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 Any ideas? 
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Joined: Wed Feb 20, 2013 11:38 pm
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Last 2 runs yesterday produced logs like this. Any ideas?
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Mon Jun 23, 2014 10:52 am
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Joined: Wed Feb 20, 2013 11:38 pm
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Greg says it's a bad ground or RF interference for those that may see the same problem.


Last edited by Ron Gusack on Tue Jun 24, 2014 7:26 am, edited 1 time in total.



Mon Jun 23, 2014 11:42 am
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Boy howdy.. or a wet-cell battery with a broken plate, a loose battery cable, a dangling wire grounding on the fuel line, etc. Had some fun with a wet-cell battery with a broken plate one time, long ago and not so far away, it acted like a plugged up fuel filter, limited the revs (point ignition). V-drive boat vibration will kill a cheap battery. Some batteries are made by the devil. A few years ago an optima acted like a 6000 RPM rev limiter, MSD 6al's (three 6al's), carbs, alternator, torque converter, etc, damn optima. Lucky the guy who owned the car, owns the dyno too. I don't quite see how a gel battery can be frequency sensitive, a wet battery with dangling plates ..... OK, but a gel??


Mon Jun 23, 2014 11:30 pm
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The car runs fine and some of the data appears to be okay. The O2 drops out completely so I'm going to replace it and see what happens.


Tue Jun 24, 2014 7:29 am
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You may have a bad diode in the alternator. Turn on every load you can, fan, pumps, lights, etc, run the engine at about 3000 RPM and check for AC volts at the alternator B+ output. Put the digital voltmeter on the lowest AC volts scale. There should be no more than .1 AC Volt. Your log looks like some I have from a Mopar with a bad alternator.

I thought Racepak stuff was perfect, never does a thing like this. LOL?


Tue Jun 24, 2014 10:00 am
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It's a single wire deal and I'll check it there.

I've been chasing a strange charging problem for a very long time. Charging voltage goes down as the day goes longer. On June 8 I took the average charging voltage from starting line to finish line. I got 12.9, 12.5, 12.6, 11.9, 11.7, 12.3. I did a bunch of stuff to try to fix it and on 6/22 I got 13.2, 13.1, 12.7, 12.7, 12.6, 12.6, 12.7, 12.4. I know these numbers suck and I'm still chasing it. I bought the stuff to run 4ga welding cable from the alternator to the back of the car.


Tue Jun 24, 2014 10:48 am
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A CS130 alternator with the "sensing" wire will fix you right up Ron


Tue Jun 24, 2014 1:09 pm
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Joined: Wed Feb 20, 2013 11:38 pm
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You might be right, but this should work. I measure 14.4 at the back of the alternator and the logger just showed 13.8. I'd be happy with 13.8 if it stayed there all day at the track but the hotter it gets the lower it puts out. I need to do some measuring at the track instead of in the garage.


Tue Jun 24, 2014 2:16 pm
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Wire from the alternator to the battery is not big enough or there is resistance for some reason.....
.
.....and you need to check for AC Volts at the alt. output. One-tenth Volt is maximum permitted with a DVM. If you have an oscilloscope you may see more than that. A bad diode can allow 28 V AC into the system. Trust me, that will make the data system crazy.

I have logs that look just like yours and it was because of a bad alternator. The car was killing alternators because the battery ground cable connection was not adequate where it attached to the roll bar tubing and the finest Chinese rebuilt alternators just couldn't take it.


Tue Jun 24, 2014 5:31 pm
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I tried to measure AC volts at the back of the alternator and my meter jumped all over, very hard to read.

The charge wire is 6 gauge at the moment. I'm gathering stuff to install a 4ga welding wire. This is a drag only car with water pump, fuel pump, fan, 2 electric temp gauges, the MSD and the tach as the only draw on the system. That's why I thought a 6 was big enough.


Tue Jun 24, 2014 5:55 pm
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