Idle Worse After Plugs and Wires, WWYD?

[swathdiver]

5 hp! Was that ever proven on a Dyno? I remember when you had to change plugs every 5-10k. Now they're 100k rated. Does it smooth out with a small increase in idle? Could it be coincidence? How's the IAC? For me, a rough idling 5.3 is normal.

Better than a dyno, time slips!

 

[swathdiver]

Do you think your helper put the wrong lead on and removed it to replace it on the correct bank?

As a matter of fact, one of the plugs was not tightened enough so the wire was taken off to tighten the plug. It'll be the 2nd week of March at the earliest before we can look at that issue.

 

[KeithinTX]

On New Years Day I hired a neighborhood kid to help change out the plugs and wires on the Yukon XLs 5.3 motor. Used the new 41-162 spark plugs and 748UU GM OE wires.

Truck idles worse than before with plugs and wires that were installed in 2017 and about 48K miles ago. Those old plugs were 41-985s and all were gapped between .041-.043 when pulled and wires had resistance between 780 to 835 ohms.

The new plugs were all gapped at about .041 and the wires had resistance of within 1% for all. She just doesn't idle smooth anymore, motor mount is new too.

What do you think? Should pull them all and check them again? Should I just replace them? Should I put the old ones back in? Is now a good excuse to spend the coin on some Magnecor wires?

FYI: The wires have a spec of resistance between 397 and 1337 ohms, which is an average of 867. The new ones averaged around 867 if memory serves.

Your young mechanic could have discontinued a vacuum line.
Open the hood to listen for a air type whistle.

 

[avalonandl]

I bet one of the back plugs is cracked or wire not seated.

 

[Rocket Man]

Agreed^^^. I’d be willing to bet one wire isn’t seated all the way, likely the infamous #8.

 

[avalonandl]

Agreed^^^. I’d be willing to bet one wire isn’t seated all the way, likely the infamous #8.

Thats why I had dealer service my plugs and wires. They last 100k and as much as it cost doing the rear shocks and air pump myself from RA saved me the $ to have dealer do the plugs.

 

[Doubeleive]

Your young mechanic could have discontinued a vacuum line.
Open the hood to listen for a air type whistle.

this isn't a 1980's rig, vacuum line for the brakes (you would know if this was off) otherwise you have pcv lines and those wouldn't do anything other than throw a code eventually... same for fuel evap solenoid. you could pull those off and it would start and run perfectly.

 

[swathdiver]

this isn't a 1980's rig, vacuum line for the brakes (you would know if this was off) otherwise you have pcv lines and those wouldn't do anything other than throw a code eventually... same for fuel evap solenoid. you could pull those off and it would start and run perfectly.

Man remember working on those 1980s GM cars? After the first nightmare the firs thing we did was go to the auto parts store and buy a ton of caps and disconnect all that stuff! LOL I tried a few times to make it all work, worked better when we threw it all away.

 

[Geotrash]

Man remember working on those 1980s GM cars? After the first nightmare the firs thing we did was go to the auto parts store and buy a ton of caps and disconnect all that stuff! LOL I tried a few times to make it all work, worked better when we threw it all away.

I had an '82 Toyota Celica with the carbureted 22R engine back on the early 90s. There were more than 2 dozen vacuum lines in/out of that carburetor. They were all made of neoprene, IIRC, so they were super durable. American-made cars at the time were using cheaper rubber and hard plastic lines that would get brittle and crack over time, leading to all kinds of problems.

 

[Doubeleive]

Man remember working on those 1980s GM cars? After the first nightmare the firs thing we did was go to the auto parts store and buy a ton of caps and disconnect all that stuff! LOL I tried a few times to make it all work, worked better when we threw it all away.

I had a 79 trans am I could not get to smog for the life of me I tried everything, replaced a bunch of stuff and was pulling my hair out and then one day I was in the junk yard looking for parts and noticed the vacuum lines on a junker were on different, and son a ***** that's what it was, vacuum lines were on backwards ran perfect but would not smog, swapped the lines and passed smog with flying colors.....