1999 Ford E350 5.4L
The van drives good for about 1 hour, then it losses power
to below 40 miles or going up hill to under 20 miles.
Injectors, plugs, coils, fuel filter, gas pump all new. What
else can it possibly be??
Could be PCM putting engine into limp mode, see if there are any codes being set such as from a cam, crank or knock sensor. Can check also trans fluid, low fluid can be letting TC slip. Honestly there's a lot of thing to check over given vehicles age.
After the engine ran good for about 30 minutes, the check engine light came on. 4 and 6 miss fire coils at random and then again 8 and 3 will also come on and off at random. That is the weird part that they come on and off at random Once the engine has warmed up for a bit. When the truck is cool everything works proper and after 30 minutes maybe 40 minutes the engine is warm and it comes across this problem where I loose all the power slowing me down to under 30 miles an hour going uphill.
Usually random multiple misfires are not a good thing, could indicate a problem with the timing chain. A computer diagnostic might indicate if car is going into limp mode when these occur, as that's how the engine's PCM minimizes risk to itself. You could also try a compression test and see if you're losing power from lack of compression. There's no given solution until the problem manifests itself as a hard fault, you're not sure what you're dealing with. An OBD scan tool that can scan live data while you're driving might give you a better indication than just a few fault codes.
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