Lose power and sputtering uphill

Randy Lahey · June 26, 2021

I have a 99 Sierra 2500 with a 6.0L and 295,000 km. I've been having this same issue for several years now (I only drive the truck a month of the year, so I just put up with it). It takes a bit to warm up the engine otherwise it will just completely tank when I press the gas pedal more than slightly. It runs fine at speed on the highway, but starts doing the same thing when going uphill, load or not. It doesn't throw any codes. I've replaced the fuel filter, and haven't tested it uphill yet, but could it be the fuel pump?

diyer2 · June 27, 2021

EGR valve?

Needs a tune up?

Check fuel pressure.

thx1138v2 · June 27, 2021

You might check this if it has catalytic converters. I had the same symptoms on a 94 Sierra. Mine turned out to be a canister withiin the catalytic converter got turned sideways some how. I pulled the exhaust pipe off and saw it right away. I knocked the canister out with a 1/2" steel rod about 3 feet long, buttoned it back up, and it ran fine. I replaced the converter when I got some money.

With the canister turned sideways , it was blocking too much of the exhaust gases. If you know what it should feel like you can put your hand over the end of the tail pipe to see if the exhaust feels too weak. Other than that, disassembly is the only way I know to check it. Maybe if you have a friend with the same engine you could feel his exhaust for comparison.

Randy Lahey · June 28, 2021

Took it for a drive today, about 35km each way out to my acreage, up and down hills, highway and gravel. It ran fine! Seems like it was just the fuel filter. I still find it hard to believe that it was just a $9 fix. The only other thing I can think is that maybe pulling the fuel pump relay reset something? Can that happen?

New issue (old one that I notice more now) is that there is a 'shuddering' when I first accelerate from a standstill (i.e. green light). It runs fine otherwise. Maybe a u-joint? Hopefully not a torque converter issue...

Edited June 28, 2021 by Randy Lahey

thx1138v2 · July 1, 2021

I don't know anything about the second problem but if the first problem recurs it could be the catalytic canister turned sideways and restricting the exhaust gases again.