Ok for those of you that don't know I have been having a miss in my truck for the last week. It all started just before the lima trip. Truck starting spitting and sputtering at highway speed. Jerking cutting out acting like it was gonna die. Not a fun drive when you're going to a truck show. So anyway. I naturally thought it was the plugs because they haven't been changed since I fixed my plenum. I brought it home took the stang and went got 8 new plugs. Put them in and drove up to Lima a 2 hour drive for me. Everything seemed fine. till saturday night into sunday. The truck started missing on saturday night and wouldn't go over 65 mph. So I was like wtf. well I'll check it when I get home. Well on the drive home I got a CEL. Code 0307. Misfire cylinder 7. ok didn't think much of it cleared the code cause the truck didn't give any symptoms of a miss. No rough idle no random pop. Just idle like normal. So was driving home and the truck started to ping really bad. like worse then before my plenum fix. Couldn't figure it out. Got home pulled the #7 plug and this is what it looked like. Now remember this was a brand new plug on friday this is now sunday.



Good reason for a miss I'd say. Took it back got a freebie thinking it was a faulty plug. Still same code but this time actually could feel the miss. So changed wires, no change, has new plugs still in good shape this time, change cap and rotor, no change, and coil, no change. SO I have been asking around what would cause the miss. I have the answers from a bad cylinder to bent valve bad valve spring, cracked head, bad injectors, and to top it all off needs a rebuild. Ok so maybe its all of them. But where in the world to start. I started with the simple stuff. Didn't work. So now where do I go? I'm going to do a compression test today or tomorrow to see if maybe it is a cracked head. But can you guys help me to narrow it down on what it could be? I'm a little overloaded on info. I need help getting it all straight. I have been following the cylinder 8 misfire thread but haven't heard any solutions yet. Long post i know. Rant is over.

For the skimmers:

Have a miss.
changed plugs, cap, rotor wires.
Still have the miss what else to check??

 

Do the compression/leakdown test first. See what the results are.

If that checks out ok, switch the 7 and 5 injectors, and see if the miss follows the injector.

Side Note: The rest of that electrode had to go somewhere...... hopefully it just blew out the exhaust..... might want to pull that plug, disconnect the injector, and crank the engine a few times, and see if anything blows out......

 

Yea I'm hoping it went out the exhaust. But worst case scenario if it did get knocked around inside the cylinder could it have cracked the head??? or maybe chipped a valve?? I can' get a compression tester from any parts store right?? Think I could rent one at the parts store??

 

Well, the problem started before the plug broke.... and that bit of metal bouncing around in there is unlikely to break anything, more of a concern is scored cylinder walls, or, getting it jammed between the piston and cylinder wall.... that would be bad. It would have to be extremely bad luck for it to jam in one of the valves.... and it would probably work its way loose right quick.

That said.... I have found that even a small piece in the cylinder makes a LOT of noise..... So, if you don't hear anything..... it probably isn't there any more. Never hurts to be sure though. (hence the pull the plug, crank the engine bit, just be careful who is standing where, it will come out at a rather high rate of speed.... would hurt some. )

Should be able to find a compression tester and/or leakdown gauges at most any parts store. I think Advance/Autozone even rent them. Personally, I prefer the leakdown gauges, as they will not only tell you if you are leaking, they also give a good clue as to where.... Trouble is, they require an air supply, If you don't have a compressor, won't do ya a lotta good.

 

Ok I got a compressor that's no problem. And I don't hear any rattle other than the normal rattle. I'll check the leakdown and give ya the results so maybe you can help me figure out whats what.

 

With the gauge installed, you should be able to hear where the air is going. (out the intake, out the exhaust, thru the crank case, bubbling the radiator, (yeah, take the cap off))

Anything above 20-25% leakdown is too much. GM says 25% is 'acceptable'...... That seems a bit high to me... but, that's just me.

 

Ok good tidbit to have. So the leakdown judging from the name measures the percent of air leaking out right?

 

Check the resistance of all your injectors.

 

Good deal thanks fifthwheelin. I did replace my plenum about 6 months ago. I'll do a leakdown test after I move the injector. I had the injectors off when I did my plenum so I have all the stuff to take care of them.

 

Yep. Has two gauges. One is supply side pressure. The other is cylinder pressure. (needless to say, you need to have the cylinder you are testing at Top Dead Center, both valves closed..) Divide the cylinder pressure by supply pressure, and multiply by 10. Subtract from 100 to get % leakdown.

I make it easy on myself, and run supply pressure at 100lbs. Then it is simply a direct reading.