I accidently left my parking lights on and it ran my battery down. Car was running great prior to this but after recharging the battery it will not start - turns over fine but won't start. Checked everything and found the pump (whihc is brand new) isn;t pumping so I checked the voltage and I only have 5 Volts going to the pump - shouldn't this be 12V during cranking?

What would cause this? As I said, everything was runnign great until the battery drained. The battery is also brand new and is holding a good charge so it isn't a battery drain problem.

BTW, the car is a 1991 Convertible with automatic

Thanks

Bob

 

Sounds like your fuel pump resistor may be bad (i think they still have them on s5 check with a services manual to be sure) or fuel pump relay. I believe it is located behind the passenger side headlight near the airbox. Try jumping the coupler (near the passenger strut tower) and see if the pump works or if you get 12v then.

 

I tried jumping the coupler and that didn't help. I will check the relay next.

 

You should get approx 12vdc when you hold the key to Start. Let go, and the engine has started, the voltage drops to approx 9vdc. Five is a bit shy of 9vdc. Jumpering the fuel pump check connector will still give you only approx 9vdc UNTIL you drive the car and put it under a Load. When that happens the ECU removes a ground from a relay in the Fuel Pump Resistor Relay assy, and now the voltage will rise to generally what your alternator is putting out.

What you might try is to make sure the gnd for the meter your using is a good ground or not. As an example, the followiing happen to me today connecting my trailer to the car today.

I checked the output voltage from the car to the trailer and it was way low. Then I realized the gnd wire for the connection b/t the trailer and the car was not connected and the only gnd b/t the trailer and the car was the trailer hitch. Connected up my gnd wire b/t the trailer and the car and the voltage went to the 12vdc battery voltage I was looking for.

 

A little off topic but I just have to be sure.
I just put in a walbro 255 pump, and i just ran the stock wires to it for pwr and grnd. I know they need to have a constant 12v. And I noticed its very very quiet. I can't even tell its on.
How do I make sure it gets 12v all the time

 

Access the fuel pump connector behind the left rear strut tower and back probe the large Blue wire on the chassis side of the connector. Start the engine and look. Then if a series four turbo or a series five n/a or turbo, go for a ride and look at the meter when your under a load. Such as full throttle going up a hill. It should drop down to approx 9volts after you start the engine and under load go to 12 plus vdc.

Series four n/a are wired to a constant batt voltage all the time the engine is running.