Engine bogs down

Asked by Aug 15, 2010 at 10:12 AM about the 1997 Subaru Legacy

Question type: Maintenance & Repair

I have a 97 Legacy, when friving the car after 3 or 4 miles, the engine bogs down, like one that has restricted exhaust. Mechanic has checked the back pressure, 1.2psi@2500rpm.Fuel pressure 28psiKoer volume 1pt in 10 seconds. When engine runs normally, fuel injector pulse width is 3ms @idle in park. Wehn engine bogs down, fuel injector pulse width on #1 & #2 injuctors is .5ms and #3  is 3ms @ idle. o2 sensor voltage is 0 Fuel pressure and volume are still ok. No change in any other sensor voltage while engine is bogging down. No engine DTC's stored.

2 Answers


a couple things come to mind, have you replaced all the filters yet (air, fuel, etc.)? another possibility is that the rings on your pistons or even just 1 piston are bad causing bad compression, the last thing that pops into my mind is that the rod bearings could be sticking from lack of lubrication caused by a bad oiling system or sludge in your oil. Now I don't know what all test have been run for sure because I don't know how you can simulate the conditions of driving with a load on the motor whil runing tests upon these systems you listed but I hope this helps.


Where are you reading fuel pressure at? Hopefully at the rails. Still sounds like a fuel filter is most likely culprit, or some other problem with the fuel system. Hell, I've had the exact same symptoms from getting bad gas, which is happening a lot more often nowadays. May even be an injector issue and sure you can check pulse width but thats just the electrical input, one may still be sticking or something. I would make sure fuel delivery is on par and find a way to test Air/Fuel ratio, find a quickie wideband tester or something :). Gotta remember, it IS a 12 year old car.

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