I am working on this 2004 van for my sister… It will idle fine… when you drive you can get to 25 or so but wont go any faster even with foot to the floor… was thinking fuel filter but you have to buy the whole pump for this car? any other ideas before i start??
Put the transmission in neutral and try revving the engine. If the engine only hits 2-3k RPM and sounds sort of like a vacuum cleaner while doing it, you probably have an exhaust system restriction, likely a plugged catalytic converter. If these symptoms prove to be so, finalize your diagnosis by removing the upstream oxygen sensor or disconnecting the front pipe from the exhaust manifold and driving the van again. If it suddenly has better power and top speed, that proves the exhaust is plugged and you need to inspect the catalytic converter since that is most likely to cause a restriction that severe.
Check engine light on? Codes?
What results did you get from the steps that mark9207 suggested?
If you want help you’ll have to do better than that.
Mark’s advice is the place to start.
At 25mph with your foot to the floor what are the rpms? Is the van actually shifting gears or is it maybe stuck in 1 or 2?