Viper 791XV and 02 Mustang GT
Printed From: the12volt.com
Forum Name: Car Security and Convenience
Forum Discription: Car Alarms, Keyless Entries, Remote Starters, Immobilizer Bypasses, Sensors, Door Locks, Window Modules, Heated Mirrors, Heated Seats, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=26888
Printed Date: July 18, 2025 at 3:58 PM
Topic: Viper 791XV and 02 Mustang GT
Posted By: jmccreary
Subject: Viper 791XV and 02 Mustang GT
Date Posted: February 21, 2004 at 10:14 AM
I'm installing a new 791 in my 02 mustang; I had a audiovox alarm/remote start in it that i installed a while back. My problem is i can't get the 791 to find a tach signal. I'm just tapping into one of the coils, and that worked fine on the audio vox, but the 791 won't see it. I've tried changing the jumper to "low threshold" and that will make the LED flash rapidly when i go through the learn process. But it won't go on solid showing it has learned the tach rate. I know the mustang gt has separate coils for each cylinder, should I try using diodes and tapping into several coils? Or am I just missing something? I have double checked and the unit is programmed for "tach sense" not "voltage sense". Any suggestions are greatly appreciated.
Replies:
Posted By: kgerry
Date Posted: February 21, 2004 at 11:22 AM
what are you using for a tach source?
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Kevin Gerry
Certified Electronics Technician
MECP First Class Installer
Owner/Installer
Classic Car Audio
since 1979
Posted By: jmccreary
Date Posted: February 21, 2004 at 11:25 AM
I'm using the negative side of just one of the injector coils right now, just like i used on the audiovox remote starter i had. Thanks
Posted By: daniel2002p
Date Posted: February 21, 2004 at 7:53 PM
try the other side of the coil
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2005 Toyota Corolla S
1.8L VVT-i I-4
Always double check your wires with a DMM!!!
Do Not Use A Test Light!!!
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Best Buy 665 - IN IT TO WIN IT! TEAM MOBLE!
Posted By: speakerman
Date Posted: February 21, 2004 at 11:24 PM
Make sure your ignition wires are hooked up right. The 791 gets the ignition input from the large gauge pink not the pink with white. If the unit does not see the ignition signal then it will not go into programming mode. I have even had the ribbon cable come undone a little bit and the unit did not get the ignition input.
Posted By: jmccreary
Date Posted: February 24, 2004 at 1:45 PM
Thanks for the help, the unit will now detect a tach signal. (the butt connector i used to connect the wire from the coil to the alarm wasn't put on right) My problem now is that after the unit detects a tach signal when i do the remote start it will run for about 5-10 sec then shut down and re-start. I don't think it's my 555U becuase i never see the "theft" light come on during the process. I've double checked to make sure the unit is in tach sence, and it is. I've never had this much trouble doing an install before.
Posted By: JMaxx93
Date Posted: February 24, 2004 at 4:55 PM
whats happening i believe is the tach sense is sensing an over-rev condition and shuting it down. i believe you can perform a shutdown diagnostics on the 791xv by holding the valet button turning the ign on then off and releasing the valet button then press and release again. the led should flash a certain number of times. you may find it easier to just give up and go voltage sensing. just make sure if you do disconnect the tach wire completely. PS i hate doing remote starts in those mustangs. i had a bad experience with one that wouldn't stay away after it was installed. still don't know what the problem was. its the only one i gave up on. i think i've been hexed by mustangs. blah blah blah
Posted By: jmccreary
Date Posted: February 27, 2004 at 12:07 PM
Thanks for all the help, finally got it working. I decided to tap into the negative side of one of the injectors itself instead of going to the coil. It works perfectly now. I was thinking about just giving up and going to voltage sense. But i can't let a machine beat me ;-) Thanks again for all the help James
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