P0308, cylinder 8 misfire help
08-27-2013, 08:02 PM
#1
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P0308, cylinder 8 misfire help Ok 98 camaro SS 6 speed, full suspension, muffker delete so straight piped, new volant twin filter intake kit, new ls7 lifters, tsp performance pushrods, new gm gaskets n bolt kit, new spark plugs, msd wires, 96k miles...
I got a misfire in cylinder 8, i got new plugs, i switched the coils and the wire to cylinder 1 n still misfire cyl 8, cant find the problem help
I got a misfire in cylinder 8, i got new plugs, i switched the coils and the wire to cylinder 1 n still misfire cyl 8, cant find the problem help
08-28-2013, 12:37 AM
#2
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Does coil #8 connector receive the fire pulse from the PCM...?
Does injector #8 connector receive the fire pulse from the PCM...?
Swap injector #8 with another and see if misfire follows or stays.
Does injector #8 connector receive the fire pulse from the PCM...?
Swap injector #8 with another and see if misfire follows or stays.
08-28-2013, 07:50 AM
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The misfire happened right after you installed all the mods?
watch data stream on scan tool and see what long and short term fuel trim look like.
if numbers are high, its a lean mis= fuel injector issue or vacuum leak
if low its a rich mis= no spark and fuel being unburned.
after you figure out if its the fuel side or ignition side,
you can zero in on where the problem might be.
DON'T RULE OUT BENT PUSH ROD OR BROKEN ROCKER/VALVE SPRING.
watch data stream on scan tool and see what long and short term fuel trim look like.
if numbers are high, its a lean mis= fuel injector issue or vacuum leak
if low its a rich mis= no spark and fuel being unburned.
after you figure out if its the fuel side or ignition side,
you can zero in on where the problem might be.
DON'T RULE OUT BENT PUSH ROD OR BROKEN ROCKER/VALVE SPRING.
08-28-2013, 11:08 AM
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Code goes away n comes back, if i do a wot pull it comes back for a couple hours, then goes away, sounds like i got a lil tiny exhaust leak, the long fuel trim is 4.6 n the short is -0.7, i got freeze frame data here wat else do i look at? I blew a shift so im trying to replace full valvetrain
08-28-2013, 03:03 PM
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those trim numbers tell me its a ignition misfire.
when you watch the live data, do all the O2 sensors
voltages move up and down like they should?
fronts should be constantly bouncing. rears hold steadier.
if you can watch and misfire count, see if the mis goes away
if you hold RPM at 2500,
if it does then maybe you folded a intake gasket putting on
intake mani.
can you feel the misfire at idle if you just put your hand on engine?
looking at freeze frame does it happen when engine is cold or hot?
when you watch the live data, do all the O2 sensors
voltages move up and down like they should?
fronts should be constantly bouncing. rears hold steadier.
if you can watch and misfire count, see if the mis goes away
if you hold RPM at 2500,
if it does then maybe you folded a intake gasket putting on
intake mani.
can you feel the misfire at idle if you just put your hand on engine?
looking at freeze frame does it happen when engine is cold or hot?
08-28-2013, 06:30 PM
#6
Ok 98 camaro SS 6 speed, full suspension, muffker delete so straight piped, new volant twin filter intake kit, new ls7 lifters, tsp performance pushrods, new gm gaskets n bolt kit, new spark plugs, msd wires, 96k miles...
I got a misfire in cylinder 8, i got new plugs, i switched the coils and the wire to cylinder 1 n still misfire cyl 8, cant find the problem help
I got a misfire in cylinder 8, i got new plugs, i switched the coils and the wire to cylinder 1 n still misfire cyl 8, cant find the problem help
08-28-2013, 10:32 PM
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P0308 came back, after work i saw a lincoln ls v8 n it was cocky, so i smashed out n rapped it, i had the ses light on car shaky mussfiring i even heard a lil tick maybe exhaust leak idk, but after i smashed it went away n car runs so beautiful i might shed a tear drop, but can anyone explain that?
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08-29-2013, 03:41 AM
#9
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The misfire happened right after you installed all the mods?
watch data stream on scan tool and see what long and short term fuel trim look like.
if numbers are high, its a lean mis= fuel injector issue or vacuum leak
if low its a rich mis= no spark and fuel being unburned.
after you figure out if its the fuel side or ignition side,
you can zero in on where the problem might be.
DON'T RULE OUT BENT PUSH ROD OR BROKEN ROCKER/VALVE SPRING.
watch data stream on scan tool and see what long and short term fuel trim look like.
if numbers are high, its a lean mis= fuel injector issue or vacuum leak
if low its a rich mis= no spark and fuel being unburned.
after you figure out if its the fuel side or ignition side,
you can zero in on where the problem might be.
DON'T RULE OUT BENT PUSH ROD OR BROKEN ROCKER/VALVE SPRING.
08-29-2013, 08:42 AM
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A O2 sensor does not detect "unburnt oxygen"
that's not really possible,
it looks at how much unburnt fuel is in passing thru exhaust
by measuring the amount of oxygen compared to fuel unburnt.
more unmetered air in engine will give you high trim numbers.
less, from fuel not being burned by ignition fault will give lower trim numbers.
but if he fixed it by ripping it thru some gears, then none of this matters. lol
08-29-2013, 09:35 AM
#11
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( a no-burn/misfire is different than a rich burn... a no-burn has excess oxygen in the exhaust, a rich burn has very little oxygen )
When there is unburnt fuel, the O2 sensor sees the excess air and shows lean (low voltage), and the trims peg high positive (adding more fuel), and the O2 sensor continues showing lean... (and the cat glows red hot).
08-29-2013, 11:25 AM
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Do not rule out a fuel injector problem, those back
ones (really, any end-of-rail position, but back seems
worst) get to keep all the line silt and will crust up
first. You'll see this as short fuel. Swap with #6 to
see.
An overgapped plug is another way to get high-MAP
misfiring, unable to overcome the higher breakover
voltage when cylinder pressure is high. This condition
also exposes any insulation weakness in the wire and
coil, where the spark energy goes when the plug is
being uncooperative.
ones (really, any end-of-rail position, but back seems
worst) get to keep all the line silt and will crust up
first. You'll see this as short fuel. Swap with #6 to
see.
An overgapped plug is another way to get high-MAP
misfiring, unable to overcome the higher breakover
voltage when cylinder pressure is high. This condition
also exposes any insulation weakness in the wire and
coil, where the spark energy goes when the plug is
being uncooperative.
08-29-2013, 02:51 PM
#13
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No... oxygen sensor sees oxygen, not fuel... it determines the exhaust oxygen content by comparing it to outside air
( a no-burn/misfire is different than a rich burn... a no-burn has excess oxygen in the exhaust, a rich burn has very little oxygen )
When there is unburnt fuel, the O2 sensor sees the excess air and shows lean (low voltage), and the trims peg high positive (adding more fuel), and the O2 sensor continues showing lean... (and the cat glows red hot).
( a no-burn/misfire is different than a rich burn... a no-burn has excess oxygen in the exhaust, a rich burn has very little oxygen )
When there is unburnt fuel, the O2 sensor sees the excess air and shows lean (low voltage), and the trims peg high positive (adding more fuel), and the O2 sensor continues showing lean... (and the cat glows red hot).
