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96 960 surging problem S90-V90

posted by  RB on  Tue Jan 6 04:32 CST 2009
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last visit: Mon Jan 26 02:20 CST 2009
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My trusty 96 965 has been so reliable I don't think I've posted with a problem here for maybe two years, but a recent issue has me looking for help.

The car has 197,000 miles on it, and has been without doubt the most reliable car I've ever owned. I give it regular maintenance and treat it kindly, and it rewards me with mile after pleasant mile of excellent transportation.

Recently, however, it's been developing a surge. I say developing because it's been slow in coming. I thought I started to notice this as long as a year ago, but I couldn't peg it exactly and it wasn't regular. Recently, however, it's become pretty obvious. Mostly it's a hard throttle issue, where you feel the engine, well, surge. It picks up, flattens, picks up, flattens, does this a few times and then levels out. It's not dramatic, and you can drive around it easily with light acceleration. But it's definitely getting worse. Possibly related, for the last six months it has developed an unpredictable symptom of a hard restart when warm. You'll drive somewhere, park, come back a few minutes later, turn the key and the engine fires, stumbles and stalls. Restart and it fires right up and the condition is gone. It might happen again the same day, or not at all for a few weeks.

I keep thinking throttle position sensor (or maybe just a dirty throttle body, I haven't had time to look), but there are no codes. Any thoughts?

Thanks in advance,
Richard in Kansas








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    96 960 surging problem - now need fuel pump S90-V90

    posted by  RB on  Fri Jan 16 05:26 CST 2009
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    last visit: Mon Jan 26 02:20 CST 2009
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    Turns out my fuel pump is failing. Any suggestions on best source? I find there are options for using what are basically universal high-pressure pumps. Looks like you have to retrofit the fuel line connection and the electrical connection. They are substantially cheaper than either the original complete unit or the Bosch replacement, but maybe there's a reason for that? I have no desire to be penny wise and pound foolish, but I also have no desire to spend more money than i actually have to. Any suggestions much appreciated.

    Richard in Kansas








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    96 960 surging problem S90-V90

    posted by  volvito on  Tue Jan 6 04:45 CST 2009
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    last visit: Sun Mar 23 04:59 CST 2014
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    Could be an air leak arround the intake gasket. Gets worse when the car is warmed up. If you think this may be the case you can test it with a propane bottle with a torch end. With the engine running, point the torch end arround each injector and leave it there for at leas 10 seconds, move to the next. If you feel the idle changes to better, then there is a crack in the gasket. Common thing around the 200,000 mile marker.








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      96 960 surging problem S90-V90

      posted by  RB on  Tue Jan 6 05:45 CST 2009
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      last visit: Mon Jan 26 02:20 CST 2009
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      That's a great suggestion. I'd forgotten about intake gaskets. The original gasket was replaced around 80,000, if memory serves, and after that I put it out of my head, thinking that was a problem unique to the original gaskets they used.

      Richard in Kansas








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        96 960 surging problem S90-V90

        posted by  poolman on  Wed Jan 7 08:18 CST 2009
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        last visit: Sun Dec 26 02:03 CST 2010
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        You have a vacuum leak for sure--just where it is --is the problem.
        If the intake gasket was replaced--it probably was replaced with the updated green gasket--they seem to last forever---I would take the time to remove the throttle body--replace the gasket there--replace all of your vacuum hose's
        don't just inspect them--junk the old ones and get new. The vacuum tree that is locted on the intake where all the vac lines run too--there's a 10mm bolt holding that onto the intake--remove the bolt and remove the vacuum tree--there is an 0 ring there--you can replace it or do what I did--use sensor safe gasket sealer on it and plug it back in--then wait till the next AM before starting her up again-next is the air box--there's a temp stat there that controls cold and hot air coming into the engine--fix that stat to where there is just cold air coming in--do away with that ,it's nothing but a problem-you do those things and I belive you'll have her back in shape








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          96 960 surging problem - solved S90-V90

          posted by  RB on  Mon Jan 26 02:28 CST 2009
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          last visit: Mon Jan 26 02:20 CST 2009
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          Update on the surging: It was, in fact, caused by a bad fuel pump. Near as I can tell, the pump was bleeding pressure internally. I got to this conclusion after checking fuel pressure and finding that with the car in gear and the engine loaded up, the surging would duplicate and fuel pressure would rise and fall in time with the surge. Fuel pressure was 35-45 and dropped to as low as 25psi. Then, with the system dead-headed (return to tank blocked off), when you would expect the fuel pump to crank to its highest rating it rose instead in steps, first to something like 50, then 60, 70 and finally 80. Curiously, after that, the surging disappeared, and when dead-headed the pressure would rise almost instantly to a full 80psi., leaving me with nothing else to conclude but that the fuel pump's internal pressure relief valve was malfunctioning. So, I replaced the fuel pump this weekend (what a PITA), and we'll see what happens. The surge is most certainly gone. Thanks for all the feedback.

          Richard in Kansas
          --
          86 740T/87 745GLE/96 960 Wagon







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