starts but will not stay running

1994 BUICK ROADMASTER
200,000 MILES • 5.7L • V8 • 2WD • AUTOMATIC
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JOHNORPEN
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This engine and transmission has been installed in a 1951 Chevrolet. I had it running well last time I started it about a week ago. Now it starts as it should but shuts off within a few seconds. The fuel pressure is good. It doesn't run long enough to get any real info from my test equipment and hasn't set any codes. I used the stock engine and transmission but removed all the emissions systems. I have a tuner that allowed me to turn off VATS, EGR, and other non-essential items. The car ran very good last week.
Jun 25, 2020 at 4:24 AM
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ASEMASTER6371
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Good morning,

Do you have the key with the resistor in it?

Does the security system still work with the ECM?

Roy
Jun 25, 2020 at 4:28 AM
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JOHNORPEN
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The security system is disabled in the computer. As I stated, it ran good last week and I haven't changed anything on the engine, computer, or wiring.
Jun 25, 2020 at 4:41 AM
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ASEMASTER6371
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Okay, does it start right back up or do you have to let it sit for a while?

If it starts right back up, it could be electrical. The module could be the issue.

If it does not, it could be fuel related. The LT1 motor runs around 41-47 pounds. Do you have this?

I would also check the distributor. Common for the cap and rotor to get wet and cause this type of issue.

Roy
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Jun 25, 2020 at 4:57 AM
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JOHNORPEN
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It is a project vehicle and has never been out of the shop so I know it isn't moisture related. Fuel pressure is 48 psi with the vacuum line disconnected. It starts every time I try it and then shuts off, no waiting required.
Jun 25, 2020 at 5:29 AM
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ASEMASTER6371
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This does sound like you are losing spark.

Can you test the power to the distributor with the key on? I am wondering if you have power in the start position and not in the run position.

Do you have a scope that can monitor the signal from the distributor to the ECM?



Roy
Jun 25, 2020 at 5:40 AM