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Old 05-01-2019, 03:35 PM   #1
CaliforniaGrown
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ETA fuel pressure issue

Hello, I have an 86 325e and when I hooked up my fuel pressure tester (new snap on so im fairly sure it's accurate) it read 36 psi when cranking, and 30psi at idle. Unhooked vacuum line to FPR, and it went up to 36psi. Hooked the line back up and it went back down to 30psi. When I turned it off, it held the pressure for longer than 20 mins. I jumped the fuel pump relay with a random jumper wire, and it went up to 40 psi. After I removed the wire it held at 36psi until I started the car back up, and it went back down to 30. I swapped different relays and even replaced both relays for the pump. Same results every time. When holding it at 3000rpm it jumped to 32-33, then came back to 30 immediately. I've replaced most fuel hoses and the filter. Any ideas? Thank you,

Josh
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Old 05-02-2019, 07:38 PM   #2
TobyB
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Well, etas have 2.5 bar regulators, so it's just about dead- nuts on.

Because that line to the intake is a reference, and your manifold is at -.5 bar or more.

Stick a vacuum gauge on it, but your numbers seem just about right.

Certainly in the range that works.

t
1 bar = 14.7 psi
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Old 05-02-2019, 09:59 PM   #3
Andre3127
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Thats exactly how they're supposed to work. 2.5 bar or roughly 2 bar under vacuum.
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Old 05-03-2019, 04:18 AM   #4
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Are you having any issues with starting or drivability?
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The E30 collection:
1987 325es M52 - Schwarz / Taurus Red Sport (son #2's)
1987 325is - Delphin / Black Sport (son #3's)
1987 325i Convertible - Triple Black
1989 325iX Coupe - Diamondschwarz / Black Comfort
1990 325iX Coupe - Sterling Silver / Grey Sport

1981 Fiat 124 Spider 2000 - Green / Tan
1998 Volvo V70 GLT - White / Tan
1998 Volvo S70 T5 manual - White / Taupe
2001 Ford Windstar - Silver / Grey (parts hauler)
2006 Lexus GX470 - White / Tan (tow rig)

Last edited by 101; 05-03-2019 at 09:58 AM.
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Old 05-03-2019, 06:06 AM   #5
CaliforniaGrown
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Oh okay, I understand. Thanks for the help! And only drivability issue is a long cranking time on startup in the summer on hot days
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Old 05-03-2019, 10:05 AM   #6
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Something to check -

Make sure the fuel system is holding pressure after the engine is turned off. Leave the pressure gauge teed in to the system and see how much the pressure is dropping after 15 minutes, 30 minutes, etc.

If the system is losing pressure quickly, the check valve in the fuel pump might be bad. Unlike modern cars, our E30's do not prime the fuel pump for a few seconds when the key is moved to the "on" position. The E30 fuel pump only begins to run when the engine computer senses that the engine is rotating.
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The E30 collection:
1987 325es M52 - Schwarz / Taurus Red Sport (son #2's)
1987 325is - Delphin / Black Sport (son #3's)
1987 325i Convertible - Triple Black
1989 325iX Coupe - Diamondschwarz / Black Comfort
1990 325iX Coupe - Sterling Silver / Grey Sport

1981 Fiat 124 Spider 2000 - Green / Tan
1998 Volvo V70 GLT - White / Tan
1998 Volvo S70 T5 manual - White / Taupe
2001 Ford Windstar - Silver / Grey (parts hauler)
2006 Lexus GX470 - White / Tan (tow rig)
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Old 05-03-2019, 05:46 PM   #7
CaliforniaGrown
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101- thank you, I appreciate the advice. I've done my research on the fuel system, and am familiar with how it functions. I just somehow missed the fact about the vacuum having an effect on the pressure. In my op I stated the system holds pressure for at least 20 mins. After about 45mins-1hr it starts to drop slowly. I'm wondering if my inline pump is getting weak and maybe that's why the long cranking, but haven't thouroughly investigated yet :/ thanks again
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Old 05-04-2019, 09:58 AM   #8
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Yeah, the in- tank pumps aren't very robust. If cranking gets worse as the tank empties,
that's a sure sign that the pump's dying or dead.

t
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