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bought my car with a p0300 code and later on came a p0171 and a p0174 code
i’ve replaced a few things and done some test and not sure what the problem is
Parts i’ve changed on car
-spark plugs & wires
-coil packs
-fuel pump
-camshaft sensor
-map sensor
-maf sensor
-no vaccum leak after smoking car
-compression test was good on one side of engine
-fuel pressure is good
-catalytic converters are good
-used can of seafoam & lucas upper cylinder lubricant
-battery is good
•misfires only at idle , not under load
•hesitates under acceleration when going slow sometimes
•traction control light comes on when idling and goes away once driving
•car doesn’t overheat when driving
•feel no loss of power
•oil cap is not milky
any suggestions on what to do next ? thinking of just taking it to the dealership at this point
You didn't mention a new air filter, so I would do that. Then, check out your oxygen sensors. I use the Torque app on my Android phone. It has a feature called test results, which shows many important parameters, including oxygen sensors.
bought my car with a p0300 code and later on came a p0171 and a p0174 code
i’ve replaced a few things and done some test and not sure what the problem is
Parts i’ve changed on car
-spark plugs & wires
-coil packs
-fuel pump
-camshaft sensor
-map sensor
-maf sensor
-no vaccum leak after smoking car
-compression test was good on one side of engine
-fuel pressure is good
-catalytic converters are good
-used can of seafoam & lucas upper cylinder lubricant
-battery is good
•misfires only at idle , not under load
•hesitates under acceleration when going slow sometimes
•traction control light comes on when idling and goes away once driving
•car doesn’t overheat when driving
•feel no loss of power
•oil cap is not milky
any suggestions on what to do next ? thinking of just taking it to the dealership at this point
WELCOME to the Forum…my FIRST suggestion is DON’T take the car to a dealership for a diagnosis…THEY ARE CLUELESS !!…if you need help take the car to a diagnostic shop…you really fired the parts canon on this one…for a P0171 and 0174 I’ll look at fuel trims first…I’ll be looking at MAF in grams/second (should be roughly the liter displacement of the engine), MAP (should be around 9.4-9.5 in Hg at idle)
, fuel trims, O2 sensors…you said fuel pressure is good…WHAT ABOUT FUEL VOLUME ??…if long terms fuel trims are elevated I run the car at 3000 RPM…if short terms quickly correct (go negative) and long terms slowly decrease you have a vacuum leak…if fuel trims elevate you have a fuel delivery or MAF issue…what cylinders are misfiring ??…now you changed a bunch of parts but did you check them electrically…before I suspect a sensor I check the wiring…power, ground and signal…let us know what your fuel trims are doing first and we can go from there.
okay update !
p0171 and p0174 went away after changing the maf sensor ( had to drive it around a bit and it went away)
so now i just have the p0300 code
a shop that i took it to for the fuel pump did say it was a hard misfire and they told me to rebuild the heads / replace cam / lifters
was hoping it’s something else before i spend a bunch of $$ on that
You didn't mention a new air filter, so I would do that. Then, check out your oxygen sensors. I use the Torque app on my Android phone. It has a feature called test results, which shows many important parameters, including oxygen sensors.
forgot to mention previous owner did put new o2 sensors
and i also did replace the air filter because it was all nasty
okay update !
p0171 and p0174 went away after changing the maf sensor ( had to drive it around a bit and it went away)
so now i just have the p0300 code
a shop that i took it to for the fuel pump did say it was a hard misfire and they told me to rebuild the heads / replace cam / lifters
was hoping it’s something else before i spend a bunch of $$ on that
What EVIDENCE did they have to come to the conclusion it’s a head, cam, lifter issue or is this only a GUESS…what cylinders are misfiring ??…I use a scope and in cylinder pressure analysis to confirm these kinds of driveability issues…I don’t have to do any engine disassembly to confirm this…if they didn’t they don’t have any idea what your issue is !!…like I said find yourself a diagnostic shop…where are you located ??
What EVIDENCE did they have to come to the conclusion it’s a head, cam, lifter issue or is this only a GUESS…what cylinders are misfiring ??…I use a scope and in cylinder pressure analysis to confirm these kinds of driveability issues…I don’t have to do any engine disassembly to confirm this…if they didn’t they don’t have any idea what your issue is !!…like I said find yourself a diagnostic shop…where are you located ??
all of the cylinders are misfiring i saw on one of my friends snap on scanners and the shop also confirmed that they all are
that shop was the place where they did some of the testing like the vaccum leak / compression test.
i’m located in san jose CA.
ALL the cylinders are misfiring???…do you actually feel the misfires ??…if all cylinders were misfiring it would be running like S**T !!…a bad crank sensor can cause this since it is the ECM’s misfire “monitor”…when you changed the crank sensor did you do a crankshaft variation relearn ??…sorry but I don’t know any diagnostic shops in that area…dude, I’d call around and see if any shops do in cylinder analysis…they will know in 10 minutes if you have a mechanical issue without you having to spend thousands of dollars in ANY engine disassembly…this is what an in cylinder waveform looks like on my 01…doesn’t look like much but it shows me a lot of info.
ALL the cylinders are misfiring???…do you actually feel the misfires ??…if all cylinders were misfiring it would be running like S**T !!…a bad crank sensor can cause this since it is the ECM’s misfire “monitor”…when you changed the crank sensor did you do a crankshaft variation relearn ??…sorry but I don’t know any diagnostic shops in that area…dude, I’d call around and see if any shops do in cylinder analysis…they will know in 10 minutes if you have a mechanical issue without you having to spend thousands of dollars in ANY engine disassembly…this is what an in cylinder waveform looks like on my 01…doesn’t look like much but it shows me a lot of info.
i only feel the misfiring at idle because it’s a bit rough,i can hear it a bit…but it starts up every time just fine and drives normal. i feel 0 loss of power which i also find unusual since all cylinders are misfiring.
i changed the camshaft sensor but i haven’t changed the crankshaft sensor… maybe i should change that ?
but i’ll definitely call around and get that cylinder test done
i only feel the misfiring at idle because it’s a bit rough,i can hear it a bit…but it starts up every time just fine and drives normal. i feel 0 loss of power which i also find unusual since all cylinders are misfiring.
i changed the camshaft sensor but i haven’t changed the crankshaft sensor… maybe i should change that ?
but i’ll definitely call around and get that cylinder test done
Can you confirm that you don't have any exhaust leaks around the front o2 sensors (where the exhaust meets the manifold, it tends to leak)?
Is there any way you can find out if the previous owners installed an aftermarket camshaft?
Anything more aggressive than stock will trip misfire codes even if it isn't truly misfiring. Also, it's possible that if it does have a swapped cam, the tune hasn't been compensated for hence the lean codes on both banks. Many possibilities here, see what you can find out from the previous owners as far as modifications.
i only feel the misfiring at idle because it’s a bit rough,i can hear it a bit…but it starts up every time just fine and drives normal. i feel 0 loss of power which i also find unusual since all cylinders are misfiring.
i changed the camshaft sensor but i haven’t changed the crankshaft sensor… maybe i should change that ?
but i’ll definitely call around and get that cylinder test done
A bad crank sensor can cause the car to run rough and throw misfire codes…yes, I see that sensor wasn’t changed but I thought it was and use an OEM sensor…find a shop that can test it instead of shot gunning more parts…a scope is needed to test it properly.
How do you remove the physical sensor from the front of the engine. It will rotate but will not come out of the hole, Any help would be appreciated, I also do not know how to post a new thread. Thanks
P0300 Code on my 2008 Vette
