L31 Distributor Cap

[Road Trip]

I swapped the cap and rotor and discovered that it was not the only source of my #4 misfire. I find it very odd though, that with a substantial misfire history and current misfire counts, the only time this has ever thrown a misfire code is when a plug wire burned on the header previously. I feel dumb admitting this, but I finally performed a running valve adjustment. Most of the poly locks turned right at 2 times before the rockers started tapping. #4 Intake was closer to 3 turns. After I started backing off on that poly nut the engine instantly smoothed out. I must have missed zero lash a bit on that rocker arm when I set them.

A lifetime ago it seemed that when you had 16 new lifters, you submerged them one
at a time into a Folger's coffee can filled with engine oil. You then pumped the innards of
that lifter (usually with a #3 Craftsman phillips) until all the air bubbles quit coming out
of the inlet hole on the side? It would start with easy, full strokes, and then once all the
air was gone the lifter became incompressible?

And subsequently you would install the pumped up lifters in the motor.

And they all acted exactly the same (fully pumped up) ...so when we added
the pushrods, rocker arms, pivot balls, and self-locking nuts, we would go through
the firing order, adjusting the valves for the cylinder currently at TDC for zero-lash
by twirling the pushrod with our fingertips until there was resistance, followed by
adding whatever preload (1/4 turn, 1/2 turn, full turn, etc) best matched the
engine's planned usage. And our expectation that the engine start would be clean
& quiet was always met.

And that was it.

And then (closer to today) I noticed that with any batch of 16 hydraulic lifters,
most would pump up like the old days, but 1 or 2 would pump up, but not completely solid,
but still a bit 'squishy' as compared to it's brothers & sisters? And that the cold
setting could no longer be done strictly by feel, but now you had to watch the top of the
inner hydraulic cylinder for when it was just coming off of the retainer clip on these 'squishy' lifters?

...and for me, this was the start of our new default practice of always hot-lashing our
hydraulic lifter-equipped engines after initial break-in. I will admit in public that, try as we might
during a careful cold-lash adjustment during initial assembly, I have found a lifter or two that
were outliers from all the others after the fact, discovered when we did the running hot-lash
after the fact. (!)

What can I say? My hunch is that the internal lifter clearances are no longer quite
as uniform as they once were in the good old days? As in the cold pump up no longer
is exactly the same across all 16 lifters...but at the same time they are still
good enough to work as expected after a careful hot lash session?

Given all of the above, when it comes to today's hydraulic lifters (and even with the best
lifters on the market challenged by today's aggressive cam lobe profiles) I definitely consider
myself in the 'once bitten, twice shy' hydraulic lifter camp.

Not only do I 'hot lash after break-in' any engine with my name associated with it, I have
several times resorted to performing a hot lash check on other people's engines that refuse
to run like they were supposed to...and getting the lash correct would be the final piece of
the misfire-free puzzle?

In English, the point I'm trying to make is that given the unknown variability of the hydraulic
lifters we now have to work with these days, expecting yourself to really dial in all 16 valvetrain
assemblies with just a cold lash adjustment is not realistic. I mean, it's possible, but not
if you have the kind of luck I do. FWIW, personally I've added the 'running hot-lash'
adjustment to today's "Trust, But Verify" pile in the engine building hobby.

By the way, Good on You for going through the effort to check/fine-tune all 16 assemblies,
and not just the ones for the problem cylinder.

And also sharing your experiences with chasing the #4 misfire in your engine -- this *will* help
others with their random misfiring SBCs that nobody can figure out...

PS - That's the baddest sounding van I've ever heard - if I pulled up next to you I'd definitely
give you a thumbs-up for the soundtrack!

 

[L31MaxExpress]

Another factor with the late model GM lifters since we are on the tolerance subject. All of the newer GMs are net lash, meaning you throw pushrods in them, torque the rocker bolt and that is that. The compressibility of the lifter's inner workings in a static environment does not create an issue adjusting them, except when we put them in an older small block. I have a set of really nice look Lunati lifters to go on the new cam when I actually swap it in.

Thank You for the compliment. It definitely catches some second looks in parking lots and idling around town.

 

[L31MaxExpress]

I drove it around a bit this evening. Its a lot better than before, but not entirely fixed. #4 is still showing misfire, but it is at a really odd time. It shows misfire in an overrun condition. Under load it does not show misfire. If the intake manifold is above about 65-70 KPA MAP it runs perfectly. When I back off the throttle it shows misfire. I am actually now wondering if it has a leaking injector o'ring or intake manifold gasket on that port. It has a fiber paper gasket on it and those have worked well for me in the past. I pulled the PCV vent tube off and it does generate a fairly strong suction. I need to cap off the PCV valve and recheck the vent hose. If it is pulling air from under the manifold, it should show up with the PCV blocked off through the vent port. Always fun chasing down this stuff. Might also dig out the bore scope and have a peak in #4 if I get time to tomorrow. On the plus side the valvetrain is much quieter and it pulls like a freight train even though I only got into it about 1/2 pedal from a 25 mph roll in 2nd gear. It no longer has a shudder under 1,500 rpm and has noticeably more low-speed torque.

 

[L31MaxExpress]

So it is not the intake gasket. With the PCV valve hose unplugged and blocked off, no suction on the vent hose. Also sprayed the injector o'ring a bit with a cold engine and it is not leaking. I will try a replacement plug in that cylinder after I go get one. Old plug looks fine and it has good compression in #4. It could be a bad/weak flowing injector, but they were brand new Ford 6.2L injectors when the marine intake went on. It is looking to be a plug or fuel issue in that cylinder. It has compression and it has spark. If the plug does not correct the issue, I will swap a the #8 injector into #4. Test the injector theory prior to getting the #4 injector warrantied out. If the misfire moves with the injector swap I will know it is the problem. If the misfire stays, it pretty much would have to be a lifter acting up.

 

[L31MaxExpress]

#4 plug

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[L31MaxExpress]

Changed the spark plugs, still showing some misfire. I never messed with the misfire monitoring other than idle with this setup. It is very smooth now, but still showing some counts. I disabled the misfire detection entirely so that it stops messing with my torque converter lockup. Is what it is and it runs great now. I believe it is false detection due to the camshaft and loose torque converter. I have seen stone stock LS1 5.7L cars start showing false misfire detection merely putting a loose converter in it. I can find a misfire easily enough without the computer telling me which cylinder is misfiring, especially since the misfire detection is acting weird anyway. I also ended up adding a bit more timing to it when the engine is lightly loaded which smoothed it out even more. Runs good and I am over messing with it until I tear it apart for the cam/intake swap.