Hi I have a problem with my 2008 Ford ranger 4.0 v6 4×2 supercab for the last 3 months that is driving me crazy. It started of as a small miss between 1000rpms and 1500rpms so I gave it a service including changing the spark plugs then it was OK for about 3 weeks and it started again with the miss then I changed the petrol pump and then had a problem starting only after the 3rd turn did it take. Then drove it for a week like that and went up a hill and it had no power it didn't want to rev up and eventually cut out and wouldn't start again had to tow it home. Took the tank out again changed the petrol pump and did a pressure test on the feul line and when it idles it is on 65psi but when I switch the motor of it drops right down to 0psi so I went and put a non return valve on the line between the tank and filter no it stars after the first turn and the pressure stays on the line when I switch it of. But now when I drive it it gets to 3000rpms and starts missing and searching and doesn't want to rev up but when it idles it revs up all the way to 6500rpms without any problems. What is causing it please can some help

 

"Petrol", are we British?

I would remove the "non return valve" to see if gets above 3,000rpms while driving
REVing in drive way uses little fuel, when driving fuel demand goes way up, so RPMs are not a good comparison

Did you replace the whole petrol pump assembly or just the pump?
Because there is a "check valve"(backflow preventor) in that assembly
Yes, fuel pressure should hold above 30psi for a few MONTHS, with key off

Lack of power in general can also be partially blocked exhaust, you can test for that with a Vacuum gauge

Any obvious drop in MPG?

 

I am from South Africa and I only replaced the pump coz the whole pump assembly is a very expensive part over here that I can only get from Ford $600 for the assembly. When I take the non return value off the line it does the same thing at 3000rpms it feels like something is blocking or preventing it from revving up and if you put your foot all the way down it comes and goes like searching for power

 

Can it maybe be the Dpfe sensor from the exhaust that is causing the problem have read that on some Fords these sensors causes lots of problems

 

No, not DPFE for that problem, but DPFE sensor does wear out

The computer has a REV LIMITER set for 3,000RPM

If you are in Park or Neutral RPMs will be limited, Park or Neutral are set by the DTR sensor on the transmission

With manual trans its done by clutch pedal switch

The fact you can REV engine to 6,000rpm when parked means something is wrong, shouldn't be able to do that
So you may have DTR sensor issue
DTR = digital transmission range sensor