howards11 Posted June 24, 2009 Share Posted June 24, 2009 My 2000 Forester hesitates and then backfires periodically. The problem seems to worsen as the gas level declines. THERE ARE NO CODES being generated. I have an appointment with local dealer as my regular mechanic has given up. There is 71K on the car. The fuel cap, fuel filter and air filter have been replaced but have had no effect on the problem. I tried various "fuel system cleaners" and that hasn't helped either. I suggested to the service adviser about updating the ECU but he poo pooed that idea. The service adviser is already talking about 2 hrs of diagnostic time which he said would be about $200. Does anyone have any suggestions? Thanks in advance for your help. ~Howard Link to comment Share on other sites More sharing options...
nipper Posted June 24, 2009 Share Posted June 24, 2009 whenever this happens, you have to start with a tuneup. This rules out plugs and wires and clogged filters. Backfire could be a vac leak, a extra lean condition, leaking valve, leaking injector. nipper Link to comment Share on other sites More sharing options...
CNY_Dave Posted June 24, 2009 Share Posted June 24, 2009 Ka-bang out the tail-pipe, or ka-thump out the intake? Dave Link to comment Share on other sites More sharing options...
OB99W Posted June 24, 2009 Share Posted June 24, 2009 Ka-bang out the tail-pipe, or ka-thump out the intake? I believe we're talking afterfire (cat/muffler), not backfire (intake). There was a previous thread that should be referenced: http://www.ultimatesubaru.org/forum/showthread.php?t=98943 With respect to that thread, depending on exact conditions, the EVAP system can produce a slight vacuum in the fuel tank when the engine is running. However, if the engine is shut down (as for refueling) there shouldn't be a noticable vacuum when the gas cap is removed. Cougar gave some hints to diagnosing that condition in the other thread, and it makes sense to follow up on it. It's certainly possible for an EVAP/vent problem to develop that hasn't (as yet?) triggered a code. Link to comment Share on other sites More sharing options...
tcspeer Posted June 24, 2009 Share Posted June 24, 2009 My high mileage Subaru backfired on me once, and the problem was the coil pact. A few years latter I had a cly. misfire code which also turned out to be the coil pact, but the second time they was no backfire. The coil pact is very easy to check with a meter and Haynes manual. Link to comment Share on other sites More sharing options...
howards11 Posted June 25, 2009 Author Share Posted June 25, 2009 My high mileage Subaru backfired on me once, and the problem was the coil pact. A few years latter I had a cly. misfire code which also turned out to be the coil pact, but the second time they was no backfire. The coil pact is very easy to check with a meter and Haynes manual. Coil pack and plug wires were replaced last July. ~Howard Link to comment Share on other sites More sharing options...
howards11 Posted June 30, 2009 Author Share Posted June 30, 2009 I took the Forester back to a local dealer. It seems I had 2 loose plugs and 4 fouled with oil. Plus one of the O2 sensors was bad (out of range error). The plugs were replaced and the O2 sensor was replaced under warranty. The O2 sensors were replaced along with the cat back in Nov 2008. The parts warranty for Subaru is 1 year. All is now OK and the Forester is running like new. ~Howard Link to comment Share on other sites More sharing options...
Olnick Posted June 30, 2009 Share Posted June 30, 2009 All is now OK and the Forester is running like new. ~Howard Congrats! Here's to years of happy driving for you. And thanks for letting us know how it resolved. Link to comment Share on other sites More sharing options...
Cougar Posted July 1, 2009 Share Posted July 1, 2009 Thanks for the update Howard and glad you got it fixed. It seems kind of strange these problems weren't caught earlier. Link to comment Share on other sites More sharing options...
howards11 Posted July 1, 2009 Author Share Posted July 1, 2009 Thanks for the update Howard and glad you got it fixed. It seems kind of strange these problems weren't caught earlier. COUGAR: I don't understand why the problem with the O2 sensor did not generate a code. I can't figure out how 2 plugs were loose. But the car runs like new so I'm glad everything has been resolved. ~Howard Link to comment Share on other sites More sharing options...
Cougar Posted July 1, 2009 Share Posted July 1, 2009 I would guess the plugs were not tightened enough when they were worked on last. As for the O2 sensor they can degrade over time and that will not cause a code to be set. Link to comment Share on other sites More sharing options...
nipper Posted July 1, 2009 Share Posted July 1, 2009 Lazy O2 snesors wont always throw codes, they are working just slow to respond. Loose plugs, you are so lucky they were caught. usually a loose plug sint found untill a loud PING followed by a loss of power is discovered. The plugs come flying out and take the threads with them. It is rare but it happens from time to time. nipper Link to comment Share on other sites More sharing options...
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