Just throwing this out there. I noticed at my last race that my rpm graph on my racepak was not smooth like it normally is. The graph is rough with around a 75rpm swing. This is with a crank trigger and a Digital ignition. I swapped out the crank pickup but I haven’t raced the car yet. Just trying to get a handle on it before heading out to Vegas tomorrow.

Where is the graph showing rough?

It starts half way through first gear and again after the shift. If I knew how to post the picture I would. Funny as last time it did this two years ago in Chicago it ended up being some kind of feed back from the alternator. This time it looks similar but different. Hopefully the pick up clears it up. It doesn’t seem to effect the run as minor as it is.

check your spark plugs

Is it choppy or wavy or up an down ? I had a carburetor issue that made my rpm graph goofy. What is fuel psi doing at this point in the run ?

I would call it choppy. Fuel pressure is being read off of my nitrous fuel regulator and it is steady at 5.7 just where I have it set at. The plugs,distributor cap and rotor have all been replaced. Plug wires were all ohm’s checked. Like I said it doesn’t seem to slow the car any it just is something I noticed that has shown up since my Sonoma race’s back in July.

Are your tires feathered?

Just out of curiosity, why do you not have a 16v battery and have not gone away from running an alternator?

quote:

Originally posted by T/D6591:
I would call it choppy. Fuel pressure is being read off of my nitrous fuel regulator and it is steady at 5.7 just where I have it set at. The plugs,distributor cap and rotor have all been replaced. Plug wires were all ohm’s checked. Like I said it doesn’t seem to slow the car any it just is something I noticed that has shown up since my Sonoma race’s back in July.

Spikes up are interference and down is loss of signal.

I have also seen a bad battery cause graph issue too. Not sure what caused it but the battery got weak so I replaced it and the spikes were gone.

Strange(Andy) the tires are not feathered and the pinion graph doesn’t show any signs that match the rpm graph to make me think it is the tires. But I won’t rule that out. As far as the 16 volt battery goes I have been running those for the last 6 or 7 years if not longer. I also run an alternator because of the electrical load I have from the ignition,fan,water pump,fuel pump and 4 solenoids for the nitrous. My car usually runs a steady 17.2 volts throughout the run. Top38 good point on the battery. This battery is barely a year old and I run the heavy battery because it has move reserve than the lightweight battery that came with the car. Like I had mentioned before I had something similar but more pronounced that ended up being the feed back from the alternator. I do have a spare alternator from HOP that I may swap out in Vegas also. Thanks for all the ideas.

Here ya go Moe

look for loose wire connections on the tach circuit(s). Mine is usually where the tach wire hooks to the K&R mother board when it happens.

So that is Moes graph?

Possibly lean?

quote:

Originally posted by DragRaceResults:
So that is Moes graph?

Yes.

If that is Moe's graph, I wish mine looked that smooth lol

quote:

Originally posted by T/D6591:
Just throwing this out there. I noticed at my last race that my rpm graph on my racepak was not smooth like it normally is. The graph is rough with around a 75rpm swing. This is with a crank trigger and a Digital ignition. I swapped out the crank pickup but I haven’t raced the car yet. Just trying to get a handle on it before heading out to Vegas tomorrow.

which ignition box Moe?

also can you e-mail me the actual log file?

email procedure #21 Here

quote:

Originally posted by Big Steve:
If that is Moe's graph, I wish mine looked that smooth lol

I hear ya!

I didn't see where you said it lost some ET, because if it did, then i would look at ignition. if it didn't slow down i would look at the recorder side.
Does the Digital ignition show the input signal like the grid?


Joe

quote:

Originally posted by "The Bender":

quote:

Originally posted by Big Steve:
If that is Moe's graph, I wish mine looked that smooth lol

I hear ya!

Must be a blower thing...

are you pulling timing?