P0300 and hesitation going up hills

[Meccanoble]

In the past I complained about transmission stutter which recently improved with another transmission fluid/filter change. But lately i'm getting the P0300 code for misfire and really feeling it going up hills. Truck sometimes loses a lot of power. I have done the following:

1. Replaced air filter
2. Cleaned MAF
3. Spark plugs changed about 50k miles ago or less
4. Tested spark with spark tester on all 8 coils


If all these tests are good, my next concern is fuel. Some research states a bad fuel filter could cause loss of power especially going up hills but it seems its much harder to change on this truck than previous generation so holding off. I think its in the gas tank?

At one time I got a code for P0305 which was for Cylinder 5 misfire but this never came back. I swapped coils in cylinder 5 and 6 to see if code would repeat or switch to different cylinder but same or different code never came up. Plus spark tester seems to confirm they are all functional.

I was in the process of creating a home depot intake just to feel better about myself with breather filter for PVC but i'm sure this wont help. Any suggestions on where to look next? How can I test fuel pressure? I have pressure gauges for the A/C stuff but doubt i can use for any troubleshooting here.

I'm going to purchase some fuel cleaner and refill with premium (95% of the time I get regular from the same 2 or 3 gas stations). I refilled somewhat recently so possibly bad fuel...

 

[BG1988]

put 6 bottle techron buy 1 get 1 at autozone

 

[Meccanoble]

6 bottle? I think i know what you mean. Put 6 bottles though?

 

[BG1988]

6 bottle? I think i know what you mean. Put 6 bottles though?

you think it's going to diluted in 25 gallons
don't worry it's flammable it's basically gasoline in a bottle.. PEA based system cleaner designed for gas engines

i would not use a non PEA based such as seafoam (could cause damage)

it's cheap enough to be worth it it's only 3.50 a bottle BOGO (6.99 for two bottles)


so it's inexpensive enough

i would check for vacuum leaks as well

the MAF or IAT could be faulty simple enough to replace your self



i would just buy gas that all ready includes it from chevron

since these engine burn oil you have no choice but to use it

 

[Meccanoble]

Just to confirm, you saying 6 bottles of chevron fuel cleaner wont do harm?

 

[Rocket Man]

Just to confirm, you saying 6 bottles of chevron fuel cleaner wont do harm?

After all that he says he would just buy gas that already includes it from Chevron.

 

[Meccanoble]

After all that he says he would just buy gas that already includes it from Chevron.

Ahhh thanks for confirming

 

[kbuskill]

You said your plugs only have 50k miles but you didn't say what type of plugs you installed or where they came from.

I bought a set of "AC Delco Iridium" plugs from Ebay only to find out that they were fakes.... not Iridium... they were shot in less than 75k miles.

I replaced them with NGK Ruthenium plugs from Rock Auto.

I have never ran anything but AC Delco plugs in all my GMs, but since NGK is making the plugs for AC Delco now I figured what the heck.

 

[Meccanoble]

You said your plugs only have 50k miles but you didn't say what type of plugs you installed or where they came from.

I bought a set of "AC Delco Iridium" plugs from Ebay only to find out that they were fakes.... not Iridium... they were shot in less than 75k miles.

I replaced them with NGK Ruthenium plugs from Rock Auto.

I have never ran anything but AC Delco plugs in all my GMs, but since NGK is making the plugs for AC Delco now I figured what the heck.

I replaced plugs with the OEM AC Delco 41-110 Professional Iridium plugs off Amazon in Summer of 2017. I only go with what is recommended in this forum. I just did more testing and took a video showing some of the symptoms. I wonder if this is a sign of clogged cats as I can hear some exhaust issues or possible leaks. Uploading video now.

 

[Meccanoble]