Tank to pump hose routing

[Zed Head]

If I recall correctly the very early AFM's did not have a back/front fire protection spring on the AFM vane.  It was added later.  So Nissan was aware that it could damage the AFM.  The simplest check would be to confirm that the AFM vane moves freely.  Your AFM might be out of order.

There's always more to the story...

https://www.thezstore.com/category/150/air-flow-meter-parts

[chaseincats]

4 hours ago, Zed Head said:

If I recall correctly the very early AFM's did not have a back/front fire protection spring on the AFM vane.  It was added later.  So Nissan was aware that it could damage the AFM.  The simplest check would be to confirm that the AFM vane moves freely.  Your AFM might be out of order.

There's always more to the story...

https://www.thezstore.com/category/150/air-flow-meter-parts

I have a '78 so if front fire protection was added later-on, I should have it.

I just went through the FSM's checks both with moving the flap and all of the multimeter tests and everything came out in spec

Edited January 20 by chaseincats

[Zed Head]

A new thought - maybe the front-back firing caused a vacuum leak.  Split a hose, blew a gasket, popped an injector seal.  I'd check those, maybe even try the propane or carb cleaner test (don't start a fire).  Don't forget the PCV hose under the intake manifold.

Edited January 20 by Zed Head
spling

[chaseincats]

37 minutes ago, Zed Head said:

A new thought - maybe the front-back firing caused a vacuum leak.  Split a hose, blew a gasket, popped an injector seal.  I'd check those, maybe even try the propane or carb cleaner test (don't start a fire).  Don't forget the PCV hose under the intake manifold.

I was curious about that and so I blasted my engine with carb cleaner (with a fire extinguisher right next to me haha) and got nothing - but it might be time for the cigarette/hand pump vacuum leak test.  That said, I had been in a situation where the engine acted like this before, and it was when an injector connector somehow had 2 seals in it and so wouldn't be able to be plugged in far enough.  The injector could fire but did not get enough power to fire enough and so the car could idle but whenever you'd press the gas it was just anemic as hell...

[siteunseen]

5 hours ago, Zed Head said:

Don't forget the PCV hose under the intake manifold.

And where the EGR tube connects to the intake manifold. Mine came loose and rotted a hole in the aluminum. 

[chaseincats]

On 1/20/2025 at 8:53 AM, Zed Head said:

A new thought - maybe the front-back firing caused a vacuum leak.  Split a hose, blew a gasket, popped an injector seal.  I'd check those, maybe even try the propane or carb cleaner test (don't start a fire).  Don't forget the PCV hose under the intake manifold.

It just hit me - the car idles at the same rpm it always has - between 600 and 800 depending on the season.  If there was a vacuum leak, the idle would be higher - so it has to be a fuel delivery problem because I haven't changed the configuration of anything and the idle hasn't changed indicating a vacuum leak, right?

[Captain Obvious]

On 1/18/2025 at 11:15 PM, chaseincats said:

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?

Those numbers all look fine. I am a little concerned that you would be loosing 2 psi between the pump and the engine compartment, but that could just be different measurement methods or gauges. And those numbers are under low (or no) fuel demand conditions. I'm still wondering about some delivery issue that is only apparent under higher load conditions. Maybe you could tape your phone inside the engine compartment aimed at the gauge and take a short video? 

So about that whole front fire thing and looking for vacuum leaks... Make sure you take a good look at the rubber boot that fits between the AFM and the throttle body and all the associated hoses connected to it. PCV, etc. If you popped a crack in that boot, it'll run lean. Or if you damaged your PCV hose it will also.

[Yarb]

I struggled with my 78 280z for quite awhile on vacuum issues. @Dave WM A known test for pretty much being sure you don’t have any leaks is while at idle loosen the oil cap and slowly remove it. The engine should sputter and begin to stall.

[chaseincats]

3 hours ago, Captain Obvious said:

Those numbers all look fine. I am a little concerned that you would be loosing 2 psi between the pump and the engine compartment, but that could just be different measurement methods or gauges. And those numbers are under low (or no) fuel demand conditions. I'm still wondering about some delivery issue that is only apparent under higher load conditions. Maybe you could tape your phone inside the engine compartment aimed at the gauge and take a short video? 

So about that whole front fire thing and looking for vacuum leaks... Make sure you take a good look at the rubber boot that fits between the AFM and the throttle body and all the associated hoses connected to it. PCV, etc. If you popped a crack in that boot, it'll run lean. Or if you damaged your PCV hose it will also.

I've smoke tested the car a few times and at this point we're all set in that department (the car will die if you pull the oil cap).  Since the idle is actually lower than usual (600) I'd have thought it would raise if there's a new vacuum leak?

Regarding the 2psi drop - I ended up checking it with a new gauge spliced in between the pump and fuel dampener (34 psi), between the fuel dampener and the metal fuel line (34 psi) between the metal line and fuel filter (32 psi).  We ended up blowing out the metal rail with a mechanic shop's compressed air tank system and still sitting at 32 psi.  The car has been at least weekly driven for the past 8 years so there wouldn't be anything in the line especially since you can get 40 psi out of the pump if you pull the fuel regulator hose.  That said, the car is definitely slower even when that is pulled than when it was running properly.

Any ideas? 

[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

 

On 1/15/2025 at 12:42 PM, Zed Head said:

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

 

On 1/15/2025 at 12:47 PM, Zed Head said:

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

 

On 1/15/2025 at 2:19 PM, Zed Head said:

Something else happened at the same time you replaced that hose. 

 

On 1/19/2025 at 1:10 PM, Zed Head said:

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

 

On 1/19/2025 at 7:57 PM, chaseincats said:

Looking on my AFR gauge on the dash, it went from 14.7 on the highway to 19, and was sputtering with no power. 

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

 

On 1/20/2025 at 12:35 PM, siteunseen said:

And where the EGR tube connects to the intake manifold. Mine came loose and rotted a hole in the aluminum. 

 

53 minutes ago, chaseincats said:

 (the car will die if you pull the oil cap).  Since the idle is actually lower than usual (600)

Seems like you're stuck in the classic "what happened" versus "make it run right" dilemma.

Cliff's EGR suggestion might not cause a vacuum leak but might cause full-time EGR.  Diluting the fuel-air mixture, lowering power.  Might explain the lower idle RPM.

Also not clear if your focus on the gauge reading is coloring your impressions or not.  Trying to tune to the gauge instead of the actual performance.  No offense, the human brain is a strange thing.  You're discounting people's suggestions, but aren't showing that you fully understand the source of the problem.  You're in the nope, nope, nope regime.  If running without the vacuum hose helps power then using the potentiometer should also.

Does the engine still "front-fire" if you try to accelerate at a moderate rate?  Off of the full throttle area of the TPS?  You're saying it has low power and lean gauge readings.  How is power if you just go full throttle?  When, exactly, do you feel that it has low power compared to before?

Maybe all of the chaos broke some junk loose and clogged some injectors.  My engine still ran well with these, below, after I replaced the AFM.  Those injectors came with the car.  But it ran a lot better with new injectors.  I probably never needed a new AFM.

[Yarb]

The EFI harness will throw the ECU into scramble mode lack of a better term. Have you rebuilt your harness from top to bottom? If not I highly recommend it. That was my saving grace. Labor intensive including soldering each connection. Not expensive but will take a major variable out of the issue. My two cents. It’s an old girl and wiring connections are critical.

[chaseincats]

1 hour ago, Zed Head said:

 

 

 

 

 

 

 

Seems like you're stuck in the classic "what happened" versus "make it run right" dilemma.

Cliff's EGR suggestion might not cause a vacuum leak but might cause full-time EGR.  Diluting the fuel-air mixture, lowering power.  Might explain the lower idle RPM.

Also not clear if your focus on the gauge reading is coloring your impressions or not.  Trying to tune to the gauge instead of the actual performance.  No offense, the human brain is a strange thing.  You're discounting people's suggestions, but aren't showing that you fully understand the source of the problem.  You're in the nope, nope, nope regime.  If running without the vacuum hose helps power then using the potentiometer should also.

Does the engine still "front-fire" if you try to accelerate at a moderate rate?  Off of the full throttle area of the TPS?  You're saying it has low power and lean gauge readings.  How is power if you just go full throttle?  When, exactly, do you feel that it has low power compared to before?

Maybe all of the chaos broke some junk loose and clogged some injectors.  My engine still ran well with these, below, after I replaced the AFM.  Those injectors came with the car.  But it ran a lot better with new injectors.  I probably never needed a new AFM.

Interesting - ill check on the egr

No more front firing from the engine if you don't push it too hard

The car's injectors are probably around 2 years old

@Yarb - I had the injector plugs replaced/soldered/heatshrunk/wrapped in electrical tape a few years back 

Could the fuel pump be weak, or do electric fuel pumps either work full force then die?

Edited January 22 by chaseincats