PO301 code. Did my research and just need a little guidance.

**transaman98** · 02-28-2011

Alright so I have a bone stock 2003 GP GT with 124k on the clock. Up until a week or two ago it has been a great car that I have owned since it had about 40k on it. So cutting to the chase the car had a flashing check engine light when I was getting on the highway. Had it checked and it pulled a P0301 code. Cylinder 1 misfire.

So I decided that the plugs in it were probably the same ones that rolled out from the factory(They were). Changed them to a set of NGK stock replacements and gaped them to .060. Put the plugs in and the problem went away.(Or so I thought.) A couple 2 or 3 days later the light came on and threw the same code again. I did notice that it only comes on when I seem to be putting the pedal down and the tach is reading 5K or more. Possible bad coil causing this? I plan on getting plug wires for it tonight and checking to see where that lands me since it is the cheapest option.

I was just reading around on here and noticed people talking about a possible problem being an (ICM) ignition control module. How common is it that these things go bad? I am no dummy when using a DMM so if there is a way I could test it before throwing parts at the car in hopes of fixing things, any direction on how to test the module would be great.

Thanks in advance.

**dpzelenak** · 02-28-2011

i dont know alot about the 3.8s but from what it sounds like the icm or a fuel injector problem, i would do a ohms test of the coil first but if the coil was the problem i would think it would be affecting more then one cylinder because its a waste spark system but im not 100% sure but i would check that first before i would check the other systems

**OH4CompG** · 02-28-2011

If you haven't done wires you should. That's probably a contributing factor to the issue. Plugs and wires should be done on the outer limits at 100k miles if you're stock.

**transaman98** · 02-28-2011

What should the injector resistance be if its healthy? Same question for the coil packs.

**Poil336** · 02-28-2011

most likely a plug wire or coil. did you get the right heat range plugs? all i've ever heard of with people using ngk are the ones that are like 3 heat ranges colder. i'd replace wires, even if that's not it, it should probably be done anyway

**transaman98** · 03-02-2011

I went to Vatozone and they looked it up in the computer. The computer said it was a stock replacement. The plugs I used are : NGK "G-Power" TR55GP. I gaped them at .060. Hopefully the guy didnt make a mistake and give me the wrong ones.

**transaman98** · 03-02-2011

I am thinking I will probably get some AC Delco plug wires since I am not trying to do anything with this car other than to use it as my daily. Is it usual for the plug wires on these cars to have problems? I have another car that has almost 100k on it and its a '98. It also has swapped heads, cam, nitrous, etc. The stock plug wires, and coil packs have done just fine so far.

**transaman98** · 03-03-2011

Put new plug wires on it today and put a can of seafoam through it. The car seems to be running pretty top notch. I ran it up to 5500rpm or so and it didnt skip a beat. Hopefully this was the fix. I will be sure to post again if the problem continues.

**powerranger262** · 03-03-2011

Did you run seafoam through your new plugs?

**transaman98** · 03-03-2011

Yes. Despite what others said about it occasionally causing plugs to foul out. Plugs are so cheap that I didn't feel like taking them back out to put the old ones in and then seafoam it. I figured if it caused a problem then I would just put new ones in it again. It didn't cause a check engine light after it was done so I suppose I lucked out. I'm a member on ls1tech.com as well as here and there is a very good write up on how to use it correctly. I wish I would have thought about doing it before I changed my plugs in the first place.

**transaman98** · 03-03-2011

BTW the same s#!* is still happening. After I did the seafoam and wires I drove the car around and it didn't seem to want to throw a code when I was mashing on it going down the street. I thought I was good to go. Well this morning I was on my way to work and decided to mash it getting on the on ramp to the interstate. Runs all the way up to 5500 or so and shifts into second, then runs all the way up to 5500 or so and the service engine light comes on again and does its blinking show for me that I am getting so used to. It is the same damn problem all over again. Still cylinder 1 misfire. I think I am going to flip flop my coil packs around and see where that gets me. On a side note I am going to fill up my car on my lunch break today and see what kind of mileage I got on this tank vs the last with the old plugs and wires.

**tc300** · 03-03-2011

mine does this also when i get on it good... kinda sputters/misses... only some times the CEL flashes..???

**transaman98** · 03-03-2011

CEL? Still learning my acronyms for these cars.

**Scottydoggs** · 03-03-2011

cel = check engine light

**transaman98** · 03-03-2011

I suppose that is the same thing. I have a "service engine soon" light that flashes when it happens.

Found this using google.
http://repairpal.com/OBD-II-Code-P0301
I might just take it to a mechanic to have them look at the car.

When the code P0301 is set in the Power Train Computer, it means that the Misfire Monitor has detected more than a 2 percent variance in RPM between the firing of any two (or more) cylinders in the firing order. The Misfire Monitor constantly checks the rotational speed of the Crankshaft by counting the pulses of the Crankshaft Sensor. The Monitor wants to see a smooth increase or decrease in engine RPM. If there are jerky and sudden changes in the speed output of the Crankshaft Sensor, the Misfire Monitor begins to count the RPM increase (or lack thereof) contributed by each cylinder. If it varies beyond 2 percent, the Monitor will set a P0301 code and illuminate the Check Engine Light. If there is more than a 10 percent variance, the Check Engine Light will blink or pulse in a steady manner to indicate that a harmful Catalytic Converter misfire is occurring.

**Poil336** · 03-03-2011

sooo.... clogged cat?

**dpzelenak** · 03-03-2011

its not the cat, it has to be something to do with just cylinder 1, like a plug wire being routed the wrong way or a cracked head gasket on the outside of cyl 1, it could be alot of different things..im gonna say that you have a weak coil(ign coil), just because you said it only happends at high rpms and if the coil is weak then it cant fire enough voltage to over the high rpms..to test it i would take the coil for cyl 1, and swap it with a differnt coil, like taking the coil from the outside and moving it to the middle, if it is the coil then it should stop missing on cyl 1 and it should start to miss on whatever cyl you moved it to, and set another p030_ code for that cyl..

**transaman98** · 03-03-2011

Originally Posted by dpzelenak

its not the cat, it has to be something to do with just cylinder 1, like a plug wire being routed the wrong way or a cracked head gasket on the outside of cyl 1, it could be alot of different things..im gonna say that you have a weak coil(ign coil), just because you said it only happends at high rpms and if the coil is weak then it cant fire enough voltage to over the high rpms..to test it i would take the coil for cyl 1, and swap it with a differnt coil, like taking the coil from the outside and moving it to the middle, if it is the coil then it should stop missing on cyl 1 and it should start to miss on whatever cyl you moved it to, and set another p030_ code for that cyl..

Bingo! I don't think it is anything major like a head gasket. I am crossing my fingers that its a bad coil. Under high RPM the coils obviously draw more current so I can easily see that being the problem. If I swap the coils around and the computer still throws that P0301 then I suppose its back to the drawing board. When you guys replace coils do you usually go with an aftermarket coil like the MSD, Accell's or with a factory replacement. I was shocked to see that it was only $150 for the MSD's. The last time I looked at the price of MSD coils was when I was in the market for my trans am and those suckers were $600 or more!