Multiple misfire p0300 after tune up?

[Jacob Alan]

Okay so I bought a truck and it ran perfectly fine.. 2001 silverado 1500 4.8 2wd.

 

The guy I got it from seemed to have no knowledge of when it was last serviced so I did a full tune up...

 

Plugs/wires/oil/oil and fuel filter... I should've left it alone lol.

 

 

Now i'm getting multiple misfires and the engine is fluttering..

 

I checked all the plugs multiple times, and even put the old plugs back in...

 

I used one of them other spark testers to check the coil packs, and got spark fine.

 

I used water to mist my wires and got no spark

 

 

What should I do now? I bought a brand new set of wires for the 2nd time and was going to try them, my buddy said I should use the new coil pack I bought and replace them one at a time until it fixes.. But with multiple misfires would I need to change all the coils at once?

 

 

[rjgti]

what brand of of plugs and what gap?

[XSKIER]

Perform a Crank Variation Relearn. Should be done by the GM dealer scan tool, but I have heard that snapon scanners can do it. P0300 is tripped when there are unexpected variations in the crank rotation, specifically it is looking for the difference between 4 power pulses/rev, verses dragging one or more cylinders around. After doing this, go back to the basics if it still stumbles. Compression, Fuel, Spark.

[Jacob Alan]

I put my old plugs back in and this morning the truck light went off and started running a lot better... It still sounds like a sewing machine if I push the gas hard though... Put some seafoam in my tank to see if it helps anything..

 

Also I used AC Delco plugs.. I tried .040 and .050 gaps.... The guy at the store told me 50 so put them to that. The old plugs were gapped pretty small though, smaller than .04

 

Online I thought it said .06 but read people going down to .04, so figured the gap wasn't the issue.

[txab]

.040 gap is the recommended gap and the only you should use. What plug #? If you used iridium you should not re-gap them. Breaking the center electrode is possible. The correct plug # should be gapped properly already. Check fuel pressure and flow. Check fuel filter

[Jacob Alan]

^{AC Delco R44LTSM, well wish I would of seen this reply because I just gapped them to .06 since my manual said that... My manifold is still off so ill go pull them back out,}

[txab]

http://www.gm-trucks.com/forums/topic/121181-did-i-ruin-my-new-iridium-plugs/?p=1079941&do=findComment&comment=1079941

 

Since you're using a copper plug and not iridium or platinum, no worries on damaging center electrode. I'd still use a smaller gap as recommended by gm. Were the old plugs plat, iridium or copper?

[Jacob Alan]

old plugs are iridium ac delco, should I go buy the same ones or does it make much of a difference... Sorry don't know much about the difference between the plugs.

[Colossus]

same ones, my friend.

[Jacob Alan]

Dang okay well one of them were cracked from removing my manifold, should have removed them first obviously... But its running good with the copper ones in it right now, I gapped them to .04 and no lights or anything.. I'll go up and grab a set of iridium's tomorrow, though if it's better for my truck. Thanks for your help!

[txab]

Plenty of people running copper. With no issues. They just don't last as long. If you have your problems cleared up, run this set for a bit. You can use platinum or double platinum also. Difference is plug life.

 

Iridium- longest life

 

copper - shortest life

 

Plats fall in the middle.

 

Lots of people don't put expensive iridium in older, high mileage engines, because you probably won't get the long life anyway. Especially in an oil burner

[muddkatt]

^{My manifold is still off so ill go pull them back out,}

 

Glad you got it figured out, but why did you pull the manifolds?