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snapontech, Auto Mechanic
Category: GM
Satisfied Customers: 3803
Experience:  2 Year Automotive Degree Very experienced in the field on GM motors
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GM Yukon SLT: I changed the spark plugs in my 2005 Yukon SLT.

Resolved Question:

I changed the spark plugs in my 2005 Yukon SLT. Now it runs rough and the check engine light is on?
Submitted: 5 years ago.
Category: GM
Expert:  snapontech replied 5 years ago.
Welcome to Justanswer, My name isXXXXX am here to help.

Did it have any problems before the plugs were changed
Customer: replied 5 years ago.

Only an oil leak and I have an appointment with GMC to look at it. But the engine was fine.

Expert:  snapontech replied 5 years ago.
What brand of plugs were used?
Customer: replied 5 years ago.
Champion platinum. I gap them at o.040 got them from Pep Boys and bought new wires as well. I noticed that the wires were about 2" longer than the Delco originals, however, Pep Boys said that it would'nt be a problem.
Expert:  snapontech replied 5 years ago.
You have one of three possible problems, 1 the plugs are bad got bent on one of them when you installed them have seen it drop in and bend the tip or they are just bad plugs. 2. the plug wires are not getting a good connection. 3 the firing order is off or something was disconnected that you didnt see when doing the job. 18726543 is the firing order the plug type you should always use only AC DELCO part # XXXXX # XXXXX is in the front right check all connections make sure they are plugged in correctly and check all the plugs. The vehicle is indeed misfiring causing the code and the vehicle to run rough. Thanks

Expert:  snapontech replied 5 years ago.
Will look like this image now I really stress the plug issue because this vehicle is made to run on the AC delcos if there is one issue with the plugs it will not work properly also I am concerned you got very long wires this can be a problem they should be short go right from the coil to the plug I think you got the wrong stuff from the store. Hooked up it will look like this image graphic
Customer: replied 5 years ago.



Why would the firing order be off. What could I have done to change the firing order? Also, what do you mean that something was disconnected. What could have been disconnected? Of course I disconnected the negative terminal from the battery before starting.

Expert:  snapontech replied 5 years ago.
If there was a wire disconnected this is most likely not the problem I would still look over all the connections make sure they are plugged in tight. Look at the image above each coil gets a wire and goes to that plug if they get mixed up it will be out of order causing the problem. If the problem is not the firing order than its the plugs or those long wires. You can remove the plugs and make sure they are not bent down it happens or better yet I would go down and get the AC delco plugs I gave you above from napa they carry them in stock than get proper wires for the vehicle check napa if they also try to give you really long ones put the old ones back on and order some from the dealer save your self the trouble. Than the gap is correct reinstall them with correct plugs. I am telling you I am positive the vehicle is misfiring which can be the plugs or the wires. Thanks

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