Codes PO305 and PO316

Hi Chairman.

There are many potentials that involve a cylinder misfire. Your computer upon detection of a Misfire type B (1,000 revolutions) which will exceed the emissions threshold, or cause a vehicle to fail an inspection tailpipe emissions test, the MIL will illuminate and a trouble code will be stored.

The "most likely" is an ignition related issue for that single cylinder. Bad plug or plug wire. Cylinder 5, if you are standing at the grill with the hood up, it's the 3rd one back on your right hand side (odd cylinders on your right, even on the left).

What I would do is change the plug and plug wire for that cylinder, and while the plug is out, do a compression check on that cylinder to rule out, or confirm, a mechanical issue. The next part would be a fuel/fuel injector issue and that is much more involved as the injectors are under the intake plenum.

https://www.2carpros.com/articles/how-to-test-engine-compression

Start with simple, and let us know. Glenn

Hi Glenn, thank you for the reply.
Could the coil for the cylinder be a culprit?
If I go out on a limb and replace just that one, and it solves the problem, do I have to change the other 7 coils?

Hi again.

Yes. That is on the list of potentials. The nice part about individual coils is if one goes bad, that's the 'only' one that would need to be replaced. And apologies! I said "coil wire" from force of habit, and you don't have any. Doesn't sound like I led you astray though.
I would do just the ignition plug. If that fixes it, then you are done. But, that is an indicator that a complete tune-up is on the close horizon. If it doesn't, then switch coil 5 with another cylinder and see if the miss moves to that cylinder, or it stays at 5 (mark/label the ones you moved, and you will need to clear codes first to erase old codes).
If it moves, then the coil likely is bad. If it doesn't, then there is something else going on -- mechanical, fuel, or electrical to the coil for cylinder 5.
Start simple, cheap, and easiest. Move on from there if needed. Even with all the computer controls these days, most problems are still basic automotive issues as they were 40 years ago.

Keep me updated. Glenn

Hi Glenn,

Thanks for the reply. No apologies necessary, I truly appreciate your assistance.
One question though.

Looking at the coil I need to replace (#5) ,
Just to clarify is the 3rd from the front on the drivers side???

Do I have to remove the fuel rail to get the coil out? (Seems like it’s in the way)
Thank you in advance.

The Even are on the left (passenger side) as you are standing at the grille.. 2 - 4 - 6 - 8 front to back. The odd are on your right (drivers side) 1 - 3 - 5 - 7 front to back.

I can see where the fuel rail would make it tight, but remove and replace specs say that removing the fuel rail is not required. Remove the bolt on the coil, grab it (magnet) and set aside, and the coil 'should' wiggle out. Inspect for any residual oil. Thoroughly clean if needed (coil boot too). remove and replace the plug...

If there is excessive oil on the boot and/or plug housing area, then that means there is an oil leak. The oil will basically create an easier path for the ignition to go to than the plug, and thereby cause an ignition miss.

And if I remember correctly, the coil bolts are 7mm.

This reminds me why I love my 1975 truck. I can climb in with the engine and close the hood!!!

Much Luck.... Glenn