Transmission issues after DOD delete

superdave160 · March 2, 2023

I have a 2017 Silverado 4x4 with the 5.3L engine and the 6 speed transmission. I've had a Black Bear tune in the engine and transmission for over 2 years, the 70 degrees C thermostat was installed in the transmission at 32,000 miles. The dealership performed the transmission fluid drain and flush and put in the new fluid at about the same time that the new thermostat was installed. At 40,000 miles, I took the truck to my mechanic and had him do the DOD delete. A BTR Stage 2 cam was installed. The heads were taken to a machine shop to be reworked (mechanic does this every time he does DOD delete because he had one that had a bent valve and he didn't realize it until after the engine was back together). I also had an intake manifold and throttle body from a 6.2L installed on my 5.3L engine. While the truck was being worked on, I emailed Black Bear to see if I could get an updated tuning file for the engine due to the changes that were being made. I received the updated file and loaded it into the ECM before the truck was started for the first time.

When I got the truck back from the mechanic, it idled very rough. It seems to run well when you step hard on the gas pedal, but still idles rough. Not "big cam" rough, just rough in general. It also wants to die when maneuvering at slow speeds such as in a parking lot or when stopped at a stop light. If I attempted to perform a WOT run, the CEL would flash and then come on steady. The code indicates cylinder 7 misfire. However, this only happens when hard on the throttle. No codes when normal driving. Another issue is that the truck "jerks" just after shifting into a higher gear when the load on the engine increases or when driving starting up a hill. When the jerking started, I could simply step down on the gas pedal and force a downshift to stop the jerking. I mitigated the issue by placing the transmission in "M" and controlling the downshifts manually. We attributed it to the tune not being optimized yet, so I made a recording and sent it off to Black Bear. The new tune arrived and I loaded it into the ECM. This made the truck run much better, but the issues remain. The jerking issue seems to get worse as the truck warms up. I made a recording with the updated tuning file loaded and Black Bear responded by telling me that the engine is running as it should. I did not send a transmission recording because, at that point, I believe the issue to be with the engine, not the transmission.

I've taken it to a couple other mechanics and they believe that the torque converter is failing. I tend to agree with this, but this issue began when the engine was modified. I read numerous posts on this forum and others about other issues causing symptoms like this, such as something as simple as a vacuum leak. My plan is to take the truck to a transmission shop and have the pan removed to see if it is full of debris. If it is, then rebuild the transmission and install a better torque converter.

My question is, what if the pan is not full of debris? Is it possible that the engine could cause this issue?

Snowcamo · March 2, 2023

The trans will act like it has issues if you have a misfire or two in the engine.

You are correct the issue is with the engine.

I experienced this with my truck and when I resolved my misfire in cylinder 5 the trans shifted better then before. No issues after that.

Now I'm having the trans rebuilt due to it slipping, but that is totally unrelated

These trucks are wonky...

CamGTP · March 2, 2023

No mail order tune will ever get close to a real in person tune. These are highly advanced torque based computers, everything about of the engine runs and the transmission shifts comes down to the tune.

Black bear is fine for tuning some things but never would I ever use them for a cammed LT engine. It takes a lot of time to dial in the airflow model and the torque model on these trucks. There are a few guys that do email/team viewer tuning on the HP Tuners forums but you'd need HP Tuners for that. Plus you need a wideband oxygen sensor for tuning as well.

I'd take it to a place that can do dyno tuning and really knows the LT based controllers.

superdave160 · March 2, 2023

I took the truck to a transmission place today and they believe that it is a bad torque converter. They connected a tool to the OBD port and we went for a drive. With this tool, they can lock and unlock the torque converter clutch on command. With the torque converter clutch unlocked, the transmission acted like it should. With the torque converter clutch locked, bad vibrations. The tool also did not detect any cylinder misfires. I was told that the transmission vibration was being sensed by the knock sensor on the engine, which led the computer to believe that the engine was knocking because the timing was advanced too far, so it was retarding spark timing. I did a few WOT runs today that resulted in a CEL. The code was P0506; Idle Air Control System RPM Lower Than Expected. So, I made an appointment to have the transmission rebuilt.

We'll see what happens when the new transmission is in. I pull a camper with this truck so it will be getting a heavy duty billet torque converter, heavy duty clutch packs, and other upgrades.

superdave160 · March 2, 2023

CamGTP I totally agree. I'm having a local tuner take over. He runs a shop where he builds performance engines. The first day that I went there, he was fine tuning a late model Camaro with a 6.2L and a supercharger. The name of the shop is Smoke Johnson Customs in Huntsville, AL. After the new transmission is installed, it is going back there for tuning.

superdave160 · March 2, 2023

CamGTP I just saw in your post that you mentioned a wideband oxygen sensor. Can you expand on that?

Thanks in advance.

Snowcamo · March 2, 2023

Getting the transmission rebuilt is not going to fix the misfiring or other engine issues.

Drive in tow mode and see if the shifting issue is nonexistent.

Best of wishes to you and your truck issues. You'll get it nailed.

CamGTP · March 2, 2023

GM uses narrowband oxygens as standard on these engines, they work great for what they are but they can not report real time air fuel ratio readings in the exhaust like a wideband oxygen sensor.

Narrowband perform in a mv (milivolt) range of 0-1. Think of .450mv as stoich for whatever fuel you are using. If regular gas it's 14.7 AFR (air fuel ratio). The o2 sensors will swing lean and rich of stoich in real time to alter the fueling. If you watch a scope or a data log of the o2 sensor readings on the upstream sensors they will be sorta like a wave going up and down making corrections to fueling on the fly. The narrowband sensor is never able to tell you the exact air fuel ratio in the exhaust, it's just a ball park. So at like full throttle the o2 sensor might just show .800-.900mv, which means it's richer than stoich because the commanded air fuel dropped from 14.7 to say 12.5. The problem is that you never know if the actual fueling is 12.5 using a narrowband sensor. You may command 12.5 but in reality it could be 11.6 which would be rich or it could be 13.5 and it's super lean.

Each would be bad because too rich can make less power and wastes fuel and too lean could burn up valves or pistons. Wideband sensors are tuning tools that tell you exactly what is happening in the exhaust, they are a must for tuning so that the airflow model is correct.

You could install one yourself or have the tuning shop use theirs to tune it. I keep one installed in my truck all the time just because I want to and it's nice to just glance it every once in a while to make sure things are safe while going full throttle. This was just a quick explanation, maybe not the best but you get an idea of what I'm talking about.

superdave160 · March 3, 2023

Snowcamo I had to move my camper last week. I had Tow/Haul mode turned on and I couldn't get above L4 (on the Interstate) without getting the "kicking."

Snowcamo · March 3, 2023

Give the trans full power from the engine first, before you drop 4+ grand on a trans rebuild. It will provide a better outcome. Your lacking designed function as is. That's what I gather from the issues you have stated.

Snowcamo · March 3, 2023

The kicking is due to the misfire. The engine is not putting out rated power under load. You will see the miss on the handheld diagnostic

rav3 · March 3, 2023

Just my simple thoughts here. If you had a "miss", it should set a "Service Engine" light on the dash, which when you read the codes should indicate the miss & which cylinder.

I had a similar situation on my '17 Silverado with the 5.3 V8 & 6L80 6 speed transmission 4x4 with 3.73 ratio w/G80 rear axle form when I bought it in 2020 'Certified Truck' with 30k miles. I did the transmission fluid change 3-4 times, did the "pill flip", added LubeGard & installed the Range AFM Delete, but still felt what I thought was a miss or stumble. After some research, I found that the Torque Converter was made to slip & had a type of carbon fiber clutch on the lock up piston. I also read that the way GM makes the Housing of 'thin steel', that when they are welding the flex plate mounts on, it can spot harden the surface that the Lock-up clutch engages. I feel that due to lack of friction modifiers, they will produce a "pulsing' as the Piston hits these hard spots, which make the truck feel like it has a miss. With this thinking, sort of like how a limited slip differential will do when it's friction modifier has worn out. So, I added the "Shutter Fixx" additive, which is nothing more than a friction modifier, and now my transmission runs MUCH smoother.

It's pretty well known that the 6L80 torque Converter is not a robust unit & is subject to failure, which is hastened by the high temperature transmission thermostat. Heat is the main killer of the torque converter.

I have seen videos where they have programed the transmission module to increase the lock up pressure to also eliminate the jerking feeling. However, GM designed it to slip, for their reasons, I guess.

Anyway, that's my input...good or bad. But I don't have the jerking/stumbling feeling in my truck anymore.

Edited March 3, 2023 by rav3

superdave160 · March 4, 2023

UPDATE: I spent some time trying to figure out why the engine was running so rough. It just seemed like a vacuum leak to me. I inspected all of the connections to the intake manifold and they all looked good. So, I decided to check the torque on the intake manifold bolts. They were all loose. I looked up the torque value and found that they should be 89 in/lbs. I set my torque wrench and properly torqued the bolts. When I started the engine, it ran much smoother. I could now hear the "cam lope". I took it for a drive and I still had a CEL during hard acceleration. The code was cylinder 7 misfire again. I figured that the most likely cause of this was going to be a bad coil pack, bad spark plug wire, or bad spark plug (mechanic replaced the plugs). I bought a set of plug wires and replaced the #7 wire. I also moved the #3 coil pack to the #7 position and the #7 coil pack to the #3 position. I took it for a drive and I could not get the CEL to come on again during hard acceleration. I took the truck for a long drive (about an hour) that included county highways and Interstate. The transmission issue appears to be completely gone. I had the cruise set on the Interstate and the truck cruised up hills with no issues. I'm going to pull the camper tomorrow to verify that it still doesn't do it. The plug wire must have been damaged when they removed it, or it wasn't connected properly.

Now the truck drives like I expected it should. It also appears that the fuel mileage numbers are trending up as well. I'm glad that I found this before dropping $4K on a transmission that I didn't need. Granted the new transmission would be far superior to the factory unit, but I'll put it off for a while as long as it doesn't act up when pulling the camper.

The thing that surprises me most about this is how dramatically an engine issue affected the transmission.

Thanks for the responses! Your advice kept me focused on getting the engine figured out when the local mechanics kept telling me that the transmission was causing the engine issues.