The Hemi has a miss. Any thoughts?

I'm really having trouble with this one and need some advice.

The 331 in my T coupe has a really strange miss. It is intermittent throughout the power curve and when it gets to about 4500, it misses really hard and pretty much cuts out.

I have a Mopar Perf 318 distributor with the orange box and the special long end Taylor 8mm wires. I also made sure that the system was very well grounded frame to block, battery cables are HD, the whole bit.

It was like one day it just started doing it and has gotten worse ever since.

I thought maybe I had a valve out of adjustment but I run them regularly and they are always good.

I have not changed the coil but I will if you guys think I should.

Could it be a varying voltage problem?

Anything is much appreciated. Any questions please ask.

Hack

 

How new is your plugs, cap and rotor?

What is the total advance at 4500?

Are your valve springs definitely strong enough?

jack vines

 

Plugs, cap, rotor all in nice shape. Maybe 2000 miles on em. The springs are good to 500 lift and the cam is about 460 lift, 280 duration. The spring seats have never been cut or shimmed. The miss is intermittent and is not on every rotation.

Im not sure on the advance at 4500 but I set the initial advance at 10 deg.

 

Is a voltage regulation problem out of the question?

 

This is going to sound real stupid, but are the threads on the plugs clean and dry?
Years ago we had a 440 with an intermittent miss. Turned out to be the plug threads were oil coated and the plugs were loosing their ground. We ended up cleaning all the plug threads, and all the plug hole threads with carb cleaner, adding just a touch of anti seize and reinstalling the plugs and the miss was gone.
I watched the miss spike on all the plugs throughout the firing order in random order on the Sun Scope (that should give you an idea how long ago it was.) We were the 3rd shop that car was in, everyone before us had installed plugs, cap, rotor & wires, only to still have the miss. If things were weird or strange, it seemed to happen to me. Gene

 

reluctor/pickup clearance in the distributor - should 0.018"
electronic ?

 

Low battery voltage will cause a high rpm miss. I have also seen issues with that gold box on the street, they tend to break down from getting too hot on the street.
Check that total timing, if the box is going bad, the timing advance will be inconsistent. A bad coil will give you the miss as well.

I would start with checking batty voltage because that is easy. Then check the timing for a consistent steady reading. The plug thread check is also easy and cheap.
The coil and the box will end up being a swap to test deal, but swap out known good parts, these days new does not mean the part is good anymore. Gene

 

How are the plug wires??? crossfireing maybe?

 

Ya know, this may be the problem. The spark plug tubes always have oil in them when I pull the plugs. I never thought that they could lose their ground this way. If you think about it, the hemi spark plug tube holes in the head are an oil trap. I am just running the stock stuff and I guess I just didn't know any better.

The plug wires are separated nicely and are nearly new.

I think I will replace the coil anyway and see if anything changes.

Thanks again to everyone for the info and I will post my findings.

Hack

 

I just fought the same problem on my 392 in my 32 ford. Nasty miss that got worse when the rpms go up. I'm running an old magneto.. I replaced the mag cap, plugs, wires, and even ran the car without valve covers because I thought it was a stuck valve. I spent a week going nuts..thought it might be oil on the plugs too like you said. After all the aggravation ..as a last resort I swapped carbs.. And that was the problem... Something with the idle circuits ..

If all else fails I'd try that

 

As someone else stated check the battery voltage. Are you running a Generator ?

 

Good info guys.

I am running a Gm 1 wire alternator. The gauge shows charge but I will check it for sure.

I yanked the plug wires this morning and a couple were wet. When I get home I will investigate further.

Thanks guys

 

The orange box has had a problem with quality. Make sure the orange box has a good ground also. Remove it clean the sheet metal surface of the box and where it attaches to your car. if that does not work, If you have a know good/ spare box swap it out to see if that helps.

 

Every EarlyHemi engine that left the factory had oil in the annular space around the plug tube. Yes, when you pull a plug you get a dose of oil in the hole and plug fouling can occur if the plug runs too cold...what are you using? how do they look when you pull them?
Be cautious about flushing the head with too much of any cleaner as this will end up in the hole as well. I also use a never-seeze type compound on the plug threads.
As noted, the quality of some of the ecu can be suspect and an insufficient ground will cause problems.

.

 

The plugs are autolite R44xls. They look very nice and the carbs seem to be jetted properly.
I am going to try a ground wire to the ignition box firest and see what happens.

thanks
Hack

 

That plug looks way lean to me depending on how many miles are on them...................

 

Not many. Maybe 100 miles. I have not driven it much since this goofy miss shit has been goin on.

 

my guess is plug wires. you might just throw some cheapo's on there and see if it does anything

 

I agree.

 

I'm not a fan of one wires because of voltage spikes lost a radio and noticed the needle in my volt gauge was stuck in the maxed out position.

 

Ok. So I changed the coil, ground the ign box mounting surfaces and ran a ground wire to the block. I also pulled the plugs and checked them for cracks, all good. Added never seize and re installed. I even unhooked the tac wire for thought of a grounding out problem.

And . . . . . Its the same. Soooo I'm going to try another ignition box.

The only other thing I can think may be happening is that the phasing in the distributor is whacky. I will update my progress, or lack thereof. haha

Its a machine, I will win.

Thank you for all your info fellas

Hack

 

If you have access to a scope it would tell you which cylinder is miss firing. It sounds like high resistance some where at high RPMs and not enough spark energy to fire the plug. We use to pull each plug to see which cylinder was not firing but if your at 4500 rpm that would be a little hard to do.

 

Only 100 miles on the plugs, try anew set. The quality of of plugs is not what it used to be. Plug does look lean. Maybe carb related. Good Luck. Your right a hemi is quite a machine.

 

Update.

So you guys won't believe the thrash I have been on with this thing.

Ill just list the attempts at diagnosis.

First I tried 2 different ignition boxes. Nothin. I then thought maybe I had too much timing in it or something. Set it all kinds of ways. Nothin. So then I'm thinking maybe a cracked cap or bad rotor, both looked nice but I tried some new stuff. Nothin.
Next I pulled the distributor, wires, and plugs. Installed a points distributor, dif wires, new plugs. Same exact symptoms! I even bypassed the wiring and went direct from the battery to the ballast resistor, then straight to the coil. Nothing. Doing the same exact shit.

So then I moved to the carbs. I installed larger main jets. They had 61's in them at first.
Then 67. Nothing. Then 70. Nothing.

OK so back to electrical. I checked voltages everywhere in the car. At every switch every terminal, ran more grounds. NOTHING.

Next I'm thinking I will just unhook the alternator and run on the battery to see if there is some odd voltage issue that I'm not seeing.

If I get nothing there I'm going to try a dif battery. Maybe the wet cell that is in the car has some issues internally that are any happening under acceleration?

The odd thing is that you can stand next to the car and actuate the carbs and it runs like a dirty bastard. But as soon as your under acceleration, its all over but the beer.

I am genuinely interested at this point. I am really reachin here haha.

Anyway, what do you guys think?

Hack

 

I forgot to mention that I also adjusted the valves while I was at it.

They were really nice anyway but I figured it couldn't hurt.

 

You might want to change the plugs again. If you dropped one hard on the floor or table. They run gun under idle but break up under a load or high rpm. Just a thought. I had it happen to me. I dropped a plug on the tailgate at the track. Brand new set. Engine sounded good in the pits but when the green flag dropped it was breaking up bad. So I come in got another set of plugs and it run like a champ.

 

The plugs were well checked and gaped prior to install. The symptoms are exactly the same as with the old plugs. Its just has to be some uncommon problem that I cannot pinpoint as of yet. I appreciate the thought though.

Hack

 

Might have a lifter pumping up. I had a desoto hemi in my T and I was running 64 383 style lifters and at about 4500 rpm it would start missing, I would pull my foot out of it and it would continue to miss for a few seconds till the lifter bled down. I never did change anything ,I just quit reving it to high as it was just a grocery getter.

 

Well that is certainly a good thought. But the engine has a solid cam in it.

Thank you for your thought tho.

Hack

 

Did you give it a compression test.Anything coming out the exhaust apart from normal.Have you done a resistance check on the leads.Im sure you may have done all these things.does this engine run triple strombergs? If so be carefull and have a look from the side and see if you can see even atomisation.Ive seen fuel flow up the side of an emulsion tube in the carb.Causes all sorts of fuel issues.All these checks are easy to do.Ive also had issues with air filters on strombergs.Take them off and see?If you run those chrome carb horn type on top,make sure they point backwards to the firewall.You dont want to much air as i noticed your plugs looked lean.Just a few ideas .Hope you get a handle on it soon.