asilverblazer

The wire harness for the trailer lights at the rear bumper has a circuit for third brake light.

Just now getting around to it?

Does the miss begin when the engine switches to closed loop operation or simply when things get warm? For the sake of avoiding prematurely condemning major mechanical parts - re-evaluate injectors, coil, plug wire and plugs. Were new parts genuine GM parts (not counterfeit)? Try swapping individually to a non miss firing cylinder. Understand you've done this once, but I'm reluctant to say a mechanical condition would clear up off idle and not be present when cold. Carefully inspect injector and coil wiring, where the fuel pipe connects to the injector, manifold gasket... anything isolated to cylinder #3.

Grease the u joints and clean up the driveshaft yoke going in to the transmission. Carrier bearing present? Condition?

Any change warm vs cold? I would be thinking about inspecting everything from the cam to the valve. Maybe an injector balance test. Have you confirmed via a scanner the miss does go away off idle (or does it just become undetectable)?

0 compression on one entire bank is very rare, if true, problems with the head or valvetrain.

Codes?

Can you explain this another way? Braking doesn't stop the shutter but letting off the throttle does - are you letting off the throttle when braking? When it is shuttering, do not let off the throttle (to keep it shuttering) and apply the brakes lightly. Try manually selecting a lower gear, neutral and using tow haul mode. Report any changes. I would not consider the front differential. Can the transfer case be locked in 4 high to bypass any clutch packs of the AWD? I missed the Denali AWD part and don't remember well enough its functions. Try wiggling the output yoke of the transfer case and the input yoke on the rear differential. Confirm there is no carrier bearing and that if there is one it has no play. Check the rear mounts of the transmission/transfer case. Does it occur at any speed? Any gear? Try loading the bed to squat the rear of the truck to significantly alter the driveshaft angle.

All the log data seems to be what is expected except the O2 sensors. It might be a sensor quality or signal integrity issue. Once that occurs I'm not sure how the computer compensates. The sensors should work better hot, yours appear to be doing the opposite. The apparent intermittent O2 signal performance could be wiring. However, seems like you indicated the part quality might be suspect of the O2 sensors - based on that and if no questionable wiring conditions exist I would strongly consider new/better sensors.

That log shows some weird stuff happening. At line 296, short term fuel trims go to 0 and stay there for the remainder of the log. At line 344-425, the upstream O2 sensor readings stop fluctuating, throttle is showing 100% but commanded AFR stays at 14.9 instead of going to 11.5. Line 696-733 O2 sensors stop reading. Focusing on lines 250-300 show what I would expect: Throttle goes wide open to 100% commanded AFR goes rich. The problem as I see it is that the upstream O2 sensors show lean when they should be reading richer. I looked at the timing advance to see if the advance is correlating to the O2 readings but not seeing a pattern there. I do see a correlation between the timing advance and long term fuel trims. Fuel flow and air flow are tracking together consistently. When the O2 sensors are reading, the difference between the upstream and downstream is negligible, The catalytic converters could be bad. The voltages are fluctuating together, but the fluctuations look abnormal to me. My conclusions are leaning towards the O2 sensors are reading poorly cutting of short term fuel trims.

I haven't read up the latest here (or looked at the latest logs) but it WAS lean according to O2 sensors at WOT, when it should be rich - power enrichment. I'd check out the MAF sensor too. Has it ever used an oiled air filter?

The factory LEDs in the front are only 5volts? Were brighter 5 volt LEDs not available? I'm considering adding some lights in the rear of our Yukon.

Start checking the cables themselves. They can corrode internally. Check grounds.

I don't think a Corolla or Maverick can tow and/or haul heavy. To buy one in addition to a truck would be unnecessarily expensive.

The problem has already been identified and presumably corrected. So there should be no issues going forward. The problem as I see it is that there have been several QC issues regarding the 5.3 and 6.2 engines in the last few years. 1. Bad lifters 2. Bad lifter bores 3. Bad crank bearings 4. Bad crank bore/machining debris I don't recall the specifics, but it seems there has been one major QC issue after another. I wonder if tooling is wearing out... these engines have been in production for a LONG time and prior to these recent issues have been exceptionally trouble free.

I agree with newdude, multiple parts failing at once is unlikely. Unrelated example - once had a coworker who limped in to work one morning with all sorts of engine trouble. Checked codes and they were all over the place and quite numerous. Popped the hood and started looking around, a rodent had likely gotten trapped under the engine cover and when things started getting hot, made a very desperate escape by chewing through everything in its way out - including a very thick engine wiring harness full of wires.

Drive it like any other vehicle and chances are you'll end up with it on the highway often enough. The idea of getting them on the highway for an amount of time is to make sure all the fluids get up to temperature and particularly burn off any built up moisture. The only addition to this is the diesel exhaust particulate filter regen. My truck typically takes about 20-40 of continuous highway miles to do this. Regarding the iDash, I have one, and use it to monitor when regens are taking place. I also watch the EGT's for the particulate filter, and filter soot load. A regen on my truck happens when the soot load reaches 100% and continues until it is under 5%. The EGT runs 1150 degrees at the filter. Complete cycle of the regen is less consistent without the continuous highway driving, I've noticed that when driving around town during regen the EGTs fluctuate, such that the filter is staying hot enough to burn off the soot. I can't say that this is a problem, but I prefer to have the regen start and finish in one drive cycle. However, I also don't go out of my way to extend a drive cycle to complete the regen either. That might be because my drive habits are such that if a regen starts during one drive and doesn't complete, it will probably finish during my next drive. I suppose that since I do monitor the regen cycle process, and if I noticed that after several short drives the truck is still entering a regen cycle because it hasn't had time to complete a full regen, and I didn't anticipate a long enough drive to complete it in the next few days I might go ahead and extend a drive down the highway to wrap it up. Again, my truck takes about 20-40 miles or 30+/- minutes of sustained high EGT to go from 100% down to 5% soot load - a full regen. Lastly, DEF hasn't been any kind of problem for me. I'm not even monitoring how often I'm adding fluid. For conversation sake say once every 4-8 weeks the notification pops up, I buy 2 boxes and dump them in (basically filling the tank) and carry on. I've never had a problem finding DEF so when the light comes on, the next stop I make I buy the 2 boxes (Big box store, truck stop, gas station, auto parts store, etc.).

Really old thread, but the idea is that there might be a tolerance issue with the master cylinder, brake booster rod. The rod length might be keeping the brake booster slightly 'open' applying the brakes. A couple things to check, unhook the vacuum line from the booster and plug it so the engine doesn't have a massive vacuum leak and carefully test drive. You won't have power brakes so it will be difficult to stop. If the problem doesn't present itself then proceed with brake booster master cylinder diagnosis.

When it is vibrating, lightly rest your foot on the brake pedal - just enough to turn the brake lights on - while maintaining the level of 'acceleration' you were. This will cause the torque converter to 'unlock' or cease its attempts to do so. Could also be a miss fire but I would expect a check engine light. Maybe driveshaft is out of balance.

How'd you do that fix so fast?

I wouldn't focus on the downstream O2 sensors reading low voltage; yet... Log should include bank 1 sensor 1 and bank 2 sensor 1. I suppose there could be a scenario where clogged catalytic converters are slowing the exhaust gases so much that it is altering the upstream sensors readings, and if the exhaust gas is spending to much time in the catalyst media, it could cause a low voltage reading on the downstream sensors. Drop the y-pipe and see what happens?

Looking at your data, the truck runs lean at full throttle. Not seeing it richen the mixture accordingly via the fuel trims though, not really studying it fully though. Based on what I see I'd be looking at fuel delivery.

The O2 sensor codes are for the downstream sensors. Those should not factor into the PCM's fuel trim and should not be CAUSING the miss fire, they could be detecting a lean condition caused by something else and are left to interpret it as a sensor low voltage condition. This would mean that the upstream sensors are either not accurately sensing the air fuel ratio - thus the PCM doesn't enrich the mixture accordingly, the PCM may not be getting an accurate signal from the sensors via a wiring fault, or the sensors are fine, the PCM is reading them correctly but isn't able to deliver the fuel volume needed due to a mechanical fueling problem, fuel pump, filter, or injectors (maybe dirty). I would watch fuel trims to see what the PCM is trying to do to correct the P0300. High fuel trims indicate its commanding a richer mixture vs. low trying to lean it out. A high fuel trim with lean O2 readings indicate an insufficient fueling problem.

I'm not a heavy guy and usually have a cross bed tool box in my trucks, just me and a full tank of fuel, all my half ton trucks have been about 6500 lbs, 60:40 weight distribution.

A carefully loaded truck (empty), with a carefully setup weight distribution hitch might be able to have a 13K lb trailer attached with 10% tongue weight carefully balanced between the trucks front and rear axles to a stay with in every rating on the truck. The only way to know is to spend some time at the scale. You must load everything you intend to travel with in the truck and trailer. Unhook the trailer and weight the truck. This reveals how much much weight you have left in the GVWR. That amount cannot be exceeded by the tongue weight of the trailer. You will also see how much weight each axle of the truck is carrying. Next, attach the trailer with out any weight distribution. Weigh again. You will now know what the GCWR amount is. It cannot exceed the trucks number. You can also see how much tongue weight is added to the rear axle on the truck, and how much it unloads the front axle. This won't really matter because adding the weight distribution system will re-allocate that weight among the axles. Next, the weight distribution system. Some amount of tongue weight from above will get put on the front axle and some will get put back on the trailer axles, that weight gets lifted off the rear axle. Lastly balancing the system, you will adjust the weight distribution hitch to maintain about 10% of your tongue weight from step 2 on the truck with out exceeding any maximum weight ratings, FAWR, RAWR, GVWR. You may find that it is not possible to do it. You may find that you're close or...