P0300 misfire

[screwloose13]

I'm new to all this and I'm trying g to learn how to fix my own vehicles. I'm having a p0300 code as soon as i start my 2007 tahoe 5.3. After idling for about 60 seconds the check engine light comes on and flashing. Sets off the stabilitrak and traction control messages. I've replaced spark plugs, coil packs, plug wires, new gas cap, battery, I've cleaned the maf sensor and throttle body. I've checked for vacuum leaks. I did notice the map sensor is loose and moves around a bit because one sides little bracket is broken. Could that cause a misfire? I need help.

 

[OR VietVet]

Welcome to the forum.

Well, you know you have a map sensor problem, so fix that, no matter what and do not replace with anything but GM parts. What is the manufacturer of the parts you replaced because there is some crap out there and recommend you stick with GM parts. Likely not the source of multiple misfires though. You said that a code set and you replaced all these parts. Did you ever actually feel a misfire or misfires? I would get a fuel pressure gauge attached and drive the rig with a long enough hose on it to tape to w/s and watch where the pressure is while driving and at idle. How did you check for vacuum leaks? You said you want to learn to fix your own vehicle, so that tells me some of these processes may be over your head but it is good that you want to learn. How many miles on the vehicle? The maf sensor may be bad enough that cleaning will not help.

Other members will chime in.

 

[wjburken]

Is the P0300 code the only code you are getting? Who is reading the codes? Are you able to check for ABS codes?

How does the engine sound? Rough? Tapping? Clanking? I ask because a rough running engine can cause Stabilitrak to be disabled.

Do you have AFM disabled?

I agree with @OR VietVet in that you should get the MAP sensor situation taken care of first as it can affect a lot of things.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

 

[solli5pack]

Your definitely going to need access to a good scanner that can view live data to see what's going on with the engine while it's running. Things like which cylinder or cylinders are misfiring, fuel trims and O2 info will help with the diagnosis. A quality scanner can pay for itself pretty quickly by preventing unnecessary purchase of parts while taking guesses at the problem.

 

[screwloose13]

I will take pics of the truck and post. It runs pretty good I think. It smokes a little. It doesn't have a lot of power it seems. And it drives kinda weird like the handling. I don't know if they are normally like that but. It rides right up no problem. But just smokes a bit and idled a bit rough. I got from auction and have only driven it minimally. I don't want to make things worse. I have a mucar cde900 scanner. I don't know where to look for the misfires. It has live data. One of the o2 sensors voltage was out of range after I started it. Do I need to let it warm up or cold start? I'll replace map sensor and see. Thank you all for the advice so far.

 

[OR VietVet]

I think I would do a compression test and post pics of the 8 plugs, in order by cylinder number. First I have heard about the smoking problem. Not having enough power? O2 sensors and cats causing clogged exhaust maybe but typically that will set a code as well.

 

[Robochop]

Is the P0300 code the only code you are getting? Who is reading the codes? Are you able to check for ABS codes?

How does the engine sound? Rough? Tapping? Clanking? I ask because a rough running engine can cause Stabilitrak to be disabled.

Do you have AFM disabled?

I agree with @OR VietVet in that you should get the MAP sensor situation taken care of first as it can affect a lot of things.

Hello everyone, I am having a similar issue (09 Yukon SLT 5.3 engine). I am feeling a missfire (Cyl #5) when I step on the gas, the check engine light comes on and flashes and so does the stabil-trak and traction control dash lights. And it also triggers the alarm bells through the speakers. I bought it used with 105k miles and it now has 142k. This problem popped up all of a sudden like with no warning. I changed spark plugs about 3000 miles ago as I figured it was time. I have heard stories about this motor having cam shaft issues. I did pull the # 5 spark plug and swapped it with the #1. They both looked the same, a almost a little wet with some brown coloring. I also did a compression test and #5 only had about 100 but #1 had about 150psi. I didn't check any others. I turned off the light with my OBD2 reader, but the codes immediately returned after a short drive. Any suggestions? Thanks

 

[OR VietVet]

@Robochop, this is an old thread. To get more responses, you really should post this in your own thread. Hopefully a mod can move this for you. @Fless

 

[Fless]

@Robochop, this is an old thread. To get more responses, you really should post this in your own thread. Hopefully a mod can move this for you. @Fless

Mods can't move posts like that, so please stop suggesting it. It would be best for @Robochop to start a thread so he/she/it/they -- let me know if I missed any pronouns -- has/have control of the thread title and get notices of follow-up posts.