Hey I just changed out my plugs for my 07 MC LS w/ 3.5 engine & the wires. I'm not sure what went wrong but the engine shaking really bad & my engine light flashes. I thought the wires were mixed up maybe but they're in correctly. Any suggestions on what may be wrong, besides go to a mechanic?

 

Just check to see if all wires are pushed on spark plugs,sometimes wires don't get on all the way, and they arc out ....

 

Make sure the wires are on the plugs and in the correct order. Also did you tighten down the plugs and made sure they were gapped correctly? Did you crack the plugs?

 

I tried all that but I took it to my mechanic & he couldn't figure it out all he said was cylinder 3 was misfiring. Any ideas what the prob could be & how much it would cost to fix?

 

Did your mechanic check plug gap on #3 cylinder some times the gap is not right and can lead to misfire...

 

My only misfire was attributed to when my MAF sensor went out. Bad coil pack maybe?

 

If the problem happened directly AFTER changing the plugs, 90% odds a wire is damaged or a plug is damaged. Take the plug out of cylinder #3, since now you have the point of failure and inspect it. Look for if ithere is a crack in it, is the ceramic still properly attached to the metal, smell it for strong traces of gas. Also, inspect the wire, look for "burn" like marks (this could be a sign of arcing), look for any damage to the sheething. Inspect where the wire plugs into the coil, is the tip of the coil dirty, is the tip/tower of the coil damaged.

If everything checks out, reseat everything and see if simply reseating solves it.

I know a guy that battled this with cylinder #6 on a 3800 and found a bad plug.

Also, did you use BOSCH plugs? If so, my experience is, BOSCH plugs (not other BOSCH products, just plugs) suck. Switch to AC Delco (or I've had luck so far with the first set of NGK's I've used).

 

X2 on plug brand. Acdelco is the best.
It has to be something you've changed or that you've done if it ran fine before. For only 1 cylinder to set a code the coils has to be working or 2 would miss fire. Like previously mentioned the coil post could be corroded or dirty or cracked. You can never verify a firing order and correct wire position too many times. i still mess them up occasionally maybe once a year.

 

Myron did you ever figure out what the problem was?

 

I just had one plug in wrong, the #3 one I ended up taking it to the dealer to get it fixed