2014 Silverado hesitation when accelerating from stop

[MisfireMagnet]

Hello,

 

I am hoping that you can help me diagnose what is causing a hesitation on my truck when accelerating from a stop. It sometimes also hesitates when shifting at low speeds 10-30mph

 

Truck Specs

• 2014 silverado 1500 WT
• 4.3L V6
• locking rear end
• 32,000 miles
• no codes, using bluedriver scanner
• red

 

Problem

• two weeks ago truck took two tries to start
  • never done this before
  • has not happened again
• last week truck started hesitating on acceleration from stop every time
• rpms drop from 1500ish to 500ish and then jump back up and truck accelerates
  • I have attached one of the drive logs where you can see the fuel rail pressure drastically change when the engine rpm drops
    • You can see the seven times the truck hesitated at the drops in the graph
• Started logging other items to see what is happening and found this spike in the temp sensor, attached picture also.
  • intake temp sensor is yellow line and engine rpm is blue line.
    • I highly doubt the temperature actually went from 55F to 135F during my commute.

 

What I have done

1. Checked transmission fluid, truck level and hot.
   1. Fluid in the dashed good zone between the holes.
   2. No burnt smell.
2. Found the strange temp reading.
3. Truck off
4. Unplugged the mass air flow sensor and drove around large parking lot.
   1. Hesitation completely gone truck drive normally for 5 min.
   2. Check engine light off.
5. Truck off
6. Plug in mass air flow sensor and drive around parking lot again.
   1. Hesitation back
   2. Check engine light on with codes for MAF unplugged.
7. Thought MAF was the issue.
8. Bought new MAF and air filter
9. Installed MAF and air filter
10. Problem gone on test drive for 15min, truck fine, no codes.
11. Next day, hesitation is back, no codes
12. Realize I need help.
13. Post on forum.

 

I'm sure I have left out some important information, just let me know and I'll try to answer.

 

I greatly appreciate the help. Thank you.

 

Edited March 18, 2021 by MisfireMagnet
adding additional diagnostic step i did

[MisfireMagnet]

Update on diagnosis:

• I have tried unplugging the battery for 15min to reset sensor parameters. Still having the problems.
• Truck shifts without hesitation in manual when I am controlling shift points.
  • When I manually shift over/at/under the rpm where the truck automatically tries to shift it is working correctly without any hesitation/jerking.
• Tried cleaning the original MAF sensor again and re-installing but same issue.
• Dealer told me without an engine light or code the most they would do is just start cleaning the intake and intake manifold and see if anything changes.
• Tried fogging the engine compartment with fine water mist to see if rpm dropped slightly.
  • This is probably not as effective on new computer controlled engines. They might adjust before the scanner senses rpm drop.

 

[MisfireMagnet]

Update:

• Check engine light off.
• Now has some permanent codes.
  • P0097 - intake air temperature sensor 2 circuit low bank 1
  • P00F4 - humidity sensor circuit low
  • P0102 - mass or volume air flow sensor "a" circuit low
  • P0113 - intake air temperature sensor 1 circuit high bank 1
• I can view the sensor data live for the above codes and they all appear to be working fine.
  • I am thinking the codes could be from my test drive with mass airflow sensor unplugged.
  • Do you know how long it could take for the truck to clear these codes?
• Checked every wire connector I could reach to make sure it was not loose.
• Filled truck with 89 octane and added Lucas fuel treatment with injector cleaner.
• 10 min test drive around neighborhood
  • Hesitation present and some rough idle.
• Took truck for 30min drive down highway to get everything up to working temperature.
  • Drove in tow/haul to keep engine rpm up, hopefully get the fuel treatment moving through faster.
  • Highway driving 55-65 mph nearly entire time.
  • Accelerated pretty aggressively from low speed after truck was warmed up down highway.
  • Truck acting good at speed.
  • Back in neighborhood after test drive the truck did not hesitate at all and accelerated smooth like it should.
• I will see what happens tomorrow when the truck is cold.

Edited March 20, 2021 by MisfireMagnet
typo

[ic3man5]

I'm not exactly sure if this is your problem but look into the HP fuel pump. Early models (2014s) were known to have failing fuel pumps (Its under the intake manifold). If your scanner can read the LTFT and STFT (Fuel trims), I would try monitoring that. I'd also check for a vacuum leak.

 

Codes more than likely will stay until you clear them manually. I would say they are probably codes from when you removed the sensor.

 

 

edit: while you are at it inspect the coolant level (OEM radiator / t-stat suck).

Edited March 22, 2021 by ic3man5

[MisfireMagnet]

Thanks. I will log the fuel trims next and see if anything is strange.

Codes are now listed as permanent and the truck will have to clear them when it determines the problem is gone. (according to my reader anyways)

All fluids are at correct level.

[MisfireMagnet]

Okay, so the truck ran great for two days and now the hesitation problem is back.

I have taken some snapshots of the fuel trim readings over a time period where there is two hesitations present.

I am going to have to do some research because I don't know what is good for fuel trims.

 

Long term fuel trims against engine rpm here.

 

Short term fuel trims against engine rpm here.

 

Driving steps here. You can see as I start to accelerate from a stop the RPM increases to 1300ish for a split second and then falls to 600ish before jumping rapidly to 2000ish.

This is engine rpm on the left vertical axis and time in seconds on the horizontal axis.

You should be able to map this activity back to the upper two graphs if needed.

 

Not sure what to do next. The previously listed four codes are still present when I try to read them but the check engine light is still off.

 

 

[MisfireMagnet]

Okay, so I have looked into fuel trims slightly and it seems they ideally should stay even with perfect air/fuel ratio.

Since my STFT is maxing out at +25% that means the PCM is detecting a lean condition short term and is trying to add more fuel.

However, my LTFT is consistently negative at 0 to -14% like the PCM is detecting a rich condition on average and is reducing fuel.

 

[MisfireMagnet]

After noticing that both banks are roughly the same acting I believe it has to be something that must effect both sides.

So ruled out, for the moment anyways, injectors, coils, plugs, and O2 sensors.

Going to check evap purge valve to see if it has any vacuum on the port at idle. After that I might suspect one of the fuel pumps.

[MisfireMagnet]

After driving home from work the engine was hot and I restarted the truck to idle in the driveway.

The evap purge valve was shut for about 20 seconds and then it started to make a popping noise and I could feel intermittent vacuum. 

Should this purge valve be open at hot idle?

[MisfireMagnet]

I tested the evap purge valve on my workbench and I believe it is good.

-held vacuum without leaking no power.

-released immediately when power applied.

 

I monitored my STFT and LTFT and they were negative with the evap hose connected. LTFT was around -15%.

When I unplugged the hose and covered the port with my finger the STFT went to near zero and LTFT about -4%

The truck was warmed up and the ambient temp is 80F.

Does this seem strange? If so I guess the problem might be upstream of the evap purge hose towards the tank.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[MisfireMagnet]

Okay, so I have been recording every trip in my truck and stumbled across the following reading.

My engine RPM read over 12,000 rpm for almost two seconds while I was driving steady at 1100 RPM.

This happened several times but I zoomed in on one occurrence for clarity.

You can also see my negative LTFT and maxing out STFT.

At this point I would guess one of the following things is happening.

1. My BlueDriver scanner malfunctioned several times.
2. Crankshaft position sensor going bad.
3. Camshaft position sensor going bad.

Guess I will try to test both of those sensors and see what happens.

[MisfireMagnet]

Also probably important to note is that when fully warmed up the hesitation is less noticeable or gone completely.

[MisfireMagnet]

I have now moved on to checking the throttle position sensor.

My scanner allows me to view Absolute Throttle Position (%)

With engine-off key-on I went from not-pressed to pressed-to-floor several times and saw the below reading.

Does anyone have the in-spec values for this?

[MisfireMagnet]

Okay, so continuing down the path of the throttle position sensor.

I recorded the following data while the truck was hot idling.

I tried to push the pedal with my hand and hold it at the same position repeatedly.

You can see the pedal position at each attempt stay relatively constant but the throttle position sensor dips right after pressing the pedal and then comes back up.

I am thinking that maybe the TPS is bad. Going to look into how to test this sensor next.

 

 

[ic3man5]

On 3/31/2021 at 1:05 PM, MisfireMagnet said:

Okay, so continuing down the path of the throttle position sensor.

I recorded the following data while the truck was hot idling.

I tried to push the pedal with my hand and hold it at the same position repeatedly.

You can see the pedal position at each attempt stay relatively constant but the throttle position sensor dips right after pressing the pedal and then comes back up.

I am thinking that maybe the TPS is bad. Going to look into how to test this sensor next.

 

 

You need to turn the engine off and with the key on push the throttle all the way down (WOT). It should be around 80-85%. Bottom should be around 10-20% I believe. You won't see 0-100%.