rpm drops below learned tach signal

I'm in the process of installing a Viper 5902 alarm system in a 2005 G35 Sedan and having issues with correctly learning the tach signal due dropping engine rpm.

When I start the engine the rpm is at approximately 1200 rpm.  After about 8 seconds it drops to around 600 - 700 rpm.  The problem is that you only have 5 seconds to start the tach learning process and the engine rpm doesn't drop until after the tach signal has been learned.  As a result the engine remote starts correctly and then shuts off after 10 seconds due to a low tach signal.  To verify that this is the problem, I tried placing my foot on the accelerator pedal after remote starting and holding the engine rpm at approximately 1500 rpm.  This works and the engine continues to run until I remove my foot from the accelerator pedal after which the engine shuts off about 3 seconds later.

I'm using the XK09 module flashed with the niss2 firmware.  It's wired D2D but I had to add the tach wire connection between the XK09 and 5902 to pick up the tach signal.  The tach setting on the 5902 is set to tachometer (option 4).

FYI - Virtual tach did not work either as the starter wouldn't disengage.

Any help is great appreciated!

Where did you grab tach?
A solution that costs more money but is sure to work is to get a 454t tach generator.. i'm sure you can find someway but if it comes down to it.

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A DMM is a beautiful thing.

MECP Advanced Installer Certified.

The tach signal is being picked up off of the CAN system by the XK09 module and then transmitted to the 5902 (the 5902 tach wire is connected to the tach output from the XK09).

I would try to connect to the true tach wire in the car. using the xk09 can skew the actual tach voltage a bit causing this kind of issue. grab a wire at any ignition coil or injector that isnt WHITE/ blue, red, or black

hmm yeah you should go ahead and run an actual tach. i've never trusted tach through a module.

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A DMM is a beautiful thing.

MECP Advanced Installer Certified.

i find tach through any module is slow in response so you get a little starter drag, but not much

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Ted
2nd Year Tier 1 Medical School
Still installing as a hobby...pays for groceries
Compustar Expert

Does quickly placing the car in gear ( assuming an automatic - reverse is best )  slow the engine enough before the Tach Learn period is over?

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Soldering is fun!

I had the very same idea but when I put the car in gear the ECM seems to compensate increasing the engine RPM to ~1100.

I also tried tricking the RS to delay the tach learning process by removing the ignition input/output wire (12 ga pink)  from the 5902, starting the engine and waiting for the rpm to drop to ~700 (where it normally is) and then re-inserting the ignition wire back into the connector and then immediately starting the tach learning procedure.  Didn't work.  All I achieved was putting the car into valet mode...  Does anyone have any idea which other input the RS is watching to detect when the engine is started?

Is seems like it isn't an issue to pick up the tach signal with the module and I'm guessing if I use a hardwired  tach input I'm still going to have the same issue with engine RPM.  If all else fails I'll likely still try this though.

Is there any way to delay, extend, or re-initiate  the tach learning time?

FYI – I remote started  the car today with the engine totally cold and it ran for several minutes until the engine warmed up enough that the RPM dropped below the learned tach signal shutting down the engine.

honestly just quit being lazy and hook up an actual tach wire. it shoudl take 10 minutes max...

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A DMM is a beautiful thing.

MECP Advanced Installer Certified.

Ya I guess that's what I'm going to have to do.  Hopefully it works...

Can't say I think much of the XK09 module.  So far the only thing it seems to do right is the bypass.  Everything else either doesn't work or is flakey.  Is there another brand that works better?

Just can't beat the iDatalink modules for Nissan / Infinity.  I have no problems with their Tach signal output either.

https://www.idatalink.com/helpdesk/

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Soldering is fun!

  I'm not sure if your G35 has an 'iac" idle air control solenoid on the engines throttle body, but disconnecting an iac usually drops the idle down to a base number or possibly even stall, especially on a cold engine. It may also set an engine code so you might have to clear a code.

Well I hardwired a true tach signal today and now everything works correctly.  No more low rpm shut downs!

good job doing it the right way.

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A DMM is a beautiful thing.

MECP Advanced Installer Certified.

OK now I have a new problem with the remote start.  If I try to remote start the car with the alarm armed I get a false trigger from the trunk which sets of the alarm.  Obviously this prevents the car from starting.  If I disarm the alarm first the car starts correctly with no trigger. 

All of the trigger inputs for the doors, trunk, hood, are picked up from the CANBUS using the XK09 module.  The XK09 is connected to the brain of the 5902 using the D2D cable.

Anyone had this problem before?

Is there a way to get the alarm to ignore the trigger signals during the starting process?

sounds like you should run dedicated triggers now haha.

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A DMM is a beautiful thing.

MECP Advanced Installer Certified.

So after trouble shooting for a bit it turns out that the trunk trigger signal that was setting off the alarm when I tried to remote start the car with the alarm armed wasn't from the XK09 module at all.  Rather I have several sensors tied into the trunk trigger/instant trigger pin on the brain of the 5902 per the instructions.  This pin isn't actually used for the trunk pin at all as this is being read off of the CAN BUS. What's actually setting off the alarm is the module for the backup battery which sees the drop in voltage during cranking to be an attempt to disconnect the battery. 

Any thoughts on how to correct this (short of just disabling the instant trigger output from the backup battery module)?