Shutter/Misfire under low RPM and load

ic3man5 · May 20, 2020

On 2/8/2020 at 6:40 AM, Doublebase said:

But does that make sense to you? A vacuum issue would introduce air into the intake, the computer would compensate and add MORE fuel, not take away fuel, right? So you'd have + fuel trim, not negative. Vacuum leaks skew the fuel trim positive.

And there is no PCV valve on these trucks, it's a fixed orifice, it won't get any larger and cause excess flow. You can replace it, but it's not a PCV valve. And if you did have a vacuum leak in that part of the system, I think it would cause a misfire at cylinder 5 (because the PCV line dumps right above cylinder five at the intake). If you have a catch can, potentially you may have a leak at one of the lines causing a vacuum situation, but I still think your fuel trim would trend +, not -.

I could be totally wrong, let me know what you find out/how it goes.

I think I've come to the conclusion its a vacuum leak, high pressure pump is going bad, or fuel injector is blown out (not likely since it seems to be on both banks). I decided to wait until it gets worse to figure it out since I can't do much without better tools or taking it to a shop. I always get stuck with the stupid issues with everything.

Ozer · May 20, 2020

My suspicion is the torque converter because all this is very similar to what I experienced and I was chasing a misfire, when all along it was the TQ slipping.
That is covered till 120k miles so I suggest you have the dealer take a look, pay the $200 diagnostics fee. If it's the TQ you won't have to pay that fee.

Mine went about 30k after getting it flushed

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Edited May 20, 2020 by Ozer

roland siller · May 23, 2020

is it coil over plugs they tend to get weak from engine heat, just a thought sounded familiar.

Doublebase · May 24, 2020

On 5/20/2020 at 1:45 AM, ic3man5 said:

I think I've come to the conclusion its a vacuum leak, high pressure pump is going bad, or fuel injector is blown out (not likely since it seems to be on both banks). I decided to wait until it gets worse to figure it out since I can't do much without better tools or taking it to a shop. I always get stuck with the stupid issues with everything.

I probably missed it, but how many miles do you have?

I still don't think it's a vacuum leak, a vacuum leak would cause fuel trims to go positive, not negative. And you'd feel the vacuum leak at idle, not so much when driving or shifting gears/under light acceleration, because the throttle plate opens up and the air pressure (outside/inside intake manifold equalizes, causing vacuum leaks to disappear). So I don't think it's that, although if you have a catch can you can always check your hoses and make sure.

And if it was your high pressure fuel pump you'd have a code for it, plus those aren't really common problems with these trucks...torque converters are. Transmissions are. Fuel injectors are. I think your problem is in one of those three areas.

And I'm in the same boat. Just a little shutter under light acceleration going up a hill on the highway. No codes (except one for five seconds, five months ago misfire cylinder 5). Hooked up a scan tool and when the "event" does happen, cylinder 5 seems to act up. It could be dirty valve, fuel injector (plug looked great, wire looked great). Only 50,000 miles. Honestly it feels more like a torque converter. Pulled pan, everything looked fine. I'll keep driving it until a hard code comes on...dealer already said they'd charge me a diagnostic fee to even look at it...I'm an ASE master certified tech, I'm not sure they'll find the problem.

carnau · May 25, 2020

On 5/20/2020 at 1:41 AM, ic3man5 said:

Everything I could test with the fuel injectors showed they were okay from the computer side, I can't test more without actually taking it to a shop and seeing if they are balanced properly. I did individually turn off each injector idling the truck @ ~2500 RPM and there was no difference in any of them.

Check this post out where I explain the drop on these injectors.

ic3man5 · May 27, 2020

On 5/20/2020 at 6:59 AM, Ozer said:

My suspicion is the torque converter because all this is very similar to what I experienced and I was chasing a misfire, when all along it was the TQ slipping.
That is covered till 120k miles so I suggest you have the dealer take a look, pay the $200 diagnostics fee. If it's the TQ you won't have to pay that fee.

Mine went about 30k after getting it flushed

Sent from my SM-N960U using Tapatalk

I had a known reputable transmission shop look at it and they said it wasn't the transmission so I'm ruling it out for right now.

ic3man5 · May 27, 2020

On 5/23/2020 at 5:56 PM, roland siller said:

is it coil over plugs they tend to get weak from engine heat, just a thought sounded familiar.

Yeah I thought the same thing but no misfires being thrown at all, spark seems to be perfect.

ic3man5 · May 27, 2020

On 5/24/2020 at 7:08 AM, Doublebase said:

I probably missed it, but how many miles do you have?

I still don't think it's a vacuum leak, a vacuum leak would cause fuel trims to go positive, not negative. And you'd feel the vacuum leak at idle, not so much when driving or shifting gears/under light acceleration, because the throttle plate opens up and the air pressure (outside/inside intake manifold equalizes, causing vacuum leaks to disappear). So I don't think it's that, although if you have a catch can you can always check your hoses and make sure.

And if it was your high pressure fuel pump you'd have a code for it, plus those aren't really common problems with these trucks...torque converters are. Transmissions are. Fuel injectors are. I think your problem is in one of those three areas.

And I'm in the same boat. Just a little shutter under light acceleration going up a hill on the highway. No codes (except one for five seconds, five months ago misfire cylinder 5). Hooked up a scan tool and when the "event" does happen, cylinder 5 seems to act up. It could be dirty valve, fuel injector (plug looked great, wire looked great). Only 50,000 miles. Honestly it feels more like a torque converter. Pulled pan, everything looked fine. I'll keep driving it until a hard code comes on...dealer already said they'd charge me a diagnostic fee to even look at it...I'm an ASE master certified tech, I'm not sure they'll find the problem.

66K now, about 58K at the time of the original post I believe. I shouldn't have said vacuum leak but something wrong with the vacuum like maybe something plugged from the catch can (I doubt it though).

I seen a few posts early on that the hp fuel pump goes bad but I think those were just faulty ones from factory.

I came to the same conclusion that a mechanic won't be able to find this problem and most people won't even notice it. Waiting for it to get worse but I don't have it at all now that I tuned the VE table in HP Tuners.

ic3man5 · May 27, 2020

On 5/25/2020 at 5:49 PM, carnau said:

Check this post out where I explain the drop on these injectors.

Do you have a link to the video it seems to be missing in that link, how did you test the fuel injectors? Special software and hardware?

EDIT: Nevermind it loaded second time I went to the page. I don't like if this is the solution because that means I'll be forced to upgrade the intake manifold that I've been looking at for years.

Edited May 27, 2020 by ic3man5

albone3000 · April 18, 2021

Im having the same problem. Happened shortly after I got the trans flushed and changed the plugs myself. I originally figured I screwed something up with the plugs but its clearly shuddering and its not detecting any misfires. Also it ran great for a few days with the new plugs and trans fluid. MAF seems to shoot up when it shudders. Im just monitoring with a bluetooth obd tool. Anyone else figure this out yet?

bone450 · May 26, 2021

I’m having similar issue; I take it the cause to the issues have not been determined other than tuning it out. I started getting the shutter in my 2015 5.3l w/ 6 speed at around 83k miles. Light load, light throttle position, from a cold start is the most likely conditions for it to shutter, if it does it at all. I can normally get it to happen around 1,000 – 1,500rpm and 40mph or 60mph range. From a cold start with a slight incline is the most reproducible conditions. Adjusting throttle position will make it go away. A CEL will only show up if you let it shutter/chug long enough so it thinks it’s a misfire. Maybe it is a misfire for all I know.

Had it at the dealer twice for this, I told them transmission, they were adamite it was plugs and wires, I was skeptical, but did not have time to deal with it myself. Plugs and wires did nothing, had the same condition on the ride home. Took it back they could not reproduce.

Are the handheld scanners worth it or do you need the thousand-dollar items to do any real DIY troubleshooting?

I think it’s the transmission (torque converter) but am resisting dumping more money into this thing or the dealer that is guessing the same as I could.

ic3man5 · June 4, 2021

I finally fixed my shutter! I had a shop replace my radiator (thanks GM for great radiators). Turns out I had a couple minor vaccum leaks due to hoses on the catch can I had installed becoming lose over time (originally press fit with no hose clamps). The biggest offender that actually set off the CEL was the hose on the top left hand side of the engine above/near the valve cover oil cap. It's behind some stuff so it's easy to overlook. Pull that hose with the engine on and it starts running like you are drowning it in fuel and have a super aggressive cam profile. The one under the intake throttle body seemed to be an offender also but not nearly as bad.

I'm now within 2-4% negative fuel trim readings.

RandyxGM · September 15, 2022

On 5/20/2020 at 6:59 AM, Ozer said:

My suspicion is the torque converter because all this is very similar to what I experienced and I was chasing a misfire, when all along it was the TQ slipping.
That is covered till 120k miles so I suggest you have the dealer take a look, pay the $200 diagnostics fee. If it's the TQ you won't have to pay that fee.

Mine went about 30k after getting it flushed

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Funny, I am chasing a TC issue and now looking for misfire (no code).

pokismoki · September 18, 2022

I once was playing with the TC in HPT, and decided to zero my slip in v4 mode on TC lock up. this created the harsh vibrations everyone talks about. it went away after i added the 100 rpm slip to lock up, instead of 0 rpm slip in v4

pokismoki · September 18, 2022

On 6/3/2021 at 10:19 PM, ic3man5 said:

I finally fixed my shutter! I had a shop replace my radiator (thanks GM for great radiators). Turns out I had a couple minor vaccum leaks due to hoses on the catch can I had installed becoming lose over time (originally press fit with no hose clamps). The biggest offender that actually set off the CEL was the hose on the top left hand side of the engine above/near the valve cover oil cap. It's behind some stuff so it's easy to overlook. Pull that hose with the engine on and it starts running like you are drowning it in fuel and have a super aggressive cam profile. The one under the intake throttle body seemed to be an offender also but not nearly as bad.

I'm now within 2-4% negative fuel trim readings.

you need to install the 170 thermostat in motor to make the radiator last longer, it's made of plastic and stock temp is too high for this material to last.

catch cans are a waste of time. get a pair of uni- filters on the valve breathers and plug the intake ports to the CAI, and run a tad thicker oil 5-30 or 10-30 from redline