BOGGING BADLY! - SOLVED

hagar said:

It isn't your knock sensors. Is it still loading to .56 grams per cylinder when you get into it?

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. 56 is exactly where it needs to be at full throttle eventually, but it shouldn't be hitting that point when you are low rpm trying to get full throttle. It is a symptom, not the problem. It's a chicken and the egg thing most times with efi trouble shooting. If your exhaust is plugged, and you floor it at 1k, it will load the engine down into timing range it shouldn't be. The ecm in your truck is a torque based system, so it has almost nothing to do with throttle position vs rpms like older systems. If you have the truck floored, and something isn't working right, it can still calculate the engine as being under full load, then pull tons of timing. The fact it goes into that timing zone, then it still isn't happy and needs to pull more timing, means something is probably actually causing the drag. I got one thing to check for you now that I typed this. I had a friend that changed his engine in his silverado because he thought it was seized. This is a guy that has owned a mechanic shop for 30 years. Once he got the engine out, he realized the alternator was seized. Try popping your accessories belt off and turning over all your pullies by hand. His alternator seized so badly that the truck wouldn't even turn over. I could easily see a part of the pulley system causing enough drag to load that engine right down into crazy heavy timing pull zones, yet still not being enough, and the knock sensors get the rest. It sounds like it's acting like you have a 20 thousand pound trailer behind you.

Only other thing I can think of is a heavy contamination in the fuel you get. Not sure if you tried a different station yet, but it's not unheard of to have something super bad with a tank of fuel. It would be showing misfires like crazy if that was the case, so I doubt it. Anywhooo. Send me a message if you want me to whip you up a custom pid group that only has the info we need to take the next step. This won't be hard, the info is all there.

Lol, is your park brake on? Hahaha

That reminds me, couple of times after cold startup, pulling away semi-aggressively, thought I heard belt chirp..
Took off accessory belt. idler/tensioner/waterpump/alt/steering all smooth and free.
Unless it's the AC compressor... I do have a new AC belt and could cut the old one off.. tomorrow!

Nope, not park brake. Coasting I can still feel the park brake, but accelerating it feels like something stronger than the park brake is holding me back!

About the fuel thing.. When it suddenly happened, I was low on fuel.. (Drove the whole tank no problems?)
Due to being low and the truck running funny, I did fill up at the nearest small gas station...
Seems like the calculated ethanol % went from 8% pre fillup to 0% then back to 10%.

mikez71 said:

That reminds me, couple of times after cold startup, pulling away semi-aggressively, thought I heard belt chirp..
Took off belt, idler/tension/waterpump/alt all smooth and free. Unless it's the AC compressor... I do have a new belt and could cut the old one off..

Nope, not park brake. Coasting I can still feel the park brake, but accelerating it feels like something stronger than the park brake is holding me back!


About the fuel thing.. When it suddenly happened, I was low on fuel.. and due to being so low.. I did fill up at some small gas station...

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Just another thing to add to the list, all we can do is spit ball here. You sound like you have a really good grasp on things, it is the most fun to figure something out when it takes some thinking. You can pop your fuel feed line off in the morning then run a rubber hose to some Jerry cans. Then go into your vcm controls and under fuel system, command pump on and pump that sucker dry. If it doesn't fix it, you can put it back in no money wasted.. if it does fix it, you have a bunch of fire starter.
Obviously go to a different station for the new fuel

Be safe and at least wrap some electrical tape around the connector before pumping, it has a bit of a kick to it. Ideal would be to get a hose clamp on there. I can't tell you how red neck to be.. I get pretty darn redneck sometimes. Safety first or second

Only reason I dont feel like messing with the gas, its a full 20+ gallons, and now no misfires.. ?
If it doesn't get worse, its driveable. Scary pulling away from a stop sometimes, but I could try and burn the gas off..

It's NOT the AC compressor. A little gummy feeling to turn compressor by hand, but pulley spins freely. Tech2 showed engine load go from 20% to 23%.
So 3% doesn't sound bad. But 20% at idle seems kinda high?

Don't think it's my MAF. the readings seem to be around 6g/s after warmed up. (according to autosync display)

Didn't check primary cats yet.. Does feel like something is dragging it down. Felt good first start, I swear it warms up a little and gets worse. Idle still smooth.

What if I had really low octane gas? Would it still show misfires?

I still feel like it's worth cracking the head pipes at the manifolds loose, just leave the bolts in but just so the pipe can vent a 1/4 to half inch. do a quick drive. it will be loud as hell should let you know if the cats are plugged up pretty quickly.

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..

yeah.. I get it. makes sense if the cat was clogged it would get worse at high rpm, not better.


I honestly don't know. haha. hopefully you can get that scanner setup and post a log. I've been interested in watching it play.