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Discussion Starter #1
I was trying to trace some fuel odors last weekend in my '91 164S and since I decided to replace the short piece of hose which feeds the fuel rail I took the opportunity to hook up a fuel pressure gauge. I connected it between the hard line and the fuel rail inlet at the front of the engine.

When starting the pressure almost instantly jumped to ~38psi and stayed there nice and steady while idling, but as soon as I shut the engine off the pressure fell to zero. Should the system hold pressure after the engine is shut off? If so what is the most likely culprit?

The car has 107K miles on it and the injectors were replaced with rebuilt ones about a year ago.

thanks,
-Obie

Tacoma, Wa
'91 164S
'83 GTV6
 

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Tu es bibendum?

FP should be a tad higher, 42 -ish psi is ideal, and yes, FP should hold at 40 psi for hours / days after engine shut-off. You probably have a crack in the hose in the FP assembly -- search "tank dive" and you will find Alfisto Steve;s excellent write up.
 

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Although the short hose in the fuel pump is usually the cause of this, don't overlook that the check valve (top of fuel pump) can also be the reason for pressure bleed down after car is turned off. You might consider installing a small check valve in the engine compartment before you do that miserable tank dive. I like the one made by Boomba 5/16". Boomba Racing, Inc. :: Check Valve
(it solved a hard starting problem I had after changing the short hose)
 

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Discussion Starter #4
Goats and Pinino -- thank you for the suggestions. I will check the short hose and check-valve and report back.

-Obie

Tacoma, Wa
'91 164S
'83 GTV6
 

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But Mad North-Northwest
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Be careful with the pressure spec. The fuel pressure regulator is designed to keep constant fuel pressure versus the air pressure in the plenum. That's why it has a vacuum hose on it. If you've got a 42PSI regulator (if that's the spec) and you're at 5PSI vacuum in the plenum you'll only have 37PSI fuel pressure at the rail.

When checking fuel pressure vs the Bosch spec you need to disconnect the vacuum hose from the FPR and plug it (that is, plug the rubber hose and leave the port on the FPR open to air).
 
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