ok so i got my car dyno and tuned today. every since the tune when you turn the car on the walboro fuel pump is very loud for at least 10-20seconds then it quiets down but that has never happed before. After the tune it threw the P300 code (multiple/random misfire) but i do not feel anything at all.

 

Walbros area always loud like that. The misfire code could be a fake code, where the ecu is thinking the car is misfiring but it is really not. Is the car idling rough? Usually that is what triggers a P0300 multiple cylinder misfire. I highly doubt that it is an actual misfire, or the car would run like crap and really rich.

 

The fuel pump noise it just it catching up with the demand of the motor. The sound stops because the pump is full of fuel, nothing to worry about. As far as the P300 code your tuner should be able to change the settings to have that stop and if they already have then there might be a problem that they need to address. I would say have the tuner relook at it.

 

What are your mods on the car? Do you have bigger injectors? When scaling injectors, a tuner has to set the low and mid fuel trims within range or the car will run rough and ecu will think it is a misfire.

 

Big cams and a lumpy idle could cause a misfire code also. Fuel pump whine is normal