GMC Troubleshooting Questions? Ask a Mechanic for Answers
Hello, my name is***** definitely sounds like the relieve valve inside junction block is problem, nothing else would cause pressure going back into return line like that so you will need to replace the junction block. Here are replacement instructions, let me know if you have more questions. Thanks
Injector could not cause fuel to go back into return line at a high rate. Injector would also usually set specific injector codes. Let me know if you have more questions, thanks.