so i have a 91 rs 305 tbi and it has only happened 2 times but what its doing is it will run fine all day long then it gets shut down and upon trying to restart the SECURITY light comes on and stays on...... the first time it happened it wouldn't start then the next morning fired up like a champ..... same thing today went to the store turned it off light come on and wouldn't start then 20 min later fired up like a champ........ can anyone help with a diagnosis....Some insight would be greatly apprieciated

 

Security light is due to VATS. Which basically means the chip on your key sends a small voltage that has to be in range of what the VATS (Anti-theft system) if not it will not start and the light will come on.

Have you messed around with the steering column? The only thing I can think of is that some wire is loose or not giving proper connection. I don't know if key chips can loose their charge or stop working so idk if it might be the key.

Try reading the voltage of the key with a multimeter and when it works record or remember the reading. When it doesn't turn on check it and compare. If its the same it might be some wiring.

 

Actually thats not true. The "chip" in the key is just a small piece of carbon with a tuned resistance. The vats module sends voltage thought the circuit and reads the resistance of the chip. If it doesnt get the correct resistance, it doesnt ground the start enable relay, and tells the computer not to let the injectors pulse or the ignition to fire.

It sounds like maybe your contacts for the "chip" in the column are starting to wear out, which isnt uncommon. If you dont care about the VATS, you can wire in a resistor of the correct value in the circuit and it will trick the module into thinking the correct key is always inserted.

 

My 1997 Z28 did this - the contacts in the ignition switch are wearing as stated - they have little tiny springs behind them that wear out, and thus the contacts don't spring outwards to amke contact with the pellet i the key.

Another option for bypassing the VATS is simply finding the starter enable relay in the driver side kick panel behind the black goo under the hood release - clip the ground wire to the relay, and ground that wire anywhere.

The VATS system provides the ground to activate the relay - when the VATS gets the right resistor, it provides the ground - simply giving the starter enable relay that needed ground to activate and provide 12v to the starter bypasses the VATS as well. Key will still be required to start the car - the ignition switch provides the 12v+ to the starter enable relay, but the pellet or even lack of it won't matter anymore - and you can get $2.49 keys made instead of $24.95 keys if you ever need another spare.

 

The correct resistance is still needed in the ECM to allow to the injectors to pulse and the ignition to fire the spark plugs. Simply grounding the start enable relay will only allow the starter to spin. Youll get no fuel or fire unless you fix the contacts in the column, or bypass them by wiring in the right resistor. Im not sure about 4th gens, but I know for sure thats how it is on 3rd gens.

 

Ahhhhh - very good point. Didn't think of that!

I'd been having starter issues, and was reading alot of threads, and someone kept saying that that ground was all that was needed. At the time I read it, I knew there was a reason it didn't make sense, but couldn't put my finger on it. After tearing into my starting system and replacing everything, I saw what was being talked about with the starter enable relay and the VATS ground, and so I thought 'well just maybe he's right'.

But I see what you are saying - maybe gets the starter turning, but won't run the car! I knew there was a good reason it sounded too easy - I just couldn't get my old brain to think it through! Another case of "always follow your gut"!

So - simply providing the ground will NOT work - you have to do the resistor method as mentioned to bypass the VATS!

 

Its really easy to bypass the vats. All you need is a volt meter/ohm meter, some soldering ability, and a trip to radio shack. Take a volt meter/ohm meter to the keys "chip" to measure the resistance, take that trip to radio shack for the correct resistor, unplug the small 2 prong connector under the dash and snip it, solder the wires to the resistor so it connects the 2 prongs in a loop then plug it back in.

 

okay so i was checking connections on the starter and i shorted it out everything still works except now when you go to start it the starter goes KUNK and wont start could it need a new solenoid/starter or what because all the accesories work, fan, gauges,fuel pump all of them

 

that clunk sound sounds like your solenoid is engaging, but the starter isnt spinning. you can always pull it and take it to autozone and get it tested for free.

 

What if the security.light doesn't even on

 

Security light is just a light bulb in the dash. Could be burned out and needing replaced.

Also might check the ECM-IGN fuse because it also powers the PASSkey module.

Anything beyond that will need more advanced troubleshooting.