Tank to pump hose routing

[Yarb]

The aftermarket pumps are used from what I’ve read here. My 2 cents are to go back with what the factory designed for the system. You stated earlier you only focused on the hoses themselves. Chances are as @zedhead mentioned it could be a coincidence. I recommend buying a roll of fuel line and run the gauge through the window and monitor as you drive. Either way you will accomplish the test result with an answer and you can reuse the hose elsewhere.

[Zed Head]

On 1/13/2025 at 8:19 PM, chaseincats said:

- With the car turned on we're still sitting at ~30 psi at idle with the vacuum hose connected to the fpr and 38psi with it unplugged, idling, with my finger over the hose to prevent the vacuum leak.

 with 38 psi, the car is a rocket again - so the gauge fuel pressure gauge is right 

 

22 minutes ago, mayolives said:

 eplaced my 260's pump because it wasn't running well and the fuel pressure was reading too low. 

38 is actually high.  Spec. is 36.3.  Avoid the urge to break out the parts cannon.  It can get expensive.

[chaseincats]

4 hours ago, Zed Head said:

 

38 is actually high.  Spec. is 36.3.  Avoid the urge to break out the parts cannon.  It can get expensive.

In the past, my idle was at 36 with the vacuum line connected but now its 30 and the car is running lean.  I believe the FSM says it should idle at 36 too.

[Captain Obvious]

22 hours ago, chaseincats said:

In the past, my idle was at 36 with the vacuum line connected but now its 30 and the car is running lean.  I believe the FSM says it should idle at 36 too.

At idle, you SHOULD be seeing around 30 psi. If you goose the throttle, it should shoot up to 36 for a brief period. But at steady state idle, a reading of 30 is not a problem.

That fuel pressure spec is a differential reading. Think about it this way.... There should always be 36psi across the injector. Fuel line pressure on the inlet side of the injector, and intake manifold pressure (vacuum) on the other. If the manifold vacuum is 17 inches of mercury (which converts to around 6 psi of vacuum). You need to subtract that six psi from the fuel pressure in order to maintain the 36 psi differential.

Fuel line pressure - manifold pressure = desired differential across injector (which is 36)
30 - (-6) = 36   << fuel line pressure = 30

When you are at WOT, the intake manifold vacuum is zero:
36 - 0 = 36   << fuel line pressure = 36

Does that make sense?   

[chaseincats]

3 hours ago, Captain Obvious said:

At idle, you SHOULD be seeing around 30 psi. If you goose the throttle, it should shoot up to 36 for a brief period. But at steady state idle, a reading of 30 is not a problem.

That fuel pressure spec is a differential reading. Think about it this way.... There should always be 36psi across the injector. Fuel line pressure on the inlet side of the injector, and intake manifold pressure (vacuum) on the other. If the manifold vacuum is 17 inches of mercury (which converts to around 6 psi of vacuum). You need to subtract that six psi from the fuel pressure in order to maintain the 36 psi differential.

Fuel line pressure - manifold pressure = desired differential across injector (which is 36)
30 - (-6) = 36   << fuel line pressure = 30

When you are at WOT, the intake manifold vacuum is zero:
36 - 0 = 36   << fuel line pressure = 36

Does that make sense?   

It does but that makes me curious why it originally sat and idled at 36 psi before I messed with the hoses.

[Captain Obvious]

6 hours ago, chaseincats said:

It does but that makes me curious why it originally sat and idled at 36 psi before I messed with the hoses.

Me too. You shouldn't  see 36 psi at idle under normal conditions. You should see 36 minus intake manifold vacuum.

Can you double check these numbers? Zed-head questioned the numbers found here, and I agree. I don't get how the idle is richer with the line connected, and ZH questioned how the car can be having a performance problem with WOT numbers like you're getting.

- after hose change (with FPR vacuum line connected): idle 14.7, cruise 16-19ish, WOT 13.7

- after hose change (with FPR vacuum line dis-connected): idle 16.9, cruise 15ish, WOT 12.8

There is a small inlet screen on the stock fuel pump. Is there anything like that in your aftermarket replacement?