p300 misfire
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Teching In
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From: Lees Summit Mo
p300 misfire Hooked up friends shop scaner and had 25000 missfires on cyl#3 and 80 to4 on all other cyls,note this was dove 2-3 days before used scanner.also 110000 miles stock but maniflow exhaust. 6 speed. he wanted to tune it up i am a old mechanic became dissalbed in 2003. worked for chevrolet till 94 then went to ups nights to repair fleet of 32 trucks and blew my back. Back to car. tuned it with all gm plugs wires with help of my 17 year old daughter.cleared codes and drove fine for about a week and a half. light on scanned again,p300 ck history and not as bad on missfires so friend at shop or Mike sugested new coil put on new b/w coil. cleared ,drove and light back on. sorry i forgot 1 thing engine misses and light comes on at idle every time im idleing. sometime on the road but cant tell if its missing.now he want to replace injector. where will this stop? please help not much money to just keep replacing parts. and yes it had been tuned new plugs at sometime. i just got car with 97k on it ran ok then.one other note every now and then i will hear noise under valve covers,kind of a knock to ticking sound and it can be on right or left side. then it just goes away.sorry so long and hope this is in right post.thanks
If the misfire is on Cyl 3 you should have started swapping parts (plug, wire, coil, injector) from that cylinder with other cylinders since they are the same and all interchange. Keep track of what part went to what other cylinder. See if the misfire moves to another cylinder. If it doesn't move then it is time to pull the valve cover and look at the valve springs, rockers and pushrods for that cylinder. Then maybe a compression test or leakdown test on that cylinder. Someone with your experience should have these diagnostic skills. Not just throw parts at it especially if money is tight.
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From: Lees Summit Mo
well dont think swaqping parts would help when the wires had 110770 miles coil and injectors too.Plug been changed with a ngk that fits a ford cobra. so i'm told ngk ptr5c-13 12556483 #s off plug.all the cyls on 1st scan showed missing #3 was the most with around 25000 in history. i think i have leaking injectors and #3 is the worst. I have not turned a wrench in twelve years due to my back being sick they cut off 5 toes and i have a blood cancer. I'm a big dummy #3 just shows up on scanner as most misses, but the car as far as i can tell only misses at idle NOT all of the time.you can idle for thirty mins. and ntf. then it will start missing not like dead cyl just like i said i think its inj dripping??
Last edited by skypuppy99; Nov 18, 2010 at 11:36 PM.
are you sure that is the right plug number? a TR-55 would be the number to use for stock.
Also if an injector is leaking a little bit which i doubt, wouldnt cause a missfire code like that on one cly, it would lean out all cyl though on that bank. But he would see that with his scan tool and the ltrims on that bank would be really - values.
Also if an injector is leaking a little bit which i doubt, wouldnt cause a missfire code like that on one cly, it would lean out all cyl though on that bank. But he would see that with his scan tool and the ltrims on that bank would be really - values.
Thread Starter
Teching In
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From: Lees Summit Mo
thats the plugs that were in it. i put ac 41-110 is what part store said goes in it, the plug is gaped at 0.040 factory plugs were .060 could it be wrong plugs? you cant change the gap to .060 i tryed and had to buy a new plug. That is for the ac 41-110 plug. My owners manuel shows dif plug but the #s shows no good. have to get that plug # .
Thread Starter
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From: Lees Summit Mo
P300 missfire I got the car all most 2 years ago with 97k on it and now it has 110k on it. Speaking of o2s i was under it when i had my oil changed and the last o2 sensor is not pluged in and has somethink that the harness is pluged into. its about the size of a c size battery but square with wires comeing out of it.
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On The Tree
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The little box with wire is a dummy o2 sensor. probably at one time was put in because the cats are pooched or gone altogether. if your hearing a noise under the cover id definately check that out first of all and get the right plugs in it, just improper gapping can cause a misfire let alone the wrong plugs altogether. Maybe a bad lifter or spring causing the noise which is giving you the misfire.
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From: Lees Summit Mo
p0300 well i havent been able to work on car due to health. i finally got correct plugs in it and intake bolts were loose some alot,1,3,5,7 side was worse than 2,4,6,8 side. i also had a bad injector #5 so with 110k i replaced all 8 with rbs. the noise i heard is the clutch or bearings, because it only make noise when clutch pedal push in. when i said #3 was my miss it was missing the worst. all cyls had shown they had missed in history more than 20 or 80 misses. just #3 had the most with like 25k in history.the shop i take it to has only see it miss one time with chk eng light on but was to busy to hook up scanner. now going to put some miles on it after get codes cleared see what happens next. will get back to you all and thanks for input. kim
