03 GMC Yukon P0300 misfire 5.3

[Jeffs5-3]

Hello everyone I have an 03 Yukon with 5.3l L59 171k miles on it and it’s been a love hate relationship with the truck tbh. I have a dreaded misfire that’s just been kicking my ass and i want to address it because I want a reliable daily. I bought the truck about 2 months ago the truck had given me a reduced engine power message but with no check engine light I figured it would be spark plugs so I changed them out perfect I then went ahead and changed out the wires while I was at it. The truck ran good somewhat I figured I still had a misfire because going down from 2-3k rpm I would hear the engine backfire a lot. Yesterday as I was heading home I felt the truck didn’t want to accelerate as much as it would normally and then it started shaking and idle very rough then check engine light came on first flashed me then it stayed lit I pulled over I turned it off and waited 15 seconds. I’ve dealt with reduced engine power before but the message never came I tried to turn it on but the motor just sounded like it was struggling to start up and crank over it started coughing and sputtering I thought the worst of the worst and was like shit what now I waited a bit longer I managed to get it started okay great went to autozone that was down the street scanned me the code and there it was P0300. I love the truck but I just want it to run right I’ve been looking online saying coil packs, air intake manifold gasket, fuel injectors, 02 sensors, air filter, fuel pressure, all those things but obviously no solution so before I go ahead and start buying and just replacing everything I want to pin point it to one thing. P0300 is the only code that popped up no other cylinder or code besides the abs malfunctioning but I had that already but the damn dreaded p0300 is making me just wanna get rid of this thing your solutions will be greatly appreciated and looked into!

 

[Doubeleive]

Hello everyone I have an 03 Yukon with 5.3l L59 171k miles on it and it’s been a love hate relationship with the truck tbh. I have a dreaded misfire that’s just been kicking my ass and i want to address it because I want a reliable daily. I bought the truck about 2 months ago the truck had given me a reduced engine power message but with no check engine light I figured it would be spark plugs so I changed them out perfect I then went ahead and changed out the wires while I was at it. The truck ran good somewhat I figured I still had a misfire because going down from 2-3k rpm I would hear the engine backfire a lot. Yesterday as I was heading home I felt the truck didn’t want to accelerate as much as it would normally and then it started shaking and idle very rough then check engine light came on first flashed me then it stayed lit I pulled over I turned it off and waited 15 seconds. I’ve dealt with reduced engine power before but the message never came I tried to turn it on but the motor just sounded like it was struggling to start up and crank over it started coughing and sputtering I thought the worst of the worst and was like shit what now I waited a bit longer I managed to get it started okay great went to autozone that was down the street scanned me the code and there it was P0300. I love the truck but I just want it to run right I’ve been looking online saying coil packs, air intake manifold gasket, fuel injectors, 02 sensors, air filter, fuel pressure, all those things but obviously no solution so before I go ahead and start buying and just replacing everything I want to pin point it to one thing. P0300 is the only code that popped up no other cylinder or code besides the abs malfunctioning but I had that already but the damn dreaded p0300 is making me just wanna get rid of this thing your solutions will be greatly appreciated and looked into!

well generally speaking:
reduced engine power message is often caused by a throttle body error, be it the throttle body it's self or the harness wiring
a misfire could be a whole bunch of things, but you can try to rule some things in or out
first thing to always look at is the battery cables and main grounds particularly on the block
plugs and wires you said are new or new-ish, so I would then start looking at coil packs, injectors, and coil harness and injector harness. broken grounds are not entirely uncommon.
also check fuel pressure and check for a vacuum leak
are the plug wires oem? cheap wires can be a possible problem also FAKE (knockoff) acdelco spark plugs are found all the time
those are some basic things to really look over, if all of that is FOR-SURE good then you have to start looking more internally or use a scanner to see if anything is happening that you cannot find visually
for instance you can find a dark area at night and pop the hood, lights off and see if you see any electrical arcing anywhere

 

[Jeffs5-3]

well generally speaking:
reduced engine power message is often caused by a throttle body error, be it the throttle body it's self or the harness wiring
a misfire could be a whole bunch of things, but you can try to rule some things in or out
first thing to always look at is the battery cables and main grounds particularly on the block
plugs and wires you said are new or new-ish, so I would then start looking at coil packs, injectors, and coil harness and injector harness. broken grounds are not entirely uncommon.
also check fuel pressure and check for a vacuum leak
are the plug wires oem? cheap wires can be a possible problem also FAKE (knockoff) acdelco spark plugs are found all the time
those are some basic things to really look over, if all of that is FOR-SURE good then you have to start looking more internally or use a scanner to see if anything is happening that you cannot find visually
for instance you can find a dark area at night and pop the hood, lights off and see if you see any electrical arcing anywhere

The Spark plugs I had put In it at NGK original ones were acdelco and those were shot the wires I used were some autozone duralast ones I didn’t find any acdelco wires unfortunately but I settles for these I ruled those 2 things out as they’re both new parts. Next I need to check the grounds on the vehicle as I’ve heard they’re a common culprit for things as well as when I roll windows up the motor surges for power then runs fine when I let go so grounds I have to check. Fuel pressure I would have to check as well as for a vacuum leak. The truck came with an oiled air filter could that also b a common issue that maybe the filter is dirty

 

[Doubeleive]

The Spark plugs I had put In it at NGK original ones were acdelco and those were shot the wires I used were some autozone duralast ones I didn’t find any acdelco wires unfortunately but I settles for these I ruled those 2 things out as they’re both new parts. Next I need to check the grounds on the vehicle as I’ve heard they’re a common culprit for things as well as when I roll windows up the motor surges for power then runs fine when I let go so grounds I have to check. Fuel pressure I would have to check as well as for a vacuum leak. The truck came with an oiled air filter could that also b a common issue that maybe the filter is dirty

the "oiled" air filter can cause issue's because it causes the maf to collect dirt/dust and that can make the vehicle do ALL kinds of weird stuff, so ya I would at minimum clean the maf and throttle body for sure. I have personally seen a bad/dirty/faulty maf make the vehicle throw dam near every code you can think of and make the transmission buck like a unridden horse

 

[Jeffs5-3]

the "oiled" air filter can cause issue's because it causes the maf to collect dirt/dust and that can make the vehicle do ALL kinds of weird stuff, so ya I would at minimum clean the maf and throttle body for sure. I have personally seen a bad/dirty/faulty maf make the vehicle throw dam near every code you can think of and make the transmission buck like a unridden horse

Will do ill definitely clean it out or go as far as just ditching it because damn if it makes my engine run like absolute dog crap I’m getting rid of it

 

[Doubeleive]

Will do ill definitely clean it out or go as far as just ditching it because damn if it makes my engine run like absolute dog crap I’m getting rid of it

In (my book) anyway, completely in my experience on the gmt800's that after 160k the maf should be replaced because they just get goofy or can go bad period and it just leads to headaches and tail chasing.

 

[Jeffs5-3]

In (my book) anyway, completely in my experience on the gmt800's that after 160k the maf should be replaced because they just get goofy or can go bad period and it just leads to headaches and tail chasing.

So would you recommend cleaning the filter or ditching it completely and replacing maf sensor just to make sure as well

 

[strutaeng]

This is probably not what you want to hear, but it may be better to take it to a good honest mechanic. I know a lot of DIY guys will start with the parts cannon approach and may fix the issue by luck.

Or it may not, leading to frustration and money spent replacing perfectly good parts with possibly inferior replacements and creating unnecessary unknowns (is the new MAF sensor you just replaced bad out of the box?!). It can't be bad, right? Or can it? How do you know? Now you got yourself a real mess if that brand new sensor is new and you've ruled it out. And still have to figure out your original issue(s) and you've spent $120.

You either have to take time and learn fundamental diagnostics and invest in tools, use the parts canon approach and get lucky or take it to a mechanic. Often times vehicles will have more than one issue.

Some shops may charge you a fee for diagnosis only, and you can replace whatever is bad yourself.

 

[Doubeleive]

So would you recommend cleaning the filter or ditching it completely and replacing maf sensor just to make sure as well

well a can of cleaner is only a few bucks I would at least give that a try first, I can't recommend a parts cannon approach, a misfire cause is usually figured out with some basic troubleshooting but..it's not always simple

 

[Jeffs5-3]

well a can of cleaner is only a few bucks I would at least give that a try first, I can't recommend a parts cannon approach, a misfire cause is usually figured out with some basic troubleshooting but..it's not always simple

I figure a parts cannon would be costly and just replace parts I’d get lucky and all but at the result of it still misfiring is just a waste I’ll try to clean the maf sensor and get a new air filter see if it makes the truck run better if it still doesn’t then I’ll take it to a reputable shop to do live data check and see if it’s running well or not