GMC Troubleshooting Questions? Ask a Mechanic for Answers
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Usually if it was a loss of fuel pressure it would start harder when cold and better when warm but still possibly a fuel issue.This may be an issue with the fuel pressure regulator leaking fuel into the vacuum hose that connects to it.On your fuel injector rail you will see the fuel pressure regulator and it has a vacuum hose attached to it.When warm remove this hose and see if fuel runs out.If it does then the fuel pressure regulator needs replaced.You may need to observe the regulator for several minutes to see if any fuel leaks out.
If this is o.k. this may be an issue with the check valve in the fuel pump itself with the check valve being faulty not holding fuel pressure.Install a fuel pressure test gauge onto the fuel rail test port and turn on the key,the pressure should rise and hold.If it starts to drop slowly or rapidly right away this can indicate the fuel pump needs replaced due to a weak check valve not maintaining pressure.
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