what is the vacuum pump on my car and is it related to the fuel injector pump

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the dealership said at first they it was the vacuum pump didn't know what was wrong when engine light came on after testing sent info to Detroit they said they couldn't find anything wrong now the dealership thinks its the fuel pump engine light came on took it to shop they couldn't find anything wrong went off and stayed off for 5 months just came back on again I feel like I'm getting the run around wasting money please help me if you can Thank you