HELP!! Code P0300 random missfire !!!

[ireyesjrss]

So I got a check engine light on my 03 silverado

Took it to autozone and it read a P0300 which the guy told me was a random missfire that I could of been either wires spar plugs vacuum leak low fuel pressure etc .. I said ok I started looking for more Info regarding to the random missfire and I came across this video on YouTube describing the most problems with the code and how to take care of it and he show how to check all plugs and how to spot a vacuum leak how to check the fuel pressure and last but not least he mention that a random missfire can be caused by a BAD BATTERY !! So I went back to autozone to check my battery and it was a bad battery went to another store to have my baterry check and again it came to be a bad battery I got a brand new battery took the old one out install the new one and now the check engine light had gone away .. My question is should I still go and get my truck check my a certified mechanic to they can identify what's causing the Ramdom missfire or could the bad battery have caused a missfire ?? If you have came across the same code tell me about your experience and let me know what I should do ?? Thanks for your guys time I hope someone here can relate to the Ramdom missfire code thanks again

[Blown 346]

I have never had a bad battery cause a miss fire code. It is possible. This is what i do when I have had these codes pop up. Check all plugs and wires. Check wires for cracking or insulation issues. If they havent been replaced in some time I would replace them just under normal wear. Dont forget to use electric grease in both ends of the wires. Check plugs for a good clean burn, the plug shouldnt be black or white. You should have a nice grayish ashy color to the plug. Check plug gap and make sure you are using the correct plug. Just because the parts guy tells you this plug will work since it says in his computer doesnt mean its best. I only stick to either Ac Delco or NGK TR55 plugs for all motor.

 

Clean your throttle body, and the sensors that attach to it. Clean the MAF sensor with electrical parts cleaner. You can use brake clean on the throttle body only. I would even go as far as spraying brake cleaner ona clean towel or rag and stick your arm in the intake if you can and wipe out any oil residue. ( its normal to have some or alot if thats never been done. I would also add some sea foam to your gas and some to your vacuum line that comes off the brake booster. This will allow you to clean out the fuel system and remove any moisture. In the engine it will remove oil from the PCV system, carbon deposits in the motor like on pistons intake etc. Just make sure you follow the directions on the can and it will do its job.

 

Basically what i mentioned is my preventative maintenace I do on all of my vehicles along with oil changes. The plugs and wires I check 2 to 3 times a year.

 

 

 

Edit.... The thing about random mis codes are they can be a number of things. The guy at the parts store will tell you its this or that, and wants to sell you whatever the scanner says. The best thing to do is the easiest things first like self checking and cleaning If that doesnt take care of it, then it could be anything from bad cats, MAF, to bad gas.

Edited November 26, 2013 by Blown 346 (see edit history)

[ireyesjrss]

Thanks for your response I will check and clean all the parts you mention today in the morning and let's hope for the best

[BLNAWAY]

I have never had a bad battery cause a miss fire code. It is possible. This is what i do when I have had these codes pop up. Check all plugs and wires. Check wires for cracking or insulation issues. If they havent been replaced in some time I would replace them just under normal wear. Dont forget to use electric grease in both ends of the wires. Check plugs for a good clean burn, the plug shouldnt be black or white. You should have a nice grayish ashy color to the plug. Check plug gap and make sure you are using the correct plug. Just because the parts guy tells you this plug will work since it says in his computer doesnt mean its best. I only stick to either Ac Delco or NGK TR55 plugs for all motor.

 

Clean your throttle body, and the sensors that attach to it. Clean the MAF sensor with electrical parts cleaner. You can use brake clean on the throttle body only. I would even go as far as spraying brake cleaner ona clean towel or rag and stick your arm in the intake if you can and wipe out any oil residue. ( its normal to have some or alot if thats never been done. I would also add some sea foam to your gas and some to your vacuum line that comes off the brake booster. This will allow you to clean out the fuel system and remove any moisture. In the engine it will remove oil from the PCV system, carbon deposits in the motor like on pistons intake etc. Just make sure you follow the directions on the can and it will do its job.

 

Basically what i mentioned is my preventative maintenace I do on all of my vehicles along with oil changes. The plugs and wires I check 2 to 3 times a year.

 

 

 

Edit.... The thing about random mis codes are they can be a number of things. The guy at the parts store will tell you its this or that, and wants to sell you whatever the scanner says. The best thing to do is the easiest things first like self checking and cleaning If that doesnt take care of it, then it could be anything from bad cats, MAF, to bad gas.

good info here , and just to add about the light disapperaring it was cause you had the battery out for a extended period of time, id drive it see if it comes back up, if it dose and you already did the recommended check/cleaning then at that point id take it in to get checked out

[ireyesjrss]

ok just for the record this morning it was obviously cold right i turn the engine on eveything

seem ok after like 2 minutes the engine started to iddle up and down i drove the truck a mile

and at a stop sign i stopped and the iddle would go up and down still to the point where

it felt like the engine wanted to shut down i keep driving it and when it got to regular

hot temperature the truck was now on iddle again but this time it was normal iddle

what could this mean ??

[Blown 346]

Could be several things. My buddys truck did the same thing and it turned out to be a dirty maf and throttle body.

[ireyesjrss]

sounds good than i will go ahead and get thoes part cleaned up and check everything

you have listed for me i really thank you alot for taking your time to read and reply to my problem

i really appreciated it

[Blown 346]

no problem

[ireyesjrss]

should i also add seafoam to the oil ?

[Blown 346]

I dont know about the oil, Ive enver done it as Im leary on the cleaning agents in the sea foam. If they can remove moisture and clean a fuel system, and then remove varnish and carbon from a engine, I look at it as if it can do that, what will it do to the oils lubricating properties and bearings??

[Fireman31]

A couple of things.....

 

The code disappeared because you disconnected the battery to replace it. Anytime the battery is disconnected, the temporary memory is lost from the PCM. This is why your truck is idling like poo after installing the new battery. The PCM has to start learning how you drive and how all of your trucks parts work together from scratch. Several drive cycles and roughly 100 or so miles and things should smooth out.

 

Yes, the preventative maintenance items mentioned are good, especially a TB and MAF service, but more often then not with these trucks, a P0300 random misfire code usually signifies that a cat has begun to degrade, and is beginning to effect your trucks performance.

 

Since the CEL has not come back on, I wouldn't worry about it unless the code pops back up. Keep us posted.

Edited November 26, 2013 by Fireman31 (see edit history)

[ireyesjrss]

I got home from work and clean the maf and the TB iddles more smoothly and runs really smooth

Now I will have to wait till the morning to see how it runs when cold because when the truck it's @ at it's regular temperature it's runs like new ... And @fireman31 your right on my way back home the check engine light pop up again !!

[Blown 346]

When a cat normally starts to back up and fall apart, you can smell sulfur, or the truck will feel like it has no power. After driving it, look under the truck at the cats, if they are glowing red they are junk. To get to that point it doesnt take overnight to happen normally.

 

 

You might have to check the MAF to see if its not getting the proper signal. The MAF could be bad.

Edited November 27, 2013 by Blown 346 (see edit history)

[Fireman31]

First things first, get the truck scanned and see if the same code was tripped.....

 

If it is a P0300, slide under the truck while it is cold and wrap on both cats with a closed fist. If you hear a rattle, that means the cat is coming apart internally. I forgot to ask, how many miles on the truck??

[ireyesjrss]

check you PM @fireman31