1993 legacy turbowagon.

So I installed a fuel pressure gauge in the cabin and expected to see the fuel pressure climb with boost, but it just goes to 40psi and stays there regardless of boost and regardless of time on boost.  I thought I would see the following:

• At idle fuel pressure would be ~36.3 psi
• At 9psi of boost fuel pressure would be ~45.3 psi

1992 Manual seems to state that the fuel pressure should compensate for boost to maintain the same delta with intake manifold.  Did this change with the 1993 model year?

I think I might be due for a new pressure regulator.  In tank pump is about 1 year old so I doubt that is the problem unless 40psi is all it will output.  I'll test this.  Fuel filter isn't to old it was changed last year.

 

Edited March 16, 20242 yr by Subi81
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• Restricting the return line to the tank after the fuel pressure regulator gives 65 psi
• Restricting the hose after the fuel filter gives 75 psi

So it's not the fuel pump, it can put out more than enough pressure when dead headed.

I think the:

• Regulator is somehow not modulating but can't understand how, unless the diaphragm is ruptured but then I would see fuel getting sucked into the intake manifold at idle.
• The signal line is plugged
• The filter is so plugged it can't flow enough when the engine is at cruise RPM.

I guess that will be the next couple of things to look at.

 

 

Fixed it, the signal line from the intake manifold came off, for some reason Subaru used the smallest vacuum line known to man then didn't put a barb on any of the nipples go figure.  It's ultimately my fault though I replaced the old line with a silicon version years ago which was a little bit more slippery and obviously not the right diameter and it blew off under boost.  The manifold line was so crusty it's probably been like this for years, I am surprised it passed smog with that constant vacuum leak.

I tested the system with a compressor and pressure regulator sure enough as simulated manifold pressure came up so did fuel pressure in a 1:1 ratio.

 

Edited March 16, 20242 yr by Subi81
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