Mis-fire Cylinder #4. 2009 Sierra.

[Tklei14]

I have a 2009 Sierra with the 5.3, I'm inching up on 50,000 miles now and having a small problem with the truck.

 

After a snow storm this week my truck began to spudder slightly when at idle. I thought nothing of it, but the folowing day I got a CEL for mis-fire on cylinder #4.

 

I cleared the CEL, and it was back on in about 100 miles. The next day the CEL was gone and the truck began to run slightly better but not perfect. I'm guessing that the plug wires have gone bad and the truck is running better now after it has dried out.

 

What do you guys think?

 

Thanks!

 

Tom

[papastoy]

I'd say bad gas. Try some fuel injector cleaner or gas dry.

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If it's not doing it now, don't worry about it, but it could be the wire on 4 is arcing to ground when it's wet.

[Gone Again]

Take a jumper wire with an alligator clip on each end about 2 ft. long minimum. You'll also need a wooden handled screwdriver of average size. Clip one end of the jumper wire to the screwdriver shaft and the other end to a good ground on the engine near the problem cylinder. Get a spray bottle filled with tap water and set the nozzle to mist spray. Start the engine and spray the problem wire with the spray bottle while running the grounded screwdriver shaft up and down the wire approx. 1/4 to 1/2 inch away. If the wire is bad-spark will jump to the grounded screwdriver. Also check around both boots. Many times those wires spark to ground right through the plug boot to that metal sleeve around the plug and you can't see the arc. Check the boots for burn holes. Simply using the spray at night, when it's dark, sometimes reveals arcing plug wires also. Good luck!

[Bob D]

I wouldn't think bad gas would cause a cylinder specific misfire.

At 50K, your wires should (?) be OK.

Per Gone Again's suggestion, spray #4 (in darkest environment possible) and look for the light show.

If same #4 misfire persists, I would swap wires to see if misfire changes to another cylinder.

If misfire remains on #4, look at fuel inj.s.