VATS and fuel pump enable circuit? - Chevy Impala SS Forum
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post #1 of 11 (permalink) Old 12-27-2015, 10:00 PM Thread Starter
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VATS and fuel pump enable circuit?

Does a faulty passkey system (where the key resistance can no longer be read by the circuit), cause the fuel pump to operate??

This morning, I try to start my car and it cranks but doesn't fire. I also cannot hear the fuel pump whine, as is normally the case, when I turn the key. Looking at the factor service manual for my 96 RMW and a wiring diagram in the second book, it looks like the VATS system has something to do with enabling the PCM to allow operation of the fuel pump. My Pass Key light has been on (solid) for perhaps 4-5 months. Is it now not letting the FP work? As a check, the FP relay is fine, and the fuse is also fine. I WAS able to get the fuel pump to work using the underhood jumper to B+...

Any help appreciated.

'95 DGM Impala SS, 383, LT4 cnc heads, LT4 matched intake, Holley 58 mm t/body, GM 846 cam, GMPP 1.5 rr's, F-body MAF, BH OBD I PCM, LT4 knock module, K&N cold air, Edelbrock headers, Flowmaster exhaust, BBHP #73 6-speed, 4:10 gear, sloted and drilled rotors, Z28 cluster.

'96 Buick Roadmaster Limited Wagon, mostly stock.

74 Ford F100, 390 HP pulled out of a 67 Fairlane GT

91 Mustang LX notchback, 5.0L, 63,000 miles, pristine.
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post #2 of 11 (permalink) Old 12-28-2015, 09:21 AM
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In a properly working VATs system, if the correct resistance from the key pellet is not seen upon a start up attempt, VATs will disable the cranking circuit/starter and fuel injectors (not fuel pump) for 3 minute intervals.
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post #3 of 11 (permalink) Old 12-28-2015, 10:28 AM Thread Starter
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Quote:
Originally Posted by Goldmaster View Post
In a properly working VATs system, if the correct resistance from the key pellet is not seen upon a start up attempt, VATs will disable the cranking circuit/starter and fuel injectors (not fuel pump) for 3 minute intervals.
So my engine cranks fine. And the fuel pump can be manually run (via the red jumper wire under the hood). But when starting now, I don't hear the fuel pump energizing. That damn Pass Key light has been on for months and no issues at all, but wondering if you can have problems with just the fuel circuit and not the cranking/starting circuit?

'95 DGM Impala SS, 383, LT4 cnc heads, LT4 matched intake, Holley 58 mm t/body, GM 846 cam, GMPP 1.5 rr's, F-body MAF, BH OBD I PCM, LT4 knock module, K&N cold air, Edelbrock headers, Flowmaster exhaust, BBHP #73 6-speed, 4:10 gear, sloted and drilled rotors, Z28 cluster.

'96 Buick Roadmaster Limited Wagon, mostly stock.

74 Ford F100, 390 HP pulled out of a 67 Fairlane GT

91 Mustang LX notchback, 5.0L, 63,000 miles, pristine.
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post #4 of 11 (permalink) Old 12-28-2015, 11:02 AM
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If the pump works with the prime wire, it may just be a bad FP relay or the incoming signal to trigger the relay. Try to swap the relay and see what happens.

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post #5 of 11 (permalink) Old 12-28-2015, 11:24 AM Thread Starter
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I swapped out the FP relay with another known good one. No luck.
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post #6 of 11 (permalink) Old 12-28-2015, 12:27 PM
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Probe relay socket

The other quick test is to probe the relay socket coil contacts and confirm that the coil is getting voltage from the PCM. This can be hard to do as the PCM only turns the pump on for a short time at key on.

Last suggestion is one I have not done. Unplug the (orange?) wire between the ignition key lock and the VATS module. My 94 Manual says the car will not start the internet say it will but will light the VATS light.

The only sure way to rule out the VATS system is to look for it's 40-60HZ (AC) signal at the PCM. And the voltage out of the PCM to the relay

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post #7 of 11 (permalink) Old 12-28-2015, 01:02 PM
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Quote:
Originally Posted by Alchemist View Post
I swapped out the FP relay with another known good one. No luck.
It sounds like you checked the schematic and it should resemble this circuit here for a 96.....

http://www.goldsswagon.com/diagrams/...ngine_3of3.pdf

....assuming you are getting the signal from the PCM to E9 and the ground is good, that should energize the coil and pull the relay contact over. You have bypassed this successfully using the override wire. As another test, try to jumper pins F9 and E11 and see if the pump runs.

If so, then I suspect you either don't have connectivity to E9 from the ECM or most likely you don't have a good connection to ground foil the coil in the relay at pin F11. Look where the coil in the relay is grounded. Good idea to remove that group of ground wires from the cylinder head, clean them and check them for a solid connection to the wire/ring terminal area and reattach to the head. Then see what happens. If you have no way to meter out these circuits, a quick swap of a known good ECM may be helpful.

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'95 Caprice SS conversion - Bonny Buckets - 96 Column, Shifter and Console - 3.73 Gear and Herter tune - Z/28 Cluster - Blazer OH Console - Green/Pink bushings - Chromed Impala Wheels - Eibach Springs and Bilstein Shocks - Corvette Engine Dress - the list goes on and still more to do...it never ends.
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post #8 of 11 (permalink) Old 12-28-2015, 02:02 PM Thread Starter
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So are you all saying that the VATS would shut off BOTH the fuel and the starter, and not just the fuel?
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post #9 of 11 (permalink) Old 12-28-2015, 02:50 PM
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If the car runs when you manually supply power to the FP, then it is definitely not VATS. As I mentioned, VATS disables the fuel injectors - not the pump.

Here is some good reading on the VATS system
https://www.impalassforum.com/vBullet...d.php?t=227294
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post #10 of 11 (permalink) Old 12-29-2015, 09:30 AM Thread Starter
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Ok. It's nothing to do with VATS. It's grounding. I think. The wipers also don't work and now they do. Along with the fuel pump. And car starts fine. I did run the FP jumper directly to battery and car started up just fine. I took the wire off and still runs. Restarted too. Does the ground for both the FP relay and wipers go to the front of left cylinder head??
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