Loss of power (stumbles)
 

i have a 97 chevy stepside with a 4.3 vortec in it. last week it started to develope a hesitation problem and is just getting worse. when the vehicle is cold or started for the first time in the morning it runs great better then it ever has but after about 5 mins. of warming up it developes a hesitation or stumbles from a stopping point and troughout driving at normal accel. you can feel the vehicle holding back and surge a bit. if you increase the accel the surge goes away for the most part but the lack of power is still there. it has also dropped my MPG a lot.

Ok the thinks i have done to this point are. new plugs (first cheap ones then went with Double PLat.) cap, rotor, TPS, Fuel Filter, Air filter, and a new PCV. There is no codes stored on the vehicle and it does not trigger a code. I figure if it was a sensor it would give me a code by now (one week later).

My question is has anyone ever run into this problem and what was the cure? I am goin to check the Fuel pressure today but it seems to run fine till it warms up so I'm not sure if thats the problem. With no codes it is making it a little difficult to diag.

the reason for the parts replaced was it felt like it needed a tune up. it now feels like the fuel is restricted or something. i do use lucas inj cleaner in the tank every third tank si i dont think the injectors are clogged.

I'm just at a loss with this and need to find out the problem soon. I don't want to throw parts at it. I was also told it could be the Cat. I prefer to not take it to a shop because most places here have no Idea what they are doing. ( was told by a shop yesterday that it need a tuneup cause they pulled the plugs and they were dirty and need to be replaced. i just replaced them two days earlier and removed them again to look at them, they are fine. see my point.

I'm sure there is more info needed to diag. this problem so just ask me and i will get the info needed as fast as i can.

PS. the truck starts up with the slightest turn of key everytime. even when warmed up

Hey there, how many miles are on the truck? Also what types of conditions or driving habits is the vehicle been subject to?

Hi
sorry the vehicle has 106000 miles on it and it is babied when driving. about two weeks ago I checked the MPG and was averaging between 22 and 24 mpg on the hignway and around 16 to 18 in town. it also has a 5 sped manual trans if that matters.

where i live its pretty hot here but not humid. we have not had rain in a while. the temps are around 80 - 100 most days during the summer. dry heat

Unplug the coolant temp switch and drive it. If it runs better replace it.

I tried the temp sensor on the way home but the only difference was that it was harder to start and a CEL came on. I didn't have time to check fuel pressure yet but noticed that the fuel pump gets really noisy and i have almost a half tank. I know some will make noise but i can here it at a light with my windows up and the radio on.

FYI
so i worked on the truck this weekend and wanted to relay what i found out. First i checked the fuel pressure and it was holding steady at 52psi witch is low for the vehicle (60-66psi according to mitchell OD5). i replaced the fuel pump and noticed a little bit of difference but not fixed. so i started looking into sensors going bad and not giving codes. i tested the MAP and it was going bad. the test i performed was i unpluged it and test drove the truck. i noticed a huge difference in the way it ran. so i replaced it. I no longer have the stumble or hesitation i had before (just a very slight stumble). now the problem i have with the truck is it losses power on hills and has a loss of power and just does not have the power it use too. im think i had multiple problems with the truck and this is why i had such a hard time figuring it out. i think the next thing im goin to have to try is to see if the Cat is clogged.

If anyone else has any suggestions to what it might be that would be great..i will post what i find out when i can afford to replace the CAT, if its bad.

ok so i fixxed the problem with my truck. it had a clogged Cat. i removed the two o2 sensors befor the cat and test drove. i saw an improvement right away. instead of replacing it i went ahead and made a filler peice of pipe that i will use till i have to have the vehicle inspected again in two years.

I should have known to check the Cat. but for some reason or another it was always overlooked. the only advice i can really give everyone is, don't over think the problem. it may be as simple as a clogged Cat.

Thanks for the advice I will try it when i face the same problem

I think Im having the same problem with my 02 chevy. Do the o2 sensors need to monitor the exhaust or can they dangle until I can replace the cat?

Just try to change the coolplant it would be quite very helpful.