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]

 

[Rocket Man]

That’s some serious misfires imo. I don’t think it’s clogged cats but it could be I guess. I say you need a scanner that can show live data so you can see if there’s maybe 2 cylinders that are misfiring badly, it could be as simple as bad wires or coils. If you can narrow it down then you can swap parts around to see if the misfires follow. I had a couple wires that got burned inside the boot protectors because of my headers and my truck ran just like that. If you have wires that broke where they snap onto the plugs or they weren’t pushed all the way on they could be making bad contact. Sometimes it takes awhile for them to wiggle enough to lose contact. Just guessing here. It’s just easier if you can watch misfire data live. If you see it happening to all the cylinders then that’s a big clue towards fuel or cats.

 

[Meccanoble]

That’s some serious misfires imo. I don’t think it’s clogged cats but it could be I guess. I say you need a scanner that can show live data so you can see if there’s maybe 2 cylinders that are misfiring badly, it could be as simple as bad wires or coils. If you can narrow it down then you can swap parts around to see if the misfires follow. I had a couple wires that got burned inside the boot protectors because of my headers and my truck ran just like that. If you have wires that broke where they snap onto the plugs or they weren’t pushed all the way on they could be making bad contact. Sometimes it takes awhile for them to wiggle enough to lose contact. Just guessing here. It’s just easier if you can watch misfire data live. If you see it happening to all the cylinders then that’s a big clue towards fuel or cats.

I have the torque app. How would i test? I'll go back and make sure all is connected. They all show spark through spark tester. At one time i did get cylinder 5 misfire but same message hadn't come back since switching coils with cylinder 6

 

[Rocket Man]

I have the torque app. How would i test? I'll go back and make sure all is connected. They all show spark through spark tester. At one time i did get cylinder 5 misfire but same message hadn't come back since switching coils with cylinder 6

Can you see misfire data as the engine is running? I’m not familiar with the torque app. I use my Tech2 and can watch misfires for cylinders 1-8 and it counts them up to 100 cycles and then resets and starts over, and also shows history so if you sit there and watch for awhile it might do say 10 reps of 100 cycles and shows the total misfires for each plug which has fired 1000 times by then. If I’m getting more than a few misfires per 100 then something isn’t right. I was getting 20-40 per 100 on a couple cylinders.

 

[Meccanoble]

i dont remember seeing anything discussing misfires on torque

 

[kbuskill]

Can you see misfire data as the engine is running? I’m not familiar with the torque app. I use my Tech2 and can watch misfires for cylinders 1-8 and it counts them up to 100 cycles and then resets and starts over, and also shows history so if you sit there and watch for awhile it might do say 10 reps of 100 cycles and shows the total misfires for each plug which has fired 1000 times by then. If I’m getting more than a few misfires per 100 then something isn’t right. I was getting 20-40 per 100 on a couple cylinders.

Yes you can see misfires per cylinder with Torque Pro.

Personally I would pull at least 1 or 2 plugs just to put eyes on them and rule out it being a (fake) plug issue.

If the plugs look good then you can move on to looking at other possible culprits.

Thus is what my fake Delco Iridium plugs looked like when I pulled them compared to the new Ruthenium plugs...

 

[Meccanoble]

Yes you can see misfires per cylinder with Torque Pro.

Personally I would pull at least 1 or 2 plugs just to put eyes on them and rule out it being a (fake) plug issue.

If the plugs look good then you can move on to looking at other possible culprits.

Thus is what my fake Delco Iridium plugs looked like when I pulled them compared to the new Ruthenium plugs...
View attachment 249516

how many miles on those? Wouldnt i have issues a while ago, like within first 10k miles?

 

[kbuskill]

i dont remember seeing anything discussing misfires on torque

In the Torque Pro app go into Settings > Manage Extra PIDs/Sensors > press the 3 dots at top right of screen > select Add predefined set > Pontiac/GM/Opel/Vauxhall

Now scroll down about 40-45 PIDs and you will see this...

They are not in order... I don't know why... but all 8 cylinders are available.

 

[kbuskill]

how many miles on those? Wouldnt i have issues a while ago, like within first 10k miles?

Nope... mine had roughly 75k miles on them and I didn't have any misfires... only reason I changed them was because I wanted to try the Ruthenium plugs and I figured why not.

 

[Meccanoble]

In the Torque Pro app go into Settings > Manage Extra PIDs/Sensors > press the 3 dots at top right of screen > select Add predefined set > Pontiac/GM/Opel/Vauxhall

Now scroll down about 40-45 PIDs and you will see this...
View attachment 249517

They are not in order... I don't know why... but all 8 cylinders are available.

You are a God send. Great instructions except...mine only shows 6 cylinders. I have the free torque app. Not sure if that matters. It has 2 sets of misfires (current & history)

Also, what should be happening on this view? I can only edit or delete these options. They are set at 1000 max value.

 

[kbuskill]

You are a God send. Great instructions except...mine only shows 6 cylinders. I have the free torque app. Not sure if that matters. It has 2 sets of misfires (current & history)

Also, what should be happening on this view? I can only edit or delete these options. They are set at 1000 max value.

Once you enable the PIDs then you will want to go back out and go to Realtime Information and long press on a blank screen and Add Display then choose which type, I use the Digital Display then you scroll down,like you did before, until you see Misfire Cylinder (X) current or history and select the one you want to see. Do this for each cylinder.

I'm not sure why yours only shows 6 cylinders... maybe it is because you have the free version.