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Tach jumps while on the limiter
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DRR Sportsman
Picture of TD6297
posted
I noticed something this past weekend. When on the trans brake and running against the limiter, the engine is not as smooth as it was before and the tach jumps around 4 or 500 rpm. Is there anything I should be looking at in the ignition that could cause this? MSD crank trigger, MSD 7AL and Autogage tach. On the runs, I could hear the engine had a little flutter, not quite a misfire, just not clean sounding.

I had chased something similar before, and it was a dirty crank trigger connnector, but after cleaning this one, it still does this.

Any thoughts?
 
Posts: 149 | Location: Canada | Registered: April 17, 2013Reply With QuoteReport This Post
DRR Sportsman
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I'd disconnect the tach and see if it sounds "cleaner".


Denis LeBlanc

 
Posts: 347 | Location: Manchester, NH | Registered: February 03, 2006Reply With QuoteReport This Post
DRR S/Pro
Picture of Mike Rietow
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I had one do that back in the day, on 7al analog ignition.

Ended being the adjustable rpm plug in. I stuck a regular chip in the three step, all good.


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Posts: 8831 | Location: Madeira Beach Fl. | Registered: June 12, 2018Reply With QuoteReport This Post
DRR Sportsman
Picture of TD6297
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Thanks! I will try these two things. I have other chips and can replace that and not hard to disconnect the tach either.
 
Posts: 149 | Location: Canada | Registered: April 17, 2013Reply With QuoteReport This Post
DRR Pro
Picture of Don Higgins Crew Chief Pro Software
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When mine did that it turned out to be a voltage drop problem. Changed grounds and a few wire ends and problem disappeared.



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Posts: 1361 | Location: Bartonville Illinois | Registered: October 18, 2002Reply With QuoteReport This Post
DRR S/Pro
Picture of Lenny5160
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quote:
Originally posted by Mike Rietow:
I had one do that back in the day, on 7al analog ignition.

Ended being the adjustable rpm plug in. I stuck a regular chip in the three step, all good.


I’ve had the same issue with the same solution.

I was also killing main bearings at the time, and when I put a good chip in the 2-Step I stopped having bearing issues.


Tony Leonard
 
Posts: 2945 | Location: Inver Grove Heights, MN | Registered: March 18, 2004Reply With QuoteReport This Post
DRR Top Comp
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I dumped the analog ignition for digital simply for the cleaner rev limit functions. I carry a spare analog ignition but hopefully never have to use it. The tach circuit went out one time and that caused a miss also. This 6AL Programmable has worked flawlessly so far, don't miss the analog stuff one bit.


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Posts: 5152 | Location: stuck in the middle with you! | Registered: March 11, 2002Reply With QuoteReport This Post



DRR S/Pro
Picture of Mike Rietow
posted Hide Post
quote:
Originally posted by Lenny5160:
quote:
Originally posted by Mike Rietow:
I had one do that back in the day, on 7al analog ignition.

Ended being the adjustable rpm plug in. I stuck a regular chip in the three step, all good.


I’ve had the same issue with the same solution.

I was also killing main bearings at the time, and when I put a good chip in the 2-Step I stopped having bearing issues.


Hmmmm bummer, that's wild. I don't doubt it.


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1996, 1998, 2001, 2003, 2005, 2006, 2008 Super Pro Champion Sunshine Dragstrip, Clearwater Florida
 
Posts: 8831 | Location: Madeira Beach Fl. | Registered: June 12, 2018Reply With QuoteReport This Post
DRR Pro
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quote:
I dumped the analog ignition for digital simply for the cleaner rev limit functions


Good suggestions on what to try for resolving that tach problem.

I agree with the quoted statement. Digital can offer more usable options and you could keep your present analog system (any analog system with a rpm chip port) and upgrade to digital by adding a Grid 7730 controller. The Data Acquisition in Grid can be a time / money saver when diagnosing an electrical problem. If you don’t know how to use digital, there are many today that use and understand it to help. Many have laptops loaded with MSD software while at the track.

You don’t need a laptop to go digital. You can preprogram Grid with a home computer (No 12v power needed, computer powers Grid through usb connection) and install Grid into the car with only one plug connection. Adding a 7751 Manual Launch Control to Grid would allow you to adjust the Launch rpm in 100 rpm increments at any time the ignition is On. Grid launch can be adjusted in 50 rpm increments with laptop. Shift outputs adjust in 1 rpm increments to include timed/ rpm outputs with a laptop.
 
Posts: 1992 | Location: 53056 | Registered: December 30, 2009Reply With QuoteReport This Post
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