I've got an 07 Monte with the 5.3 in it. I had the transmission rebuilt in September, and replaced plugs and wires at the same time. And ever since, I've noticed it doesn't sound the same, and to me it seems to run rich by smell, but doesn't throw a code. It sounds like it does when it goes into 4 cylinder mode, but I've got that disabled by plug in. Any help with direction would be awesome!!

 

If it happened exactly when you did plugs and wires, I'd go back through them 100%.

Look at the wires idling at night with the hood open to see if you see any arcing. Then I'd pull the wires and check resistance.

While they're off, Id look at the plug ceramic to see if any are cracked. If still nothing, I'd pull the plugs too and check for internal damage as well as verify gap is still good.


The transmission swap is tricky as there's a lot of stuff that gets unplugged for that. About the only thing you can do is go over the vacuum lines and plugs / grounds with a fine tooth comb.


If none of that yields any results, you really should get an OBD sensor scan tool to read the live data to see whats going on. Otherwise you'll just be shooting in the dark on the next steps.

 

I'm a dumbass. In putting the spark plugs in, they lie and say the iridiums are gapped from the factory and don't need to be regapped. Ya, well when their gapped at between .080 and .085, ya, that's going to take a ton of fuel. Regapped to the correct .040, let run at idle to burn off all the fuel out of the cylinders, and low and behold, my baby sounds so much better, runs better and even smells better. Thanks for the help.

 

Always check gaps first.

 

Ya, no ****. I've been in the automotive world for 25 years as parts salesman and service writer and you'd think I would have known that. Like I said, I had a dumb *** attack! Lesson learned, and I used to tell people to check em...🤦

 

I'd say you're pretty lucky. I always feel bad for these people that ask these questions and spend weeks / months trying to trace down some obscure issue. At least yours was a really easy find / fix! Glad to hear you've got her running all better again!