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Q: 4.0 lt is very sluggish. no exhaust restriction, fp is ok 45psi, all new tune up.

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This is a 4.0 lt 94 ford ranger. The engine is very slow to come up to speed and doesn't have much pickup speed on the highway. The exhaust has been checked, has new plugs, wires, coil pack. air filter checked, maf sensor cleaned. I have a 3.0 v6 that will run circles around this 4.0. Probably something simple but what?

My car has 107000 miles.
My car has a manual transmission.

Hi there. What you’re describing may be an underlying fuel pressure concern. Check for any stored codes in the engine computer before replacing any more components. If there are no stored codes, a diagnostic tool will be required to monitor the voltage fluctuations for the MAF sensor; sometimes cleaning the sensor does not correct improper readings and the concern will continue.

If the MAF is ok, I would definitely suspect a low fuel pressure concern. This could be caused by a restricted fuel filter, restricted fuel line, or a weak fuel pump. A fuel pressure gauge can be connected before the filter to check for a weak fuel pump and after the fuel filter to check for a restricted fuel filter.

A bad fuel pressure regulator could also be the cause if the fuel pump and filter check ok and would need to be inspected by a qualified technician. YourMechanic has several technicians available to provide a low engine power inspection for proper diagnosis.

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