1999 C1500 GMC Suburban 5.7 fuel issue

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Schurkey

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START by chasing the Security light.

When you get that figured-out, if there's still a driveability issue, verify fuel pressure, then connect a scan tool, verify all the sensors, and computer outputs--EGR, spark advance, etc. Look at the condition of the plugs, plug wires, cap 'n' rotor, etc.
 

Supercharged111

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No I removed the hose from the valve cover, plugged and spray in the throttle body bonnet at that point of access. However the security light does not go out.

That's a 3/4" vacuum leak. Does the security light flash when it dies? I forget what it does when it's happy as it's long disabled on my trucks.
 

Mister1500

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There is still an open port where I removed the hose off of the throttle body bonnet. So I have tried pulling codes an I have no power to the ALDL. I find nothing in the owners manual in the fuse diagrams about power to the ALDL. Not sure if this may be part of the issue or not. Need more advice. Thanks again for all help!!
 

Supercharged111

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There is still an open port where I removed the hose off of the throttle body bonnet. So I have tried pulling codes an I have no power to the ALDL. I find nothing in the owners manual in the fuse diagrams about power to the ALDL. Not sure if this may be part of the issue or not. Need more advice. Thanks again for all help!!

That's a huge unmetered air leak and will cause the truck to run like crap.
 

Mister1500

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I only removed the hose to spray directly into the throttle. If I spray it runs. If not it dies after 2-5 with the hose connected. I have proven to myself that I still have spark if the external fuel source is used. I am trying to determine why it dies after 2-5 secs of running smooth. I have checked my fuse for the lighter circuit which seems to be power for ALDL. It is good. Not blown. Need siggestions
 

Mister1500

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I have an Autel. It does not power up when plugged in as it should. I have used it on my other GM’s in the family without issue
 

JOHNGAAA1

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You have a vats issue. Been there. The dead give away is that it runs with an external fuel source. I chased this problem before. Replace the vats module with a rebuilt unit or boneyard unit, or have a tuner disable it.
 
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