LS2, starts and shuts off immediately

[simonhc]

Having problem with a recently purchased vehicle (80' Camaro).

Setup:
LS2 w. Magnuson compressor
GM ECM E40

The car started, drove and was working perfectly fine. Did some suspensions adjustments on it, and read (only read) the tune using HP Tuners MPVI3.
Now the car starts up perfectly fine, but shuts off after 1second (very consistently).

- It has no issues starting
- It doesn't build fuel pressure until you crank it, and it looses fuel pressure AFTER it shuts off, but fuel pressure is steady around 50 psi while its running. So although its a bit odd, I don't think this is the issue.
Also tried bypassing the fuel pump relay, to build pressure before cranking - Made no difference
- It doesn't struggle to stay running, it shuts off as if the key is turned.
- Used a test light on a spark plug wire, it doesn't cut ignition, it keeps flashing until the engine is completely stopped
- Tried cutting power to it for 10 mins, tried charging it overnight - Nothing makes any difference.
- I have tried many times to read data using VCM scanner, but it looses signal as soon as you turn the key
- With ignition on, engine off I get reasonable values from sensors, such as: Intake air temp, coolant temp, MAP (102 kpa).
- We tried attaching a second battery to it, with thick jumper cables, just to ensure its wasn't due to voltage drop, made no difference.

I can't record any meaningful live data, but I've attached the tune.
But again, the car drove here, and has not had any issues in the past week or so.

I am at a loss...

Open to suggestions

[simonhc]

As you can see in the tune, VATS is disabled. And as I said I only read the tune, never changed anything.

[horsepowerguru427]

any DTCs?

[simonhc]

No DTCs, I've checked multiple times.

[Alvin]

See if this doesn't help.


Original Tune 06032023.2.hpt

[simonhc]

Alvin, I see you made some changes to the MAF settings.

The car has no MAF sensor, and the MAF frequency fail high is set to 0Hz.
So MAF settings should not make any difference, right?

[Alvin]

Just try it. Some of the E40's... GTO's especially take a second to get into SD. For some it turns into a no start situation.. especially after reflash/battery disconnect. etc

[simonhc]

Alvin - thanks a bunch!
I wrote the tune you shared, and it fired right up and idles!

[streetking408ys]

Just for the record, my 2005 Corvette (E40) is SD and after battery disconnect/reconnect or code clearing or reflash it always starts up but immediately dies. Then you never have the issue again until again messing with what was listed at the beginning of this reply. I believe the PCM has to fail the MAF. After the 1st time it's fine.

[Alvin]

Just for the record, my 2005 Corvette (E40) is SD and after battery disconnect/reconnect or code clearing or reflash it always starts up but immediately dies. Then you never have the issue again until again messing with what was listed at the beginning of this reply. I believe the PCM has to fail the MAF. After the 1st time it's fine.

For some reason early E40's can be a pain about this.