4.0 random loss of power loss of mpg

[longroad]

The truck is a 94 ranger 4x4 4.0 5 speed 256,000 k when cold it runs sluggish with a lack of power until warm then seems to get better . On hills the truck will almost cut out and loose power but not completely if u take the foot off the gas when it does this and get back on the throttle the problem will go away for a bit when it does this the check engine light will flash on then when the problem goes away the light will go off it comes and goes and is not a constant problem the truck seems to be running on the rich side . Im going to pick the truck up this weekend the guy that owns it hasn't had it scanned but did replace the fuel pump but didn't help . Im leaning towards the egr but dnt have much exp with this motor. Any ideas?

 

[RonD]

It will need new O2 sensors at 200+k miles, they are good for 100k.

When you get it, start it cold, RPMs should go up to 1,100, that means "Choke Mode" has kicked in, computer runs this when engine temp is below 140degF.
If idle is low, then replace ECT sensor, this is the TWO wire sensor just above thermostat housing, there is a ONE wire sender next to it, that is for the dash board temp gauge.
If ECT sensor is telling computer engine is already warm then it would run poorly until it was actually warmed up.

Near this area, front passenger side of the engine, is the Fuel Pressure Regulator(FPR).
FPR has the Return Fuel line connected to it and a vacuum line, pull off the vacuum line and check it for fuel, FPR diaphragm can leak and fuel is sucked into engine via the vacuum line, causing rich burn and sluggish performance.

Pull a few spark plugs, older plugs will perform poorly until warmed up.
Plugs should have a very light brown look, dark brown or black means rich burn.
If just one spark plug has that look then could be leaking fuel injector.

The 4.0l OHV engine likes Motorcraft or Autolite spark plugs, it will "use up" other brands pretty fast.
My '94 4.0l had original spark plug wires for 18 years, what a difference when I changed them, local Ford dealer had a sale on Motorcraft and they were cheaper than other brands and my regular parts store, go figure, wish I did them 5 years earlier

While engine is running listen for exhaust manifold leak, exhaust manifold leak sucks in air.
O2 sensors only "see" oxygen, that's the "O" part of O2, if there is an exhaust leak in manifold then O2 sensor on that side will see "extra" oxygen in the exhaust, too much oxygen is Lean burn, so computer will add more fuel to that bank.
Since it is a false Lean engine would be running Rich.

I think only the Calif. Ranger 4.0l's had EGR system.
But if you have it then yes a leaking EGR valve would make engine sluggish.

And the old standard "Clean the MAF sensor and the IAC Valve" still apply

 

[Meanman480]

Already changed temp sensors no luck my truck was manufactured Canad and I'll dose have a egr system and of corese a cracked egr tube I'll try the rest in the morning

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[longroad]

Ok thanks for all the info ill have to dive in more when I pick the truck up I might be lucky with the check engine light being able to point me to the problem to

 

[Meanman480]

Well cleaned the maf and so far works better...

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