What would cause my truck to lose power?

Question

I just finished replacing my intake manifold gasket and I had a misfire problem I fixed thanks to correctly timing it with a yahoo answers user's directions. But after the misfire disappeared I was out test driving my truck. It stumbles a little after taking off from a dead stop (when it's first started) and then gradually smooths out. I figure this is just the PCM re-learning the engine since it hasn't been driven in over 3 months and the battery was disconnected for 2 months. The gas hasn't been changed either for 3 months. And that doesn't really concern me as I can fine tune that. What concerns me is that while I was test driving it, it ran fine under a normal load, so I decided to test it under a hard one. I opened the throttle half way open and the engine reved up and made noise like it was accellerating really fast, but the car itself was moving like it did under a normal load. The speedometer barely climbed any faster. I checked for trouble codes and there are none.

So I don't think it's the transmission or the clutch sticking, also the brakes operate fine so I don't think they're binding (in fact I looked at the rotors and they're fine). So I'm at a loss as to what could cause the problem. For your reference here's the information about my truck:

1998 Chevrolet S10
4.3L V6 Vortec engine vin X
4 speed automatic transmission
Central Sequential Electronic Fuel Injectors
Enhanced Distributor Ignition
2 wheel drive (rear wheel)

This truck was bought December of 1997, I didn't get my driver's license until 2001 and it was given to me by my parents when they got a minivan. I've driven the truck since then so I know how it behaves. It's been roughly idling for a while, that's normal because of its age. But this truck usually has to be worked hard to go slow. In other words, when I try to idle it down to 25mph it wants to go up to 30mph or more. But now it seems to not want to go fast anymore, especially when floored. There was no load in the truck at all, it was just me half throttle (for below 25MPH) then full throttle at 30MPH and the speedometer slowly moved up. Almost like I had a cheap 4 cylinder instead of a V6. It REALLY feels like it has lost power.

Answer 1

If its onl been doin it since you changed the timing,maybe,just maybe you might need to finely adjust it till it runs smoother.Put the whole timing light away for a sec get a glass of water and sit it on the motor somwhere flat and the idea is to try and get the water as still as possible...This is the best way to time somthing apart from the timing lights as they all differ from brand to brand and price range.Just give that a try might find it works.Other wise id be lookin at a fuel filter.

Answer 2

You have an auto gearbox so you don't control which gear you are in, If you increase the load you are pulling you change the vacuum pressure in your manifold which causes the gearbox to kick down to a lower gear and the revs to climb! Do you have a rev counter? This would be normal under heavy loads or if you plant the accelerator down hard, how much experience do you have with this vehicle? If the sensors are fouled up or the PCM is not working properly or air is getting in somewhere then this kick down in the gearbox may happen too early and you will not get good acceleration. If you let someone test drive who knows how it should behave then you will get answers much faster and better than in a forum like this!

Answer 3

I dont know but i sure would like to knoww. My vortec 350 did the same thing so i changed the timing chain and set the timing per the manual and did a complete tune up and it did not help 1 bit.

Answer 4

weak fuel pump, or plugged fuel filter.