Losing Power When Accelerating

[BOB4254]

My 1998 Exp 5.4L, will accelerate to 2000 RPM. Then when I floor it engine bog's down. When I let up on the gas pedal half way, engine accelerates and takes off as long as I keep her around 2000 RPM. No miss firers. New plugs, coils and wires. New fuel pump. Cleaned MAF. Getting Codes P0171 & P0174. 1998 Ford Expedition 5.4L, 130k miles.


Fuel filter changed 20k miles ago. Fuel Pressure at rail = 29

Feels like she's not getting the fuel she requires when accelerating bogs down.

Installed new Fuel Pressure Regulator. Condition did not improve.

Something very interesting someone may have an answer to. I installed a new fuel filter. OMG she accelerated like she did when she was new. I thought my acceleration problem was solved. Next day I started her she started fine and idles smooth and quiet.

Took her for a spin and now she when back to very poor acceleration. Same problem I had.

(will accelerate to 2000 RPM. Then when I floor it engine bog's down. When I let up on the gas pedal half way, engine accelerates and takes off as long as I keep her around 2000 RPM).

I'm thinking to install new MAF Sensor.

Any advice. Very confused at this point.

 

[TM_Bob]

Any codes suggesting low fuel pressure? Sounds like this could be dirty fuel with solid particulates in it. If you change the fuel filter again, does this repeat itself with good performance then the bogging down comes back again? If so, check the fuel ahead of the filter to see if it is normal

 

[BOB4254]

No low fuel pressure codes. When installing new Bosch fuel pump I noticed solid particles in the fuel and brown dirt on the bottom of the tank.

I have always maintained a locking gas cap so I know the contaminates came from the Shell gas station.

I only drive 50 miles per week so 3 years ago I decided to start using the Shell Nitro.

Shortly after that is when the acceleration issue started.

I did change out the fuel filter and she ran great for one day then back to the same issue of poor acceleration.

Washed out the tank, it is perfectly clean now.

Going to install tank with new filter and fuel pump today 09/30/2024.

Will let you know the results.

I'm really disappointment in Shell Nitro Gasoline.

I'm think that not that many people buy the Shell Nitro because of price so it sits in it's tank with sentiments settling into the suction value and up into a consumers gas tank like me. May post a video of the contaminated Shell Nitro gas.

 

[Hamfisted]

I would recommend a smoke test on the intake system. The codes are both banks running lean. Which generally means a vacuum leak. If you have a can of starting fluid you can spray that around the intake too and listen for rpm increases or the sound of sucking air. The common culprits are the rubber hose adapter on the back of the intake manifold and the elbow on the PVC valve. But there may be others.






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[BOB4254]

I installed a new Bosch fuel pump which solved the no acceleration issue.

She runs like the day I bought her brand new in 1998.

I did not install a new fuel filter as I installed a new fuel filter four weeks ago.

When Mechanical fuel pumps fail, they only fail, car will not start.

Electric fuel pumps can become weak before they fail.

Weak = not able to supply the fuel required for acceleration.