BOGGING BADLY! - SOLVED

[mikez71]

Just happened today..
~85-90 degrees Fahrenheit. Has been 110 degrees lately, gonna be 112 for a couple more days..

Drove about 15 mins to my uncle's. No issues.

Leaving 45 mins later, the Tahoe (2012, 5.3) feels like it's in REP mode pulling away from every stop, until I get around 20mph and then it starts to pull mostly normally.
No engine related dtc's in autosync, no REP mode. I was low on gas, filled up. Still boggy for a few miles, but seems to have cleared up. Will need to test drive more.

Bad gas? I drove a whole tank of it with no issue, and I've run the tank lower than that before.

Hooked up the Tech2, no stored codes. no misfires, current or stored (unless I missed it somewhere)

LT fuel trims seem off, but Short fuel trims look good.. Maybe the fuel change? was showing 8% ethanol after filling up, which went to 0%. Unfortunately I forgot to check it while bogging..


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THE CULPRIT: Loose and 1 missing motor mount bolt(s). !!!

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[Fless]

That's the fuel PUMP trim, not to be confused with general fuel trims.

 

[mikez71]

totally missed that! Thanks.

I will have to investigate more. I find it odd there were no codes or misfires and yet it drove like it did.
Could retarded timing do that or a VVT failure? I haven't found any clues.

 

[j91z28d1]

is it possible it was taking off in say 2nd or 3rd gear? or maybe the converter locked early. these fly by wire cars won't always let you open the throttle blade all the way at to low of rpm and lug like the old cables did.

other than that, I got nothing.

 

[Doubeleive]

totally missed that! Thanks.

I will have to investigate more. I find it odd there were no codes or misfires and yet it drove like it did.
Could retarded timing do that or a VVT failure? I haven't found any clues.

check the maf data, that is something the maf could cause, it may also affect shifting, hence a bogging feeling

 

[Fless]

If you look at MAF readings use g/sec. That should roughly equate to the engine's displacement at warm idle.

 

[mikez71]

Thanks for the help! Still runs like poop.

8.5 g/sec at hot idle. Driving it spikes up to 130 g/sec, i never went past 71% throttle that run.
Knock retard upto 13.5 degrees.. whenever over 45g/sec in 1st or second gear..
Just doesn't feel right like there is an ebrake on, or worse.

Looking at previous logs, the MAF readings seem to be in similar range. WOT previously had 220g/sec, idle ~6.5 g/sec.

Will take a look at the MAF and plumbing and check for misfires once more..

 

[mikez71]

is it possible it was taking off in say 2nd or 3rd gear? or maybe the converter locked early. these fly by wire cars won't always let you open the throttle blade all the way at to low of rpm and lug like the old cables did.

other than that, I got nothing.

Nope, but that's about what it feels like I'm taking off in 4th gear or something. mostly through 1st and second it seems..

 

[Doubeleive]

Nope, but that's about what it feels like I'm taking off in 4th gear or something. mostly through 1st and second it seems..

take a look at the throttle position and see if it matches what is commanded, you would think something like that would throw a code but maybe not depending on if it is actually moving or not. just thinking out loud....
maybe pull the intake off and have a look at the butterfly see if it moves free and isn't getting stuck.

 

[Doubeleive]

also just for sh*ts and giggles check your battery post's and grounds, these trucks are very sensitive to voltage