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?

[chaseincats]

On 1/17/2025 at 7:17 AM, Captain Obvious said:

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?

I have some fuel pressure numbers for you.

When I connected a fuel pressure gauge between the fuel pump and dampener in the rear of the car, I got 40 with the key off but pump on, and 34 with the car running with 32 psi reaching the front with the fpr vacuum tube on.  Is 34psi out of the pump's fuel outlet while running correct?

[Zed Head]

The pressure in the rail is what matters.  But your numbers at the pump seem about right.

[chaseincats]

29 minutes ago, Zed Head said:

The pressure in the rail is what matters.  But your numbers at the pump seem about right.

Arg.  Looks like I’ve hit a dead end with the fuel pressure then?  Any suggestions  on where to look?  The car was front firing a lot when the fuel line blew and it ran very lean.  Could the AFM been damaged by that?

[Yarb]

Not the AFM. IMO

[Zed Head]

On 1/14/2025 at 8:44 PM, Zed Head said:

You might try the fuel tweak modification and see what happens.

https://www.atlanticz.ca/zclub/techtips/tempsensorpot/index.html

 

5 hours ago, chaseincats said:

The car was front firing a lot when the fuel line blew and it ran very lean. 

Front-firing is a good term for what happens when the system is running lean.  That's where the noise is, in the intake manifold.  Many of us have had the problem, it seems to be because of fuel changing since the seventiies or electronic component "drift".  But it's common enough that people like Blue/240/260/280 have written up ways to fix it.  It's a real thing.  

The fix easier than it seems.  Hardest part is finding a potentiometer.  Find the bullet connectors on the coolant temperature sensor circuit and insert the potentiomemter.  Turn the knob until it runs right.

Might be that you've been on the edge or maybe there's something in the ECU that fails and it finally happened to yours.  Who knows.  But the fix is simple and will tell you something.

Linked above.

[chaseincats]

4 hours ago, Zed Head said:

 

Front-firing is a good term for what happens when the system is running lean.  That's where the noise is, in the intake manifold.  Many of us have had the problem, it seems to be because of fuel changing since the seventiies or electronic component "drift".  But it's common enough that people like Blue/240/260/280 have written up ways to fix it.  It's a real thing.  

The fix easier than it seems.  Hardest part is finding a potentiometer.  Find the bullet connectors on the coolant temperature sensor circuit and insert the potentiomemter.  Turn the knob until it runs right.

Might be that you've been on the edge or maybe there's something in the ECU that fails and it finally happened to yours.  Who knows.  But the fix is simple and will tell you something.

Linked above.

This is kind of my fault because I didn't explain the scenario that got me to where I am (since I was so positive it was a fuel pressure issue).

I was driving when one of the fuel hoses in the back of the car (that I later learned was quite old) blew.

The car lost power as expected since it wasn't getting the amount of fuel it needed due to the split hose.  Looking on my AFR gauge on the dash, it went from 14.7 on the highway to 19, and was sputtering with no power.  After trying the accelerator a few times with no improvement, I put it in neutral and killed the engine - coasting to a stop in a CVS parking lot.

I turned the car on and it was front firing a lot - turning around I noticed a massive puddle of fuel spraying out from under the car - I turned it off immediately and called a tow truck.

After getting the car home, I put it up on jack stands and changed the split hose (the only one I didn't change a year ago for some reason, go figure).  The hose that I replaced hung a bit low (like I was talking about at the beginning of the thread) so I zip tied it up. I turned the car on and it was sputtering and front firing and later discovered that I zip tied it too high/tight and kinked the hose.  After cutting the zip tie and re-hanging it, we were back to the 32psi we've been chatting about.

Long story short, the car was running great in its current setup until a fuel line blew, causing it to do quite a bit of front firing on the highway, parking lot, and home when looking into the hose kink.  I've heard front firing can damage the AFM, which is the only reason I keep talking about front fire.

I can richen the car with the AFM (or the potentiometer) but that isn't solving the problem since it was running fine with the current configuration until this event with the fuel hose and the running lean/front firing as a result of the split hose only allowing a fraction of the fuel needed to keep a proper AFR entering the engine.

I hope that makes sense @Zed Head?

Edited January 20 by chaseincats