850 850 will not rev

A friend of mine has a 1997 850 10 valve, it was running perfectly then it started cutting out and losing power, to the point where it would not go up a hill. Idled fine, but when touching the throttle it starts jerking and running really rough. If you gently open the throttle by 1/8, the revs go up, try to open more and it just starts misfiring badly and won't run at all above idle. The idle is super smooth however so very strange

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  • edited December 3

    I had a Subaru in the other day with a blocked cat convertor that wouldn't rev. You can feel there's not enough exhaust flow at the tailpipe.

    Also worth checking what the fuel pressure is doing at the valve on the fuel rail if you have the appropriate guage

    I also once had a Volvo towed to my work from a workshop in Cooma that wouldn't rev after a service....there was a rag in the air filter.

    ALVO360
  • Far out, I took the car for a drive and the damn thing is working perfectly!

    Talk about intermittent!

  • Fuel pump relay?

  • edited December 3

    Possibly

    How can I test it? Is it the same operation as in redblock cars? Trouble is if it's fine when cold but plays up when hot (it was very hot when it started bogging) I won't know

    I can hear the pump priming with each attempt

  • Fuel pump relay will get hot and play. If it's original it will have a date on it.

    https://youtu.be/gLoO-D4yOcU

  • fuel pump relay will work or not working so don't go down that path,

  • When this happens, the engine will sometimes not start, and when it does it runs at what seems like 100rpm and it cuts out, try again it will idle, go to accelerate, starts hesitating pretty badly. Put it in neutral, bring the revs up slowly, no problem. Open the throttle more than that, starts misfiring badly, seems to be misfiring on two or even three pistons, plugs and leads are recent, checked them and all ok. The next day, the car will drive like it was new, no dramas at all

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