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Old 03-20-2022, 12:15 PM   #1
HiSPL
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Default 1 out of 10 starts is slow. Fuel Check valve?

So 9 times out of 10 my car (88 LH2.2) starts even if I just breathe on the key. Like instantly. But that one magic time out of every ten or so starts it takes some cranking (3-4 seconds) and slowly starts running as if I have to get fuel pressure up before it starts running properly.

Will the Fuel pressure check valve fail like this? It's the only thing I can think of that would cause it.
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Old 03-20-2022, 02:56 PM   #2
2manyturbos
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Short answer, yes. If you have a fuel pressure tester just check the rest pressure. If it drops immediately, the check valve is most likely the cause of the slow starts.
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Old 03-26-2022, 08:48 AM   #3
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check valve
Fuel Pump Check Valve....@....fuel filter
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Old 03-29-2022, 03:17 PM   #4
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Short answer, yes. If you have a fuel pressure tester just check the rest pressure. If it drops immediately, the check valve is most likely the cause of the slow starts.
The pressure does not have to drop immediately. Sometimes the leak back will take 30 - 90 minutes to occur. My 1987 745 T suffered from the slow pressure loss following shut down leading to a slow restart. In addition to a leaky check valve, the fuel pressure regulator valve may not be completely sealing leading to a slow loss of rest pressure following shut down.
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Old 03-30-2022, 03:32 AM   #5
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The pressure does not have to drop immediately. Sometimes the leak back will take 30 - 90 minutes to occur. My 1987 745 T suffered from the slow pressure loss following shut down leading to a slow restart. In addition to a leaky check valve, the fuel pressure regulator valve may not be completely sealing leading to a slow loss of rest pressure following shut down.
That would be considered totally normal. The spec calls for the check valve to hold rest pressure for 20 minutes.
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Old 03-30-2022, 06:55 AM   #6
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...pressure....Sometimes the leak back will take 30 - 90 minutes to occur.
Years ago @ fuel pump relay, I "hot wired" relay so I could manually prime the fuel rail.

I'd have to look at schematics again, but IIRC, a ground wire can fire-up the fuel pump relay.
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Old 03-30-2022, 02:46 PM   #7
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I made a similar special tool for myself for hot wiring the pump.

My car had a similar problem that turned out to be a weeping fuel pressure regulator diaphragm.
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Old 03-30-2022, 09:43 PM   #8
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a similar special tool
IIRC, LH 2.1 grounds out fuel pump relay...no need to use a positive hot wire. LH 2.2 most likely is the same.

On my VW K-Jet, I used a ground to energize the cold start injector with a momentary switch on the dash. Great for cold starts.
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