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PO300 help

EJOUIE

EJOUIE

New member
I keep getting a PO300 and I can't seem to find what is causing it. I have already replaced the plug wires and the MAF. Spark plugs are fairly new. It only seems to misfire sometimes as in some drives it will be fine, other times it has problems right from the initial startup. This has been going on for a month and its really pissing me off so any help/genius ideas would be appreciated.
 


the idle is rough with lots of vibration for a few seconds, then the revs increase and it smooths out and all appears to be normal. then it misfires when driven.
 
Start the car,pop the hood and look at your spark plug heat sheilds.Look to see if they are coming into contact with any metal around them from either the exhaust manifolds or heads.I had this same problem and it was just the spark plug heat sheild sparking with a bolt.Just pull it off you dont really need it.
 
when your engine is misfiring unplug one spark plug wire at coil with engine off. then turn it on and see if the coil is sparking. check each wire at your coils to make sure all coils are working. Do you smell any strong odors of gas when it misfires?
 
^I sometimes I do, sometimes I don't. Probably due to the bad blend door. so ur thinkin that the coils would be next to check as a potential trouble maker? What else could cause this as in what other things to check.
 


a bad coil could fail and that would mean that 2 plugs wouldnt be sparking. could be almost anything. most common are either bad coil, ignition module, fuel pressure should be checked with gauge, stuck open or closed pcv valve, bad signal from crank or cam sensor, or failing injector(s), and lastly a vaccum leak or bad Idle control valve. Your saying it misfres sometimes or all the time?
 
Also, if you smell gas when its misfiring. it means that one or more cylinders arent sparking at that time and all the gas that injectors throw in isnt being burned and it is getting pushed out the exhaust, a stuck open injector(s) or a leak at one of hoses on fuel rail.
 
It misfires sometimes, so i thinking its more electrical. For example it misfired like crazy (I couldn't get it to rev past 2500) and barely made a 3 mile round trip this morning after sitting all weekend. just half an hour ago I drove it to the repair shop and it was fine. i took it to the shop because they have the tools to perform the repair (however this forum is more useful in diagnosing the problem so I use it to give them a starting point).
 
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Not really. The cam sensor only requires to remove the powersteering pump to make it easier. Its only two bolts, you put a 1/2 deep socket in through one of holes on its pulley. then you can remove the right tire to get to the sensor. its on the bottom left side below water pumpit is held on by one small bolt. To get the crank one off you have to remove the Center bolt of crank. Next, use a puller to remove the harmonic balancer. Then remove the plastic cover and the bolts that hold the sensor. its on the right side of crank snout.
 
thanx. I just wanted to know so that I shouldn't expect a massive price for labor if they determine that one of those are the problem.
 
P0300 is a random misfire...so its something ignition related about a billion times to one...not really fuel or anything...they have their own codes.

I saw ICM...I know they are pricey but its what I'd try next.
 
found the problem. surprised nobody suggested it, but maybe you all assumed as I had that it could not have been the source, but it was.

It turned out to be a bad battery.
 


hmmm. i thought it was the battery. one day the car struggled to start and when it it it misfired and shook violently. I juiced up the battery with a charger and it ran fine. I then put in a brand new battery. problem free for about a month and a half. now the misfires have returned. any ideas?
 
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