Chasing down cyl. 2 misfire (P0302)

[alvaroemg]

before heading home from work, i re-gapped both sp to .060 and installed back in. Cleared CEL and headed home. CEL came back on after driving about 20 miles only for cyl 2 misfire, not random as before.

Early morning cold weather has an effect on misfires and idle. Some reving up and down by itself only in cold weather makes me think it’s maybe the IAC or a small vacuum leak. I had previously cleaned the IAC with some throttle body cleaner.

New parts will be here tomorrow, as mentioned earlier, all plugs will be gapped to .045 and I’ll go from there. Maybe will purchase a new Delphi IAC as my current is what I’m assuming original, so over 25 years.

All 4 O2 sensors are getting replaced as well as soon as I squash this misfire issue.

 

[alvaroemg]

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Detonation? I'd have said "oil fouling".

Oil fouling? Maybe, i’ll take a closer look tomorrow when I take them back out for re-gapping

 

[Orpedcrow]

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Detonation? I'd have said "oil fouling".

I agree with oil fouling. I was referring to the autolite spark plug chart that was referenced earlier.

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[Road Trip]

Detonation? I'd have said "oil fouling".

Hi @alvaroemg,

That plug is showing a significant fouling in a short period of time.
How many miles per quart of oil are you currently using?

What is the history of this engine prior to the head replacement?

If this cylinder is oiling, the only sources I can think of would be
a damaged intake valve stem seal or a broken piston ring(s)?
(Not necessarily just wear because the other cylinders aren't
showing the same kind of excessive deposits on their plugs?)

And a bad valve stem seal on the exhaust wouldn't normally foul
the chamber/spark plug. And I would expect an intake manifold
gasket leak pulling from the lifter valley would also cause a bad
misfire at idle?

As mentioned elsewhere by others, what has been worked on
recently is the higher probability of a problem. In English, I'd
lean more towards an intake valve stem seal as opposed to
a broken piston ring -- unless of course the excess oiling
led to hard detonation, and then all bets are off.

Not trying to be an alarmist -- instead, I'm just trying to account
for what we are currently seeing deposited on that spark plug.

Q: When is the last time that a compression test has been run
on this engine? If all 8 cylinders share similar readings then
the excess oil must be drawn in via the intake passage? But
if the suspect cylinder has a way lower reading than the others
then piston/ring issues may be the root cause?

Just trying to cover all of the bases.

Now to see what happens with the fresh cap/rotor/wires/plugs.

 

[2drXmobb]

before heading home from work, i re-gapped both sp to .060 and installed back in. Cleared CEL and headed home. CEL came back on after driving about 20 miles only for cyl 2 misfire, not random as before.

Early morning cold weather has an effect on misfires and idle. Some reving up and down by itself only in cold weather makes me think it’s maybe the IAC or a small vacuum leak. I had previously cleaned the IAC with some throttle body cleaner.

New parts will be here tomorrow, as mentioned earlier, all plugs will be gapped to .045 and I’ll go from there. Maybe will purchase a new Delphi IAC as my current is what I’m assuming original, so over 25 years.

All 4 O2 sensors are getting replaced as well as soon as I squash this misfire issue.

Wait a second, before you spend more money on parts let's do a leak down test and compression test to see the health of the motor. Also a smoke test can help narrow down some things as well. Have you check to see if your getting spark to the number 2 wire? Replacing your o2s still might get fouled up until to fix the misfire I would hold of first , you can use a adapter for the time being.. eventually it's clog your cats for running to rich and your end up spending a lot more money. Best bet is to diagnose it first.

 

[alvaroemg]

Wait a second, before you spend more money on parts let's do a leak down test and compression test to see the health of the motor. Also a smoke test can help narrow down some things as well. Have you check to see if your getting spark to the number 2 wire? Replacing your o2s still might get fouled up until to fix the misfire I would hold of first , you can use a adapter for the time being.. eventually it's clog your cats for running to rich and your end up spending a lot more money. Best bet is to diagnose it first.

This morning I rented a compression tool from O’Reilly. Will be checking compression on all cylinders. I’ll take my butt to youtube and see how people do those since I’ve never done one.

What I’m thinking is removing all the SPs, removing the main ignition wire and unplugging the fuel pump fuse. I’ll probably run my battery pretty low so I’ll have it on a charger as well.

Also, leak down test tool will be here(at o’reilly) by 5pm. Picking it up tomorrow or saturday.

Will also watch some YT on how to set that up

 

[alvaroemg]

also rented a fuel pressure tool

Here are the results:

62psi at prime
Drops to 56psi after a small audible click, and it settles at 52psi.

At start of engine(idle), it settles at 54psi.

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[Orpedcrow]

What I’m thinking is removing all the SPs, removing the main ignition wire and unplugging the fuel pump fuse. I’ll probably run my battery pretty low so I’ll have it on a charger as well.

All that plus wide open throttle while cranking.

 

[alvaroemg]

All that plus wide open throttle while cranking.

I was actually about to go compression test now.
Why the open throttle?

Thank you!!

 

[Orpedcrow]

I was actually about to go compression test now.
Why the open throttle?

Thank you!!

Hopefully somebody smarter than me can explain it, but I get more consistent and repeatable results with WOT. Think it’s something to do with the vacuum in the intake.