2003 Silverado Misfire

[timmdogg2]

hey, I have a 2003 chevy silverado exd cab 5.3L. I recently changed my spark plugs and now i have misfires. I have been trouble shooting this problem for 3 days and it seems to be getting progressively worse each day. My neighbor has a code checker and it says that i have a random cylinder misfire (code p0300). We checked to see what cylinders were misfiring and in a 5-10 minute span i had over 1200 misfires in cylinder 1, about 500 in cylinder 8, and only 1 or 2 in every other cylinder. My ignition timing is going nuts ranging from 3 to 27 when the truck is just idiling. I have changed sparkplugs, and serpinteen belt prior to this happening. Since the problem has started, i have changed spark plug wires, cleaned my k&n air filter, and changed fuel pressure regulator. I have taken the spark plugs out made sure they were the correct ones and that i did not have any damage to them. Since i have a random mis fire i know that it eliminates any problems that have to do with individual cylinders or parts such as sparkplugs, wires and individual coil packs. It also back fires on acceleration occasionally, i do not have a clogged cat, my fuel pressue is a bit low at idle (50 at idle-62 when steppin on gas). I have also eliminated mass air flow sensor and fuel mixture is good at 14.6 I have used differents types of gas and did not effect it either way. it only seems to really mis under load(in gear) in low rpms, when i am above 2000 rpms u can not really tell anything is wrong, but like i said it is getting worse. somebody told me to change crackshaft sensor and im going to try that tommorrow. does anybody have any ideas? im getting frusterated!

I also have 2 new codes that popped up today, they dont sound like they relate to my problem above but u never know they are u1026 and u1041

[minibike132]

The P0300 is very missunderstood to the general public. You would only get a P0301 if it was a flat dead miss and sometimes not even then. Of the thousands of P0300's I've ever diagnosed about 80% trace down to an issue at a single cylinder. Just because it's not a 301 does not make it random.

Since i have a random mis fire i know that it eliminates any problems that have to do with individual cylinders or parts such as sparkplugs, wires and individual coil packs

 

Now I'm not saying that it isn't something related to fuel that would affect all cylinders but I would investigate that cylinder #1 first. #8 is right after it in the firing order and your probably seeing a false miss on 8 because of the #1. You said you took out the plugs and checked them out did you swap cylinders by chance. This motor is simple to diagnose ignition failures on because everything is accessable and exactly the same. Without anymore equipment than you have you can swap the 1 and 3 parts out (I suggest plugs first and see if the miss moves to #3, if it does you know you found your problem. If it's not the plugs move on to wire then coil swapping.

 

I have changed sparkplugs, and serpinteen belt prior to this happening

This would make me lean the plug route if there was no miss prior to the plug and belt replace. The tinyest crack in an insulator can cause a hard to find miss. Also double check belt routing, proper belt and check the tensioner. All of those things have been known to cause false P0300's because the miss is seen as a variation in crank speed, a jumpy belt can make that minute change in crank speed that is picked up as a miss.

 

Oh and I almost forgot about this

I also have 2 new codes that popped up today, they dont sound like they relate to my problem above but u never know they are u1026 and u1041

These codes are for lack of communication between the ABS the transfer case shift module and the PCM. 99 times out of 100 if you remove the ground on the frame at the body mount under the front of the drivers door and clean the rail and terminals real good you will correct these codes. There is a bulliten giving some more detail, someone might post it for you but I can't do that anymore.