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I've been dealing with a car that starts and then suddenly dies. I replaced the MAF (Mass Air Flow) sensor with a new one, and now it stays on until I press the gas pedal. The throttle body is clean.

Before the car acted up, the spark plugs had a nice white/normal look at the tip, now they're fouled. Car lets out a little black smoke, and I do recall the car seeming to have unsteady throttle response from one day to the next.

My problem is I'm broke, and my motorcycle needs repairs also, and I'm in a pretty bad spot, so I need to make every dollar count. Another concern is that it could be the throttle body, but more signs point towards the FPR (Fuel Pressure Regulator). I'm just wondering if anyone has knowledge enough to know that the FPR is the problem

Car is a convertible 1999 Volvo c70 2.3 t5

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  • how's fuel pressure?
    – Ben
    Commented Jul 6, 2016 at 18:25
  • Good question I don't have a fuel pressure gauge but during my tests the fuel sprays about 2 feet away from the injectors, and I had the same results before and after the filter
    – Spenser Hicks
    Commented Jul 6, 2016 at 18:55
  • I'd say it's a Fuel Pressure Regulator. If all the spark plugs are fouled and throttle body clean (automatic choke included), then it can be only the regulator that gives way too much fuel.
    – Arturs Bolsunovskis
    Commented Jul 6, 2016 at 21:24
  • Pull vacuum with a handheld vacuum pump and see if it can hold vacuum before replacing it assuming it's a vacuum FPR.
    – Ben
    Commented Jul 6, 2016 at 23:07
  • I think it is, there's three openings, what would that tell me?
    – Spenser Hicks
    Commented Jul 7, 2016 at 0:08

1 Answer 1

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Nice engine you got there! While your issues do sound like a MAF problem (check the MAF readings via OBD!), some turbocharged Volvos are notorious for fuel pressure regulator issues. Basically the regulator diaphragm ruptures and fuel gets into the pressure regulation vacuum hose. Typically this causes poor starting (especially cold) because of an excessively rich mixture. Black smoke out of the exhaust you noticed supports this as well.

Here is a simple way to make sure that your fuel pressure regulator on your T5 is toast: after the engine has been running for a while, remove the fuel pressure regulator vacuum hose and look if it's leaking fuel from the regulator side with the engine running. The hose is on there tight with the vacuum present, you might need to turn off the engine, remove the hose, plug the engine side to prevent a vacuum leak and start it back up again. If you see fuel dripping/spitting - the regulator diaphragm is ruptured and you need a new regulator. Don't make quick conclusions if you see nothing, sometimes it takes a while for the fuel to show up. If you noticed a strong fuel smell from the hose - that is an immediate bad sign.

Vacuum port

If you are somehow unable to carry out this simple test you could also connect a pressure gauge to the schrader valve on the fuel rail and check if the pressure maintained by the fuel pressure regulator is correct. Value should be stamped on the FPR itself or can be found online (probably around 3 bar). This value should only be true when you prime the system without starting (ignition on) or with the FPR vacuum hose disconnected, otherwise pressure will be altered by vacuum/boost. If the pressure is completely wrong, your FPR is probably dead. Unless your pump is in a horrible condition, but I'd say it's much less likely.

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    Damn that's one of the best responses I've received in a long time thank you, ita good to hear they're notorious for that considering the part is under $100.
    – Spenser Hicks
    Commented Jul 7, 2016 at 14:18
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    @SpenserHicks do make sure it's the regulator before saying goodbye to that 100$. If the regulator does not vomit fuel and keeps pressure then there is no reason to mistrust it.
    – I have no idea what I'm doing
    Commented Jul 7, 2016 at 14:40
  • Oh, and do let us know how it goes!
    – I have no idea what I'm doing
    Commented Jul 7, 2016 at 14:45
  • Alright I'll let you know and would 5 mins be enough time for the car to be on
    – Spenser Hicks
    Commented Jul 7, 2016 at 14:52
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    @SpenserHicks correct.
    – Ben
    Commented Jul 7, 2016 at 20:13

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