I have about 160K on this truck, head gasket was repaired about 50k ago by former owner, has run pretty well and trouble free since I purchased it four years ago. Recently replaced plugs, coil packs, wires resulting in improved running/mileage. However, I’ve been getting a secondary air injection system error code for six months or so, (both before and after ‘tune up’), performed snorkel modification to prevent uptake of road splashed water, checked fuses next to battery (good). Up to now I just ignored this sole error code since engine was running well. TPS checks ‘good.’ Recently the engine would occasionally run poorly for short durations (@ all RPMs & regardless of throttle) and up to now simply parking overnight or just stopping briefly at a store would seem to reset the poor operation. Unfortunately within the last week it now runs like crap all the time: over revs for upshift, poor power, almost feels as if a cylinder is missing entirely, or timing has gone horribly ‘off.’ No other error codes, no obvious vacuum leaks. Ran through two bottles of Techron, no change. Does the ‘toggling’ of the engine running poorly/well offer any clues? Sticky injector? Any direction for this shade tree mechanic would be appreciated…
If this is a flex-fuel vehicle, there’s a sensor in the engine management system called a fuel discriminator. What this does is it measures the amount of ethanol contained in the gasoline.
So for example, if you were to fill up with E10 gasoline, the computer makes adjustments to the ignition/injector timing from the information it gets from the discriminator sensor. And if you fill up with E85 gasoline the computer makes adjustments to those same systems for that fuel from the sensor.
I would check to see if the discriminator sensor is sending the right information to the computer.
I am not getting a “Fuel composition sensor low/high” error but I will look into it: thank you for the heads up…
Any more ideas anyone???
Is there anybody out there?
Time to put my pants on backwards and head to the dealer!