Replaced Spark Plugs, now runs worse.
 

Greetings!

I recently bought a 98/99 k1500- Vortec 5.7 that didn't run. I was able to get it up and going. The wire from the crank sensor to the fuel ground (purple) had melted through on the manifold.

The truck had been running fairly well for a couple weeks, but was bogging under load (hauling gravel/ mulch) and seemed to have a mild sputter to it at times while idling, so I decided to replace the spark plugs. They looked fairly worn.

The plugs in the truck were denso's and were gapped at .045 - I replaced them with AutoLite Double Platinums gapped at .060 and I seem to be running worse now. I idle fine with a few hiccups, but once I'm in gear and give it gas it sputters around real bad. I'm not getting any misfire codes yet, but I do have a crank sensor relearn, and ckp variance code. Those codes existed with the last plugs installed too. I hadn't made it into the dealership for the re-learn yet.

I double checked and snugged all my spark plug boots to ensure I'm hooked up properly, and I also switched out one plug at a time to ensure my wires wouldn't get switched up.

Should I gap my platinums at .045?

Maybe I broke/fractured a spark plug wire/boot? (nothing seemed brittle)

Maybe crank sensor relearn issue is more pronounced with correctly gapped plugs?

Any advice for me?


Thank you!

Adding dielectric grease to my plug boots seems to have resolved this issue.

How old are the wires?
Dielectric grease is non conductive so if that fixed your trouble I would suspect the wires are bad.

I'd suggest you may have a vacuum leak

Good point, I forgot that dielectric is non-conductive and wouldn't improve my scenario.

Maybe I wiggled a wire back into connectivity during this change. I ran about 40 miles yesterday, and seemed to do fine. I'm not certain how old the wires are. I've had the truck a month or so. The guy I bought from said distributor and wires were new, but I can't be sure of it. They don't feel brittle, but I could've damaged something while removing boots from the plugs too.

Thank you.

"I'd suggest you may have a vacuum leak"

I noticed a slight gap at the air intake. I put some RTV sealant in the gap (it looked like it had been sealed up with RTV at some point prior). I seem to be in good shape now. Thank you for your response.