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Diagnosing fuel delivery failure 700 1990

posted by  Fixquest on  Thu Jul 5 14:29 CST 2018
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last visit: Tue Jan 15 21:28 CST 2013
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1990 Volvo 740 GL wagon. 169,000 miles. Car was running smoothly with no loss of power. I put in gasoline at the usual gas station. Drove less than two miles home. The following morning, the engine turned over but died. Repeated the effort at intervals. Nothing. Car towed. The car is never run on low fuel. I have owned the car for 8 years. Sole driver.

To me, when the engine turned over, there was a sound akin to a vacuum - air sound.

Mechanic said that fuses were checked, and that fuel pressure was checked, and said that the in-tank fuel pump should be replaced. This was done. No other part was replaced. The fuel gauge ceased to function.

Four days later, driving a short distance, the engine stuttered, but kept running.

Obviously? I think the in-tank pump was fine; that the fuel filter should have been replaced first, and definitely along with the in-tank fuel pump; and the screen. If I could have the old fuel pump checked to see if it had failed, I would.

Other than the "find a mechanic you can trust," reply -

Question: How would you have proceeded with the diagnostics and repair.

Thank you.







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    Diagnosing fuel delivery failure 700 1990

    posted by  rstarkie on  Fri Jul 6 06:39 CST 2018
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    last visit: Fri Oct 24 10:14 CST 2014
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    I second Chris's advice of thinking about the fuel injection relay.

    Additionally I would ask how old is the radio suppression relay and the crank position sensor?

    Both the fuel injection relay and the radio suppression relay are easy enough to reflow the solder connections on the circuit board. I carry one of each in the glove box for back up.

    If the crank position sensor shows any signs of cracking or fraying along its length I would replace it as a precaution.

    Randy








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      Diagnosing fuel delivery failure 700 1990

      posted by  Fixquest on  Fri Jul 6 10:07 CST 2018
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      last visit: Tue Jan 15 21:28 CST 2013
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      Thank you. Your input is valued. The bottom line for today is that I'm going to have the fuel filter replaced, given that the fuel pump was replaced, and anything else will have to wait. If I could do these checks myself, or had a mechanic that could devote time to it, and I had the money...Thank you. I will be mentioning the relays, etc., to the mechanic today.








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    Diagnosing fuel delivery failure 700 1990

    posted by  Chris Mullet on  Thu Jul 5 14:52 CST 2018
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    "...Mechanic said that fuses were checked, and that fuel pressure was checked..."

    So I'm going to assume that when he checked the pressure that it read zero PSI?

    I would have first listened carefully when I turned the ignition on to see if I could hear the pump run for a couple seconds. If I didn't hear it run I would have connected a volt meter to the pink pump power wire at the disconnect located somewhere between the back seat and the tank. If it DIDN'T show 12V for a couple seconds when I turned the key on, then I would know the problem is somewhere forward of the disconnect, maybe a blown fuse, faulty relay, bad relay board, etc. If it DID show voltage, then I would know the problem lied somewhere between the disconnect and the pump, possibly the pump itself, however I would also be looking for corroded/broken wiring where it enters the sender. Or a bad ground.

    "...The fuel gauge ceased to function..."

    At this point I'm really starting to question the condition of the wiring in the vicinity of the sender unit.

    Side note: 160,000-ish miles seems to be about the life expectancy of the original pumps in these cars. (In my 1990 740 it died at around 155,000.)

    --
    Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (getting ever closer to road worthiness)








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      Diagnosing fuel delivery failure 700 1990

      posted by  Fixquest on  Thu Jul 5 15:21 CST 2018
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      last visit: Tue Jan 15 21:28 CST 2013
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      Thank you for your response. This is the last car I will ever own, and I want to be sure that I do not misrepresent any problems to a mechanic. Good to know you owned the 1990 740, and the history of that vehicle's pump failure.

      I should have written that I have the hypothesis that the gasoline was contaminated. I know this is considered rare. This was too sudden, and without any symptoms. I think, now, that contaminant clogged the filter. In any case, I want to trust what was done at the garage.

      Thank you, again.







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