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Join Date: Jul 2021
Posts: 88
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Warm start issue no fuel pressure with ignition on
Hi all, I’m having some trouble with my s4. On warm start the car is having some trouble starting when the motor is warm. It cranks for about 10 seconds before it starts and requires throttle. I found that the when the Ignition is on that it is only getting a couple psi of pressure but when the engine is on it has good pressure.
Any ideas what would cause the fuel pump to not create pressure with the ignition on? |
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06-14-2023, 06:19 PM
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What is your battery voltage with ignition off and when it is on ? What is the battery voltage when engine is running ? Everything off, voltage should be around 12.6 VDC, engine running it should be at least 13.8 VDC.
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1986 928S 32 valve engine All stock, automatic, 539 Weissgold Metallic, 70K original miles, Hankook Ventus 2 tires. Previously owned: 67 Vette, 427 L88 Stingray, 74 De Tomaso Pantera L. Latest addition: 2000 BMW Z3 Roadster |
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06-15-2023, 10:59 AM
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Join Date: Mar 2010
Location: Texas
Posts: 2,138
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Quote:
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John Curry (Drift King) 928OC member Grand Prix White 1994 GTS AT (The GTS) Black 1989 GT (The GT) and Cobalt Blue 1989 S4 AT (The Blue Car) 1986 Euro AT Indishrot 1984 Euro S AT (The Stepson) and Black Metallic 1984 Euro S 5 speed (The Schwartz) |
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06-15-2023, 01:36 PM
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Quote:
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1986 928S 32 valve engine All stock, automatic, 539 Weissgold Metallic, 70K original miles, Hankook Ventus 2 tires. Previously owned: 67 Vette, 427 L88 Stingray, 74 De Tomaso Pantera L. Latest addition: 2000 BMW Z3 Roadster |
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06-17-2023, 07:03 AM
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Join Date: Mar 2010
Location: Texas
Posts: 2,138
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I know that an internal pump was stock on 89 S4 and GTSs. I think probably 89 and up had the internal pump since GTSs had it as well. I don't know what year 928 the OP possesses.
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John Curry (Drift King) 928OC member Grand Prix White 1994 GTS AT (The GTS) Black 1989 GT (The GT) and Cobalt Blue 1989 S4 AT (The Blue Car) 1986 Euro AT Indishrot 1984 Euro S AT (The Stepson) and Black Metallic 1984 Euro S 5 speed (The Schwartz) |
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06-22-2023, 11:40 AM
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Join Date: May 2008
Location: Grapevine, TX
Posts: 1,110
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The pump doesn't run unless the engine is running. So i wouldn't expect any significant pressure other than residual that has remained in the system since it was last running.
If you jumper the fuel pump relay (force the pump to run) with the engine off, you should see full fuel pressure ~55psi. the system should hold this pressure for a few minutes after the jumper is removed, but will not hold long term. If the pressure drops shortly after removing power from the pump you likely have something in the system leaking. the check valve at the pump is one possibility. the other more likely possibility and correlates with you hard warm start, is that you have a leaking diaphragm in one or more of the fuel pressure dampers or fuel pressure regulator. when one of these is leaking, you will end up with an excessively rich mixture during warm/hot starts. disconnect the vacuum like to each damper and the FPR and see if you smell fuel at any of the vac lines, if so it is likely that that is you issue. |
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06-23-2023, 08:56 AM
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