No power up steep hill, low speed?

Tiny
HAPPYFISHER
  • MEMBER
  • 2008 GMC SIERRA
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 177,000 MILES
I do a lot of fishing in the back country. My trailer weighs 1,800 lbs and another 500lbs of gear in the bed in the bed. My truck works well on the highway, I can climb steep passes without issue at highway speeds. My transmission temperature usually runs while towing between 180 and 195 and when going up steep passes will reach 215-225 but will quickly return to 190.

The situation that occurred is as below.

I am on a steep gravel forest road that has several very steep passes around 30% grade. My truck ran with no issue with moderate passes. However, when I am climbing a steep hill in 4-wheel drive at approximately 10-15 MPH, I lose all power and the truck chugs (almost like a train would), the check engine light will go on. When I step on the accelerator nothing happens. When I stop and place the engine in neutral it will rev up with no issue. When return to Drive the same issue will occur. I even tried downshifting into gear 1 and still no better. Once I was able to turn the truck around and go back downhill, the engine light goes off and it runs perfectly well.

I have been on this road and pass many times in the past with a much heavier trailer approximately 5,000 lbs and had no issues. The transmission was serviced (regular maintenance) fluid changed etc. No issues were reported by the dealership.
Wednesday, July 5th, 2023 AT 5:12 PM

1 Reply

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Hi,

If the check engine light was on, there should be a diagnostic code or codes stored in the PCM. Have you tried scanning it?

While I was reading your description, a couple of thoughts came to mind. Anytime there is a loss of power, I question first fuel pressure and second a plugged or partially plugged catalytic converter.

On several occasions, I've found the inside of a catalytic converter come loose and move around. Under the right conditions, it restricts airflow and there is a power loss. Since you were on steep hills, I was thinking of something like that. Have you ever noticed a rattling from the exhaust?

Take a look at this link and let me know if anything appears to mirror what you experience:

https://www.2carpros.com/articles/bad-catalytic-converter-symptoms

Also, have you checked the fuel pressure? If the vehicle was under a heavy load, a weak pump could cause this to happen as well.

Here is a link that explains how it's done:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Let me know. Also, if you haven't scanned the computer, I recommend checking for codes or pending codes.

Let me know.

Joe
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Thursday, July 6th, 2023 AT 9:32 PM

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