehicles have fuel pressure available via OBD)
Wouldn’t that for sure result in high fuel trim values?
no I wouldn't say "for sure"
what if fuel pressure is able to keep up 90% of the time, until you really start getting into the pedal?