LB7: VATS problem / edge case

[DAVe3283]

So I have found a very specific edge case that causes my truck not to start. I am trying to determine if my RoadRunner ECU is the cause, and rather than swap the RR for the stock ECU, I figured I would rev up the 'ol keyboard and see if anyone wants to try an experiment for me!

Requirements: 2003+ LB7 (though I'd be interested if the LLY does it too).

1. Truck fully warmed up. Park somewhere safe in case it won't start afterwards (like your driveway).
2. Put truck in neutral, not park.
3. Put your foot on the brake, and leave it there.
4. Turn the ignition back one setting to "ACC", not to OFF.
5. Wait between 13 and 15 seconds. Use a watch/timer.
6. Turn the key straight past "ON" to "START", and let it start. (This is why it needs to be warm, so you don't need glow plugs).

The truck should start, and ideally stay running. In my case, it starts then immediately dies, and the security light blinks for 3-5 seconds. It will crank, but not start, while the light is blinking. After the light stops blinking, the truck will start (even if you have been cranking the whole time).

If anyone wants to try this and report back, I'd appreciate it. I am curious if it is just my truck, or something they all do, and I just stumbled upon a strange edge case that "normal" people don't run into :roflmao:

It appears to be really specific. If I turn the key all the way to "OFF", it won't die. Put it in park and let off the brake? Won't die.

 

[hacklerjason]

This actually sounds like the passlock2 ignition needs to be replaced

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[NC-smokinlmm]

My lb7 did this every once in awhile. The first time it did it I was like holy shit I hope its not the injectors again...

 

[hacklerjason]

If you wished to go this far, I have a circuit design that bypasses gm passlock2... You will need two 5 wire relays, a resistor, and some rewiring of the ignition...

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[DAVe3283]

I could always turn off VATS in the tune if I wanted. I was more curious if this happened on other trucks, or if mine was being a special snowflake.

It sounds like it has happened to other people. And since I have to rip most of the interior out this fall to replace a heater core, I might throw a new column in while I am at it. I have access to one for cheap/free.

I'll also be back to the stock ECU soon, so I will see if it does it on the stock ECU or not. Thanks for the input guys.

 

[hacklerjason]

I could always turn off VATS in the tune if I wanted. I was more curious if this happened on other trucks, or if mine was being a special snowflake.

It sounds like it has happened to other people. And since I have to rip most of the interior out this fall to replace a heater core, I might throw a new column in while I am at it. I have access to one for cheap/free.

I'll also be back to the stock ECU soon, so I will see if it does it on the stock ECU or not. Thanks for the input guys.

Yes you could disable vats in efi or hpt...

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