ChicagoSpeed996

So we went through the usual diagnosis for the misfire on cylinder 4. Coil was good, plug was good, injector was good. That left the lifters. Here they are. Misfire gone. Nice set of paper weights now to go with the XXX.

ChicagoSpeed996

Here they are.

ChicagoSpeed996

The offending lifter was dismantled and you can see the inner rod pushed up.

Ahsai

Nice photo and thanks for sharing. Is the center rod rotated since you removed it or it was that way when you removed it (the wear marks suggests the latter)? What were the symptoms again?

alpine003

Kinda surprised it happened on #4

Ahsai

Care to explain, Alpine? Welcome back btw

p.vanderlinden

Lotta wear, how many miles?

What type oil?

It's crazy that the hammering from the cam lobes runs off the edge of the lifter.

Paul

Macster

Did the low to high lift engagement mechanism fail and the lifter stay in low lift mode all the time?

Macster

The lifter wiping marks being partially "off the lifter" may be on purpose. The lifter/cam lobe interfaces are splashed lubed. By having the lobe intersect/engage the lifter top like that exposes the lobe to a longer edge surface which is intended to supply more oil to the lifter lobe as it begins to press down on the lifter bucket.

ChicagoSpeed996

Some answers:
Car had 39,000 miles and looks to be normal wear on the lifter surface.
Oil used for the last 7k miles was Joe Gibbs, before that I imagine mobil 1 (previous owner).
Symptoms, intermittent misfire that exhibited itself at idle. P0304. Would miss then go away. Didn't miss at high rpms.

The mechanism of failure was that the plunger in the middle (yes it is just rotated in the picture) rides the middle lobe (low lift), the outer ring rides on the high lift lobes but is pressed down during low lift operation. Once the high lift mode is engaged a pin is hydraulicly pushed in, locking the two pieces (plunger and outer ring) together. So as I would enter high lift mode and come down from it, the inner plunger would stick together with the outer ring, resulting in high lift at idle for that valve. As the cam beat on the lifter it would release and begin up and down operation in relation to the inner plunger resulting in low lift mode and regain proper firing of the cylinder.

ChicagoSpeed996

The opposite, it would enter high lift and not come out of high lift. High lift at idle on the one valve caused a misfire either due to filling of the cylinder LTA, or compression LTA due to the partially open valve

Byprodriver

I think you should call a doctor if it lasts more than 4 hours!

alpine003

Thanks.

My memory isn't 100% on this one so don't take this at 100%. I'm sure Jake will chime in and can either confirm or correct me if needed. IIRC #5 has failed historically a lot due to the lack of oil vs the others. I've seen and read about a lot more of 5 and 6 failures.

Ahsai

Gotcha. I remember bank 2 runs hotter hence more susceptible to taper/oval. Not sure about oil supply. I think the issue is the tiny oil hole on the lifter that's a dead end, which can trap debris and it can happen to any of the intake lifters.

ChicagoSpeed996

No debris noticed but scoring yes. The plunger is getting mechanically stuck in the outer ring's bore.