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Discussion Starter #1
Does this look normal, or does it look like a problem in the ignition somewhere?



Distributor and wires are one season old. About 100 passes. Plugs are 24 passes old.

MSD 7AL-2plus ignition is old. Maybe 10 years old.
MSD Pro Power Coil 8201 is also old. Maybe 10 years old.

The ignition and coil were on the car when I bought it in 2008. Car was built in 2000. So they're 3 seasons old to 10 years old.

Should the tach graph look like that when the RPMs are over 6500? It looks very smooth lower than that.

Battery is a 16V battery and voltage was perfect the entire run.

(p.s. - this was a Super Gas 9.90 run. So the dip in RPM is the throttle stop.)

Thanks for any comments & help.
 

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What does battery volts look like?
 

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A very nice 16.54 to 16.59 volts the entire time.
What is the sample rate? Can you post it up along with the RPM?
 

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Discussion Starter #5
What is the sample rate? Can you post it up along with the RPM?
1000 samples/second.

Here's the voltage for the same run. You have to really blow up the y-axis to see any variation at all.
(The beginning of the run is at about 1.0 seconds on this. The voltage dip is the transbrake)

 

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Can you not put them both on the screen at the same time? Does the car have an alternator?
 

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Discussion Starter #7
Can you not put them both on the screen at the same time? Does the car have an alternator?
No alternator. When they are both on the same screen the scale makes the battery voltage look perfectly flat.
 

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Who's logger is that anyway? I know we talked about a Sportsman at one point in time.

It looks like there could be an ignition problem, the voltage does seem to fluctuate. I have also seen that if the engine doesnt have enough timing in it. I think you have said before you run methanol, is that correct?
 

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Discussion Starter #9
Who's logger is that anyway? I know we talked about a Sportsman at one point in time.

It looks like there could be an ignition problem, the voltage does seem to fluctuate. I have also seen that if the engine doesnt have enough timing in it. I think you have said before you run methanol, is that correct?
Yes. Methanol. 35 degrees. Locked timing.
(Altronics Dataquest logger)
 

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If it were me I would put a new set of MSD wires, cap and rotor on it and yeah a new set of plugs of NGK -8 or -9 plugs gapped at .025 and test again. Also I would double check the rotor phasing.
Jmatt do you have EGTs or 02 sensors on your ride?
 

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JMatt

Yes it's a classic issue with the Pro power coil we see it all the time. Lose it Now Please. We recommend the MSD 8251 coil, the pro power starts to short between the winding as it it ages & as the oil evaporates off. Besides that the Pro power losses output as it starts to warm up. So what you start with & what you finish your event with is not the same. The MSD 8251 will get everything there is currently out of your MSD box. The 8251 can usually be had for $125 from most suppliers. Donate the Pro Power to someone you Really Like! :) I hope this helps.....
 

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Discussion Starter #13
I have seen them do that when they are too fat.

One car was a mech injected deal that needed a high-speed lean out. the other is my own procharger car when I have just been over cautious.
Hmmm...

I'm mechanical injected alcohol WITH a high-speed bybass and log EGT's on all 8 cylinders. They run 1050-1150 in all cylinders. If that's fat, it's barely fat.
 

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Discussion Starter #15
I agree Matt. My EGT's were in the 800's and the O2's were in the 8.5 - 9 range.
Yours was a good comment though, as a fat stumble could look like that I would guess.
 

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Discussion Starter #17
Your EGT's are good. Give your ignition system a tune up and drive it like you stole it.
My distributor cap is literally loose. You can pick it up about 1/4" off the distributor as if the hold downs have bent over time.

I'm thinking that at high rpm the cap is vibrating loose and the rotor isn't making reliable contact.

New cap and rotor ordered today. Log some passes Thursday.

If that doesn't work, new coil next.

Thanks for everyone's input.
 

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Like Uncle Paul said, I would double check the rotor phasing. If that is ok some new parts look to be in order.
 
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