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2008 2.4L code P0301

4956 Views 26 Replies 6 Participants Last post by  Mechromancer
I got the car a few weeks ago. the previous owner drove it as is for 15k miles. when i acquired the car it had barely any power through 1st and 2nd with an obvious misfire that would clear out once up over 40mph. always throwing ESC and Service TPS. and at redlights would bounce around and misfire bad enough to where id have to start shifting into N while pulling up to stop signs and redlights just to avoid the situation entirely. the misfire is still there in neutral just not nearly as bad. you can smell fuel like its running lean when outside the car. no smells inside really besides the must A/C but im working on the cabin airfilter and a/c cleanout as soon as i get her running right.

For what ive done to the car, after getting the codes ran and recieving diagnostic of P0301, I will place in a list below,

New Battery
air filter
spark plugs
MAF sensor
throttle body
o2 sensors
new pcv hose that goes to intake
purge valve solenoid
sea foam in gastank

after doing all that^ drove for 100 miles or so and there was still a misfire and rough idle.

so i removed the header and catalytic converter as previous posters seemed to have similar issues. the header seemed to have alight crack but it was hard to tell if its just on the surface or not.

no light would shine through the 1st catalytic converter, so i punched a hole through the middle with a piece of fence pipe. (i know its frowned upon but before buying a new header/cat assembly i wanted to try to remove it from the list of problems or diagnose it as the problem.)
put it all back together and
started it up and the misfire and rough idle was still there only now it sounded like a ricer from me mangling the catalytic converter. needless to say the malibu isnt leaving anytime before the new header gets here.

ive since then drained and replaced the oil, new filter and o-ring.
replaced the VVT solenoids, intake and exhaust.
and performed a pressure test.
first thing i'll note is when i removed the plugs cyl1 was wet with fuel, black and cracked on the upper porcelein. the other three looked rough for 100 miles but nothing compared to cyl1. ive read in other posts that these le5's just dont like NGK so i bought AC delco to replace these after the pressure test.

1/55 2/140 3/135 4/135

I closed the engine back up with new AC/delco sparkplugs and havent started it as I am waiting on the new header and catalytic converter.

when i was unplugging the injectors to perform the pressure test i noticed that the boots which hold the injectors inplace were kind of misaligned and when i tried to straighten them out i felt like there was way to much wiggle room. I wish i noticed this when replacing the injectors but hindsight is 2020 LOL, i will be replacing the Injector boots and orings as well.

and deleting the OEM engine cover air box thing just to remove it as a culprit for any vacuum leaks.

before installing the new header and cat i was planning to use the AC delco Engine top cleaner through the spark plug holes and through the throttle body just to remove any carbon build up as im praying that is the cause for the cyl1 low compression.

That's where i am at currently. waiting on parts reading a decade of 2.4 Le5 posts.
any tips advice experience or help would be greatly appreciated. I feel like im on the right track now? but maybe not. im open for discussion
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1 - 5 of 27 Posts
55 lbs compression in #1 is your problem. All 4 cyl. should be within 10% at the most of each other.
It needs a teardown, head taken off, to inspect valves and piston. Or as least valve covered pulled to check cam at the minimum.
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Carbon would increase cylinder pressure not drop it. An only a very small amount of increase well within a few percent.
Low compression / dead cylinder = misfire and carboned up sparkplug and cat failure due to misfiring cylinder.
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You have a '08. That's not a DI motor but port injected so carbon on the intakes is not a issue like in later Direct Injection motors.
Repairing the low compression in #1 is the priority and your immediate problem, cracked exhaust manifold can be addressed at the same time if head has to come off motor.
Other than solving the bad cylinder issue any other money spent is a waste of time and money as you do not know if your motor is even repairable or economical to repair.
Low compression in #1
I myself would get the air adapter to put compressed air into the cylinder thru the spark plug hole, moderate 50 psi pressure, and listen for air leak in the throttle body, oil fill cap and exhaust pipe. That is the quickest way to roughly check if valves or piston has issues.
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ESC and traction messages will display anytime a P code gets triggered.
1 - 5 of 27 Posts
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