'03 Forester Jerky Acceleration

[zakrak4]

Hello,
Hope a post like this isn't a bother. We are just looking for a little advice. Our usually very reliable 03 Forester has had issues with jerking when getting up to highway speeds. At times, it has a downright hard time getting up to speed, you can hear and feel it "chug chug chug"ing in an attempt to accelerate. Once highway speed is reached, the car is normal again. We just dropped $400 on getting the O2 sensors replaced, but that did absolutely nothing to fix it. Could it be something as serious as the fuel pump? The jerking is about all that goes wrong with it, additionally the "Check Engine" light flashes when the chugging is happening. Would appreciate any advice/ accounts of how similar problems were fixed.
Thanks so much,
Zach

[Caboobaroo]

You are killing the engine while running it with a flashing CEL. This means you have a cylinder not firing and should be looked into. I would start by checking the spark plugs, spark plug wires and coil pack terminals for arcing or corrosion. If they are good, drop the exhaust header off of the bottom of the heads and look into the exhaust ports for possible dropped valve guides. When one drops, it holds the valve open and the cylinder never compresses the air and fuel mixture.

[zakrak4]

You are killing the engine while running it with a flashing CEL. This means you have a cylinder not firing and should be looked into. I would start by checking the spark plugs, spark plug wires and coil pack terminals for arcing or corrosion. If they are good, drop the exhaust header off of the bottom of the heads and look into the exhaust ports for possible dropped valve guides. When one drops, it holds the valve open and the cylinder never compresses the air and fuel mixture.

 

Thanks for the response! The diagnoses of the flashing light helps narrow it down. We will check the spark plugs, though those aren't too old so we aren't too hopeful.

[nickb21]

Mileage? Like Caboo said, you can easily fry your catalytic converter by driving it around with a flashing CEL (probably other bad stuff as well).

 

If the wires haven't been replaced I would do that first thing. OEM (or NGK) brands only.

 

Also see what the codes stored from the CEL are - probably a specific cylinder misfire.

 

Do a little searching around the board - you can also diagnose misfires (caused by wires/coil pack) when it's a bit dark out by misting some water around the engine bay near the wires and coil pack.