New fuel pump, no fuel pressure?

Tiny
WELDERWILL
  • MEMBER
  • 2005 VOLVO V50
  • 2.4L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 250,000 MILES
The car had a new fuel pump installed but gets no pressure at the Schrader valve on the rail. I jumpered the pump to a drill battery and ran it for a few seconds and got high pressure at the rail. When ignition on the fuel pump connector gets12 volts momentarily then drops to 7 when cranking. After this there is not a drop of pressure at the rail. The battery in the car is very drained. (1.5V) so I ran my jumper cables directly to the battery terminals with them disconnected to circumvent the dead cells. I know this adds some resistance, but the plug still reads 7 volts, I would think it would be slightly higher if there were no other issue. The tachometer needle moves slightly when cranking but doesn’t necessarily read an RPM per se. I need to hook up my better scanner to check rpm when cranking. Any other suggestions for diagnosing the issue? I haven’t been able to find adequate wiring diagrams for the car but that would be quite useful.
Tuesday, September 5th, 2023 AT 4:08 PM

3 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,144 POSTS
I would replace the battery first, a battery that drained can remove operational voltage from the system which can cause the problem you are describing. Here is a generic guide to help you step by step with instructions in the diagrams below to show you how on your car:

https://www.2carpros.com/articles/how-to-replace-a-car-battery

Check out the images (below). Please let us know how it goes. I can get you any wiring diagrams needed which ones do you want?
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Wednesday, September 6th, 2023 AT 10:40 AM
Tiny
WELDERWILL
  • MEMBER
  • 3 POSTS
As stated in the OP, I circumvented the battery with the dead cells and tested to make sure I was getting operational voltage to the circuit. Obviously, a new battery would be ideal but I’m 99% sure that isn’t the problem. Test results on fuel pump electrical system came back the same as when the battery was and wasn’t circumvented. If you have any other suggestions, I’d love to hear them. I will replace the battery eventually, but I’m focused on diagnosing the actual issue with the fuel system. This was a friend's car that I am flipping, not a daily so I’d rather wait to put a battery in it so it doesn’t sit and drain. Don’t want to fool with putting it on a tender.
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Saturday, September 9th, 2023 AT 5:01 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,144 POSTS
Battery voltage is important, and a battery will dead cells will low the voltage for the systems to operate.

"gets 12 volts momentarily then drops to 7 when cranking"

This is not good and will cause the fuel pump not to work.
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Monday, September 11th, 2023 AT 11:17 AM

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