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Pete, Auto Service Technician
Category: Ford
Satisfied Customers: 28254
Experience:  Over 17 years diagnosing and repairing automobiles various makes and models with some training and certifications.
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99Ford RangerXLT 4x4 4.0 L engine loses power under load.

Customer Question

99Ford RangerXLT 4x4 4.0 L engine loses power under load. New plugs, wires, fuel filter, cleaned throttle body air mass sensor. No check engine light. Help?
Submitted: 1 year ago.
Category: Ford
Expert:  Pete replied 1 year ago.

Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay.

The two most common causes for this fault here are a weak fuel pump not supplying enough fuel pressure.The fuel pressure will need tested with a fuel pressure test gauge.The fuel pressure needs to be around 58 to 66 psi.If the pressure drops below the 58 psi when the fault occurs this usually indicates the fuel pump is weak here needing replaced.You will have to have the pressure monitored on the pressure test gauge while driving when this occurs to check this.

The other issue is a fault with a restricted catalytic converter.If the catalytic converter is plugged this also causes this.To determine if this is the cause here an exhaust back pressure test needs done with an exhaust back pressure tester.The tester threads into the pre catalytic converter oxygen sensor port and the engine is ran at idle to wide open throttle.If the back pressure exceeds 1.5 psi at any rpm range then the catalytic converter needs replaced.

I would have these tested as one will be the issue here.I have seen the catalytic converter plug on this model before and had to replace it.You can usually rent the back pressure tester and fuel pressure test gauge from a local parts store to test this here.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

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