FUEL PRESSURE ISSUES

  • Tiny
  • jared455
  • 2000 Volvo S40
  • 103,000 miles

Two days ago on my way home my car stated losing power. The rpms would drop every time I would press on the gas pedal. I was able to limp it home by barely giving it any gas. Since then I have cleaned the throttle body, the IAC, the TPS, checked the FPR and replaced the fuel pump and fuel filter. Also checked the fuel pressure and it is at around 12 psi at the fuel rail and also right before the fuel filter coming right off the sending unit which seems rather low. Also took out and cleaned the spark plugs which were pretty black. After all that work the car will start but whenever I give it gas the rpms drop and it will not run steady at all. I pulled off the hose coming off the intercooler going into the throttle body and sprayed starting fluid into the intake and it wakes the motor right up. Also checked the plugs after just a few minutes of running the car and they have quite a bit of carbon build up on them after running it only a short amount of time. It seems like there is a fuel delivery problem but what else could be the cause?

Saturday, September 3rd, 2011 AT 4:56 AM

11 Answers

  • Tiny
  • Jacobandnickolas
  • Expert
  • 68,410 posts

The fuel pressure should be 43psi when the engine is stationary. IT should be between 54 and 57 when the vehicle is being driven. I would say the low pressure is causing the problem. As far as the issue, it could be a weak fuel pump or a bad fuel pressure regulator.

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Saturday, September 3rd, 2011 AT 5:06 AM
  • Tiny
  • jared455
  • Member

That's exactly what I thought. I've checked the FPR and there is no leaking gas coming out of the vacuum line and we replaced the fuel pump with a brand new one so I have no idea what else it could be. The fuel pressure is low at both the fuel pump and the fuel rail so what could possibly cause that?

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Saturday, September 3rd, 2011 AT 4:06 PM
  • Tiny
  • Wrenchtech
  • Expert
  • 19,822 posts

Are you sure about that spec?
Here is what Alldata says.
Fuel Pressure, Engine Running
The pressure should rise to approximately 309 kPa (45 psi) immediately after the engine starts.

Fuel Pressure, Residual
The fuel pressure must not be lower than 200 kPa for 20 minutes after the engine is shut off.

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Saturday, September 3rd, 2011 AT 4:32 PM
  • Tiny
  • jared455
  • Member

With the new fuel pump it is still at 12 psi at the valve right before the fuel filter. It seems like the ecu might not be telling the fuel pump to send enough fuel to the motor. How is this possible and what will fix it?

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Saturday, September 3rd, 2011 AT 9:32 PM
  • Tiny
  • Jacobandnickolas
  • Expert
  • 68,410 posts

The pressure I provided is from mitchel. It should be correct.

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Saturday, September 3rd, 2011 AT 11:57 PM
  • Tiny
  • jared455
  • Member

I understand that the pressure needs to be a lot closer to 40 psi than 10psi. If my pump is working and the FPR is not bad anf teh filter is new then what could be causing such a low pressure reading right off of the fuel pump? Does the 2000 s40 even have a pump relay and if so would a faulty relay cause a problem with the fuel pressure like this?

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Sunday, September 4th, 2011 AT 1:51 AM
  • Tiny
  • Jacobandnickolas
  • Expert
  • 68,410 posts

It may not be getting enough power. Check to make sure there is 12 volts to the pump. And yes, it has a relay.

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Sunday, September 4th, 2011 AT 1:52 AM
  • Tiny
  • jared455
  • Member

There is a fuel pump fuse under the hood but I do not see an actual relay anywhere. Do you have any clue as to its whereabouts?

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Sunday, September 4th, 2011 AT 2:03 AM
  • Tiny
  • Jacobandnickolas
  • Expert
  • 68,410 posts

It's been awhile, but there should be a relay block under the hood. (I can't remember the 2000. I guess I'm getting old, but I think it was on the pass side inner fender.

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Sunday, September 4th, 2011 AT 2:06 AM
  • Tiny
  • jared455
  • Member

So after days of research and trying different things to fix the issue I narrowed it down to the fuel pressure regulator in the actual sending unit. What happened was the FPR metal housing had broke loose from the plastic housing on the return line. The fuel was bypassing the FPR and it caused the pressure to drop dramatically. In testing the part it completely broke away from the FPR housing and obviously needed to be replaced. After finding a used sending unit on ebay I replaced the part and the car started up and ran even better than before since it now had a new fuel filter, clean throttle body, IAC, and TPS. I hope this will help someone that might have the same problem as I did.

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Sunday, September 11th, 2011 AT 3:38 AM

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