Hesitation at low RPM and acceleration

PRESTONN83

MEMBER
2002 FORD F-150
4.6L
V8
4WD
AUTOMATIC
278,000 MILES

I've put all new coils, plugs, crank sensor, TPS, and camshaft sensor idle air control valve. New PCV valve new vacuum lines. I've probably put $1,500.00 in new parts. When I first take off it feels like it's starving for fuel but once the rpm's get to 3,000 and up it runs fine. Once I'm up to 55 to 60 mph it does good unless I put it in overdrive then it starts stumbling again, but turn off the overdrive it's fine. Also if I I shift it manually once it hits 4,000 rpm's it's like a turbo kicks in. Any advice? Please help. Thanks, Preston

1 Reply

JACOBANDNICKOLAS

MECHANIC
109,758 POSTS

Have you confirmed fuel pressure is within spec? I ask because there could be a fuel regulator issue producing too much pressure and causing a low RPM issue that goes away at higher RPM's.

If you haven't, lets start there. Here is a link that shows in general how it's done:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

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Here are the manufacturer's specs for pressure:

2002 Ford Truck F 150 4WD Pickup V8-4.6L
Standard Models (Non BI-Fuel)
Vehicle Powertrain Management Fuel Delivery and Air Induction Fuel Pump Fuel Pressure Specifications Pressure, Vacuum and Temperature Standard Models (Non BI-Fuel)
STANDARD MODELS (NON BI-FUEL)
Item .................... Specification

Fuel Pressure
Engine Running .................... 193-310 kPa (28-50 psi)
Key On Engine Off .................... 240-310 kPa (35-45 psi)
Flow Rate .................... 19 lbs/hr
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Another thought is the catalytic may be partially plugged. Take a look through these two links and let me know if the symptoms seem to mirror what you experience.

https://www.2carpros.com/articles/bad-catalytic-converter-symptoms

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

Also, if there are any diagnostic trouble codes stored, let me know them as well.

Take care,
Joe