6.2 LS Swap is running very bad, NEED HELP!

[Kid_kevi]

Customer calls me and so of course, I come out.

The car has a Gen IV 6.2 engine that has supposedly been stroked to a 7.0L. It idles rough and when at temp the driver side of the engine makes a hard "Thud", "Ping" , "Gas belch". I hate to say knock but it's definitely reminiscent of one. When it happens, the knock sensors go wild and pull timing. the engine falls on its face and runs worse, then it will catch a good idle and anywhere from 30-60 seconds later, the hard thud happens again on the driver side and the issue repeats.

The car has an aftermarket 255 LPH fuel pump and fuel regulator setup. The corvette style. I of course, set the injector vs. pressure table to be 42lbs all the way across because it has LS3/LS7 injectors installed, a fast 102mm intake and no FSCM. I disabled the fscm in the tune as well.

The issue I'm explaining only happens when it is warmed up. I am stumped, not your typical tuning issue.

The odd thing is , it seems to idle fine during warmup but once at temp the thudding begins. It more than likely happens during warmup as well, but it's not terrible.

The car has a rowdy camshaft and I'm stumped boys, below I am going to attach the tune file and also the log of it warming up (seemingly okay) and then a log of it hot and acting up.

I coould really use some helpful insight, this definitely is'nt your run of the mill issue and it definitely isn't your typical Ls powered vehicle.

Thank you guys for taking the time to read this.

[TheMechanic]

Injector setup is wrong. You have this set up for a referenced reg. You don't give an injector so no way of knowing what the actual data is. That is just the start but one of the most important ones.

[blindsquirrel]

Pushrod length?

Does it maintain fuel pressure in the rail after it's shut off? (if it doesn't, look for a leaky injector, which could cause hydro-locking with fuel, and of course rich condition, but also if it's rich enough to cause a misfire that shows up as lean at the O2)

[rabbs88]

You need to add to your logs dynamic airflow, EQ commanded, vehicle speed, just to name a few. Your MAF and VVE need work and it idles rough because your timing goes from 25 degrees down to 4. As stated already, correct injector data would help

Edit, Just noticed you control module voltage drops into the 11's. Might want to check that out too

[edcmat-l1]

It definitely has something going on with bank 1. Need to do some diag work. It's not "in the tune". First thing to do to narrow it down is check the header tube temps with a temp gun. Look for a cool or cold tube compared to the rest.

Pull the plugs. Pull the valve covers. Check pushrod length, lifter preload, etc. Look for broken springs, etc.

Do a compression and leak down test. Buy a decent spark tester and check the spark from each coil.

[Kid_kevi]

Injector setup is wrong. You have this set up for a referenced reg. You don't give an injector so no way of knowing what the actual data is. That is just the start but one of the most important ones.

the injectors are ls3 injectors, part number verifies they are '08-'13 corvette

[Kid_kevi]

Pushrod length?

Does it maintain fuel pressure in the rail after it's shut off? (if it doesn't, look for a leaky injector, which could cause hydro-locking with fuel, and of course rich condition, but also if it's rich enough to cause a misfire that shows up as lean at the O2)

I have not checked pushrod length, I did not build the engine. What are your thoughts on what I've described? Possibly too long or short?

When I shut off the key you can hear fuel being returned, haven't checked if it maintains pressure honestly.

The o2s when warm show super lean numbers but you can smell the pig rich fuel so its kind of a mind boggler to me!

[Kid_kevi]

You need to add to your logs dynamic airflow, EQ commanded, vehicle speed, just to name a few. Your MAF and VVE need work and it idles rough because your timing goes from 25 degrees down to 4. As stated already, correct injector data would help

Edit, Just noticed you control module voltage drops into the 11's. Might want to check that out too

I've added those parameters for next time I see the car. I will try to smooth timing, I pulled a part number and they are 08-2013 corvette injectors , online stated to be 42lb'ers. Also the car has no fscm but an aftermarket fuel pump with a "corvette regulator" to keep it at 58 psi constantly.

I will look into the voltage drop!

[Kid_kevi]

It definitely has something going on with bank 1. Need to do some diag work. It's not "in the tune". First thing to do to narrow it down is check the header tube temps with a temp gun. Look for a cool or cold tube compared to the rest.

Pull the plugs. Pull the valve covers. Check pushrod length, lifter preload, etc. Look for broken springs, etc.

Do a compression and leak down test. Buy a decent spark tester and check the spark from each coil.

Okay Man, thanks for your input, I've never seen this before, for the motor to bang/thud on the driver side every 30sec to 1 min. (when warm) is odd, everything in the tune file should make it at least run without that issue.

I didn't build the motor so of course anything could be wrong, just feel obligated to try and figure it out because that's how I'm wired!

[edcmat-l1]

Okay Man, thanks for your input, I've never seen this before, for the motor to bang/thud on the driver side every 30sec to 1 min. (when warm) is odd, everything in the tune file should make it at least run without that issue.

I didn't build the motor so of course anything could be wrong, just feel obligated to try and figure it out because that's how I'm wired!

Here's the thing, and it's no offense to you. Most people think because they have the ability to pull a tune, view it and modify it, that it must somehow be able to either fix problems like this, or cause problems like this (in the case of something being incorrect). When neither are true. Hard misfires, random misfires, stutters, backfires, etc. are almost always hard part problems or wiring problems.

[Kid_kevi]

Here's the thing, and it's no offense to you. Most people think because they have the ability to pull a tune, view it and modify it, that it must somehow be able to either fix problems like this, or cause problems like this (in the case of something being incorrect). When neither are true. Hard misfires, random misfires, stutters, backfires, etc. are almost always hard part problems or wiring problems.

No offense taken, the car has wiring issues , someone mentioned the control module voltage was dropping and also the customer's car has a taillight issue, they stay on all the time! He kills the power and leaves it on a battery tender for this reason.

Again, he called me out to "finish tuning" the vehicle because the shop that built it, couldn't get it right. With me not being able to tune it properly, the stubborn part of me is trying to figure out why. Just so many things it could be man.

Seems typical for cars who are built by people who make mistakes and then are passed off telling the customer "it's fine, we just put a base tune on it, get it finished somewhere else."

[edcmat-l1]

You sound intelligent and you post in actual paragraphs. Go through a thorough mechanical diagnosis and a good wiring visual. I'm sure you'll run across multiple issues that need remedied.

I can't tell you how many cars have come to me for a tune, missing on at least 1 cylinder. And many of them from other professional shops. I had a guy drive from 1.5 hours away for a tune. When he pulled up I could hear it was missing on multiple cylinders. I said "Hey buddy that thing sounds like it's running on half the motor". 2011ish Camaro with a fresh BTR cam swap. It was literally, running on 4 cylinders, 1 bank.

[Kid_kevi]

You sound intelligent and you post in actual paragraphs. Go through a thorough mechanical diagnosis and a good wiring visual. I'm sure you'll run across multiple issues that need remedied.

I can't tell you how many cars have come to me for a tune, missing on at least 1 cylinder. And many of them from other professional shops. I had a guy drive from 1.5 hours away for a tune. When he pulled up I could hear it was missing on multiple cylinders. I said "Hey buddy that thing sounds like it's running on half the motor". 2011ish Camaro with a fresh BTR cam swap. It was literally, running on 4 cylinders, 1 bank.

Wow! That reminds me of when I had a "wiring specialist" cut down a factory harness for my personal 1998 GMC Reg. Cab that my father and I, had put a 5.3L in. Installed the harness that I paid him 350$ to cut down and tidy up. The motor fired up and was only running on bank 2. Bank 1 was dead.

Stumped because my father had went out of town, and I was young & dumb at the time, I eventually through a visual inspection realized the ground pin for the driver side coil pack was missing. I searched high and low through all the random junk we had in the small shop we were renting at the time and eventually found a pin that looked like it would work. Popped it in, ran a jumper wire to the head and she fired right up on ALL 8 boys!

That was my first wiring diagnosis & fix. I have similar stories with tuning and that is why I run my own side gig, Tuning & Wiring now, man.

I appreciate the solid advice, sadly I was expecting an "easy peasy lemon squeezy" tuning scenario but actually got invited into a nightmare. I will do my best to troubleshoot and diagnose this issue.

Thanks again, Sir!!!!!

[6.2Silverado17]

I had a similar issue going on with my L86 after dod del and stg 2 cam install. There would be a Loud thud and or Popping sound from the passenger side head at times, at idle intermittently. long story short It ended up being leaking valve stem seals. The popping/thud sound was a valve getting stuck open then suddenly slamming closed. the valve spring closing pressure was weakened from the excessive heat generated from the leaking exh.valve seal causing the valve to stick open then suddenly slam closed. This may or may not help you out but from the symptoms you have described it definitely sounds to me like it could be more of a mechanical issue going on with the cylinder head vs a tuning issue.