Idle Worse After Plugs and Wires, WWYD?

[swathdiver]

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.

 

[George B]

I have the same issue. Idle worse after installing the same parts. I just live with it.

 

[Warriorpluto]

Why are you gapping plugs? Are you not using the iridium plugs that are pre gapped?

 

[YukonRog]

Wouldn't be the first time a plug was gapped and then hit heavy going into the hole closing the gap some. Also wouldn't be the first time new parts were bad. I'd check everything just because I'm OCD and it would bug me.

 

[OR VietVet]

Remove all plugs and inspect for porcelain cracks. All plugs out, do a complete compression test and wet test if needed. Throttle bore cleaning.....basics.

 

[swathdiver]

Why are you gapping plugs? Are you not using the iridium plugs that are pre gapped?

Just checking, before putting them in and after removal. Yes, those part numbers are all iridium.

 

[George B]

@swathdiver
When I installed my plugs I was surprised at how cheap they looked compared to the ones I removed. At first I thought they might be knock offs but I got them from RockAuto. I put them in in June of last year and am just running them for now although I do still have the originals which honestly look fine and could be used longer. I thought about putting them back in to compare but it’s not high priority.

 

[George B]

Maybe a set of NGK would be better?

 

[swathdiver]

@swathdiver
When I installed my plugs I was surprised at how cheap they looked compared to the ones I removed. At first I thought they might be knock offs but I got them from RockAuto. I put them in in June of last year and am just running them for now although I do still have the originals which honestly look fine and could be used longer. I thought about putting them back in to compare but it’s not high priority.

Maybe a set of NGK would be better?

Same here and share the same sentiments. I kept the old plugs too, technically, they are at half life. The wires even ohmed out a little better than the ones I put on save for one that broke, which is what precipitated this whole thing.

Been buying up new 41-985s whenever I come across them, have 5 so far!

Thirty years ago we ran NGK Splitfires in our Buicks and they gave us about 5 horsepower at the cost of 3 mpgs over the stock plugs. I have not investigated alternate plugs.

 

[gooffeyguy]

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.

You said the motor mount is new. Is it the fluid filled OE type or the Hummer one?