Low Fuel Pump Voltage
10-17-2007, 04:52 AM
#1
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Car: 1986 IROC Z
Engine: 305 TPI
Transmission: 700R4
Low Fuel Pump Voltage
Code:
------54 - Low voltage at fuel pump OR Low voltage at Fuel pump relay OR Output failure at quad driver module.
Where should I start when diagnosing? When I start the car for the 1st time of the day it wont start right away, it just keeps cranking. I dont hear the fuel pump turn on until after the 3rd crank. Then on the 4th it starts right up and is fine for the rest of the day. Once the next day comes, the problem begins again. It doesnt have to be early in the morning when its cold, it even has the problem if i were to start it at 2pm. Again, only when first starting the car for the day. Any help?
------54 - Low voltage at fuel pump OR Low voltage at Fuel pump relay OR Output failure at quad driver module.
Where should I start when diagnosing? When I start the car for the 1st time of the day it wont start right away, it just keeps cranking. I dont hear the fuel pump turn on until after the 3rd crank. Then on the 4th it starts right up and is fine for the rest of the day. Once the next day comes, the problem begins again. It doesnt have to be early in the morning when its cold, it even has the problem if i were to start it at 2pm. Again, only when first starting the car for the day. Any help?
10-17-2007, 06:13 AM
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Car: 88 IROC
Engine: 5.7 RamJet
Transmission: T56
Axle/Gears: Dana44 4.10
Re: Low Fuel Pump Voltage
Make sure the fuel pump relay is good. Also, the system should prime the pump for 2 seconds when the key is turned to the "ON" position, before cranking. See if it does that.
10-17-2007, 09:01 AM
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Car: 1986 IROC Z
Engine: 305 TPI
Transmission: 700R4
Re: Low Fuel Pump Voltage
No it doesnt turn on at all until the end of the 3rd crank. After that its fine for the whole day, fires right up everytime. Fuel pump probably has 1k miles on it but i should also mention the car sat for months at a time. Should I start off by replacing the fuel pump relay? (probably the cheapest, and go from there..)
10-17-2007, 09:46 AM
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Car: '91 Z28 convertible
Engine: TPI
Transmission: T5
Axle/Gears: 3.27 posi disc
Re: Low Fuel Pump Voltage
Yes, the fuel pump relay would be a good thing to start with. Also, check your fuse by the battery, it's the single fuse on the fender (looks like a black connector).
The code means that the ECM is trying to actuate the relay to turn on the fuel pump but it doesn't see any voltage from the relay going to the pump.
To explain your hard start in the morning and easy start during the day: we have a backup system to power the fuel pump. It's the oil pressure switch on top rear of your intake manifold. Once you're cranking long enough, the oil pressure builds up, the switch closes its contacts and feeds the fuel pump. That's why you have to crank for a long time in the morning. Then during the day, you have residual fuel pressure in the fuel rails so it starts real quick but overnight, the fuel bleeds off so the car won't fire up easily in the morning.
Let us know what you find.
Lou
The code means that the ECM is trying to actuate the relay to turn on the fuel pump but it doesn't see any voltage from the relay going to the pump.
To explain your hard start in the morning and easy start during the day: we have a backup system to power the fuel pump. It's the oil pressure switch on top rear of your intake manifold. Once you're cranking long enough, the oil pressure builds up, the switch closes its contacts and feeds the fuel pump. That's why you have to crank for a long time in the morning. Then during the day, you have residual fuel pressure in the fuel rails so it starts real quick but overnight, the fuel bleeds off so the car won't fire up easily in the morning.
Let us know what you find.
Lou
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