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Roy
Roy, ASE Certified Technician
Category: Nissan
Satisfied Customers: 5451
Experience:  Nissan Master technician
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2003 nissan sentra se-r spec-: v 2.5L..during acceleration

Resolved Question:

2003 nissan sentra se-r spec-v 2.5L QR25DE. Fluttering and diminished performance during acceleration. Check engine code p0300, random misfire/multiple cylinders This only occurs when the car is hot and gets worse during acceleration as opposed to at idle. There is a smell in the cabin like the car is running rich, excessive fuel consuption is also a problem. Inspected vacuum hoses, could not find holes or leak. Found small oil in the air intake manifold which was coming from pcv line, replaced pcv valve with no increase in performance.
Submitted: 4 years ago.
Category: Nissan
Expert:  Roy replied 4 years ago.

Roy :

HI!

Customer :

hello

Roy :

I would start by checking the compression in cylinders , we have seen a few 2.5L engines with misfire from power valves in intake manifold screws coming loose and getting into cylinders

Customer :

wouldnt that occur when the engine is cold and at idle?

Roy :

they can bend valves or damage your pistons or just close gap on spark plugs

Customer :

the misfire is random

Customer :

that seems like a problem directed at a specific cylinder

Roy :

if you just have a misfire code and no other codes I would start with that the flaps can also block intake ports at times when loose in manifold

Customer :

only when hot?

Roy :

you only have a misfire code no other codes?

Customer :

only p0300

Roy :

OK!

Roy :

I would also use a scan tool and monitor fuel trim for a lean condition when hot

Customer :

thats it.....check the compression?

Roy :

I have seen some air flow meters not set a code but can cause a lean misfire when going bad

Roy :

the fuel trim if set high or running to lean can also be your problem

Roy :

I test drive with my scan tool attached and monitor sensors

Customer :

seems as though its running rich rather than lean

Customer :

excess fuel consumption and fuel smell in cabin

Roy :

are you getting any black smoke out tail pipe?

Customer :

not that i have noticed

Roy :

That is strange should smoke when rich and foul spark plugs black in color

Customer :

just changed the plugs, old ones were somewhat blackened

Roy :

one more thing to inspect is fuel pressure when misfires could be high or to low and cause a misfire

Customer :

but it only occurs when the car is hot

Customer :

sometimes it happens sometimes it doesnt

Customer :

sometimes it happens and goes away

Roy :

I test drive with a pressure gage attached and watch pressure it can be worse hot in closed loop from sensors

Customer :

and if it is?

Roy :

if pressure problem the pump could be going bad

Customer :

the fuel pump?

Roy :

yes if fuel pressure drops when misfiring under a load

Customer :

hello?

Roy :

if you re oiled your K&N filter this can amage air flow also from oil coating hot wire

Customer :

i re-oiled the filter in an attempt to fix the problem

Roy :

it will coat wire on air flow meter if not dry when installed

Roy :

just one more thing I have seen

Customer :

i cleaned the MAF with MAF cleaner

Roy :

ok good

Customer :

also let filter sit for 24 hours after oiling

Roy :

great I have seen people install them wet and coat air flow

Customer :

i read something about it possibly being the egr valve

Customer :

but my understanding is that the qr25de does not have one

Customer :

they use valve overlap instead

Roy :

I have seen EGR cause problems on trucks not your car

Roy :

your correct

Customer :

why would the pcv line pull oil into the intake manifold?

Customer :

im assuming thats not normal

Roy :

high vacuum or leaking valve cover could be cracked at pcv passage will suck oil into intake from top of engine are you losing oil also?

Customer :

yes

Customer :

also replaced valve cover gasket

Roy :

how much in 500 miles

Customer :

about 1qt since last oil change 2000 miles ago

Customer :

no visible oil leaks around engine

Roy :

thats not good , could have bad oil rings leaking int combustion chamber fouling plugs

Customer :

didnt find any oil in the spark plug tubes

Roy :

it will burn the oil

Roy :

if no leaks

Customer :

thats kind of what i was thinking

Roy :

sounds like it the 2.5L engine I have seen a few burn oil also

Customer :

if the tube seal was bad that would allow oil into the pcv line, the oil burning would then cause a misfire

Customer :

im guessing

Roy :

if oil in tube will cause a misfire but not a lot of oil

Roy :

you are not getting a qt. in oil tubes

Customer :

makes sense

Customer :

so where could this leak be?

Roy :

I would need to make some inspections to know for sure

Roy :

could be bad rings or valve seal we see more ring problems

Customer :

which rings?

Customer :

piston rings?

Roy :

piston oil rings

Customer :

assuming compression test would figure that out

Roy :

not always but should stat with that

Customer :

but why would it be a multiple/random misfire unless all rings went bad simultaneously

Roy :

oil can raise compression and foul plugs then burn off oil at time then refoul them

Customer :

seems like that would cause a one cylinder misfire if a piston oil ring was leaking

Roy :

it would cause a misfire in cylinder that has oil fouled spark plugs could be more then one plug also

Customer :

brand new plugs

Customer :

as in 2 days old

Roy :

ok if you new plugs and clean air flow meter , then could be fuel pressure or lean fuel feed back system from bad sensor , this is why you will need to monitor fuel trim also .

Roy :

you could have more then one problem

Roy :

Thanks let me know if you have any more questions, ROY!

Customer :

theres no blue smoke though

Roy :

will not alway smoke if burning off a little at a time

Customer :

i have had problems in the past with the car starting due to lack of fuel

Customer :

but it was very rare

Roy :

ok I would check with a pressure gage

Roy :

should keep good pressure

Customer :

so check cylinder compression, and fuel pressure

Roy :

yes to start and see if you can get a scan tool that can monitor all sensors if no problems found

Customer :

at that point its going to the dealer

Customer :

i guess what it comes down to are what are my options to check at home

Roy :

that might save you some money to know for sure for installing the wrong parts

Roy :

at home fuel pressure and compression test

Customer :

so its probably not a vacuum line?

Roy :

not likely

Customer :

well i feel this has gone beyond my abilities

Customer :

im great at replacing parts, but it seems more practical to take it in

Roy :

I wish you luck and hope it is not very expensive for you , Thanks ROY!

Customer :

unless the gauges arent too expensive, may need them later anyway

Roy :

thats true gage can be around $100.00 for both

Customer :

id just hate to pay 5x as much for a new fuel pump at the dealership when i could do it myself

Roy :

you can just get it figured out and fix it your self or take some where for less

Customer :

true

Customer :

just pay the diagnostic fee

Roy :

dea

Roy :

that is what I would do

Roy :

save some money that way

Customer :

alright, well thank you very much you have been extremely helpful

Customer :

sorry to give you so much trouble i was hoping for an easy answer i might have missed

Roy :

Thank you also wish I had a easy fix to offer you , good luck ROY!

Roy, ASE Certified Technician
Category: Nissan
Satisfied Customers: 5451
Experience: Nissan Master technician
Roy and 2 other Nissan Specialists are ready to help you

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