remote start/alarm starting problem

Okay i just Put an Alarm system in my dads' mini van (old alarm "Thor")

1998 Pontiac Montana (TransSport) so after a day of searching i finally found the wiring diagrams for this van in order to find the tach wire

So i plug everything in everything works fine so i try remote start it turns on but then after that the starter cranks once or twice more while the engine is on then the horn signals a succesful ignition. so my problem is why could this be going on.(engine stays on)

I ended up getting my tach wire from behind the display gauges (white wire) could i have the wrong cable.because without the cable plugged in at all it just keeps on trying to start. and the alarm wont go into driving mode. so ithink i got the right cable any suggestions woul be great thanks

What brand and model of remote start/alarm?  Is there any type of tach source selection or tach learn process? 

Did you use a DMM to confirm your White wire as a proper tach signal?   AudioVox has this info for the tach

1998 Pontiac Montana     

Tachometer     WHITE  (AC)      PCM LEFT SIDE OF ENG IN AIR CLEANER

Also, Fuel Injectors usually provide a good tach signal that most R/S's can use.

Well it's a cheap alaram  Brand " Thor" dont know what model it is, but it's probably korean or chinese guessing from the instruction manual (looks like it was written by a 5 year old)
  my dad bought the alarm at a flea market like 2 years ago is all i know about it

I tried checking the white cable with multimeter but couln't figure out how to check it.

 so what i did was connect it to the alarm sensor cable disarm the alarm start the van with the key and waited it didn't cutoff so i figured it was the right wire

(normally without the wire alarm rearms itself after 30 seconds and cutsoff engine)

Tach signal should be a 1 to 6 volt AC signal that rises with RPM's.  Set the DMM to a low AC scale, say 0-20 volts, Black on chasis ground and red on wire to be tested.  From your diagram, it looks like using one of the 6 fuel injectors is easy.  The wire between the injector and the PCM is the one you want.

Are you sure its looking for a tach signal?  I found this about the Thor alarm:  https://www.automotiveforums.com/t199542.html

If yours is similar, it might be looking for the oil pressure light to go off.  Is there any install guide that came with the R/S unit?  There might be some setup/configuration that needs to be done for the tach mode and tach signal to be learned or recognized.