Fuel starvation, can't fill tank to FULL?

[CSG Mike]

Originally Posted by ZDan

This morning I went to pull the basket from the driver-side fuel tank. Forgot to pull the fuel pump fuse so got a bit of fuel spray! Fortunately contained within the metal underseat area, nothing got on interior bits. Lotsa fuel vapor inhalation... Unscrewed the big plastic collar, tried to pull the basket but immediately fuel fricking POURED from all around the perimeter. Lotsa fuel, still contained in the underseat metal area. More vapors inhaled... Gave up and put it back together. The good news is that the fuel gauge went from sub-3/4-tank indicated to FULL, which by my calcs it shoulda been. Jostling the basket a bit apparently freed the level gauge up and now it works fine. I'll have to run the tank to empty to investigate further. Have to suspect recent installation of Verus fuel door, which went very smooovely but I have to wonder if it mighta busted loose from its pivot points. FWIW the part I got was a 3-D printed plastic thing and NOT the aluminum part with steel(?) pin shown on the website here: https://www.verus-engineering.com/sh...-wrx-387#attr=.

After breathing normal air for a while, took 'er out for one practice session before TT. Got fuel starvation again after ~4-5 laps. Same as yestiddy. TT is 3 laps so no prob there but damn...

The good (GREAT!) news is I went way faster in the TT than in any practice session. Expected P3 with a high 1:23, but won my class with a 1:22.2 vs. 1:22.6x 2nd and 3rd places. Hellzyeh!

Did open track, again got fuel starvation after ~5 laps. Unlike at NHMS and Palmer, where it happened after extended >180 degree banked lefts, I seemed to be getting it most often halfway through the T1-T2 *right*-hand corners at Thompson Speedway, after a long straightaway! Very very weird...

I'd love to hear any theories about wat dafuq is happening, and solutions that don't involve replacing the stock tank with a fuel cell. TIA!

I think a fuel pressure log overlaid onto lapping data, will be the next thing to do here.

[jflogerzi]

Originally Posted by NoHaveMSG

Surge tank is the next step. I don't think the fuel basket holds enough fuel for long sustained corners to keep the car feed. I am still getting fuel cut too with the verus fuel door. I need to keep at least 1/4 tank in my car.

He was getting it at nearly 3/4's full...

[ZDan]

Originally Posted by jflogerzi

He was getting it at nearly 3/4's full...

More like 7/8ths +

[ZDan]

Originally Posted by FR-S2GT86

Have you begun monitoring your fuel pressure yet? Are you absolutely sure your engine is actually starving for fuel or could it possibly be something else?

I logged data when it was doing it at NHMS and tuner had a look and said "classic fuel starvation". Same exact symptoms at Palmer and at Thompson. Happened sooner at Thompson though, and not associated with any extended/banked left-handers...

[Sapphireho]

Did you replace the black rubber seal(one time use part) and the green ring? And did you put it together properly? I have yet to meet a twin "expert" who has done it correctly.

[ZDan]

Originally Posted by Sapphireho

Did you replace the black rubber seal(one time use part) and the green ring? And did you put it together properly? I have yet to meet a twin "expert" who has done it correctly.

Didn't replace either of those parts. Re-installation went very smoothly, didn't see any evidence of leakage or weirdness when I disassembled again the other day. The green washer ring in particular, don't really see how that would be a problem. IMO it's just there to provide another slip surface so you don't rotate the basket as you tighten the ring. Honestly I think those parts were/are fine, but if/when I go back into it maybe I'll have new replacements on hand.

[renfield90]

The one thing I'll point out is that the car will not update the gauge reading unless it detects slightly more than 2 gallons added. Otherwise the gauge just assumes you parked on an incline or the fluid is sloshing around. (Fun fact, if you're on too steep an incline or jack the front end of the car high enough, it will adjust the gauge closer to full!)

The needle's movement towards empty is always a calculated value - e.g. it knows how much fuel is being used and subtracts it from the current gauge reading. So if it doesn't detect a fuel level change big enough to trip it's "this guy just added gas" logic, it'll continue its march towards zero and even give you the fuel light way too early.

It's possible that the fuel level reported by OBDII is more accurate but I haven't tested this myself.

[ZDan]

Originally Posted by renfield90

The one thing I'll point out is that the car will not update the gauge reading unless it detects slightly more than 2 gallons added.

Ah-HA!

So if it doesn't detect a fuel level change big enough to trip it's "this guy just added gas" logic, it'll continue its march towards zero and even give you the fuel light way too early.

Wow, this is GREAT info to have and perfectly describes what I was seeing with the fuel level gauge "marching downwards" with repeated ~2gal or less fills.

THANKS!

[steverife]

Originally Posted by renfield90

The one thing I'll point out is that the car will not update the gauge reading unless it detects slightly more than 2 gallons added. Otherwise the gauge just assumes you parked on an incline or the fluid is sloshing around. (Fun fact, if you're on too steep an incline or jack the front end of the car high enough, it will adjust the gauge closer to full!)

The needle's movement towards empty is always a calculated value - e.g. it knows how much fuel is being used and subtracts it from the current gauge reading. So if it doesn't detect a fuel level change big enough to trip it's "this guy just added gas" logic, it'll continue its march towards zero and even give you the fuel light way too early.

It's possible that the fuel level reported by OBDII is more accurate but I haven't tested this myself.

My gauge definitely changes with small fuel additions. We added a gallon of fuel at the Pro Solo in Bristol the other week and the gas light went off and the gauge moved pretty significantly.

With that said, it has gotten "stuck" before. I was going to Michigan a few years ago and maybe an hour into the trip, I noticed the gauge was at a quarter tank. I stopped to top off and the car only took 2-3 gallons of fuel before the pump shut off. Got back in the car and the gauge stayed at a quarter tank. Gauge didn't move until I basically emptied the tank and refilled.

[ZDan]

Originally Posted by steverife

My gauge definitely changes with small fuel additions. We added a gallon of fuel at the Pro Solo in Bristol the other week and the gas light went off and the gauge moved pretty significantly.

Maybe it has some logic built-in to ignore small changes in detected level specifically when the tank is nearly full, when it's highly unusual for fuel to be added and probably statistically a lot less likely than a weird reading due to parked on incline.

With that said, it has gotten "stuck" before. I was going to Michigan a few years ago and maybe an hour into the trip, I noticed the gauge was at a quarter tank. I stopped to top off and the car only took 2-3 gallons of fuel before the pump shut off. Got back in the car and the gauge stayed at a quarter tank. Gauge didn't move until I basically emptied the tank and refilled.

Another good data point for me to have! I had been assuming something was causing the sensor to hang up, and given that I only just installed the Verus fuel door I was definitely going to go back in and have a look. I might skip that now and just leave it alone.

Though I still had the fuel starvation (I think) issue at >7/8 tank at a clockwise track that has no extended or banked left-handers...

[TunaNoCrust]

Dan I know how to fix it....


Drive slower!!!

[ZDan]

Originally Posted by TunaNoCrust

Dan I know how to fix it....
Drive slower!!!

nevar!

Haven't done a thing to address the issue. Palmer2 coming up with a long extended lefthander (turns 1-2) that has given fuel starvation (albeit at 1/2 a tank rather than >7/8-tank).

Anybody got any suggestions? Current plan is to hope I can consistently get 4 good laps (all I need for the time trial) starting with full tank. But "hope" is often a shite plan! Sometimes works OK tho...

[Goingnowherefast]

Originally Posted by ZDan

nevar!

Haven't done a thing to address the issue. Palmer2 coming up with a long extended lefthander (turns 1-2) that has given fuel starvation (albeit at 1/2 a tank rather than >7/8-tank).

Anybody got any suggestions? Current plan is to hope I can consistently get 4 good laps (all I need for the time trial) starting with full tank. But "hope" is often a shite plan! Sometimes works OK tho...

Maybe hold out for the gen 2 swaps. They specifically addressed the fuel starvation issues with a redesigned saddle tank and lines, so maybe we'll be able to implement that as a full stop solution.

[CSG Mike]

Originally Posted by ZDan

nevar!

Haven't done a thing to address the issue. Palmer2 coming up with a long extended lefthander (turns 1-2) that has given fuel starvation (albeit at 1/2 a tank rather than >7/8-tank).

Anybody got any suggestions? Current plan is to hope I can consistently get 4 good laps (all I need for the time trial) starting with full tank. But "hope" is often a shite plan! Sometimes works OK tho...

secondary fuel pump on a manual switch that sits on the passenger side, dumping into main pump cup.

Fuel pumps are cheap, and burning one out once a year from starvation is a relatively small price for going faster. It's less than the cost of a single tire.