So I have a 97 1500 with the 5.9. I need to know if it has lost quite a bit of power over the years or if I'm just crazy. Main issues are losing speed at moderate inclines, and cannot hold speed while towing with overdrive even decently light loads. Has trouble holding speed with a 1500lb boat and trailer on flat grade, and cannot with my roughly 4000lb boat. I usually tow with O/D off anyway but should it not hold speed on flat ground in O/D? Recently threw a code for 02 sensor, and I checked plenum and it seemed ok to me? Although it is a stock steel plate.

It burns no oil, has newer plugs, good air filter, etc
All I've done to it is grind up the throttle body a bit (which helped a little) and drill a few holes in my Cat just to make sure. Doesnt seem clogged. Truck has 208k miles. Please help it feels like a damn slug.

 

Do a compression check and report back what you find

 

Ok am I just looking for weak compression? Will have to run down to parts store tomorrow as my gauge broke a while back. Will the old thumb trick work for now or does it need to be accurate?

 

Needs to be accurate. Run the test dry first, then add a teaspoon of oil to each cylinder, and test again.

 

Hey, looking forward to hearing how this goes. Just had my trans rebuilt and I have not been able to drive with O/D on over about 80 or up hills. Once it locks it doesn’t seem like it wants to kickdown (or unlock) until dropping to 2nd due to slowing down or stopping. Also, O/D OFF button will engage O/D but won’t disengage it until coming to a stop. I’m stumped, so far the oil pan gasket, valve cover gaskets, all speed sensors, cleaned all grounds, had another TC built for my tire size and to play around with.

 

Test done dry.
Front to back
Passenger 118, 125, 120, 120
Driver 120, 125, 135, 118

2 plugs broke on removal, no fouling or residue on any of them, and oddly enough the truck runs on 2 cylinders lol

 

Really low do a wet test.

 

145 to 150 all across the board with 3ml or half a table spoken of oil. Used an eye dropper to get in the whole. Low weight oil probably 5w or 10w. Dont have any gear oil. Spark plug style tester hand tight, injectors unplugged and 5 strokes per reading.

Think im getting it right? It's been a while since doing a compression test.

 

Sounds like bad rings, which is why you have little power. Definitely not a stuck valve or a bad head gasket unless it's blown in every cylinder .

 

Interesting. What should I be getting? And would it make that much difference? I dont think it's worth tearing into to do rings. I got it on trade for 1500 worth and it's pretty rusty. Also what should the plenum look like? There's no oil pooling but it is a little dark like its seen oil right in the center. Not sure if i should replace that either? Think I'll try some additive products first. Any recommendations? Lucus oil is my first thought.