5.4 Triton choking out at 3,000 rpm

Ksnyder426

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Hi, I have a 2005 Expedition 5.4 with 186,000 miles. I've replaced, plugs, coils, fuel pump, fuel filter and the fuel pump module. I've also cleaned the maf sensor. When the engine temp is cold right after I start it the truck runs perfect. After it gets up to operating temp the truck chokes out around 3,000rpm. Like it's not getting air or fuel. The Phazers have not been changed (yet) and there is No check engine light. I'm having the cats checked at the end of this week and really hope that's the problem. Any suggestions or help would be appreciated. Thank you.
 

Hamfisted

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Have you noticed any change in exhaust tone ? Could be the Cats, could even be the muffler coming apart inside, but you'd notice that tone change or hear the phiiiiiiif from the tail pipe during acceleration.
If you want your own test kit, they're pretty cheap. You can even get two gauges and connect them to the front O2 sensor ports and bring the gauges into the front cab to observe while you drive it under load and put it in the problem RPM area.

Exhaust Backpressure Test Kit on Amazon




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Ksnyder426

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It had a new muffler installed about a year ago. 40 Series Flowmaster. I'll let you know what happens Thursday after the back pressure test. Thanks
 

Vincent Vega

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I have not heard of this happening before, but I have a few free ideas. I am assuming you had this problem, then changed out all those parts, and now still have the same problem. Also assuming your 3V has no obvious timing problems or ticking.
Have someone rev up the engine to 3,000 rpm while you conduct a visual on the engine for anything obvious.
Check fuel lines and fuel rail for kinks. Could be a fuel problem, which is usually easier to diagnose than weird electrical problems, so check fuel first.
Check fuel pressure at different RPMs using an external gauge.
Check all vacuum lines and elbows, and vacuum reservoir betwteen battery and RH fender - it can crack and leak. Also check intake manifold- any high pitched sounds indicative of vac leaks?
Check cam positioning and crank position sensors (I do not know how to do this but probably info on the internet)
Last thought- this seems like a problem that could be tracked down using Forscan or a scope, if you know how to use or can teach yourself. Could be used to figure out if this a misfire problem and which cylinders, lack of fuel pressure, messed up variable timing, messed up fuel trims.
 

SafariGoneWrong

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Definitely concur with Vincent Vega. FORScan is a great tool, I use the Lite version on the iPhone. With a good Bluetooth OBD adapter, you can see all the sensors and also calculated values. Without a check engine light, it’s the best diagnostic tool.
 
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