Replaced Spark Plugs, now runs worse. - Chevrolet Forum - Chevy Enthusiasts Forums

1988 - 1998 (GMT400) Section for all discussion related to the 1987-1998 Chevrolet and GMC trucks.

Replaced Spark Plugs, now runs worse.

Reply

 
 
 
Old April 16th, 2018, 7:56 AM
  #1  
CF Beginner
Thread Starter
 
Join Date: Apr 2018
Posts: 6
Default 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!

Last edited by Spencer Kearton; April 16th, 2018 at 2:08 PM.
Spencer Kearton is offline  
Reply With Quote
Old April 17th, 2018, 7:47 AM
  #2  
CF Beginner
Thread Starter
 
Join Date: Apr 2018
Posts: 6
Default

Adding dielectric grease to my plug boots seems to have resolved this issue.
Spencer Kearton is offline  
Reply With Quote
Old April 17th, 2018, 7:42 PM
  #3  
CF Beginner
 
Join Date: Apr 2018
Posts: 7
Default

How old are the wires?
Dielectric grease is non conductive so if that fixed your trouble I would suspect the wires are bad.
a1cnc is offline  
Reply With Quote
Old April 17th, 2018, 8:32 PM
  #4  
CF Monarch
 
kevinkpk's Avatar
 
Join Date: Jul 2011
Posts: 4,232
Default

I'd suggest you may have a vacuum leak
kevinkpk is offline  
Reply With Quote
Old April 18th, 2018, 7:44 AM
  #5  
CF Beginner
Thread Starter
 
Join Date: Apr 2018
Posts: 6
Default

Originally Posted by a1cnc View Post
How old are the wires?
Dielectric grease is non conductive so if that fixed your trouble I would suspect the wires are bad.
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.
Spencer Kearton is offline  
Reply With Quote
Old April 18th, 2018, 7:47 AM
  #6  
CF Beginner
Thread Starter
 
Join Date: Apr 2018
Posts: 6
Default

"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.

Last edited by Spencer Kearton; April 18th, 2018 at 7:47 AM. Reason: Forgot to Quote.
Spencer Kearton is offline  
Reply With Quote
 
 
 


Thread Tools
Search this Thread
Sponsors

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: