Vehicle Losing Power When Accelerating

BOB4254 · Sep 8, 2024

Thanks Billme. I will test the throttle position sensor per the info you sent me.

Just finished checking the MAF sensor. Back probed the signal line. Voltage increased as throttle increased as it should. No erratic voltage spikes up or down. When engine is running and you unplug MAF sensor she should stall out indicating MAF sensor is working. If no stall out MAF sensor is bad.

My MAF sensor checks out to be working properly. Save $75.00 by not buying a new one.

Will now test the throttle position sensor. will let you know.

Thanks Billme

DougJens90 · Sep 10, 2024

I’ve got the same issue right now. With in the last 2 weeks I’ve changed out the fuel pump, fuel filter, fuel pressure regulator, throttle position sensor, EGR valve, idle air control valve, fuel tank filler neck (old one was rusted out), and spark plugs. The issue you’re describing is what is now happening after I tried all of these parts. Before, the truck would idle good but would bog down and die as I drove down the road. Mainly accelerating. With my OBD2 scanner plugged in and looking at live data, I noticed that the bank 1 sensor 2 (B1S2) O2 sensor was sitting at 99.7 while the other 3 were fluctuating as they should. Tried to remove it today but could not. Also noticed a ton of seams rusted out on one of the larger cats and a decent sized hole on one of the smaller ones. Any way could a bad O2 sensor could cause this issue OR someone at work told me that it could be a possible plugged up exhaust system and recommended that I punch out all of the cats. Suggestions?

DougJens90 · Sep 10, 2024

I apologize if I seem to be hijacking this thread. I am just lost on what to do and your having the same issue I am having. Hoping to find an answer!!

BOB4254 · Sep 11, 2024

Hi there, what a mystery of the the Expedition acceleration issue.

I have also thought about removing the cats and replacing with straight pipes. Not sure how the 02 sensors are adjusted.

My issue, 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.

DougJens90 · Sep 11, 2024

After hours of digging last night online, I came across something that I am going to try. Someone has had similar issues and he replaced the 2 camshaft position sensors and the crankshaft position sensor. I did some research on the symptoms of these sensors, if they were failing or had failed, and I believe that it is worth a shot. Ordered mine this morning and they should be here Friday sometime. Something to check out!!

johnhardrock · Sep 11, 2024

BOB4254 said:
Fuel filter changed 20k miles ago. Pressure at rail = 29

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

Could it be a bad Fuel Pressure Regulator???

Very smooth and quiet idle.

I have a fuel pressure gauge on my 2003 expedition and it reads ~50psi at idle. I can’t see it during driving because it’s in the engine compartment. But yours sounds low to me.

DougJens90 · Sep 11, 2024

Looking at those codes, I’d try cleaning the Mass airflow sensor. One of the easier things to do. AND make sure your air filter is not plugged up. If your MAF sensor is anything like mine, the tiny sensor wires can collect minute amounts of dust and throw off your sensors readings, causing the ECU to lean or richen the fuel being delivered to the motor.

johnhardrock · Sep 11, 2024

johnhardrock said:
I have a fuel pressure gauge on my 2003 expedition and it reads ~50psi at idle. I can’t see it during driving because it’s in the engine compartment. But yours sounds low to me.

I found a replacement pump at O’Reillys at 43.5 psi for your 98. Your pump has a problem I guess.

johnhardrock · Sep 11, 2024

BOB4254 said:
Hi there, what a mystery of the the Expedition acceleration issue.

I have also thought about removing the cats and replacing with straight pipes. Not sure how the 02 sensors are adjusted.

My issue, 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.

johnhardrock · Sep 11, 2024

I found a replacement pump at O’Reillys at 43.5 psi for your 98. Your pump has a problem I guess. 29 psi does not sound right

Vehicle Losing Power When Accelerating

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