Loss of power, decelerate with more throttle, multiple codes

[Taylor T.]

Okay, this is a long one. 2019 Silverado 2500HD, 6.0 Vortec gas engine vin G L96 motor. If it's important, 4x4 LTZ, approx 170,000 miles.

 

I have only had this truck for about a month, and it's given me multiple problems that were hidden.

 

First was an EVAP code which was repaired by Chevrolet, and required a new vent valve and a new purge canister.

 

Second was a rough/choppy idle that I took a guess on and managed to fix with all brand new NGK premium ruthenium spark plugs, NGK coil packs, and the premium spark plug wires. No check engine light on this one. Truck idles fine now.

 

EDIT---- Shortly after replacing spark plugs, I got check engine light, no coolant temp reading, and A/C went out. Figured out it was chewed up wiring and a broken connector on the coolant temp sensor. Replaced both plug and coolant temp sensor, wire loom, solder, and protective heat shield thing replaced. Fixed issue, check engine light cleared itself.

 

New issue is this.

Driving 500+ miles from FL to NC, pulling a trailer and cargo weighing about 5,000lbs (purely a guess). Had the truck in tow/haul mode going North to NC. Drives fine for multiple hours, and then suddenly I start to lose power in the high RPM range going up the rolling hills. It started where it would bog down (I could actually hear the truck fighting to increase RPM), drop RPM, and I would lose speed as though I was hitting the brakes. If I let off the throttle from the about 3/4 that I had it, to 1/2 position it would pick back up and increase speed (slowly, probably due to the uphill climb with a trailer).

 

As time went on, and in about 10 minutes, the bogging down got worse, and eventually any throttle would bog it down and slow the motor. No check engine light at this time. I pull over to just look everything over and try to figure out what it could be online to no avail. In this time, I also changed the air filter with a STP Premium filter, and check that the MAF sensor is not clogged/dirty. It appears to be brand new. I check that it is properly plugged in, there are no debris past the air filter, clean the filter box, and check (quickly) all the connections (ring clamps and such) to ensure no leaks. It was approx. 25 minutes later I decided to get back on the road.

 

No issues at this time, no check engine light. Truck has full power again through the entire power band. Driving through rolling hills and about 2 hours later it starts acting up again. Same as before, losing power gradually into lower and lower RPM range as time goes on. Check engine light this time. Drive to nearest parts store for code scan. Stopped after getting off expressway, and upon accelerating through the stop sign, truck sputters HARD. RPM's go from about 700 to 3000 and back about 4 times in the matter of about 4 seconds. I putter it to the parts store, codes are:

1. P069E fuel pump control module request MIL illumination
2. P0171 fuel trim system lean
3. P0174 system too lean (bank2)
4. P2096 post catalyst O2 sensor fuel trim below lower limit (bank1)
5. P2098 post catalyst fuel trim system low limit bank 2
6. (SECONDARY DTC'S) P0119 engine coolant temperature sensor 1 circuit intermittent/erratic
7. (SECONDARY DTC'S) P069E (again)

 

I do not know what to do, so I look online again, give up, and about 15 minutes later decide to try and keep rolling. Symptoms are completely gone, full power through RPM range again. About 1.5 hours later, I am off expressway travelling about 50mph. Check engine light turns off.

 

Next day, truck is now pulling empty enclosed trailer. Tow/haul off. About 3 hours into drive back south, rolling hills of SC, truck acts up again. I pull over before I lose all power. Wait 10 minutes and decide to move on. Full power through RPM range again.

 

Another hour and check engine light (undiagnosed still as of now).

 

Another hour and start losing power in high RPM again. I decide to throw it in neutral and kill the motor. Wait about 5 seconds and fire it back up, put it back in drive, full power again.

 

Did the rolling, neutral reset approx. 4 more times before reaching destination back in FL.

 

This is the only time I've taken the truck on a journey more than probably 50 miles without a break. Also haven't pulled a loaded trailer this far before. What could be causing all this? Could the previous random misfires from before new spark plugs have caused damage to the catalytic converter, causing a slow increase in manifold pressure until the back pressure starts to stall the truck, and then turning off the motor releases that pressure? I don't want to go buying hundreds in parts just for it not to solve the problem. I am also unsure if I will be able to test this repair until the next time I need to drive 500+ miles from home.

Edited July 29 by Taylor T.
Added a repair that may be relevant to current issue.

[Jsdirt]

I expected to see lean codes, since that is a classic fuel starvation symptom. Electronics throw the intermittent problems into the mix, however.

 

You would need to find out what you're losing when the symptoms happen. Is fuel pressure dropping? If so, why? Is fuel pressure low at all times, or only under load? What is the MAF grams / second reading at idle, and at full throttle? What are the o2's doing at idle, and at full throttle? ETC., ETC., ...

 

I know historically the fuel pump control module is mounted in probably the worst possible location (right where water and road debris get fired at it full speed), and is failure prone. Could very well be failing as it heats up. Could just be the pump itself failing when full duty cycle power is applied to it. Could still be a failing MAF. But that first code indicates a possible module issue - that needs to be investigated.

 

Lots of possibilities. This is the main reason my newest vehicle of 5 these days was built in 1994. Got tired of troubleshooting endless electrical issues on customer's vehicles, and have no desire to do so on my own stuff. It is MEGA AGGRAVATING when it happens, and there are never any easy fixes as you know! 

Edited July 29 by Jsdirt

[Taylor T.]

On 7/29/2024 at 4:23 AM, Jsdirt said:

I expected to see lean codes, since that is a classic fuel starvation symptom. Electronics throw the intermittent problems into the mix, however.

 

You would need to find out what you're losing when the symptoms happen. Is fuel pressure dropping? If so, why? Is fuel pressure low at all times, or only under load? What is the MAF grams / second reading at idle, and at full throttle? What are the o2's doing at idle, and at full throttle? ETC., ETC., ...

 

I know historically the fuel pump control module is mounted in probably the worst possible location (right where water and road debris get fired at it full speed), and is failure prone. Could very well be failing as it heats up. Could just be the pump itself failing when full duty cycle power is applied to it. Could still be a failing MAF. But that first code indicates a possible module issue - that needs to be investigated.

 

Lots of possibilities. This is the main reason my newest vehicle of 5 these days was built in 1994. Got tired of troubleshooting endless electrical issues on customer's vehicles, and have no desire to do so on my own stuff. It is MEGA AGGRAVATING when it happens, and there are never any easy fixes as you know! 

Is there a way that I can look back and see what is dropping when the situation happened? On the newest update yesterday my check engine light turned off before I even started the truck, so the only thing I could see is stored codes from the past. I did originally have an EVAP code that was pointing to fuel related issues, wondering if it could just be the fuel pump control module. 

 

Honestly I might just look into replacing the fuel pump control module, the fuel pump and the MAF again.

 

The only concern I have with everything, like I said, as if I shut the truck off for even just 5 seconds while still rolling down the road, and fired it back up it would be totally fine again for at least 45 minutes, under the exact same load conditions. That's the part that didn't make sense to me, because I figured if it was something such as the fuel pump control module failing as it heated up, would 5 seconds be enough time for it to cool down significantly enough to run fine for 45 more minutes? 

 

And honestly, if I could go back to my 2001 Silverado, I probably would. Been looking at buying an LB7 cat eye Duramax, but I hear a bunch of problems about the injectors on those and the fact you have to take the heads off to replace them. 

 

To stay on topic though, given the 5 second motor restart fix that last 45 minutes, do you still think it could be any of those things you listed?