n8t50 Posted July 28, 2019 Report Share Posted July 28, 2019 Hi folks, looking for some help with a misfire/sputter on a 1998 V70 N/A (537xxxkm). Car was throwing some codes for the rear O2 sensor, but wasn't doing anything funny. Coming back from a camping trip, it started to misfire/sputter while cruising at 100km/h in 5th gear. It then started stalling out while at idle. I replaced the rear sensor, and shortly after, it started to throw codes for the front O2 sensor (slow response, and lean mixture), and do the same thing. It is fine on startup, but sometimes will have little fits of stalling at idle, and sputtering/missing when accelerating/cruising. When it would stall, I used to be able to get it too restart on the first try, but now it usually takes 2-4 cycles of the ignition to get it to catch. Once I give it some gas and take off, it improves a little, and just seems to lack a little power. When at idle, you can also smell the exhaust, which normally is very clean. Today I replaced the front O2 sensor. The car ran well for 30min, then threw the same codes, and started acting up again. I've tested the PCV and the compression, and both are fine. The spark plugs are new, but the rest of the ignition system (Coils, leads, rotor) are older. I'm thinking this sounds like either an ignition system problem, or a fuel system. I'm not sure how to run the normal relay test, because it it is really intermittent with its sputtering/stalling. (Currently there seems to be about a 50/50 chance of it being fine, or acting up when I take it out) I'm probably going to redo the ignition system, because the car needs it anyways, but am wondering what else this could be. Thanks guys! Link to comment Share on other sites More sharing options...
gdog Posted July 29, 2019 Report Share Posted July 29, 2019 Could be a lot of things, but I'd check fuel pressure first. You may need to drive around with a fuel pressure gauge hooked up to the fuel rail until you hit this failure mode again, so you can check the pressure when it's happening. The stock fuel pump is typically good for 140-200K miles so this car is likely on its 2nd one. Maybe the last one was installed poorly or it's lousy quality? If you are losing fuel pressure, it could also be the fuel pump relay under the hood (another common failure point). Again, this is all speculation until you find that the fuel pressure does indeed drop when this happens. What are your actual codes? Link to comment Share on other sites More sharing options...
bmdubya1198 Posted July 29, 2019 Report Share Posted July 29, 2019 Unplug the MAF (NOT while the car is running) and see if anything changes. That could definitely cause issues like this. It would also make sense after changing the O2 sensor that it was fine for about 30 minutes, then it adapted and starting running poorly again. Check the codes again and post them. Link to comment Share on other sites More sharing options...
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