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Starts but will not stay running

Tiny
JOHNORPEN
  • MEMBER
  • 1994 BUICK ROADMASTER
  • 5.7L
  • V8
  • 2WD
  • AUTOMATIC
  • 200,000 MILES
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.
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Thursday, June 25th, 2020 AT 4:24 AM

5 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good morning,

Do you have the key with the resistor in it?

Does the security system still work with the ECM?

Roy
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Thursday, June 25th, 2020 AT 4:28 AM
Tiny
JOHNORPEN
  • MEMBER
  • 5 POSTS
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.
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Thursday, June 25th, 2020 AT 4:41 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
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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Thursday, June 25th, 2020 AT 4:57 AM
Tiny
JOHNORPEN
  • MEMBER
  • 5 POSTS
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.
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Thursday, June 25th, 2020 AT 5:29 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
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
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Thursday, June 25th, 2020 AT 5:40 AM

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