Spark plug diagnosing help, please!

[1967coronet]

Ed, set the idle to 1,100 and get it jumping, then start pulling plug wires off/on the cap until you find the cyl that is miss fireing. if you locate it switch the plug and wire with a different cyl and retest see if the dead cyl moves also.

 

[moparedtn]

Ed, set the idle to 1,100 and get it jumping, then start pulling plug wires off/on the cap until you find the cyl that is miss fireing. if you locate it switch the plug and wire with a different cyl and retest see if the dead cyl moves also.

Reminder: I just replaced the plugs after all this started. They're new for all practical purposes.
Reminder #2: I've already been through the Like-new MSD wires. No issues there, either.
Go back to what I was doing when this first started. Something happened immediately when I was goosing the throttle while testing the newly-installed oil pressure gauge.
Something "let go". Something failed instantly.
This was no gradual failure of some older part or a part I just replaced; the engine was running fine prior to the gauge install.

 

[moparedtn]

I do find it more than a coincidence, though, that plug #6 was so clean compared to the others when I changed out the last set.
#6 cylinder is also where I was spraying Brakekleen around the intake gasket when the thing would "pick up" and the vacuum would jump.
If the intake is leaking at #6, would that not explain that extra-clean plug?

 

[1967coronet]

Yep the a vac leak should make it lean. Back to the plug and wire deal , I know you had all new wires and plugs Ed. I just wanted you to confirm what cyl is dead once the miss fire starts showing, and also confirm the plug and wire on that cyl is firing once moved to a new cyl. Ive seen new plugs and or wires have a come and go hic up once they are loaded.
You prob have it nailed down with the vac leak on #6 but it is a simple test to try before you take the intake off.

 

[moparedtn]

Yep the a vac leak should make it lean. Back to the plug and wire deal , I know you had all new wires and plugs Ed. I just wanted you to confirm what cyl is dead once the miss fire starts showing, and also confirm the plug and wire on that cyl is firing once moved to a new cyl. Ive seen new plugs and or wires have a come and go hic up once they are loaded.
You prob have it nailed down with the vac leak on #6 but it is a simple test to try before you take the intake off.

True enough but like I said, it doesn't completely "miss" when idling, so your diagnostic trick won't necessarily tell me anything.
Watch the video. There is a decided thump to it, but it doesn't flat-out miss until I start trying to give it the beans - or it's decelerating back down.
Lots of outright popping then.
The bathtub intake gasket on there now doesn't have any organic gaskets on either side of it. I'm going to go that route and re-install the intake using the whole she-bang, new tub and gaskets on both sides of it.
Going to fetch a set of actual intake bolts for it, too. Currently has a hodgepodge of bolts on it, some of which I'm sure are a little too long/short/incorrect.
If this turns out to be the issue, it's going to explain a whole lot about my tuning issues with the carb, too.
I hope, anyways...

 

[chescharger]

How long has the fuel been in the tank?

 

[moparedtn]

How long has the fuel been in the tank?

Couple weeks at most.

 

[Ron H]

You have a mystery that you have no idea of the quality of the rebuild that was done or even what exactly was done, quality of the parts used, bearing adjustments etc. Floating issue sure is an indicator of vacuum "usually". This could be a warped head or poorly machined going back to the rebuild matter (if any machining was done). You still detect a vac change in the area you checked after your re-torquing? Was going to say try swapping out the carb to try that if you could find one as a loaner or spare as there could be internals - maladjustments even though I think you said it's a new carb. Though having gunk build up in the oil (was this pre-or post clean out?) after just a few hundred miles leads me to believe motor reassembly could be out of spec. And when you get the flat out at high RPM that has been indication of a cam issue (that you replaced). I'd guess when you did this a check on other wear/damage this can cause was done...lifter wear, rods...? If the lobes were wiped out what rides on them would wear as well.

 

[HEMI-ITIS]

http://superformanceproducts.com/
Try these gaskets,best I ever used!!

 

[moparedtn]

You still detect a vac change in the area you checked after your re-torquing?

Yep, sure did.

Was going to say try swapping out the carb to try that if you could find one as a loaner or spare as there could be internals - maladjustments even though I think you said it's a new carb.

The carb is new but has been on there for a while now; next to zero chance it's the culprit, hadn't been touched when all this started.

Though having gunk build up in the oil (was this pre-or post clean out?) after just a few hundred miles leads me to believe motor reassembly could be out of spec. And when you get the flat out at high RPM that has been indication of a cam issue (that you replaced). I'd guess when you did this a check on other wear/damage this can cause was done...lifter wear, rods...? If the lobes were wiped out what rides on them would wear as well.

Lifters were replaced when the cam was, both Comp Cams products.
Of more concern would be whether the engine has begun wiping another cam, indicating some serious lubricating issues internally.
I can tell you this - if it winds up wiping another cam, that motor is outta there. I won't fool with it again, short of a proper full rebuild under my supervision.
That takes $$$ I ain't got, simply put.

Thanks!

 

[moparedtn]

http://superformanceproducts.com/
Try these gaskets,best I ever used!!
View attachment 355475

Mercy, they sure are proud of those. They apparently don't offer the bathtub, either?
I went with the Mopar performance set and a new set of ARP intake bolts to replace the hodgepodge of hardware that's on there now. Permatex RTV black sealant to be used to affix the organic gaskets to the bathtub on both sides, leaving intake and head mating surfaces dry for future disassembly ease maybe?

 

[moparedtn]

In any event, if the intake gasket replacement doesn't do the trick, I'm about done with this mystery motor. I've had my hands on just about everything else on the car except for the engine and it's time to just enjoy the damn thing.
I don't have a problem getting a decent running 440 in it (doesn't have to be a HP monster) and just driving the car.
The trick is finding a known good 440 for a reasonable price.

 

[Ron H]

Wow, finding a hodgepodge of bolts doesn't give a nice signal of the quality of the purported rebuild. New bolts regardless of how good the old ones look are always the routine as you know one broken or stripped bolt or of the wrong grade can quickly ruin the day. Been there. If the rebuilder scrimped on this rather cheap phase of the rebuild what else could have been scrimped...I'd carefully run a tap in the holes before you put new ones in as could be the torqueing wasn't done correct either...

 

[moparedtn]

Wow, finding a hodgepodge of bolts doesn't give a nice signal of the quality of the purported rebuild. New bolts regardless of how good the old ones look are always the routine as you know one broken or stripped bolt or of the wrong grade can quickly ruin the day. Been there. If the rebuilder scrimped on this rather cheap phase of the rebuild what else could have been scrimped...I'd carefully run a tap in the holes before you put new ones in as could be the torqueing wasn't done correct either...

There's a reason I call it the "mystery motor".

 

[hangn0ut]

Dont rule out the carb. All that reving you did could easily have pulled some debris into a metering circuit. And a new filter does not rule this out. The debris could have been after the filter. did you use teflon tape anywhere? Besides it cost zero to disasemble the carb,look it over closely and blow it out with compressed air. Do it in a box lined with plastic so as to catch anuthing that might come out.

 

[moparedtn]

Dont rule out the carb. All that reving you did could easily have pulled some debris into a metering circuit. And a new filter does not rule this out. The debris could have been after the filter. did you use teflon tape anywhere? Besides it cost zero to disasemble the carb,look it over closely and blow it out with compressed air. Do it in a box lined with plastic so as to catch anuthing that might come out.

Yep, sure will. I'll also have it off the intake on the bench to check out my spacer/gaskets as well. I tried really hard to differentiate any vacuum gains at the intake gasket versus base of carb when I was spraying, but you never know. Worth a look for sure.

 

[moparedtn]

UPDATE 8/21/16:
I'm finally working on the car today. Pulled intake/carb off, then peeled back and off the VERY well sealed bathtub gasket (I must have gotten carried away with the RTV black last time ).
Started grabbing pushrods in the now-exposed innards of the lifter valley, looking for slop.
FOUND: One bent-to-piss pushrod on #8 cylinder intake side.
All around it seemed fine, no slop.
That's just friggin great... oy.

PS: Yes, that's close to the same cylinder that the vacuum leak appears on.
I'm going to guess I have at least one stuck valve??

 

[moparedtn]

UPDATE #2 on 8/21/16:
Hmm. I can operate that valve by hand (with judicious use of prybar, of course) with no problem.
We have pics:

Readily-apparent culprit on #8 intake.

Everything appears normal up top. I'm able to work that valve with a prybar fairly easily, too.

When I say "bent", I mean REALLY bent. The others passed the "rolling across smooth surface test" just fine.

It appears I have a set of "516" heads. Looking at the mating surfaces between the heads and the block, neither head nor block appear machined at all - it's a perfect mating right there at the "crotch" formed between the head and the rails at front and rear of block.
I assume therefore that stock pushrod lengths should be fine?

 

[moparedtn]

Oh boy.
Apparently these heads belong on 1964-1967 361 and 383 engines.
The lower-performance ones.

Mystery motor indeed.

 

[HEMI-ITIS]

That would lean out the cylinder for sure. Have seen that happen,install a straight pushrod and go.