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Old 06-15-2015, 07:31 AM
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W124 M103 fuel pressure regulator leaking?

I'm seeing fuel in the clear vent tube, been that way for ages, always ran fine, just turned 100K miles. Is it normal or does it mean a diaphragm leak?

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Last edited by tilac1; 06-15-2015 at 01:37 PM. Reason: more info
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Old 06-15-2015, 05:59 PM
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Are you looking at a device under the hood or under the car near the fuel pump?

The pressure reg is under the hood , fuel accumulator under car.

The pressure reg should have a vacuum line , fuel return.

Accumulator has fuel in / out then a vent hose that leads to the suction side of the fuel pump. This was done so if the diaphragm tears, fuel circulates back to the tank rather than being dumped on the ground / hot exhaust like some cars.
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Old 06-16-2015, 04:56 AM
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Not the accumulator. The FPR has a clear vent tube connected to the valve cover. Sometimes I see a bubble of fuel in the line.
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Old 06-16-2015, 10:54 AM
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Typically, if you see fuel in the line, that means that the diaphragm within the regulator has broken down and the reg should be replaced. Notice where the clear line leads to... the breather hose from the valve cover to the air cleaner. Fuel isn't supposed to be in that system. Too much fuel and you'll have idle issues or have a hot mess on your hands. It's a relatively cheap and easy fix to replace it with even a used one. Lots on ebay to find.
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Old 06-16-2015, 03:29 PM
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Break and undo all the fuel connections before you loosen the mounting bracket bolt.

Easiest way I found for the replacement is to reattach the smaller connection first, the fuel distributor line second and then the last one. THEN bolt down the mounting bracket.
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Old 06-16-2015, 03:32 PM
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Bosch FPRs are over $200 and I don't want to replace it if seeing a fuel bubble is a normal occurrence. It's been like this for a long time but seemingly runs fine.
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Old 06-16-2015, 04:04 PM
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Quote:
Originally Posted by tilac1 View Post
I'm seeing fuel in the clear vent tube, been that way for ages, always ran fine, just turned 100K miles. Is it normal or does it mean a diaphragm leak?
Since the FPR vent/leak line is connected to crankcase ventilation components, the liquid that is observed in the line is most likely condensed water vapor, not fuel.
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Old 06-16-2015, 05:15 PM
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Good idea. I'll check and see if it's gas or not.
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Old 06-16-2015, 11:17 PM
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$6 at pik a part

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1985 300D 198K sold
1982 300D 202K
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1992 940T

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