# fuel pump relay



## phbsoler (Dec 24, 2011)

question for all. will a bad relay effect the both pumps or just the main? will a bad relay cause the main pump to get louder or not? im getting good pressure and im getting fuel from trnafer pump to main pump.and its getting up front. its an intermittent problem that i cant figure out? help please


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## WaterWheels (Aug 14, 2005)

Yes, both pumps receive their power from the one relay. No not really to if the relay could cause the pump to become louder. Not really because I guess if the relay were to be causing the power to fluctuate it could cause the pump to make some noise, but that seems like a slim chance. Loud is most times due to being bad or starving for fuel. Have you tested the pressure?


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## onephatcabby (Dec 19, 2011)

If you have the typical VW/Bosch 321906059 fuel pump relay you can simply substitute it with your horn relay temporarily to test functionality of both your pumps and to rule out your fuel pump relay as being the culprit. Using your horn relay excludes the use of the tach signal that normally goes to pin 31b on the fuel pump relay. Also you won't have the 3 second priming of the transfer pump when you first turn the key, the pumps will continue to run. A quick test would be drive with your horn relay in place of your fuel pump relay and see if your intermittent problem arises... this will rule out the costly (but repairable) fuel pump relay. My suspicion would be a pump is on it's way out. If your problem pops up with the horn relay, you know it's most likely a pump... _however _ if it doesn't occur while using the horn relay, it still doesn't mean your fuel pump relay is bad, you could have a noisy or intermittent tach signal to pin 31b on the relay caused by a poor ground or corroded connection on the terminals of the coil. :banghead:

*NOTE: * Never permanently substitute a fuel pump relay with a horn relay... the fuel pump relay needs the tach pulses on pin 31b to keep the contacts closed as a safety precaution to automatically turn off the fuel pumps in the event of a crash, regardless of the ignition switch position... by using a horn relay you are bypassing this safety feature. A horn relay will get you home, or off of the road in a pinch though. :thumbup:


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## phbsoler (Dec 24, 2011)

well i have replace the transfer pump already,but it has been cold here for the last 3 days and no issues. now my next question is that someone said that there could be a bad ground inside the sending unit which could cause my transfer pump to shut off?
now on the relay is supposed to be a 5 pin or a 4 pin relay? also are you supposed to hear the tranfer pump come on when you turn the key bc right now i hear nothing? could i have the wrong replay in the car??????


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