1987 VATS bypass question: 30Hz 5V or 30Hz ground?
07-23-2016, 06:26 PM
#1
1987 VATS bypass question: 30Hz 5V or 30Hz ground?
Hey all -
Been fooling with an '87 for a while, and have failed to get past the VATS system. I recently installed one of these:
http://www.ebay.com/itm/GM-VATS-or-P...1WEYiu&vxp=mtr
but it did NOT fix the issue, and the Code 46 remained. That device applies a 5V, 30Hz (or 50Hz) signal to pin B6, normally the connection from the VATS module to the ECM.
From what I have found, this is the correct bypass for some VATS systems, but then a few references suggest this:
If the above is correct, the device will NOT work as a bypass.
Does anyone know what an '87 ECM actually expects from the VATS module?
Been fooling with an '87 for a while, and have failed to get past the VATS system. I recently installed one of these:
http://www.ebay.com/itm/GM-VATS-or-P...1WEYiu&vxp=mtr
but it did NOT fix the issue, and the Code 46 remained. That device applies a 5V, 30Hz (or 50Hz) signal to pin B6, normally the connection from the VATS module to the ECM.
From what I have found, this is the correct bypass for some VATS systems, but then a few references suggest this:
To signal the ECM that a correct key resistance is sensed, the VATS and PASSKey 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. This method was selected to prevent the simple powering or grounding of an ECM input to enable the fuel injectors. The signal is only needed during cranking to enable the injectors.
Does anyone know what an '87 ECM actually expects from the VATS module?
07-23-2016, 07:13 PM
#2
Let's back up some and just ASK - Do you have crank? The component you bought I believe is only intended for "fuel enable".
FE I'm quite sure is 30Hz
FE I'm quite sure is 30Hz
Last edited by WVZR-1; 07-23-2016 at 08:15 PM.
07-23-2016, 11:27 PM
#3
Race Director
The 30 Hz VATS signal is checked when the ignition is first turned on and never thereafter. My recollection is that the ECM checks the PERIOD of the waveform, so it doesn't have to be a square wave.
Last edited by Cliff Harris; 07-23-2016 at 11:31 PM.
07-24-2016, 08:37 AM
#4
Team Owner
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I don't know if this helps you, BUT when I installed VAT by pass, it was brought from what my key code was, and wasn't very effective.
Now to other side, if you think you have VAT problems of no crank GM had TCB, NOT recall to replace your ignition cylinder system cause they were defective. It's not free, and I started experience problems, and them replace and give me new set of keys, drove it for another 15 years before I sold it with no problems. I also paid GM, wasn't cheap repair.
I had 1989 ragtop, 24 years.
Now to other side, if you think you have VAT problems of no crank GM had TCB, NOT recall to replace your ignition cylinder system cause they were defective. It's not free, and I started experience problems, and them replace and give me new set of keys, drove it for another 15 years before I sold it with no problems. I also paid GM, wasn't cheap repair.
I had 1989 ragtop, 24 years.
Last edited by 1bdvet; 07-24-2016 at 08:44 AM.
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07-25-2016, 11:46 AM
#6
That's the last resort, I've gotten quotes from $300-500 to get it done!
07-25-2016, 09:13 PM
#7
Melting Slicks
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When you installed the 30hz signal to B6 of the ECM did you cut the wire coming from the Vats Decoder Module to pin B6?
Last edited by Hooked on Vettes; 07-25-2016 at 09:14 PM.
07-25-2016, 09:29 PM
#8
Instructor
07-26-2016, 09:30 AM
#9
Specifically, I used a TIP120 transistor with the output of the eBay module wired to the gate, ECM pin B6 to the source, and the drain to ground.
Thanks all for the input!
07-26-2016, 11:52 AM
#10
04-30-2019, 07:33 PM
#11
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This is the answer, folks! I verified experimentally last night by using the eBay bypass module and a MOSFET transistor to do exactly this, pulling ECM pin B6 to ground at 30Hz. The car started and ran (badly) for the first time since I owned it.
Specifically, I used a TIP120 transistor with the output of the eBay module wired to the gate, ECM pin B6 to the source, and the drain to ground.
Thanks all for the input!
Specifically, I used a TIP120 transistor with the output of the eBay module wired to the gate, ECM pin B6 to the source, and the drain to ground.
Thanks all for the input!