I have a 2004 dodge 6spd 2500. truck threw a P2121 Pedal Position Sensor 1 Performance / Rationality and P0628 fuel lift pump circuit voltage low. starting a couple months ago very very rarely and only when i was really pushing the truck it would just go into limp mode pedal completely dead but after a few seconds it would come back and we were off again. it hasn't done it in over a month but tonight i went to town to pick up my harley and while sitting at a light idling it almost just choked out and died on me came back to life and i went on my way after loading the bike and heading home about halfway there it went into limp mode on me coming out of it every now and then i could keep my speed at about 60 mph but really didn't wanna go any harder when it came back on i would have full power again but only for a second and every time i would stop it sounded like it was running out of fuel but never did die on me then when i got home it idled while i unloaded the bike parked the trailer and as i pulled in to park it it died i tried to start it again and it cranked for about 20 seconds then started only running for about 3 seconds and died again after that it wouldn't start again now i really don't know which problem to chase cause on one side it sounds like the APPS sensor but on the other hand it sounds like the lift pump and that truck still has the pump in the tank which i have been told are garbage and the P0628 DTC has been on there for years but had it checked out and was told it was fine any help would be very appreciated

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oh and when clutch is or out of gear truck will always rev up fine seems like it would only go dead when completely idling or under load

 

I would crack a fuel line or hook a gauge up to see if shes still getting fuel pressure if shes throwing a lift pump code and get that outta the way right away. Im not sure the pedal position would necessarily cause this much trouble but its not gonna cost you anything to see if your getting fuel but if you are then I would turn to the sensors.

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But you said sitting at an idle she started choking out sounds like shes lacking a little fuel when the computer throws a code i like to troubleshoot the things that cost the less and usually thats with a voltmeter and a wrench.

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but if its only under load could be possibly the map sensor?

 

i know it kinda goes both ways I'm really hoping its the lift pump cause i want one anyways haha ill try cracking the fuel line and see if it has anything in the morning i just hope its not the sensor sounds like those things are pretty pricey

 

Pedal position sensors are pretty cheap on Advance Auto but map sensors can get pretty expensive basic replacement is about 50 bucks and they go up from there.

 

ok im used to mechanical trucks whats the difference between the pedal position sensor and the map sensor? like i know what the pedal position does but no clue what the map sensor is or what it does

 

The MAP sensor is the M-anifold A-bsolute P-ressure sensor. In a nut shell The MAP sensor converts engine vacuum/manifold pressure to an electrical signal so the computer knows how much load the engine is under. This data is the basis for fuel delivery and timing control. In english its the computers way of load compensation as far as fuel and air.

 

ok and so then this could be a possibility then?

 

If this thing is going bad you could be experiencing variable idles as well as rough idles. It would also possibly be the reasoning behind your truck almost choking out.

 

is there any way to check it?

 

Wish I could tell you it was for sure this but your gonna have to do some troubleshooting obviously let me know what happens when you take a look tomorrow start with the fuel delivery and the map sensor for now. If both those check out we'll have to pursue other paths.

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Heres a way to do it with a voltmeter.... How to Test a Map Sensor | eHow.com