okay, thanks so much for your replies, i really appreciate it. i will post an upate when i fix the security bulb.

 

until I can get to checking the security bulb ... anyone know where to find the two grounds on this truck? Or what they even look like? A few people have told me to check the grounds because this is a common issue and can cause the random start - no start issue. Apparently there's two grounds, one under the hood (motor to battery ? ) which I'm pretty sure I found that one ... but the other (motor to body?) I can't find anywhere! Don't really know exactly where to look or what it might look like? Any help is appreciated - thanks!

 

Doubtful this is the problem because a faulty ground will cause a no-crank condition, (starter will not engage).


At the negative battery terminal: The larger gauge wire goes to the front of the engine block, down low on the passenger side. The smaller gauge wire grounds to the radiator support forward of the battery. There is a braided body ground cable that runs from the rear of the right cylinder head to the firewall near the blower resistor.

 

sorry for the delay... finally got my dash/cluster board taken out and checked, and come to find out, there is NO bulb where security would light up. There's actually a few empty spots with no bulbs. Even if I put a bulb in... it wouldn't be hooked up with 'security'. But also, when watch a few videos, I noticed no one's security light for this truck lights up.

 

well the 'symptoms' of my truck have sort of changed... so maybe it could give more insight on what may be wrong. Now, if it goes overnight without starting, it does the turn over - but no start situation ... where as before it would only do this after a day or so without attempting to be started. I can go out there a few times throughout the day and it will start up no problem! But the next morning when I do try to start it, after letting the key go - with no start, the truck kinda 'coughs' or sputters for a few seconds, also some smoke comes from under the hood when this 'coughing/sputtering' happens. After a while of holding the key forward, it will start to kinda 'sputter' (only way i can think to describe it) acting like it wants to start... until it gets closer and closer and eventually starts up.

 

Just a thought, 97 is the truck with the classic starter switch problem. Not sure if your 96 has the "passlock". Do some research. My 95 had very similar problems, considering it is a late 95 it has no passlock, yours might be the same as a 96. My problem was a bad ignition switch. Just FYI mine has no bulbs for those spots behind the cluster.

 

called a few auto parts stores, all said no for passlock system, not necessarily true though. Just had it hooked up to a code scanner and it says MAP or manifold absolute pressure Sensor.

 

Your 96 does have a factory security system. Pretty sure Passlock started in 1998, and yours is PasskeyII. GM made changes, almost annually, to the anti-theft systems, and I can't remember for sure which system is on your 1996, (should say in the owners manual). At any rate, the system is designed to disable the fuel injectors if it suspects a theft is occurring. The engine might start and stall, or it might not start at all. Either way, the starter will engage and crank the engine. The easiest way to see if the system is disabling the injectors, is with a capable scan tool. Depending on the scan tool, it's usually on the engine data menu, after all the sensors etc. Passlock is nearly impossible to bypass, or fool, without other problems. Passkey systems are not as difficult. PasskeyI and PasskeyII systems have a resistor in the key: https://www2.kimballmidwest.com/imag...rge/62-106.jpg << Does your key look like this?


The small silver line is the resistor. If it doesn't make contact inside the ignition lock cylinder, or the system doesn't recognize the key, the injectors will be disabled.


The MAP sensor will not cause a no-start condition. Run like crap yes, but not a no-start.

 

Well the truck does eventually start ... and after it's started it will start up and run and drive no problem. Looking at the image you provided, no that is not my key, it doesn't have a chip or anything. I actually somehow found this page: http://my.cardone.com/techdocs/pt%2077-0011.pdf
... my key is on pg 4, the top right passkey III (PK3), III+ (PK3+)... so thank you! i've finally found out which security system my truck does indeed have. So now I'm going to go do the relearn procedure and switch out my MAP sensor (mine was all cruddy and slightly melted) ... hopefully my baby will be all fixed
i will post an update afterwards... but until then, thank you all so much!

 

Good website with a lot of information about GM VTD systems. Try the relearn, see what happens. Being that it eventually starts and runs, it's probably not the problem though.