Hesitation

[Mike GMC]

I've noticed a hesitation lately when the engine is cold.  The colder it is, the worse the hesitation is.  Once the engine warms up even a little, it goes away.  Any thoughts on what could be the issue?  There are no code.  I was thinking it might be an injector issue where they don't atomize well enough for cold operation.  Plugs are new.  No misfires.  Could it also be an O2 issue?

 

Forgot to say, it's a 2000 Sierra 1500.  Was a 5.3, but now has a 6.0 long block with the original 5.3 intake and ignition.

[txab]

For starters, always check intake gaskets  since they are prone to leakage over time. Your description kinda fits intake leak.

 

Did you do any tuning after going to a  6.0?

[Mike GMC]

Thanks, I'll check it this weekend.  I hadn't thought of that.  The gaskets are only a few months old, but maybe they didn't seat correctly.

[Mike GMC]

I checked for intake leaks with both ether and carb cleaner and neither had any effect on isle speed.  So I don't think I have any leaks.  I checked to see if any intake bolts we're loose any very thing was good there as well.  It's warm enough today that the hesitation really didn't happen.  The injectors have 225 k on them, I wonder if the spray is more of a dribble these days.

[carnau]

On 1/6/2018 at 3:45 PM, Mike GMC said:

I checked for intake leaks with both ether and carb cleaner and neither had any effect on isle speed.  So I don't think I have any leaks.  I checked to see if any intake bolts we're loose any very thing was good there as well.  It's warm enough today that the hesitation really didn't happen.  The injectors have 225 k on them, I wonder if the spray is more of a dribble these days.

When is the last time you cleaned the throttle body?  

[Mike GMC]

Same time I did the intake gaskets, a few months ago.  Still seems weird that it only happens when the engine is stone cold and it's very cold outside.  I drove it Friday and it seemed fine, but it was warmer outside.  Maybe she's just getting cold blooded with age.