I'm hoping to find someone that knows more about this issue than me! Working on an '04 LLY with 222K on the clock, customer complaint is low power at WOT. Initial road test showed MAP senor readings off the charts (24 PSI at idle). After replacing MAP sensor, all air management data is now correct with the same issue. Began monitoring fuel data and found a loos of fuel rail pressure at WOT only while driving. FRP desired at WOT is right around 23K, and FRP actual will meet FRPD momentarily, then continue to drop as long as I stay in the throttle. I have seen FRP actual drop down as low as 3K, but usually stays around 8-11K at WOT with 23K being commanded/desired. Let off the throttle and FRP briefly climbs almost to 23K. Heres where it gets interesting, FRP will reach and maintain 23K WOT in nuetral, WOT in gear but power braked, and even when commanded with the scan tool, but NEVER while driving. Problem is present with 1/2 tank of fuel, so seriously doubt its a pick up tube issue. fuel system does not lose prime, starts with 2-3 seconds cranking EVERY time. Fuel filter is new with 40-50 miles on it, (old filter did not have any junk or metal in it), did the bottle test with no fuel in the bottle.All fuel lines look fine from visual inspection, no signs of leaks or damage/detioration that could cause the system to suck air. And all this is happening without a single DTC being set. I have no clue where to go from here...
JlBierbrodt
Has the cp3 ever been replaced or is it original? What does the truck normally do- just regular driving or mostly towing? Check return rates on the injectors, and on the cp3. Sounds like maybe high return under load, but could just be cp3 not keeping up.
I'm not talking about balance rates, I'm talking about actually measuring the return flow out of the injectors when its up at temp and demanding more fuel.
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