850 Backfiring under hard acceleration [solved]

nut3yNutmeg @nut3y Sunshine Coast, Queensland
edited April 21 in Troubleshooting

Car hesitates badly and backfires like crazy under hard acceleration. Cant go past ~6psi at moderate throttle either, does the same thing.

Starts and idles fine.

Only happened after I replaced the fuel pressure regulator and fuel pump. Fuel pump is GMB branded and the FPR is SKP branded. Probably should have spent the extra money. So would it be the fuel pump or the FPR that's not up to the task?


  • Do you still have the original parts?

    something isn’t right

  • nut3yNutmeg @nut3y Sunshine Coast, Queensland

    I do have the original parts but they were having issues of their own.

  • I don’t know about 850’s but is it possible the turbo and non turbo FPR’s are different?

  • nut3yNutmeg @nut3y Sunshine Coast, Queensland

    Possibly. The FPR is supposedly for my car but I can't find the rated pressure anywhere.

  • nut3yNutmeg @nut3y Sunshine Coast, Queensland

    The FPR seems to be a fairly generic part that's shared among quite a few volvos. I'm a bit concerned about this however

    "Maximum Flow Rating 100" (I'm assuming liters/hr)

    Looking at the flow rating on a delphi pump it's 32 Gallons per hour or 145 liters.

    Seems a little anemic, although wouldn't be expecting it to run out fuel at 8psi with orange injectors.

  • nut3yNutmeg @nut3y Sunshine Coast, Queensland

    The fuel pump didn't fit properly and so the pressure from the pump would push the hose off the nipple at the top. The engine was only getting small spurts of fuel, surprised it ran as well as it did in that state. The supplied sleeve wasn't gripping so the pump would just slide out the bottom under pressure so I put some hose clamps on and it seems to have stopped the issue.

    The initial issues I had with leaning out under boost and a wall at 3000RPM are fixed. That was (I'd assume) due to a bad fuel pressure regulator. No signs of leakage or anything but it just didn't work. Also explains why my injector duty cycle was so high at moderate boost. The ecu was trying to compensate for a lack of fuel pressure. Car is much more lively now and doesn't take full throttle to get anywhere. I'm still concerned about the lower fuel flow rate on this pump however.

  • That was off the first part number

    I wonder if the seller got the info mixed and it's 100psi at 44gph.

    Even 100lph would just make the 250hp at the engine. Just be maxed out...

  • nut3yNutmeg @nut3y Sunshine Coast, Queensland

    Possibly but it seems fine atm. It's fixed the knocking throughout the rev range it was having earlier but the dreaded 3000 rpm flat spot/knocking is back. Don't know what i'll do to fix it, just live with it i guess.

  • I have a Deatswerks DW 255 lph installed my 97 V70 was very easy to install on very slight mod to the sender unit the with of the dw200 is about 1mm wider than the stock pump so some sand paper fixed the plastic fuel pump holder. Has been in there for a year or more no issues and at least there is some head room for flow if needed

    I would always buy from aust dealers no ebay as to many fake units around👍

  • nut3yNutmeg @nut3y Sunshine Coast, Queensland

    Yeah ebay is very hit and miss with fakes. I'll just rock with the pump I've got for now until it dies or I feel like stepping things up a bit. I'd probably need a bigger turbo and injectors before a bigger pump anyways unless this one really is only 100lph in which case I'll find out soon.

  • Was it a physical or electronic mod required? Interested to hear

  • The only physical mod to fit the DW200 was to slightly enlarge the plastic fuel pump holder in the sender unit as the DW200 is slightly larger in Diameter not much tho than the stock pump. I think I used small flapper wheel on a drill from memory its just a snug fit between the plastic and the metal outer case of the fuel pump so the pump doesn't move in the sender unit.. I can't remember if I soldered the wires for DW or if the stock pump had the same connection either way it would be easy to do just don't do it near an open fuel tank lol

    I would of been 2 hrs max to remove out of tank fit pump and refit it wasn't hard I only replaced the pump for age of vehicle so I just fitted a slightly bigger pump while I was there

    Should of taken photo but I forget. I think @rado fitted one recently so he might be able to paint a clearer pitcure of how he did it

  • radoSteve'o @rado Shoalwater WA

    Mine was a walbro one and fitted in the og plastic casing with no mods . But the black pipe , I needed a longer one around 30mm longer apart from that it was an easy fit .

    The walbro pump is smaller in length than the og one hence the longer pipe needed .

    Hope this helps

  • nut3yNutmeg @nut3y Sunshine Coast, Queensland

    Just a quick update. Swapped the old bosch pump back in and it's running much better than the GMB. GMB seemed to really only be 100lph as it was leaning out under high load in higher gears again. For anyone who's considering buying one I wouldn't recommend them. Poor fitment, poor flow and I doubt its durability, I'm not too keen on replacing German parts with Chinese ones...

    On the other hand the SKP fuel pressure regulator seems to be doing its job. Can't comment on its longevity however, time will tell.

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