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2008 2.4L code P0301

4939 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
coils
injectors
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.

COMPRESSION TEST RESULTS
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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About 3 weeks ago the compression in cyl 1 was bad. What is the current standing of the compression in 1?
I have yet to retest the compression as the issue has proven to be intermittent I ruled out low compression as the cause for the problem I’m trying to fix. Low compression might be causing an issue of its own but I believe the shaking shuttering to be an electrical issue
I have yet to retest the compression as the issue has proven to be intermittent I ruled out low compression as the cause for the problem I’m trying to fix. Low compression might be causing an issue of its own but I believe the shaking shuttering to be an electrical issue
Ok I'm sorry, long thread. I thought the problem was related to a P0301 code. P0301 with low compression is valves or rings. Rings is constant, valves can be intermittent. Good luck!
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Ok I'm sorry, long thread. I thought the problem was related to a P0301 code. P0301 with low compression is valves or rings. Rings is constant, valves can be intermittent. Good luck!
That’s where it all started, but after addressing everything that surrounded the cyl 1 misfire, I was able to get the issue to go away temporarily. Other posters said it would be a constant issue if it was due to low compression. Hoping the fretting corrosion fix or something simple does it

alongside the fretting fix ive seen people with similar issues say it was a brake pedal or accelerator pedal sensor, some have said bad wheel bearings caused the issue, someone else said warped rotor.
Repairman54 and DrivenDaily have both been spotted in older posts discussing remedies to similar issues as mine, anything solid ever come out of your ESC/Traction issues?:unsure:
ESC and traction messages will display anytime a P code gets triggered.
Would burnt valves be the cause of intermittent hard shifts, loss of power, shuddering shaking, that can also be made to go away by resetting the electrical systems on the car?
Would burnt valves be the cause of intermittent hard shifts, loss of power, shuddering shaking, that can also be made to go away by resetting the electrical systems on the car?
Burnt or warped valves can contribute to issues like this, but you would likely see more significant evidence of mechanical malfunction. IF this was restricted to Cyl 1, with low compression, that is a possible culprit. Without a visual inspection of the valves or a scope of the cylinder its impossible to say for sure.

The hard shifting can be a combination of several issues working in tandem, but it could also be due to worn and failing parts in your transmission. If that fluid condition is any indication, your transmission is probably ailing. If you've just changed the fluid and continue to drive it, check the fluid consistency, color, and odor sometime soon. Do not "flush" the system in this condition, just do a basic fluid change. When you see trans fluid like that, it's generally an indicator of abuse or neglect; compare it to the fresh fluid from a bottle. That discoloration is an amalgam of suspended clutch material, metal, burnt residue. Worst case scenario, you need a trans rebuild to correct those hard shifts, as the contact surfaces are either worn or shellacked from excessive heat or improper lubrication. Yes, trans rebuilds can be performed by the determined DIYer. Be patient, find a -thorough- walkthrough on youtube, and follow along. Modern Transmissions have some specially coded electronic parts that cannot be easily swapped. If your issue is a hard-part or clutch issue, you should have a good shot at fixing this yourself. Get some plastic bins, take lots of pictures, and be ready for one hell of a mess.

Best case scenario, clean fluid circulating at the proper viscosity and temperature will ease some of your troubles. You can also try adding some stop-slip from an appropriate manufacturer, many will have friction modifying additives which can help provide temporary relief.

Your description of resetting electrical systems alleviating the issue temporarily is not unheard of. This is something I commonly encounter on Fords, for a number of reasons.... But here, you mentioned that jiggling the BCM connection seemed to help. With the battery disconnected, unplug the BCM and gently spray the wiring harness connector with some electronic contact cleaner, allow it to dry, and then connect/disconnect several times. Finally, apply a conservative amount of silicone grease to the connector. There is a very handy thread pinned that details this process, as well as some of the issues that corrosion / fretting can cause.

Good luck.

edit: clarification: don't spray the BCM, spray the plug/connector.
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