After reading a few post regarding the VATS I have a question regarding my starting issues. Can the VATS module fail in such a way that it allows current to the starter but does not send the ECM the fuel pulse signal? The car will crank and turn the motor over but will not fire unless I pour fuel in the TBI. The fuel system has been diagnosed and the pump, injectors, etc have been replaced. I also am 99% certain the ECM has fried. I'm in the process of checking a number of electrical things to rule them out as well, but VATS was mentioned as a possible issue. Thanks for any advice.

 

Pull up a wiring diagram and use a multimeter to check the 4 wires to your fuel injectors... not sure if yours is the same as mine, but in my case, the blue and green wires go to the ECM (ports c15 and d15, if i remember correctly) and the white and red wires go to the injector fuses... tonight I'm running a new red wire because my old one shorted out. I'll be posting *HERE* on whether or not that fixes mine, but it's been doing the exact same thing, and I did bypass my VATS and haven't had an issue with it since.

 

I know the injectors aren't getting any power. I'm pretty sure a dead ECM would cause this . However before I replace the ECM I was wondering if the VATS could have caused a similar symptom (cranks but no fuel). The ECM isn't terribly expensive so I'm seriously considering popping one in after I check for electrical shorts.

 

 

That is the normal function of VATS. To kill the injector signal, not the starter.

 

I think the someone the OP is referring to is me. You're welcome very much. Normally when the VATS is in security mode, it will prevent both starter function and fuel injector function(just in case someone finds a way around the starter relay). However, in a few of the VATS failures I've diagnosed, the module engaged the start enable relay, allowing the engine to crank and in a couple cases even run for a second. But in in all of these cases the VATS module did not produce the fuel enable signal. The cure was to install a VATS bypass module that replicates the fuel enable signal. This module sells online for about $24.

 

Not to be confused with the more commonly mentioned VATS " bypass " module that only supplies the correct key reading to the VATS module which if the module itself is faulty will do nothing

Correct module here
http://myplace.frontier.com/~vze7erz1/id1.html#vatsmod
http://myplace.frontier.com/~vze7erz1/id14.html

Diagnostics here ( bottom of page )
https://www.thirdgen.org/vats_passkey_system

 

*feels like a retard* ok, so I think I'm having the same issue with my VATS after all... after rewiring, it's still acting the same, cranking but not pumping fuel... I tried testing the module like you said, NINA, and I'm not sure I did it right, or maybe I don't understand what the readings should be... when the key was off, I read zero voltage, when the key was ON, I read 25, and when I cranked it to start I read 37... does that mean the VATS is responding as if everything is right? Thanks.

 

i have a few guestions like where does the vats module bypass go i think it goes behind the dash,but not 100% sure. Do you have a good site to buy this 24$ module.

 

25 what?

From the VATS link I posted above

To signal the ECM , VATS systems use a grounding square wave at a 30Hz rate.
The VATS module uses an NPN output transistor to pull down (ground) the 5 VDC reference voltage presented by the ECM on terminal B6.
The reference signal must be alternately grounded and allowed to be pulled up by the ECM
internal resistor 30 times per second (30 Hz) and at a 50% duty cycle.

 

Do you actually read before posting?
Check post # 7

 

Apparently i don,t read or don,t know how to do my own!

 

vetteoz, apologies. I had my multimeter set to test for voltage on the 2000m setting.

 

I'm not sure you are going to see anything change with a DVM
As noted above ;
the 5V signal from the ECM to VATS module is supposed to go lower and back up to 5V 30 times a second

 

NINA, can you verify that testing the VATS module this way would yield the results you mentioned? I don't wanna buy any more parts for this car until I find out exactly what the problem is, so if that testing method works, I'd like to know... no offense vetteoz, it's not that I think you don't know, I'm just trying to find out if there's a way to test this before I shell out any more money on this car.

 

Thanks everyone! I'm learning a ton already. If indeed the VATS will show a reduction in voltage when functioning properly I'll test that first thing this weekend. I read the VATS system overview on that link earlier yesterday (fantastic information, btw) and I'm assuming that the normal security light flashes and/or fault codes will not detect a bad VATS if the ECM is dead. I already have a spare ECM lined up so once I double check for shorts that's ready to go as well. From the sheer volume of posts about problematic VATS I'm considering installing the bypass module regardless of my results.

My plan of attack is:
1) Check for any shorts/voltage irregularities to the ECM (and a few other places)
2) Install new ECM
3) Diagnose VATS per previous link and pull any other codes
4) Install bypass module (I may do this anyway, even if step 3 passes)
5) Start car and call brother in law to rub it in (he's the one who gave up on the car and sold it to me for almost nothing)

Any show stopping problems in there? As always thanks a bunch!

 

 

i have a question that i think i was told i could do but want to make sure that it will work, i have a 91 and a 92 bird can i take the vats out of the 91 and put it in the 92 i have both keys, does the vats give you the resis. or is ti something else.

 

The resistor is in the key. 15 different values were used and the factory key code includes this resistor value. The VATS module is programmed with that specific key resistor value and will only allow starter and fuel system function when it reads that value across the cylinder contacts. So you have to use the matching key with a given VATS module. This would mean that the lock cylinder has to go with that module as well to match the key.

Another issue to be aware of is that during the 92 model year, GM changed the frequency of the VATS fuel enable pulse. As far as I can remember, the earlier units were 30/Hz, the later were 50Hz. The frequency of the module's fuel enable pulse is matched to the frequency programmed into the ECM's PROM chip. Therefore, in order for the VATS module from one vehicle to work in another vehicle, the fuel enable frequencies must be the same.

The only way to know if your 92 module will work in your 91 vehicle is to try it. If it doesn't match, it will not harm anything. The car just wont run.

 

i have the coulm out the 91 so if i put the vats and key and coulm in the 92 i don,t need a vats bypass module

 

thanks for your info i will look into it and i will order the 25$ vats module