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Discussion Starter #1
I have a high RPM miss that for the life of me I cannot diagnose. I've changed plugs, wires, went from a 6al to a 7al-2, rebuilt the dist., jetted up-down, timing up-down, new valve springs all with no difference in results.

I'm starting to lean towards valvetrain harmonics. It stutters right at 7000 but if I let it rev past 7100-7200 it clears up again. Also while in the burn out box tonight, I don't do this regularly, I matted the throttle rolling out of the water in high gear and the engine acted as if it was hitting the rev limiter at 6900, would NOT go any higher.

I was told by a knowledgable friend of mine that it was caused by how close to coil bind the springs are set up at.

Any ideas???

Thanks,
John
 

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i had a bad msd coil last year that did the same as you descibed more or less. happened first pass at the track, i changed all the parts i could (that i had with me) that whole day with no change. I almost bought a new 7531 but decided to try the coil first, (alot cheaper). in my case the problem was solved. The coil was only 1 year old. HVC-2. good luck. one other thought, if you have a crank trigger check the pick up gap. ( I run .035)
 

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Discussion Starter #3
Well I guess I forgot to change one thing. I'll give the coil a shot.
 

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i know you said you rebuilt you distributor, do you have a mechanical advance or is it locked out. i had a problem close to this and locked out the distributor and never had a problem again. either my springs or stops or weights had something to do with it.
 

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How close to coilbind are you running? What spring? Could be the prob.... could be the coil. Also, check your ground to the ignition box... I had a bad ground on my Digital 6 last year... and it would start to miss around 6000 rpm, just about burned up my box... the hot feed to the box was crispy hot when I tracked it down. Solid grounds, a must!

Good luck finding the problem.
 

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Discussion Starter #8
K-950 installed at 1.90.
intake .079 from bind
exh .104 from bind
Box is grounded to the battery
I had the dist locked out and it was too hard to start, but it still had the miss.
 

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Discussion Starter #11
My original figures were with subtracting the lash of .026 from the lift. They don't suggest this. If I don't, I get .053 from bind on the intake and .078 on the exhaust.
 

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I'd say you are fine with spring pressures.. CB clearance etc.... You do have lash cushion, regardless, which puts you well over the .060 CB minimum. I don't know a bunch on KMotion... if anything like the NexTek Manley line...? They love to be pinched tight.

What about your ignition wire routing? A non-shielded crank trigger wire run directly over a coil pair... can make for nasty signals. Just thinkin out loud.. Maybe some wiring got bumped or somethin???

You gotta sweet lookin ride.. curious to hear what you find.
 

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I fought a high speed skip a couple years ago. It ended up being the crank trigger pick up. Replaced it and all was fine. I was racing yesterday and on the first pass of the day my car is running fine the NOS is on in high gear when suddenly is starts skipping and popping so bad I thought it was blowing up. I lifted and drive to the pits and it sounds fine on motor. I try motor purge and it is terrible, banging and poppping. Check all the normal suspects and find nothing. Pull the MSD dist cap off and find the rotor base loose on the shaft. The 2 rotor screws were tight but the rotor base that has a screw in the center was loose. Tightened that, all was fine, and we made it to the finals running just fine.
 

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I'd say you are fine with spring pressures.. CB clearance etc.... You do have lash cushion, regardless, which puts you well over the .060 CB minimum. I don't know a bunch on KMotion... if anything like the NexTek Manley line...? They love to be pinched tight.

What about your ignition wire routing? A non-shielded crank trigger wire run directly over a coil pair... can make for nasty signals. Just thinkin out loud.. Maybe some wiring got bumped or somethin???

You gotta sweet lookin ride.. curious to hear what you find.
Completely agree!!! I don't think it's a spring issue either. I've read where some people where having issues with the motor nosing over at around 7800 and they found an issue with pushrod difflection.. What size pushrods are you running?

I had a miss on the top end.. Can't tell you exactly why because we threw the kitchen sink at it. We put a shielded pickup, made sure the motor was grounded real well (along with everything else), new coil, new distributor cab and rotor, sent MSD 7AL-3 to MSD, new set of plug wires and went down from 26 to 23 initially on the high speed and it was fixed.. Just a couple things to think about.. Let us know what you find..
 

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Discussion Starter #15
Thanks for all the suggestions. I'll dive in as soon as the temp drops below 95* in my garage!
 

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This may sound odd but it happened to me. Make sure you don't have a transbrake switch going bad. I had a top end miss and the vibration from the car on top end was causing the switch to turn on, which was activating the low side of the 2-step causing the miss. I had a pro style transbrake, so it could not engage the brake. Also had a cranktrigger pickup going bad causing a similar problem.
 

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another thing to check is your distributor gear to cam gear, make sure the mesh is tight, im going through problems with that right now also, once that bronze gear became worn enough for my rotor to walk back and forth just a little, i couldn't run over 55, 6000 rpms. to me it sounds like an ignition problem. if the car was running flat at high rpms then maybe valvetrain.
 

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I have a similar problem. Still haven't found it yet. Mine will make 3-4 clean passes and then start stumbling. But it will do it at about 7000 and then run to 7500 for the gear change.
 

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John


If you have an Ohm meter, check the crank trigger sensor. Your looking for 600 to 1300 ohms for a good unit. This also applys to the magnetic sensor in a MSD Pro billet dist. These sensors do go bad and cause issues like what your talking about. Also check to make sure the voltage being supplied to the IGN terminal on the 7al2 is a solid battery voltage with NO drift. If this voltage moves around during a run it will cause High rpm misses. Usually this is caused by poor connections from oxidation on the wires which changes voltage seen by the box. Also we have seen the coil wire have a slight fracture in the outer casing allowing the high voltage to find a place to arc to. With changing out the ignition boxes and things staying the same, if its in the ignition system your looking for the nickel part syndrom causing the problem. I would recommend checking all connections, and if they are 3 years old or older. Please cut off and replace with fresh for the ignition boxes and the coil. I hope this helps you narrow things down.
 

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Basically other than checking the mag sensor in the distributor, it was the first season with the distributor, I have just rewired the whole front half of the car, with new switches and connections. The wire feeding the switched wire to my box has been over 10 years old along with the switch and terminal strip.
 
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