Misfiring/ Hesitation/ Loss of power under load and High RPM

[midwestdenaliguy]

5 hours ago, R32R1 said:

Spoke too soon...exhaust back on and it's doing it again. Not sure if it's coincidental, but something tells me I'll be swapping the exhaust back to stock (yet again) for them to look at this.

 

Im starting to really dislike this truck, and that's the last thing I need right now. 

 

Symptoms are in 3rd gear and up, 40% throttle- I'll get the hesitation/ misfire feeling. I checked the maintenance records and this truck already had the torque converter replaced at 35k miles. All updates are done on it, so I'll try swapping the MAF to see if that's the cause. 

Are the cats stock or does that Corsa exhaust replace them when installed? Reason I ask is the cats can cause misfire symptoms. 

 

Also you mentioned them finding coolant while replacing your injectors. Do you ever have a rough cold start? If so there was a batch of bad heads that went out and can cause coolant to leak into the cylinders leading to misfires. Look up PIP5498, they don't describe misfires in 3rd gear though...so might not be it.

[300 Blackout]

I checked the maintenance records and this truck already had the torque converter replaced at 35k miles.

Why was the torque converter replaced? What material did it release into your trans fluid and valve body when it was failing? It’s very difficult to flush all of the debris out of the trans and trans cooler, not to mention any debris that worked it’s way into your valve body and ruined or caused damage to the valves. Perhaps not immediately noticeable, but enough to severely shorten the life of the trans components.

You also said it feels just like another car did with bent valves, etc... These trucks have known issues with the AFM lifters getting stuck. Sometimes debris can cause it. Other times, the VLOM fails to provide adequate lubrication to the lifter when it’s coming out of V4 and can cause galling of the operating components of the AFM lifters.

That’s when things get bad because there can be intermittent function of the lifter and any damage to the valve-train and cam can be compounding also.

If you don’t want to be “that guy” at your friend’s dealership, take it to another dealership with a good reputation. All scenarios above are very expensive and labor intensive.

[R32R1]

15 hours ago, midwestdenaliguy said:

Are the cats stock or does that Corsa exhaust replace them when installed? Reason I ask is the cats can cause misfire symptoms. 

 

Also you mentioned them finding coolant while replacing your injectors. Do you ever have a rough cold start? If so there was a batch of bad heads that went out and can cause coolant to leak into the cylinders leading to misfires. Look up PIP5498, they don't describe misfires in 3rd gear though...so might not be it.

 

All (3) cats are stock, Corsa is your standard cat-back exhaust:

 

Corsa Exhaust Site

 

Start-up is nice and strong, no hesitation there. It cranks slightly longer than my other ones did, but I'm pretty sure that's the nature of the 6.2l since I remember thinking that to myself when moving a dealership Yukon 6.2l one day.

 

5 minutes ago, 300 Blackout said:

 

Why was the torque converter replaced? What material did it release into your trans fluid and valve body when it was failing? It’s very difficult to flush all of the debris out of the trans and trans cooler, not to mention any debris that worked it’s way into your valve body and ruined or caused damage to the valves. Perhaps not immediately noticeable, but enough to severely shorten the life of the trans components.

 

 

 

I'm not sure why it was replaced since it was with the previous owner, and he had it done at another dealership. I noticed the papers when picking it up, but I didn't ask them to look up the details - just saw torque converter replaced.

 

6 minutes ago, 300 Blackout said:

You also said it feels just like another car did with bent valves, etc... These trucks have known issues with the AFM lifters getting stuck. Sometimes debris can cause it. Other times, the VLOM fails to provide adequate lubrication to the lifter when it’s coming out of V4 and can cause galling of the operating components of the AFM lifters.

That’s when things get bad because there can be intermittent function of the lifter and any damage to the valve-train and cam can be compounding also.

If you don’t want to be “that guy” at your friend’s dealership, take it to another dealership with a good reputation. All scenarios above are very expensive and labor intensive.

 

 

Yea I have a highly modified VW R32, and it feels similar to when I bent 3 valves in that thing. Granted, not as drastic or any CEL, but that memory never fades.

 

What's weird about this is that when I picked it up, everything felt fine (for once). I drove a bunch, felt fine, plugged my Range AFM Disabler in, felt fine. I put the exhaust back on, felt fine after that! Driving about 100 more miles and I feel like a 4.3l can pass me at times. I spoke to my buddy at the dealership and he gave me the green light to use a tuner to see if that works; he used to tune C7 Le Mans cars in his past life and is confident it has to be software related. As long as I can bring it back to stock with stock emissions, they can cover it under warranty.

 

I'm still hesitant on doing that, as I really want them to inspect the valves for any major issues like the AFM lifters screwing up. My gut instinct is telling me that I have a weak/cracked/broken valve-spring somewhere. If it's a stuck lifter, you KNOW it's a stuck lifter because it'll show symptoms at idle. But a defective valve spring can be deceiving at idle, yet when it really needs to work, that's when it'll show its true colors...then again, I'm not a tech and that's only a hunch 

[barto]

Hey, my truck is doing exactly what you are saying.  Did you ever track it down or just dump the truck? 

Edited August 9, 2020 by barto
Typo