Hi all i have a 99 cavalier and its stumbling really bad thru out the power band... i wanna say its the fuel pump.. But hoping its not. If so it is required to drop the tank correct? its throwing 2 codes system too lean and random multiple cylinder misfire. I'm gonna try changing the fuel filter and while having the line open try and check the pressure.. Any thing else you guys think it could be? is there a way to set the fuel pump into high mode? or is there a fuel pump resistor that can go bad?? Thanks in advance guys

Alright firsts thing first.

You have two DTC one for running lean and PO300 muiltiple cylinder misfire.

So to lean, not enough fuel, or to much air.

Lets assume not enough fuel.

Reasons for not enough fuel.

- plugged fuel filter
- plugged fuel line
- plugged fuel injectors
- fuel pump weak

Now on some cars, I dont know about yours. The fuel pump is controlled by how much voltage its gets, more voltage it work harder, and low voltage works less, this is done using a resistor.

But you said its stumbling throughout the powerband, so I can assume its working correctly,

The first thing I'd do is check fuel pressure, key on engine off, key on engine running, check fuel pump volume as well.

If the pressure is lower, it can be a ton of things.

clogged filter, clogged lines is the main two

if the filter is old change it, see if it brings the pressure back up

A clogged filter overtime will kill the pump because it must work harder to pump fuel through

the multiple cylinder misfire might be fuel related, it may not

good luck






- 2004 Cavalier - 124k, owned since new

alright is it possible the IAC could be causing it? as i unplugged it and it seemed to run fine... i plugged it back in began the nonsense again... I changed plugs/wires(needed it anyways) also fuel filter disconnected fuel line seems to have plenty of pressure can barely hold my finger over the end volume seemed to be good.. so i'm hoping IAC no code tho