Not down shifting properly and hesitation

[red02deuce]

My first post here so be gentle. I tried the search before asking this too. I do my own vehicle work 99% of the time and look forward to those smarter than me pointing me in the right direction. I am mechanically competent but do not want to get into parts swapping without some direction. Thanks in advance.

 

Vehicle:

2000 GMC Sierra 1500 Z71, 5.3L, ~115k miles. Oil changes regularly, tranny has been flushed by the dealer twice, at 30k and 75k, and the coolant changed. No engine work other than a set of Bosh Platnum plugs ~ 30k miles ago and a battery.

 

Some history:

A hesitation problem forced me to decide to remove the K&N set up I had as well an aftermarket TB spacer. They had been on the vehicle nearly since the vehicle was new but the recent hesitation made me wonder. I have a power stat 160 deg. thermostat that I installed with the above said items. I have tried reinstalling and removing the performance program from my Power Programmer III. I replaced the fuel pump assembly ~ 20k miles ago since the fuel gauge was dropping to E on its own.

 

Problems:

Hesitation off the line (for a while now), a feeling of a loss of power when cruising (more frequent), when mashing the gas pedal it will not down shift like it should (just since my last actions noted below). When I set the cruise control, it drops about 5 - 7 MPH below the set speed (this is very noticable and did not do this before I did what I did below.) All fluid levels are good.

 

Actions taken:

This weekend I installed a factory style air filter, Desuche PCV valve (never replaced it on this vehicle before), fuel filter, removed the throttle body and used Gumout carb cleaner to clean everything I could reach and replace it back on the intake. It was very dirty (gummy). I am blaming the K&N filter. I also looked for vacuum leaks , loose. cracked hoses, or any other obvious anomalies. I did remove and reinstall a little plastic part that sist on top of the intake plenum. It connects to an intake port on the top front part of the plenum (under the VORTEC plastic cover.) I replaced it when I determined that I could not improve on it. One thing about that part, of which I have NO idea what it does, it does not seem like it mounts very tight against the plenum. There is a small O ring on a stem that looks to seat in a taper. The shoulder bolt and rubber spacer on the mounting flange bottoms out before the part seats securely against the plenum.

 

Also, I have never noticed the 2 grommet like features that are fixed to the throttle cable at the peddle end. There is about a 4" space between them. Also, I think the second cable on the throttle body is the cruise control. It has at least 2" - 3" of slack in it.

 

Starts fine, idles real nice ~500 RPM, runs at cruising speeds fine. But I mash the peddle and I might as well have a 4 cylinder in the thing.

 

All I can think of are the following...

TPS, intake related sensors

Oxy Sensors

Catalytic convertors clogged

I did something when the throttle body was removed

Throttle/ cruise cables out of position or screwed up somehow

 

I live in the southwest so salt and corrosion are not a real issue for me. If that matters.

[ChevyTech007]

First thing I would do is unplug the MAF sensor and drive it to see if it changes anything. It might not drive perfect because it uses a calculation of airflow. With the previous K&N setup it is very possible that the MAF is screwed up by the oil in the filter. If that is not it you need to have it scanned for codes, exhaust back pressure test and fuel pressure test. Also you might want to pull the vacuum line off the fuel pressure regulator to see if there is any gas in it.

[Mr. Smith]

My first post here so be gentle. I tried the search before asking this too. I do  my own vehicle work 99% of the time and look forward to those smarter than me pointing me in the right direction. I am mechanically competent but do not want to get into parts swapping without some direction. Thanks in advance.

 

Vehicle:

2000 GMC Sierra 1500 Z71, 5.3L, ~115k miles. Oil changes regularly, tranny has been flushed by the dealer twice, at 30k and 75k, and the coolant changed. No engine work other than a set of Bosh Platnum plugs ~ 30k miles ago and a battery.

 

Some history:

A hesitation problem forced me to decide to remove the K&N set up I had as well an aftermarket TB spacer. They had been on the vehicle nearly since the vehicle was new but the recent hesitation made me wonder. I have a power stat 160 deg. thermostat that I installed with the above said items. I have tried reinstalling and removing the performance program from my Power Programmer III. I replaced the fuel pump assembly ~ 20k miles ago since the fuel gauge was dropping to E on its own.

 

Problems:

Hesitation off the line (for a while now), a feeling of a loss of power when cruising (more frequent), when mashing the gas pedal it will not down shift like it should (just since my last actions noted below). When I set the cruise control, it drops about 5 - 7 MPH below the set speed (this is very noticable and did not do this before I did what I did below.) All fluid levels are good.

 

Actions taken:

This weekend I installed a factory style air filter, Desuche PCV valve (never replaced it on this vehicle before), fuel filter, removed the throttle body and used Gumout carb cleaner to clean everything I could reach and replace it back on the intake. It was very dirty (gummy). I am blaming the K&N filter. I also looked for vacuum leaks , loose. cracked hoses, or any other obvious anomalies. I did remove and reinstall a little plastic part that sist on top of the intake plenum. It connects to an intake port on the top front part of the plenum (under the VORTEC plastic cover.) I replaced it when I determined that I could not improve on it.   One thing about that part, of which I have NO idea what it does, it does not seem like it mounts very tight against the plenum. There is a small O ring on a stem that looks to seat in a taper. The shoulder bolt and rubber spacer on the mounting flange bottoms out before the part seats securely against the plenum.

 

Also, I have never noticed the 2 grommet like features that are fixed to the throttle cable at the peddle end. There is about a 4" space between them. Also, I think the second cable on the throttle body is the cruise control. It has at least 2" - 3" of slack in it.

 

Starts fine, idles real nice ~500 RPM, runs at cruising speeds fine. But I mash the peddle and I might as well have a 4 cylinder in the thing.

 

All I can think of are the following...

TPS, intake related sensors

Oxy Sensors

Catalytic convertors clogged

I did something when the throttle body was removed

Throttle/ cruise cables out of position or screwed up somehow

 

I live in the southwest so salt and corrosion are not a real issue for me. If that matters.

 

<{POST_SNAPBACK}>

 

 

 

First off there is no reason to run that thermostat. That cold it may not come out of open loop. Go back to stock as there is no real gain to use it.

 

Second, ditch those Bosch plugs. I have not seen one Ford or GM run worth a crap with them and if you got 30K then you are lucky.

 

As far as the rest I have no clue without pics.

[red02deuce]

UPDATE: Okay here we are...

 

As dumb as this may sound, I found the issue.

 

There was an aliminum plate that spaced out the cable bracket to accomodate the aftermarket TB spacer. The pedal, cruise, and throttle response seem back to normal. The 5.3L runs nice. It has been so long since I installed the TB spacer, I forgot all about the cable bracket spacer. I feel real dumb.

 

Now that I have this tackled, I have to work on getting the parking brake fixed. It has never worked right since I purchased the truck new in 2000. The pedal goes to the floor with very little resistance and does not lock it in place. But, that is another post. AFTER I look at everything.