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fuel pressure problem

i know my pressures where good a few months ago. system was 6.2 and control was adjustable to 3.6. i also checked fuel volume out of the supply line TO the fuel dist. that was goos too.

now system pressure is down to normally 5.7 bar but it fluctuates from 5.5 to sometimes 6bar. i checked the system pressure out of the fuel head to the CSV and it was a steady 6bar. i figured since that is right off the pressure regulator that should give me a good reading. i pulled the pressure reg and it looks nice and clean along with where it goes into the FD.
checked current on each FP, around 6amps. also pulled relays to make sure each pump was running. when i pull the relay for the front pump, the rear sound really bad but sounds fine with both running.

i have not checked fuel volume since the low sys pressure but i did replace the fuel filter.

i dont think this would cause this but the bottom of the fuel sending unit fell off along with the small nut. dont know when but anychance it could restrict fuel flow?

how would i tell which pump could be bad? would it be the pressure pump since the pressure is low?

could someone run just their rear pump, with engine off, and tell me if the sound changes drastically.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 06-26-2014, 05:11 AM
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I have low mileage bosch 044 pumps front and rear.
If I remove the front pump relay so only the rear pump runs the rear pump makes a very different sound thats kind of like an oscillating groaning sound as it labors hard to suck fuel through the stationary rollers in the front pump.
Doesn't sound like it's good for it and thats the best I can describe it.
Old 06-26-2014, 05:59 AM
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When you drop out the front pump you are cavitating the rear pump. thats the squealing you hear.
This is bad for it and dont do it too long.

Check the pins on your relays and try to expand them with a screw driver tip and make them fit tighter into the socket in the fuse panel. I am having the same issues with my relays. Though 6 amps to each fuel pump is not that bad....how hot are the relays getting when you run the pumps for awhile?

Fred
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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 06-26-2014, 06:26 AM
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thanks. that describes the sound i hear when running just the rear, not good.

i have not had an issue with relays as far as i know. i have not actually checked power at the pump, but maybe i should. i split power to the 2 relays/pumps and put them on their own fuse. i used my fog light fuse for one pump and the original fuse for the other. i did check the fuse connections.

i was in fear of a restriction in the fuel head itself with the fluctuating pressure to the WUR, but then the 6bar to the CSV was steady.


what about the fuel sending unit cover. any chance that is blocking the pickup in the tank?
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 06-26-2014, 08:30 AM
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Quote:
Originally Posted by T77911S View Post
thanks. that describes the sound i hear when running just the rear, not good.

i have not had an issue with relays as far as i know. i have not actually checked power at the pump, but maybe i should. i split power to the 2 relays/pumps and put them on their own fuse. i used my fog light fuse for one pump and the original fuse for the other. i did check the fuse connections.

i was in fear of a restriction in the fuel head itself with the fluctuating pressure to the WUR, but then the 6bar to the CSV was steady.


what about the fuel sending unit cover. any chance that is blocking the pickup in the tank?
I dont think so as the fuel pickup is way down in the bottom of the tank. Plus if you had a blockage on the suction side the fuel pumps (I think should) pull alot of current and the relays should get really hot. You would start to hear cavitation on the front pump too.

Take the little spring plunger out of the fuel head and see if the spring is ok and the shims are intact that controls the system pressure. Perhaps its hung up and blowing off at 5.5bar?

Did you see a change after you adjust the relays as suggested or just replace them with new ones?

Fred
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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 06-26-2014, 09:26 AM
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pulled the pressure reg out already. looked really good except where the Orings have "deformed" from sealing. very clean inside.

did not change relays or do anything to them other than remove them to run one pump at a time.
i will pull them and clean the contacts just to make sure.
current was around 6amps. i think when i checked my brothers his was 7amps, but he has the O2 setup.

i do good electric work but i think i will go back and check connections from my modification.
i cut the wire that connects the pin 30's on the 2 relays and ran the pin 30 wire of relay 1 to the fog light fuse. then ran power from the unfused side of the normal FP relay fuse over to the fog light fuse. everthing is direct wired to the fuse panel with no splices. i think it is a really great way to modify it because it looks original and you cant tell by looking at it other than some of the tape is off the harness to the relays.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 06-26-2014, 10:29 AM
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OK, fuel volume is well in spec.
spec is:
delivery rate of FP= 1500cc per 30sec
control pressure delivery rate =160cc per minute

i have:
FP=almost 4000cc per minute or just under 2000cc per 30 sec
CP= just over 200cc per 30sec
sys pressure is 5.9bar
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 06-26-2014, 01:16 PM
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pulled the pressure reg. i have one shim 1.2(?)mm thick
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 06-26-2014, 01:34 PM
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So it looks like your flow is within spec.

Pressure is a little low: SP should be around 7.0 bar if you were setting it. I would put another shim in there or a thin washer to get it up there a little more than 5.9 bar.

Is it steady at 5,9bar or bouncing around like you indicated before?

The pressure bouncing is not easily explained....I dont know what might cause this other than a faulty CIS pressure gage or you are pulling in large amounts of air in the lines?

Silly question, have you made sure the gas tank has adequate fuel inside....maybe the gage in the dash is faulty?.....add 5 gallons to the tank and see what happens.

Fred
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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"

Last edited by fredmeister; 06-26-2014 at 05:03 PM..
Old 06-26-2014, 04:59 PM
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yea, plenty of gas. been down that road before.

i have the euro setup, sys pressure should be 6.2-6.4bar

i shimmed it up. got it to 6.35bar. thing is the shim is now about 1.5mm.
the shim that was in there was around 1mm-1.2mm. seemed rather thick.
well maybe not. now that i look at the shims, the 3 thickest would = 1.2mm
CP is 3.5, spec is 3.6. pressure out of the line to the CSV is 3.4bar.
the CSV is very steady and the WUR pressure is much more stable but just not sure what it does while driving.


i have 2 sets of gauges. one was on the FD to the WUR and the other on the out to the CSV.
i played around with opening and closing the valve on the gauges with other side of the gauges going to a jug. did this to see how the pressure reacted to changes.
the WUR side was slow to come back up when i opened the CSV side then closed it.
dont think any of it means anything.

when iwent to adjust the CP, that pressure seemed to jump around so i am curious if there is something with the WUR.

still, i dont see why the sys pressure dropped .4bar

i dont know what the mixture is doing, need to get the LM2 back.

thanks for the help. nice to bounce stuff off someone else.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 06-26-2014, 05:31 PM
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I have an 86 here that testing pressures cold gave good values. But after a few miles driving system pressure fluctuated wildly. Turned out that the vent line for the gas tank that has the orifice in it was clogged up.
Old 06-27-2014, 09:43 AM
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i ran the front pump only and got almost full system pressure with it bouncing around maybe a little more than usual. (about 6bar)
if i run the rear pump, i get a bouncy 4 bar.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 07-10-2014, 01:45 PM
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