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I have a 97 pontiac grand am that has a misfire under heavy load. I am getting a p0300 random misfire code out of it. It is primarily cyl. 1 and 3 that are missing when it acts up. I have done that following, Replaced coil housing, both coils, Coil boots and plastic protectors and spark plugs the only thing i havent replaced is the ignition module. I am a ford tech and our systems work all together diffent then gm. Oh and it seems to get worse when its hot. Does this sound like the module to u? I wanna know how it drives the coils. Oh and i have replaced the crank sensor also. Does it sound like im barking up the right tree? Any help would be greatly appreciated.thanks for your time.
Larry Hargraves
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Hi,Larry
Hey can i use you to answer my Ford tech questions?send me your email address.i hope its busy were you are.
On your Pontiac,the missfire in cyl #1 and #3 seem suspect,both of the cyl's are on the same bank and next to each other,you know were im leading?check the compression in both those cyl's,and compare it to the other cyl,i may be thinking you have a blown head gasket on Bank #1 betwen cyl #1 and #3 and your loosing compression,ive seen this before,also what did the spark plugs look like?check the new ones you put in for signs of coolant,also check the lower intake manifold for a leak,especially those 2 cyl's,they are notorious intake leakers.let me know what you find,Thanks
ED
Hey Ed,
Thanks for the prompt reply. I ordered the intake gasket today i am going to replace it in the morning. Here is why, I have been having this problem of an erratic idle after coming to a stop for the first time after a cold take off. But would go away after that. Then I replaced an injector on #1 cyl. last week and directly after that it started idling rough. It didnt idle rough at all before that except for the occasional miss. So after burning up the gears in my head last night determined to figure out this problem, I dawned on me that the ongoing problem with the idle flucuation after cold starts is a tell tell sign of a vaccum leak. What got me to thinking so hard about it was i found a diagram of the ignition module and i found that it drives 1 and 4 on one circuit and 2 and 3 on the other, I came to the conclusion its time to think outside the box. The car has 171,000 on it so im gonna give the gasket a shot. As for the plugs they look great. Thats what kept throwing me off. And no coolant loss. Oh yeah by the way you can ask me any ford questions u like and i will be more then happy to help. I specialize in driveability and electrical and diesel engine performance also. I will let u know if the intake gasket fixes it. Oh would it be worth while if im going to continue and drive this thing is go ahead as a precaution and replace the head gasket. I dont want any suprises in the future. Thanks for the help and i will keep u posted.
Larry Hargraves
AnswerHi,Larry
Good diagnosis,like i said they are pretty good at intake leaks,also make sure you didnt split the injector oring seals going back in with the injectors,i would hold off on replacing the headgaskets,if no coolant is in the chambers and the plugs look good,there is no use in replacing them,like the saying goes "Dont fix what aint Broke",but i think your on the right track.let me know how it goes.
ED
