Hello. This is my first ever post on any forum. Thanks for reading it.
My '02 2500 van has a 5.2 gasoline engine. It runs fine up until i get to around 50 then wont go faster. if i depress the accelerator pedal at that point, it will drop down to a lower gear and rev higher, but no increase in the speed. going up hills is worse. The codes were for throttle position sensor, cylinder #3 misfire, cylinder #5 misfire, and of course one for multiple cylinder misfire. i replaced the TPS. The latest codes are P0123 (throttle position sensor voltage high), P0505 (idle air control motor circuits), P1492 (ambient/temp sen volts too high), P0442 (evap leak monitor medium leak detected), and codes for large and small leaks too. Somehow the misfire codes are gone. The van has a built in fuel filter in the fuel pump that's non-serviceable. I have not checked for fuel pressure yet (though i suspect it to be a fuel supply or exhaust restriction issue). it just turned over 100,000 miles this week. One more thing I should mention is that I tested the 5 volt power supply from the PCM to the TPS and it reads 5.21 volts. the output is supposed to start at .3 volts to .9 volts with foot off pedal, to 4.5 at full throttle. I'm good at the bottom (.68 volts), but only putting out 3.75 volts at full throttle. Any help sending me in the right direction as I troubleshoot would be a big help. Thanks a lot!

 

wow man, it is hard to say with all those codes.

You have to go through them one by one. Strangely, most of them have nothing to do with the other...except for the misfires...

 

Yeah, I know. I think I've narrowed it down to two things (fuel supply or exhaust restriction). I hear that a clogged catalytic convertor can produce these symptoms. It sounds and feels as if it's "over muffled", almost like trying to blow air into pipe with a cap on the other end. I read that i can remove the O2 sensor in front of the converter to relieve back pressure, and it will run better if that's the problem.
Anyhow, thanks for responding. i joined two forums and you are my first reply since i did it last week.

 

You took all the words right out of my mouth. Start by testing fuel pressure, if it checks out then remove the O2 sensor to see if you get the power back.