Acceleration hesitation

[GCDenali]

I have a new to me 2011 Tahoe Z71 with 196k. It was a Northern vehicle, so I’ve been slowly replacing parts that are badly worn or rusted.

I’ve replaced plugs and wires with AcDelco Iradiums. Cleaned and removed the throttle body and MAF sensor.

I’ve also replaced all axle and transfer fluids, transmission filter and drain and fill. I’ve replaced sway bar bushings and arms In the rear.

As of yesterday, I did the front end upper and lower control arms and tie rods ends as of yesterday.
Those upper control arms bolts were a PITA! I had to use a ball joint fork to separate them!!

Sorry for the novel, but today on a 150 mile round trip, the truck was struggling to accelerate multiple times.

No CEL or pending codes. I’m running 89 Shell gas. I do believe this was running E85 up North. It’s an E85 model.

Could this be a failing fuel pump or catalytic converters? What would be the best way to check?

 

[OR VietVet]

Need to know fuel pump pressure.

I am going to do something I hate doing, assuming you have a 5.3 instead of the 6.0 electric/gas option.

 

[mikez71]

Does it run smoothly?

Scanner can tell you fuel pressure sensor reading.
Likely there would be a code if pressure dropped?
Reading actual pressure with a gauge even better, but don't buy amazon gauge.
Harbor freight much better! (thanks @strutaeng!)

Scanner can also tell you if you have knock retard.
I once forgot to tighten motor mount bolts on one side, knock retard was severely crippling.

Scanner can reset fuel alchohol percentage..

To test for cat blockage, you need a back pressure gauge.(amazon OK for me)
Drill a small hole before cat or remove o2 sensor.

 

[GCDenali]

Need to know fuel pump pressure.

I am going to do something I hate doing, assuming you have a 5.3 instead of the 6.0 electric/gas option.

Need to know fuel pump pressure.

I am going to do something I hate doing, assuming you have a 5.3 instead of the 6.0 electric/gas option.

ugh Ass-u-me sorry it’s the 5.3

 

[GCDenali]

Does it run smoothy?

Scanner can tell you fuel pressure sensor reading.
Likely there would be a code if pressure dropped?
Reading actual pressure with a gauge even better, but don't buy amazon gauge.
Harbor freight much better! (thanks @strutaeng!)

Scanner can also tell you if you have knock retard.
I once forgot to tighten motor mount bolts on one side, knock retard was severely crippling.

Scanner can reset fuel alchohol percentage..

To test for cat blockage, you need a back pressure gauge.(amazon OK for me)
Drill a small hole before cat or remove o2 sensor.

Yes it runs smooth. What’s the best option for a scanner that will reset the fuel percentages that won’t break my wallet? I’ll run by harbor freight this morning to pick a pressure gauge.

 

[mikez71]

Sorry, I have very little experience with scanners!

I've only used:
Tech-2 (clunky and slow, but does show all sensor info for your truck. Older GM only)
HPTuners (can graph lots of ecm/tcm variables, plus can tune! Mostly GM and a few others)

Some amazon scanner maybe a better universal tool.
Something with a screen for displaying graphs..
Probably need to spend $200-$300? I've heard names like Autel and Topdon..

Hopefully someone else has reccomendations...

 

[Joseph Garcia]

@Doubeleive posted about a relatively inexpensive decent scanner within the past week.

 

[Doubeleive]

key on, engine off 50+
engine running 43 minimum

 

[Fless]

Many inexpensive scanners (or OBD dongles and a phone app) will show you fuel trims. Check those and post up the short- and long-term trims for both banks.

Also check the fuel alcohol percentage to see if it corresponds to the fuel you're using (e.g., E10 has up to 10% ethanol in it).

 

[GCDenali]

key on, engine off 50+
engine running 43 minimum

54.82psi key on, engine off.
engine running fluctuates between 42.64 and 43.51 psi

 

[GCDenali]

Many inexpensive scanners (or OBD dongles and a phone app) will show you fuel trims. Check those and post up the short- and long-term trims for both banks.

Also check the fuel alcohol percentage to see if it corresponds to the fuel you're using (e.g., E10 has up to 10% ethanol in it).

Long term bank 1 -7.03%
Short term bank 1 fluctuating between +2.13% down to -3.13%

Long term bank 2 0.78%
Short term bank 2. Fluctuating all over the place from -.78% to +3.13%

Fuel pressure running at Idle 43.08psi

 

[GCDenali]

Long term bank 1 -7.03%
Short term bank 1 fluctuating between +2.13% down to -3.13%

Long term bank 2 0.78%
Short term bank 2. Fluctuating all over the place from -.78% to +3.13%

Fuel pressure running at Idle 43.08psi

Alcohol percent 0%

 

[mikez71]

Any knock retard?
2 degrees won't matter.
6 degrees you can tell power is down
14 degrees feels like reduced engine power.. (In fact REP is -15degrees plus throttle limiting)

 

[Doubeleive]

54.82psi key on, engine off.
engine running fluctuates between 42.64 and 43.51 psi

next you'll need to prop it up under the front of the hood/window so you can see the gauge and go drive around and see if the hesitation corresponds with a drop in fuel pressure.

 

[GCDenali]

next you'll need to prop it up under the front of the hood/window so you can see the gauge and go drive around and see if the hesitation corresponds with a drop in fuel pressure.

I’ve been driving it around the fuel pressure doesn’t go above 43 psi even when I floor it it bars down and stays at 43

 

[OR VietVet]

Fuel pump.

 

[Doubeleive]

I’ve been driving it around the fuel pressure doesn’t go above 43 psi even when I floor it it bars down and stays at 43

That's where it should be unless you accelerate fast it may go up briefly, if it drops then it's a problem. So it's probably not fuel related, start looking at air & spark/misfires/knock retard

 

[GCDenali]

That's where it should be unless you accelerate fast it may go up briefly, if it drops then it's a problem. So it's probably not fuel related, start looking at air & spark/misfires/knock retard

Appreciate the insight I’ve changed the plugs and wires cleaned out the mass airflow sensor and throttlebody new air filter too. No misfires smooth idle seemed to drive fine yesterday when I drove it up to the store to get the fuel pressure gauge when this happened on Friday I could stomp the pedal to the ground and it would barely accelerate.
I wouldn’t think a fuel pump would be intermittent. I was kinda leaning towards the clock, Catz cause I’ve been driving it all day. I literally left the house at 5:30 in the morning and didn’t get home till 9 o’clock at night.
What would your suggestions be to check for?

 

[mikez71]

Did you check for knock retard yet?

If you have a graphing scanner should be easy..
If not, you need the scanner to display recorded maximums, or watch it while you're flooring it.

 

[Doubeleive]

Appreciate the insight I’ve changed the plugs and wires cleaned out the mass airflow sensor and throttlebody new air filter too. No misfires smooth idle seemed to drive fine yesterday when I drove it up to the store to get the fuel pressure gauge when this happened on Friday I could stomp the pedal to the ground and it would barely accelerate.
I wouldn’t think a fuel pump would be intermittent. I was kinda leaning towards the clock, Catz cause I’ve been driving it all day. I literally left the house at 5:30 in the morning and didn’t get home till 9 o’clock at night.
What would your suggestions be to check for?

when mine had a clogged 3rd cat, drove fine if you were gramma, but no passing power gutless wonder complete pos otherwise
a backpressure test revealed 10 psi at idle and 15+ at throttle, should be 5 psi max
it started out slow drove fine around town and everything was good but if you were driving up a hill or mountain and needed power it would start having misfires then it just progressed over time to having no power to pass even on flat land. that took a while to figure out.
I don't know what exactly you are experiencing if it is the engine or transmission
if it is the engine it could be the throttle body, maf, knock retard
if it is the transmission you should be able to drive it around in different gears and see if the problem either doesn't occur in low gears or whatever.
I can only suggest hooking up a scanner and start getting some live data, that should point you somewhere.
the good thing is if you invest in a half way decent scanner it pays you back eventually by not having to pay some one else to scan it...for any reason.
a diagnostic at most dealers now is like $180 so. it is what it is. ya they will often apply that towards a repair but r@pe you on the parts and labor as well.