I'm thinking that it's time to step back, and look at all the events not seperately but as one. On the dead cylinders you've verified fuel and spark. Do they happen at the right time? Is it possible to turn the motor over by hand and verify that you've got a good ignition event somewhere around tdc with both valves closed?
Bob, what distributor did you use (brand, model, etc)? Is it new to the car?
I ask because we've had a rash of bad Chinese HEI dizzys in the other car clubs I'm in within the last 3-6 months. They did weird crap like this.
The dist is a used OEM with a new NAPA ign module and a good OEM pickup.
ANYONE?
4,5,6? Bent distributor as those cylinders are right next to each other. Like a Tilt-A-Whirl! And that problem might not surface at low rpm or switched off. Why don't you call Performance Distributor and share your troubleshooting woes. Don't be bashful. It's normal to wanna confirm the failure-point before > $$$. They might even offer to test your distributor on their machine to confirm. Good people.
http://www.performancedistributors.com/ 901-396-5782
Hey, I really like your project. I can't believe you only have $6K in that thing.
On the used dizzy, are you using the used cap and rotor that came with it, or new pieces?
Did the distributor come with an ignition module that is compatible with the Vette?
My thoughts are if you have the other module and it is compatible try swapping it to see if the behavior changes. Also take a look at the contacts in the cap and see if the ones for those three cylinders look any different from the other 5. Maybe the rotor is barely making contact with those three.
Have you checked for vacuum leaks? I had an odd one on my wife's Challenger. The right angle connector on the power booster was cracked. Vacuum was holding it in place, but was leaking. #5 wasn't firing. Did all the same things you are going through. Valves are moving, swapped plug wires & plugs around, etc. Started looking for vacuum leaks & found the one at the booster. Pulled the hose (connector fell apart) and put my thumb over the opening. Idle smoothed right out.
The odd thing was the runner feeding the brake booster was on the opposite cylinder bank. Either the runner for #6 or 8.
Maybe your new intake isn't sealing properly. Either at the heads or the upper half to the lower?
Used shaft, new ign mod, cap and rotor. No contact on those three cylinders on the cap. My only issue with a bent dist shaft is #3 still fires, which is between those 3 bad ones.
I have NOT checked for intake leaks or vacuum leaks yet. I hear I should have been checking vacuum some time ago. Whoops. The Miniram is a one piece critter, so if it's leaking it will be at the head...... which we may be on to something. THe inner intake bolts were a real bitch to get tight because of where they are located on that intake. Considering the cylinders I am fighting are adjacent to the 2 bolts on either side. Sum bitch.....I might try that next.
Are you experiencing misfires or no-fires? Vacuum leaks would yield mis-fires. Large vacuum leaks would also yield super lean mixtures that would show up as cherry red header tubes for those cylinders.
I still say, if those three cylinders are simply not firing, that the distributor is making you sad. You should have it tested even if just for shiFts & giggles.
I'm getting spark at the plug. Distributor is doing it's thing.
Could the intake gasket have slipped while you installed it? Pull the intake and see if something is blocking the ports for 4, 5 and 6 and check for proper sealing like Rob_Mopar said..
Bad gas? Valve sticking? Bad Coil? Throw another distributor in it just to eliminate the distributor? I would think you cylinder compression should be around 200?
Change your oil, look for bad metal.
I would start with a friend looking it over. They might (always) spot the obvious I missed.
Move the timing light from wire to wire. Make sure everybody is constantly firing.
Read my plugs. Try to determine what is going on, over-all, and cylinder to cylinder. Wet?, Pre-ignition?, Lean?, Normal?, etc. What are 4, 5, 6, doing? or not doing the others are?
Pull my exhaust manifolds and fire it up briefly. What are 4, 5, 6, doing? or not doing the others are?
Actually are the plugs in cylinders 4-6 wet with fuel at all? If there is fuel coming through and you had the engine running for a while, they should be wet with fuel.
Gasoline wrote: 1.)Bad gas? Valve sticking? Bad Coil? Throw another distributor in it just to eliminate the distributor? I would think you cylinder compression should be around 200? 2.)Change your oil, look for bad metal. 3.)I would start with a friend looking it over. They might (always) spot the obvious I missed. 4.)Move the timing light from wire to wire. Make sure everybody is constantly firing. 5.)Read my plugs. Try to determine what is going on, over-all, and cylinder to cylinder. Wet?, Pre-ignition?, Lean?, Normal?, etc. What are 4, 5, 6, doing? or not doing the others are? 6.)Pull my exhaust manifolds and fire it up briefly. What are 4, 5, 6, doing? or not doing the others are?
1.) I put fresh gas in when I first fired it up. All the valves are moving etc.
2.) I have not changed oil yet, it's only run ~40 miles.
3.)2 Different friends have looked over and come to the same "w-t-f" conclusion.
4.)Did that. Steady flicker on all 8.
5.)5 cylinders are a nice clean burn. the 3 dead are wet.
6.) I haven't pulledthem, but they do not heat up at all. According to the temp readings the adjacent cylinders are reading ~190-210F while the dead cylinders are showing 90 (~85* ambient temp)
Got compression on the affected cylinders? Like, proper, measurable compression?
Bobzilla wrote: 4.)Did that. Steady flicker on all 8. 5.)5 cylinders are a nice clean burn. the 3 dead are wet.
These two just can't go together. They can't be sparking and dead wet.
Can you fire it up in a dark garage at night and look for spark leak/jump?
Could I send you a free distributor? I should have a spare Lt1 dist.....
BoxheadTim wrote: Got compression on the affected cylinders? Like, proper, measurable compression?
Yes. dry test, lowest cylinder of the 8 was 152, highest was 160. 160 being one of the dead cylinders, 152 being one of the good cylinders.
Yes, there is spark to the cylinders. There is spark on the plug. After running, those 3 dead plugs are wet because THOSE CYLINDERS ARE NOT FIRING. There is no spark leakage, checked that multiple times and I have all new components.
This is an L98, NOT an LT1, so an LT1 distributor is of no use to me. Besides, I AM GETTING SPARK TO ALL 8 CYLINDERS, ERGO THE FRIGGIN DISTRIBUTOR IS WORKING.
How do you have spark at the plug AND no firing in the cylinder? That doesn't make any berking sense. 
Javelin wrote: How do you have spark at the plug AND no firing in the cylinder? That doesn't make any berking sense.
No, I have spark, fuel and compression and still have dead friggin cylinders. Now you understand my pain. I have all 3 components to making an internal combustion engine run. But it's not.. at least on those 3 cylinders it's not. the other 5 are plugging away like mad.
Now envision trying to diagnose this for 2 months and you start to understand my frustration.
In reply to Bobzilla:
I'm sorry I meant L98. Lt1 has opti-spark. I should have a spare for the L98 family.
Little question . . . did you swap the plugs from the cylinders that weren't firing to the ones that were to test 'em?
Gasoline wrote: In reply to Bobzilla: I'm sorry I meant L98. Lt1 has opti-spark. I should have a spare for the L98 family.
I'm using the small cap External Coil HEI used on the TBI engines to clear the miniram. The large cap HEI did not fit. Besides, the distributor is not the problem here as I am getting parts.
TeamEvil wrote: Little question . . . did you swap the plugs from the cylinders that weren't firing to the ones that were to test 'em?
Does anyone read these things? YES. Not only did I check them, but I changed them. multiple times.
I'd lean towards that intake gasket/vacuum leak thing man. Can you do a leakdown test? Or even a screw-the-airhose-to-the-cylinder-and-blow test?
Bobzilla wrote: No, I have spark, fuel and compression and still have dead friggin cylinders. Now you understand my pain. I have all 3 components to making an internal combustion engine run. But it's not.. at least on those 3 cylinders it's not. the other 5 are plugging away like mad. Now envision trying to diagnose this for 2 months and you start to understand my frustration.
That does sound monumentally frustrating... The only thing I'm coming up with is mis-wired plugs. In that case you'd get spark when testing, but since it's not firing at the right time - no combustion. But you seem pretty sure the firing order is right... so I'm not sure what else it could be.
Hope you didn't leave a rag in the motor during build.
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