misfire code on fast deacceleration
Slow down slower.
1 Like
Highly unlikely. No gas going into the engine when compression braking, nothing to fire.
How many gears are you downshifting?
How many RPMs is your engine turning when this noise happens?
On an old Volvo, use the brakes rather than downshifting for fast deceleration. The XC70 is an urban grocery getter, not a race car.
1 Like
On my Corolla, all of the fuel injectors are turned off immediately after foot is removed from gas pedal. I’m wondering if OP’s problem is one or more of the injectors aren’t turning off for some reason? Leaking injector is one possibility. Another possibility is OP’s foot is (inadvertently) still slightly pressing gas pedal. Yet another idea, injectors turn off ok when foot removed from gas pedal, but are turning on too soon. They have to turn on before engine rpm gets to the point the engine stalls.
Good advice above for work a rounds.
What prevents the engine from stalling out?
Tester
1 Like
See post above. I generally slow down when approaching stop light using engine braking in 3rd gear, and can feel them turn back on again maybe 30 feet before reaching the stop light.
Wouldn’t that be the same as running out of gas?
Tester
Yes, if they didn’t turn back on again. Wondering how there could be a misfire with no gasoline being injected?
Did you play with the tuning or exhaust? Since it’s an XC70 I’m guessing that you didn’t, but it’s worth asking. If the timing is advanced far enough the engine will detonate on deceleration due to fuel detonation in the exhaust system.
So, when I press on brake, fuel is cutoff, completely? But, when I come to stop, the fuel comes on so motor won’t die ?
Must be very interesting driving where there are lots of hills, much less the Mountains… I guess the engine can hold it’s breath for miles at a time…
Not to mention going down a long mountain grade with curves with no vacuum to the brake booster and no power steering because the engine isn’t running because the injectors shut off.
Tester
I can’t speak to OP’s car’s drivetrain computer algorithm, no experience; but my 30 year old Corolla (with M/T) shuts off the injectors when decelerating in gear and throttle position sensor indicates idle position. It bases its decision on when to turn them off & then turn them back on again presumably on its knowledge of the engine rpm, the vehicle speed, and the throttle position. IIRC this was discussed by Ray on the radio program.
Crankshaft rotation is what produces engine vacuum. Every make/model/year/configuration is different. Wouldn’t some cars produce vacuum going downhill even with injectors shut off?
1 Like
High vacuum. Some old cars will draw oil through worn valve guides while descending a grade, then when the throttle is opened there is a discharge of smoke from the tail pipe.
1 Like
Yup, my car has an option to display a boost/vacuum gauge, foot off the accelerator pedal, vacuum goes up, it I down shift for compression braking, vacuum goes way up. If the injectors are completely shut off, I don’t know nor care.
On vehicles with mechanically linked carburetors, of course the butterfly was always open a tiny bit due to the idle screw setting.