BOGGING BADLY! - SOLVED

Just to add to earlier post.. .58 g on the air mass pid is really not much.
Idle is about .20 ish or less. Medium throttle is around the .50 ish and
deep into the throttle is near .90 ++
Of course this is very general and what it would do running properly..

Foggy said:

Just to add to earlier post.. .58 g on the air mass pid is really not much.
Idle is about .20 ish or less. Medium throttle is around the .50 ish and
deep into the throttle is near .90 ++
Of course this is very general and what it would do running properly..

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You are not wrong, but it also depends on if it has an air intake or any mods. I have seen them run bone stock in the .56 range, but also .70 with air intakes. It all depends on how the torque model is scaled for mods and vehicle weight, but there is just no way it should be into the .56 range at 2 k rpm at full throttle. It should be jumping right into the higher load vs rpm ranges based on the flash of the stock converter alone. You are not wrong, but you also are not right that it is normal to go full throttle from a dig, and have the engine operate at 2k rpm in the timing table at .56. The truck shouldn't even have a chance to get below the part throttle section of the table at full throttle, without fully blasting past that point. Something is causing it to hit that point earlier than it should be. Unless the fuel is completely screwed, or the exhaust is plugged, or it's running out of fuel pressure, there isn't much else beyond load reporting that would cause it to hit that point in that low of rpm. It will make more sense with better data logs.

mikez71 said:

I may have to do that yet!

These reasons I'm not super motivated..

rear cat looked great
secondary and primary o2 sensor data line up instantly
o2 data looks normal
exhaust noise/flow is normal
more revs do not equal more bog.

It really feels like REP mode, like the computer is doing it.. Or the tranmission is dragging somehow? While shifting normally and parameters look normal..

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How many miles are on the vehicle? I'm no expert but sounds like a plugged cat.

Planning to check primary cats if nothing easier comes up! ~208k..
I'm taking a break from losing for now! Gimme a day or two.. Will probably pull downpipe to visually check

Do you think a plugged exhaust would set off the knock sensors? Hot air being stuck making it detonate?
Reason I was not leaning towards cats, because it seems to pick up at higher revs, but perhaps I haven't tested the higher rpms enough..
And it does seem to run OK on startup, once it's warming up, bog sets in quickly.. I guess they don't have to be completely clogged, so the O2 sensor data looks normal?

Alright! You's all got my hopes up that it's the cats! When did you ever wish you had plugged cats? When you can't f'ing figure out what's wrong!

mikez71 said:

Planning to check primary cats if nothing easier comes up! ~208k..
I'm taking a break from losing for now! Gimme a day or two.. Will probably pull downpipe to visually check

Do you think a plugged exhaust would set off the knock sensors? Hot air being stuck making it detonate?
Reason I was not leaning towards cats, because it seems to pick up at higher revs, but perhaps I haven't tested the higher rpms enough..
And it does seem to run OK on startup, once it's warming up, bog sets in quickly.. I guess they don't have to be completely clogged, so the O2 sensor data looks normal?

Alright! You's all got my hopes up that it's the cats! When did you ever wish you had plugged cats? When you can't f'ing figure out what's wrong!

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I had plug cats on my silverado ss and had the same symptoms as you are describing, changed them out and never had a problem after that. I only had 120k miles on it. The LS motors suck oil from the valve covers and end up plugging up the cats. Run the truck at dark and see if the cats turn red that is a tell tale they are plugged. You can also put a temp gun on them and see how hot they get.

Regarding the knock sensors they are very fragile and could set them off if that cats are so plugged that the ecm trys to adjust the timing to the point that they detect knock.

Following along and hoping to see an eventual resolution. Wish I was able to contribute to the answer.

Starting to wonder..

Drilled some holes, I saw spikes as high as 2.5psi (snap throttle) but it quickly tapered to 0.
Steady high revs (4000rpm?) it was 0 and steady.
Looking at this video, he's telling me my cats are fine.. and fueling is fine (o2 sensors go rich on heavy throttle)

Hmmmm.. don't know what to do..
something is causing knock or the knock sensors are oversensitive.
Don't know that's the cause, but forsure there is too much knock retard...

Just looked up the price of knock sensors, only $10 a piece.. will likely get some.. Now to plug the dang holes in my exhaust!

mikez71 said:

Thanks all. Here is a screenshot of datalog. LT and ST fuel trims seem to fluctuate from -12% to +3%.
Forgot I removed the O2 sensor polling, will do another log soon.. knock retard -13.7 degrees on the cursor.
Not sure if false knock, or something bogging the engine down and it's actual knock.

View attachment 432569

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OK, going back to this. I'm still confused.

fuel trims aren't useful here in this screeo cap since you're in pe mode targeting richer than 14. all 4 o2 voltage, injector pw and fp would be nice to see. I have not seen flex fuel data, is that 10% alcohol normal? sounds right cause we have e10 these days thou. Just not seen it myself.

timing is neg 9.5 deg and knock retard is 13deg.

is this displaying the actual at plug timing of neg 9.5 cause that's very low and would bearly run. like mine will show neg 4.5 deg when it's off in auto stop.

now is the ecm throwing 13 deg of retard on top of that? so like. negative over 20 degs timing. if that's the case I'm not surprised it has no power and makes enough noise for the knock sensors to pick up.


this is kinda a chicken or the egg time question for me. what came first, a lack of engine power that allowed it to get into a part of the fuel/timing map it never should sees and is more of a non running section. or is something in the tuning causing it to run so badly, like negative 20 degrees of timing that it's over there because it can't go.

I gotta think that since you've ruled out plugged exhaust, fuel quality since it started mid tank. fuel pressure is holding up. compression test plus putting air into the cyl looking for a valve not holding? maybe a intake valve leaking a bit?

I just don't know, it seems most likely to be a mechanical issue but I hate throwing hard parts at things without knowing forsure. especially with the valvetrain of these ls engine somehow magically turning into the price of gold and just as fragile. I miss the days of 100$ cam kits haha.

Here's a screencap with injector pw (bank 1 and bank 2 averages)
Cyl airmass was around .17g at idle, max recorded was .69g under throttle. Doesn't always KR when the airmass is high, though frequently does.
I rescaled the spark timing and retard to be on the same scale. (default upper/lower limits on graph were different)

Where the spark and knock retard graphs intersect prior to the cursor mark (and knock retard) the timing was around -1 and KR was 0.
The spike on the MAF sensor.. probably throttle snap.. not all accels. Still get KR without it.
spark timing bumps after the cursor are shifts. I believe spark timing is the actual timing and the KR shows how much was taken out.

As far as bad gas, I can't say I've ruled it out. But seeing as how the fuel composition reads in the correct range..
Before when it went from 8%->0%->10% was probably the recalibration after fillup. Steady at 10% now.

Will check motor mount bolts when I replace knock sensors. If no change, will do compression.
But how likely is it idling smooth, revving smooth, but power cut under load feels forced due to compression?
I might do the cylinder balance test again in the Tech2 now that the plug is fixed.

Secondary O2's stay rich near the end of that log.. They oscillate with the primaries initially...
These logs are with the bad spark plug, showing misfires. But it drives/bogs the same both ways, just idle smoother with a good plug.

Only ever showed about 3-4 degrees max knock retard in the past.
Another more zoomed out part of log.. shows fuel presure 57psi at startup, steady 43psi after that.

Something else to try. Fire it up, put it in manual mode first gear, then with your vcm special controls function, go into tcc (torque converter controls) and hit the converter on button. Make sure you aren't pointing at a garage door and that you are ******* the brake incase it tries to pull forward. The truck would never command the converter to be locked at idle, so it should be a very noticeable drag down on the rpms when you lock the converter at idle. It will bog down and probably stall. The idea with this test is to see if the lockup solenoid is leaking and the converter is locked up down low when it shouldn't be. If the converter is locking it will bog like crazy, then clear up as the engine rpms increase.