Bucking

BRODEUR

MEMBER
1998 SUBARU FORESTER
143,000 MILES

Not sure if this is a problem specific to Subaru...

I just bought a 1998 Forester from a trusted local garage. 143,000 on the car, 90, 000 on the engine.
It bucks like it's running out of gas or is starving for gas.
First time he tried to fix it said it was old gas and we put some gas treatment in it.
Ran fine for a little while (50 miles) then bucked so bad I wasn’t sure I’d get home.
After it sat for a day I was able to drive it to the garage no problem.
That time he said it was gunk in the gas tank blocking the filter. The gunk would get stirred up sometimes if I took a corner etc.
He stirred up the gas and siphoned it out and ran it through a fine filter (twice).
Ran fine for about 60 miles, then started bucking again, although not as bad as previous.
He’s a Subaru specialist and had to fix a couple of things but can’t seem to correct this one.
Starts fine. Idles fine.
Also after his last “fix” I used almost half a tank of gas to go 75 miles.
ANY ideas?

Much appreciated
Tom

3 Replies

DRCRANKNWRENCH

MECHANIC
3,380 POSTS

There could be a few things causing this problem;
Blockage in the air intake tract.
Blockage in the exhaust tract. This is common amongst cars that have sat as the catalytic converters fall apart and crumle in on themselves and clog the exhaust. Since your gas mileage is bad this makes me think this is high on the probability chart. When there is an exhaust leak near an Oxygen sensor, it will decrease the fuel efficiency dramatically.
The fuel filter, if applicable, may need to be changed.
The fuel injectors may be clogged and cleaning them can be tough. They a can or 2 of SEA FOAM or BG44K.
Depending on how much gas it was pput away with, gas turns into varnish in a month or two, you may need to drain tank and change out gas.
The fuel pressure may be low and needs to be checked.
Have the trouble codes pulled. Any Advance aAuto or Auto Zone will do this for free. They also carry fuel pressure test kits on a loaner basis.