Member
Fuel Pressure at Rail (S52)... need real world data
Last time at the track my 98 M3 had a light miss up around 5500-6500.
I have a wideband gauge on the car and everything seemed fine (12.8-13.1) up top but I figured the gauge might not catch the car momentarily leaning out if it was a fuel delivery issue. Anyhow, I changed the plugs a couple nights ago as a first step in troubleshooting. Then today rigged up my fuel gauge from the valve on the rail out the engine bay onto the windshield and went for a drive. Here are some readings:
HOT IDLE: 41-42psi
WOT: 48-49psi
This seems a few psi lower than folks are seeing. Fuel filter is 10k miles old, injectors were just serviced. It never reached or exceeded 50psi or during any portion of the drive that I saw. When I prime the pump with the ignition without starting is *almost* reaches 50 then drops a few after key release.
Does this seem ok or does it warrant investigation? Car has 126k and fuel trims have always been a little lean so the car is compensating for something. Maybe this.
Good news is the plugs seem to have cleared up the stumble up top as I didn't feel it at all during the drive.
Last edited by NotUrAvgM; 05-26-2018 at 04:04 PM.
[2004 330xi/6] Orient/Natural :: 117-142k :: ZSP :: ZPP :: ZCW
[1998 M3/4/5] Cosmos/Black :: 113-125k :: TCKline D/A (500/600) :: GC Plates :: RD Sways :: GC Rear Arms :: ZHP Rack :: 3.64 Diffsonline :: PF FCAB :: BW RTAB :: AKG Subframe :: TMS Pulleys :: AA & Borla :: XBrace :: TRM C2s :: BW lines :: DTC60 :: Safety Equipment
Past:
[1995 M3] Avus/Dove :: 141-242k :: S52 OBDI :: M50 manifold :: 3.5 HFM :: Turner Chip :: XBrace :: SS Lines :: Turner RTABS :: Vogtland CS :: Bilstein Sport :: Z3 rack
[1999 M3] Cosmos/Black :: 65-87k :: TCKline S/A (400/500) :: Turner plates :: UUC Front Sway :: PF RTABs :: AA Intake :: Borla :: XBrace :: TRM C2s :: CL RC6E :: Safety Equipment
[1993 325is] Brilliant/Black :: 135-139k :: Bilstein sports :: Eibach sways and springs :: Dinan camber plates and chip :: Borla :: LSD
[1983 320i] Safari/Brownish :: 219-242k :: homebrew CAI :: some rust :: multicolor body panels
Member
BMW E36 M3 Expert
It's possible the FPR is weak, but at least your numbers indicate that the vacuum line is hooked up and the delta is correct. It's also possible your real numbers are fine and the gauge may read low. Every gauge I have reads something different (three, it's annoying AF). I have seen FPR vary wildly too. Out of 5 I yanked from the junk yard, not one was 3.5bar and some failed as low as 2bar and some as high as 4.3bar. I use a bench tester with both analog and digital gauges.
Stick to OEM BMW Pierburg if you want to replace it. Bosch 3.5bar specific to BMW don't work.
Last edited by Braymond141; 05-26-2018 at 09:54 PM.
Member
Seems in the ballpark to me. Gauge might be 2 psi off, but it’s climbing as vacuum drops.
Member
Yeah could be the gauge. Not sure a good way to check.
Occasionally it does bleed off fuel pressure after shutdown faster then BMW spec. I pinched the feed line right out of the pump and it still bleeds down, so it could be the FPR is a bit wonky.
[2004 330xi/6] Orient/Natural :: 117-142k :: ZSP :: ZPP :: ZCW
[1998 M3/4/5] Cosmos/Black :: 113-125k :: TCKline D/A (500/600) :: GC Plates :: RD Sways :: GC Rear Arms :: ZHP Rack :: 3.64 Diffsonline :: PF FCAB :: BW RTAB :: AKG Subframe :: TMS Pulleys :: AA & Borla :: XBrace :: TRM C2s :: BW lines :: DTC60 :: Safety Equipment
Past:
[1995 M3] Avus/Dove :: 141-242k :: S52 OBDI :: M50 manifold :: 3.5 HFM :: Turner Chip :: XBrace :: SS Lines :: Turner RTABS :: Vogtland CS :: Bilstein Sport :: Z3 rack
[1999 M3] Cosmos/Black :: 65-87k :: TCKline S/A (400/500) :: Turner plates :: UUC Front Sway :: PF RTABs :: AA Intake :: Borla :: XBrace :: TRM C2s :: CL RC6E :: Safety Equipment
[1993 325is] Brilliant/Black :: 135-139k :: Bilstein sports :: Eibach sways and springs :: Dinan camber plates and chip :: Borla :: LSD
[1983 320i] Safari/Brownish :: 219-242k :: homebrew CAI :: some rust :: multicolor body panels
Member
My aftermarket FPR bleeds down after shutoff. I would not worry about that.
Member
Seems odd that it would regulate accurately while running then not be able to after shutdown.Originally Posted by pbonsalb
I have an BMW regulator sitting around so I may throw it in and see if there is any pressure difference. Might also check my buddy's S52 as a gauge sanity check.
[2004 330xi/6] Orient/Natural :: 117-142k :: ZSP :: ZPP :: ZCW
[1998 M3/4/5] Cosmos/Black :: 113-125k :: TCKline D/A (500/600) :: GC Plates :: RD Sways :: GC Rear Arms :: ZHP Rack :: 3.64 Diffsonline :: PF FCAB :: BW RTAB :: AKG Subframe :: TMS Pulleys :: AA & Borla :: XBrace :: TRM C2s :: BW lines :: DTC60 :: Safety Equipment
Past:
[1995 M3] Avus/Dove :: 141-242k :: S52 OBDI :: M50 manifold :: 3.5 HFM :: Turner Chip :: XBrace :: SS Lines :: Turner RTABS :: Vogtland CS :: Bilstein Sport :: Z3 rack
[1999 M3] Cosmos/Black :: 65-87k :: TCKline S/A (400/500) :: Turner plates :: UUC Front Sway :: PF RTABs :: AA Intake :: Borla :: XBrace :: TRM C2s :: CL RC6E :: Safety Equipment
[1993 325is] Brilliant/Black :: 135-139k :: Bilstein sports :: Eibach sways and springs :: Dinan camber plates and chip :: Borla :: LSD
[1983 320i] Safari/Brownish :: 219-242k :: homebrew CAI :: some rust :: multicolor body panels
Member
I don't know if I'd worry too much about it. That's about what mine read on two different fuel pumps. Was chasing something (ended up being a vac leak) a couple years ago and I got similar numbers to yours. I figured that was close enough given the gauge I was using and who knows what else. Filter was probably a couple years old at that point.
Actually, I'm probably due for a fuel filter now that I mention it.
-Josh: 1998 S54 E36 M3/4/6 with most of the easy stuff and most of the hard stuff. At least twice. 271k miles. 1994 E32 740il with nothing but some MPars. 93k miles.
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