1997 Nissan Pathfinder, Viper DS4+

I have a viper dS4+ Remote start with 2 way remote installed on my vehicle by PC Richard about 2 years ago. It’s worked fine since but recently it would start the vehicle and shut right back off of start and bog down to a stall and only with remote start. I tried relearning tach and it didn’t help. I took it back to PC this week and they reprogrammed the module and tried virtual tach instead, but that wasn’t working properly with vehicle. The tech set the system back to the hardwire tach and moved the tach wire from the distributor onto the number 3 injector on the uncommon wire.

Everything is working fine with the remote start and it starts every single time without failing even first thing in morning, but when the vehicle is already warm and you remote start it, it seems to drag the starter a bit after it has started. Should I try the tach relearn with engine hot and in drive?

how much is a bit? you could try re-learning tach on a warm engine, should solve the starter drag.

I would say it is equivalent to holding the key for 1-2 seconds after it started and this is mainly when the vehicle is already warm.

What is the correct rpms to learn tach and what does changing the tech value essentially do?

I had the issue again once yesterday where I remote start and it will severely struggle for a few seconds then normalize (after vehicle sat for 4 hours). This is a very occasional issue. The tech moved the tach wire to injector last Friday from distributor to try and remedy that issue along with the startup and immediate shutdown. Doing that seems to have solved the problem with remote start then shut off but doesn’t appear to have fixed the bogging down. So I decided to do a tach learn with rpms at 1800 and it causes the starter to drag even longer (around 3 seconds).

So the problem still persists occasionally, especially after the vehicle has sat for a few hours. It would start perfectly fine with the key, but if I were to remote start it instead the engine barely turns over with a rising and falling low rpm. The engine just struggles to stay on. I have tried learning tach at various rpms but it doesn't seem to solve the issue. I. know its the remote start for sure because I don't encounter any issues when manually starting it.

Tonight I remote started after the vehicle was parked for 5 hours and the engine turned over and bogged down so low that it shut off. I immediately started it with the key instead and it fired right up with no issues. I don't know what's up with this viper unit.

The tach needs to be learned at idle.

You mention about 1-2 seconds of starter overrun and then have the issue with the engine barely turning over and bogging/dying which is starter underrun (not enough crank time). You need a longer crank duration, it's too short if the engine barely catches before the starter disengages.

Depending on the engine/fuel system, a distributor tach signal is 2x faster/more accurate than a fuel injector tach signal. A distributor tach will pulse at least once per revolution (but typically more than just once) where as a fuel injector will pulse once for every two revolutions of the engine (half or lower the rate of the distributor).

This a viper, a basic logic simple computer, and not a human. It's never going to be as good as a human at determining when to stop cranking the motor on an older car where the needed crank time varies. In theory, the tach signal will give the viper the necessary input to know exactly when the engine has successfully started but if the car sometimes starts very quickly that signal has yet to come in and be recognized (why I mention about distributor vs injector accuracy) so you get starter overrun during those times.

I took it back to the installer and he pulled all the wiring to check out how the initial tech from 2.5 years ago installed it. Turns out the initial tech did not program the cold start wire. The tech verified with the tester light that the cold start wire was not programmed to work. After setting everything up properly, he showed me it was working and verified with the 12v tester.

Hopefully that puts an end to this problem.