I have a 1999 F-150 5.4 Lariat 4X4. When declerating, when I get between 45-55 mph it loses power or fuel then picks back up when applying the pedal. Could this be a throttle sensor problem or fuel pump problem? I replaced the fuel pump about 8 months ago (20,000 miles). Note: This problem only seems to occur when it has been driven a while at 55+ mph
Cars & Trucks - Ford - F-150
Answers & Comments
Possible carbon buildup on valves causing deceleration stall .
I hope you get some additional comments for this. I have the identical truck. Could be a vacuum problem as the vacuum brake booster is connected to the other systems through vacuum sensors. Most of things electric would throw a code.
Sometimes when a fuel pump is changed you have pressure adjustments to make. Fuel pressure is also controlled by the crankshaft sensor which sets pressure based on reading RPM.
The 1999 model has a defect in the fuel filler tube going into the rubber filler hose under the truck. Eventually it will throw a emissions code. Could be it is not bad enough to throw a code yet, but still leaking.
Thinking about the problem at 55mph there is a steady vacuum until you hit the brake pedal booster. Then vacuum changes and it makes things worse. A vacuum gauge could show activity.