Fuel pump and pressure

Tiny
JMORRIS0001
  • MEMBER
  • 2005 VOLVO XC70
  • 5 CYL
  • 4WD
  • AUTOMATIC
  • 175,000 MILES
We have replaced the fuel pump, but the fuel pressure reading is confusing. Initial tests read 48 PSI, but when we start the car, it just drops to 0 and the car stalls. How is the fuel pressure building up and then completely disappearing once the car has been turned on? We have double checked the hoses as much as possible from the new fuel pump, but there appears to be a slight kink in one of the hoses due to the placement of the hose on the pump. We are at the point of replacing the fuel pump again, in hopes that it is just the kinked hose that is causing the problem.
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Tuesday, July 21st, 2020 AT 11:12 AM

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Tiny
STEVE W.
  • EXPERT
When you check the pressure with the engine off, does it jump right up to pressure fast or does it build up over say 5-10 seconds. A kink that could drop the pressure to zero should also make the pressure rise very slowly.
I suspect the problem is the fuel pump control module and not the pump. It's job is to speed up and slow down the pump to control the fuel pressure based on the signals from the engine control module. Testing it requires a good scan tool that can command the pump on and off as well as control the pressure output. Unfortunately there isn't really a way to test it without the scan tool. They used 2 different modules depending on the vehicles build date, the early ones had the module mounted to the fuel tank while the later ones moved it to the interior of the car in the spare tire well. The replacement units get mounted like the later units, with a new wiring harness required.

Removal of interior components

Ignition key in position 0.
Open the trunk lid/tailgate
Remove:
- the cargo compartment mat/floor hatches
- the rear seat cushion
Fold forward the backseat's backrest.
Remove the side cushion.
Remove the right part of the backrest
Remove the child seat bracket:
- Remove the bracket from the floor
- Place the insulation to one side

The new harness runs inside the car from the fuel pump module and back under the seat to the spare tire well. With the module being stuck in place with Velcro. I attached the parts list covered in the service bulletin on the module. This is the TSB about the module if it tests bad:
https://askatech.com/AskATechLive/forums/ResourceHandler.ashx?a=13208
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Tuesday, July 21st, 2020 AT 1:46 PM

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