Sluggish performance

CURRY5252

MEMBER
CHEVROLET

I have a 2001 Chevrolet S-10 ZR-2 4x4 with the 4.3L engine (vin W) with 24K miles. This truck ran great until I had the oil changed at one of those quick lube places. Since then, this truck runs 55mph @ 2000rpm until the temp guage reaches approx 160-170 degrees. Then, once the engine reaches that temp, the rpm's fall off to 1400-1500. Once this happens, the truck has no power until you force a downshift by pushing the excellerator to the floor. I have replaced the fuel filter, all three O2 sensors, tps, iac valve, maf sensor, air filter, ran fuel injector cleaner through the tank, iat sensor, and I even boroscoped down in the intake manifold and found two wet intake valves after the truck had been shut off for thirty minutes. Maybe a sign of a leaky fuel injection system? I also cleaned the egr valve and bought a scantool with no codes present. I am at a loss. Some say check the Catalytic Converter, it does smell like the rotten eggs. Fuel mileage dropped off the face of the Earth. 70 mph is @ 1700-1800 if I am lucky. This engine doesn't have power at that rpm/speed. Can you think of anything I should check? Thanks, Curry52525

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CURRY5252

MEMBER
4 POSTS

2001 S-10. The engine sounds normal as far as no misses, no rough idle, it will climb to redline if you floor it. The big factor with the engine is that once it warms up, above 160-170 degrees, the rpms drop off about 500-600 rpm's and then you feel and hear the engine lugging like you are driving a 5-speed manual at 30mph. You can force a down shift when your climbing a small hill, but it won't do it on its own until your almost driving vertical. I haven't checked the tranny cables yet. I did have aamco go through the tranny, they found some wear on the overdrive belt or band, but minimal, they changed it anyways at my request. They said all is normal with the tranny, no codes present, and they believe something on the engine side is causing the rpm to drop once its warm. The truck basically wants to shift into overdrive as soon as it can, and stay there even if your only doing 40-45mph. I know it can do that at 40-45mph and be normal, but shouldn't the engine recognize a load of pulling a hill or slight incline and put it back into fourth? And then it just refuses to build rpm even as you start to gain speed on flat level ground. 70mph @1700-1800rpm can not be normal for that truck. It performed much better than that when I first got it and before the quick oil change place got there hands on it. This engine is rated at 190hp, where did the HP go? If it had power all the way through that rpm curve, then I would be happy with that rpm @ that speed, but it is a led sled getting it there without forcing a kick down. I'll look into all of the tranny cables, maybe I missed something. Thanks for the info, much appreciated. Does anyone know where to find Chevrolet rpm/shift points or curves? I have called the local dealer and would have gotten a better answer if I would have called the Red Cross. This truck runs, drives, and holds rpm and power, and will chirp the tires from a dead stop like there is no tomorrow as long as your below 160-170 degress. After it reaches that temp, it wouldn't pull itself out of a wet paper bag. I am going to check the engine coolant temp sensor today, maybe it is sending a bogus signal to the PCM? Thanks for the help. Curry5252