The first problem I'm pretty sure its the U-joints in the driveshaft; when pulling easy from light little to no clunk, but if I put a little foot into it there is clunk that sounds like the driveshaft area; also, say you let off to coast a little between lights and then start to accelerate again...clunk.

Second issue is a little more involved, under normal acceration everything is fine, but if say I'm cruising along and I put my foot into it to pass a car or kick down a gear there is this jerking motion like it wants to go, but accelerates for a second or two, then falls flat. It also happens on the highway under a moderate need to accelerate. I just got this truck and I'm trying to work out the many bugs. could it be the fuel pressure regulator? Or maybe a throttlebody sensor? maybe the MAP sensor? or? It just wants to stumble around when you need to really accelerate!

I just but a new fuel pump in it, (OEM) and fuel filter. I bought it not running from the original owner, a female friend who had replaced the fuel pump a year earlier with a cheap Airtech or something.
Sorry for the long post, there will probably be more, LOL.

 

What year and make is the truck? Almost sounds like a floating EGR valve to me. Pretty common on TBI trucks.

 

Thank for the reply, The truck is a 2000 Sierra Z71, 5.3, it is loaded, has all the bells and whistles. I just got this truck a few months ago and just now starting to try to get it right. It very original, nothing has been done to it. It still has the original radiator fluid, its like it just came from the dealer, only it has 225000 hard, unmaintained mileage on it. There is more worn or broken parts on it than you shake a stick at. The motor just purrs though and is surprisingly strong. The EGR sounds like an educated guess. I know it needs a complete tune up badly. I'm retired and on a limited income, so, I'll have to knock problems out once or twice monthly. The stumbling or hesitation only happens on moderate to hard acceleration, otherwise it runs ok, considering the condition of the truck.
I appreciate your reply.

 

Oh yes... Not to sound too stupid, but, what is TBI?

 

tbi is throttle body injection; 2 injectors in the throttle body which gm used in the late 80's early 90's
2000 models went to multipoint fuel injection...ie 8 injectors in the intake manifold.


the hesitation could be a number of things. any dtc's set? Can you view the fuel trim with a scan tool?


the main inputs for fuel metering are tps, maf, pre cat 02 sensors. the fuel trim reading will tell you if the truck is running lean or rich, if vacuum leaks are present.

 

I appreciate your reply primem.... I guess I might just replace all the sensors, and see what or where to go from there.

 

replacing parts indiscriminately gets expensive real quick.


Scan tool data would help rule out some things.

 

Agreed! Replacing parts with the shotgun method can get costly and I am financially challenged as it is. Must borrow a scan tool.

 

Sorry, I was going under the assumption that you had an older truck.

I would look at a scan tool to make sure the MAF works, and that the engine isn't missfiring under heavy load.

 

All is good, I really have a hard time figuring which end is which... I think I belong in an old folks home... It is what it is.