GMC Troubleshooting Questions? Ask a Mechanic for Answers
this sounds like fuel pressure regulator may be faulty
as clamping the return line will increase the fuel pressure at the injector rail
and so if the engine then starts like this then there's a lack of pressure which can be down to a faulty pump, or faulty pressure regulator on the end of the injector rail or faulty power supply to the fuel pump
so I'd reccommend to replace the pressure regulator as the next step
do you still need help?
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