Tank to pump hose routing

[Zed Head]

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

I just took the car around the block and it is incredibly sluggish (acceleration sits in the 15-17 range on the air fuel ratio gauge).  I pulled over and unplugged the fpr vacuum hose and with 38 psi, the car is a rocket again - so the gauge fuel pressure gauge is right there definitely is a fuel pressure issue here

When you unplugged the vacuum reference hose you raised the fuel pressure in the fuel rail, engine running, making the fuel-air ratio richer at low to mid-range throttle opening.  You would feel that effect if you were running lean before.  At open throttle you'll get the same effect as removing the hose since there will be very little vacuum in the intake system so you shouldn't feel any difference, hose on or off.

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

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

[Captain Obvious]

11 hours ago, chaseincats said:

Just to be sure I'm not barking up the wrong tree with blockages/restrictions - the pump wouldn't be the issue right?  Since it's an electric pump it will either work or it won't and not become weaker, correct?

I don't know what's going on yet, so I'm not ready to let the pump off the hook. Is there a way you can see what happens to the fuel pressure while you're driving?

[chaseincats]

3 hours ago, Captain Obvious said:

I don't know what's going on yet, so I'm not ready to let the pump off the hook. Is there a way you can see what happens to the fuel pressure while you're driving?

Since the pressure gauge is in the engine bay (spliced between the fuel filter and fuel rail) I wouldn’t be able to do that but I can monitor the engine in real time with my AFR gauge if that helps.

In the past I’ve always spliced the fuel pressure gauge in that location so my past reading sand this are from the same location.

[Zed Head]

Might help focus to restate the problem.  If it runs great (like a rocket), what's the problem?

I notice that you didn't report your AFR's in rocket mode.  What are they compared to sluggish mode.

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

incredibly sluggish (acceleration sits in the 15-17 range on the air fuel ratio gauge).  I pulled over and unplugged the fpr vacuum hose and with 38 psi, the car is a rocket again

 

[Yarb]

Once again I’ll throw my 2cents in. Are we ready to rule out ignition at this point?

[Zed Head]

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

I pulled over and unplugged the fpr vacuum hose and with 38 psi, the car is a rocket again

Hate to keep harping on it but this statement seems to knock out several possibilities, without it there's not much to go on.  The pump is able to make the engine run like a rocket, pressure and flow, apparently, once the regulation (pressure lowering) of the FPR is removed, and it seems reasonable to assume that ignition is fine for the same reasons.

Pressure, flow, and ignition are available.  I tried to lead to the new problem in my post above - the engine will run rich at less than close to WOT, without the FPR regulating pressure.

The clues point to a lean mixture.  The very common 280Z EFI problem.

[Zed Head]

I would guess that with the vacuum hose connected it only runs well at throttle opening greater than 34 degrees.

[Zed Head]

Or, maybe it never gets the 27%.  Maybe the TPS never shows WOT.  Could be a TPS problem.

It's not clear when "sluggish" occurs.  WOT or cruising.  That would be another good clue.

.

Edited January 15 by Zed Head
-e -,

[Yarb]

TPS is very simple to check with a meter 

[chaseincats]

This is not an ignition/efi/jetronic/TPS/sunspots/etc issue.

The car was tuned-up to factory spec with the ET chapter of the FSM and using the AFR gauge a couple years ago.  This problem started immediately after the hose changes (the post-installation test drive) whereas the drive before changing the hose was perfect ("rocket mode").

AFR readings:

- before hose change: idle 14.2, cruise 14.7, WOT 12.5

- 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

Edited January 15 by chaseincats

[Zed Head]

On 1/11/2025 at 10:38 PM, chaseincats said:

The car ran horribly after I replaced the old tank-to-pump hose (due to age) and I eventually found that I had 20psi coming out of the fuel pump due to me zip tying the tank-to-pump hose higher than where it had been before being changed.  After lowering the hose (to a couple inches over the half shaft where it had been i believe) I saw my psi go up to 32.

All of my comments were just based on logic, understanding how the system works, and the facts presented.  No need for sunspots.

Hard to see how you can still have excellent WOT performance if something at the hose from the tank to the pump was not right.  Doesn't make sense.

I'm going to go with coincidence then.  Something else happened at the same time you replaced that hose.  Good luck.

p.s. the fuel pump and FPR are at the foundation of the Jetronic system.  So if you're looking at fuel pressure you're looking at Jetronic.

[mayolives]

Your quote....Since it's an electric pump it will either work or it won't and not become weaker, correct?"  I'm supprised no one else responded to this question.  A few years ago I replaced my 260's pump because it wasn't running well and the fuel pressure was reading too low. I don't remember how low but it was much lower that FSM spec.  I used a new Nissan pump and it restored the pressure to spec and my problem was resolved. My two cents.