Popcorn popping sound after oil change, etc.

[jrandallc]

Today I replaced the lower intake manifold gaskets, then when it was back together I changed the oil and filter. Due to the manifold leaks, coolant got in my oil and brought it to a milky brown consistency. I drained the pan, dropped the pan, cleaned it out, cleaned the screen of the oil pump as best as I could without removing the pump. When I started it up, there was a popping sound that sounded like popcorn (about the same sound, and the same sporadic consistency) coming from the engine. Otherwise, the engine seemed to run fine, but I haven't driven it yet.

I've seen some posts about similar symptoms on this forum, but not exactly. They had the noise at higher RPMs, and mine is happening from the start. Any ideas? I'm afraid to drive it until I at least get a diagnosis on the issue. Is this likely a physical popping (two pieces hitting, etc.) or more of a backfire type sound (not physical, not actually causing physical damage). Thanks for any help!

Oh, and I can localize the sound to the upper intake manifold, or at least bank 2 of the engine. This is a 2003 3.0L V6.

 

[enjr44]

Lurk.

 

[RonD]

Check that spark plug cables are on tight, reads like "spark arc" noise.

And double check firing order on Coil Pack and at spark plugs
Coil pack
3 4
2 6
1 5
Front

the 5 6 4 always gets me

 

[jrandallc]

Thanks for the reply, RonD. Before lunch today I had a thought that it may be the plugs or cables, so it's good to hear another opinion in that direction. I bought new plugs and will install tonight and update. I regapped the old plugs before putting them back in (this truck is "new" to me so I wanted to double-check) so I may have gapped them to large. I'll double-check the spec on that for the new ones.

I'll double-check the firing order as well.

 

[jrandallc]

I put in new plugs, gapped properly (all around .044), and the popping sound is still there. I left the wires routed as I had them when I first tried it. After the popping was still there, I re-routed the wires as shown above and the truck would not even start. I have seen so much discrepancy on the proper firing order for these trucks.

With the wires routed as I originally had them, I get the popping but if I pull the wire to the spark plug in cylinder 5, the popping goes away. So it's definitely something in that cylinder.
I read today that if the sound stops when you pull the plug wire on a cylinder, it is likely a rod bearing. I don't think that's what it is, though, because the sound is not consistent like a rod bearing would be. It's persistent, but not on an exact repeating pattern, like a mechanical issue would be (tapping lifter sound, etc.). So assuming it's not a rod bearing, maybe it's the spark plug wire? Coil pack? I guess my next step is to confirm the proper wiring to the ignition coil.

 

[jrandallc]

It starts and runs with the following routing of wires:
Coil pack
5 1
6 2
4 3
Front

It still gets the popping on this configuration, but it does start and run.
I swapped wires between cylinders 5 and 6 at both ends. Still had popping, and the popping stopped when I pulled the cable to cylinder 5, with the previous wire 6, so the wire isn't bad. It's got to be something physical, then, in cylinder 5. I'll start tearing it apart tomorrow.

 

[jrandallc]

Finally, the popping sound is gone and my truck is running smooth as silk again! Stupid me, when I was putting the rocker arms back on from a head gasket job I did this weekend, one of the rods didn't set right in one of the lifters on cylinder 5. That's what was causing the pop.

RonD, I do appreciate your feedback and help.

 

[RonD]

Thanks.

And thanks for the update and fix.

Weird about the coil pack, the matched pairs are correct, 1-5, 2-6, 3-4, these can be reversed, 5-1, 6-2, 4-3, doesn't matter since both spark at the same time

4 6 5
3 2 1
[]
Wire connection

That the usual pattern

 

[Doofy]

Good Job! Perserverence does win out on occasion. Thanks for posting the solution.