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Discussion Starter #1
Hey this may or may not work. But if it don’t, o well. I’ll just buy a used fuel pump and replace to bucket if it makes things worse. With that being said......

So the common fix to high hp fuel starvation is to use a 8.1 fuel pump bucket. Well I have it apart as I type this. Either I got the wrong bucket or I’m just too picky at how I’m gonna rig this up. I don’t like what I’m having to do to make this work and the bottom of the fuel pump sits offset. I don’t like that.

There was also a guy who drill holes in his bucket and said it helped but I could see where fuel could flow right back out....and you don’t want that, so......

What I decided, looking at the way the 8.1 bucket is made, it allows probably twice the amount of fuel in. It has two valves and the gto only had one hole. Yes the 8.1 has more volume too. But the allowing of more fuel in may help. Like I say, experiment. I don’t care if it works or not. I’m just gonna try it. So I tried to mimic the valve hole at the bottom for a flapper. I put it at the rear bottom of the pump. Thinking if the fuel is being sloshed up the back wall of the tank it’ll be able to still go in.
Wonder if I should add another at the underside?

Here’s the 8.1 inlets





This is the single gto inlet



Here’s my eyeballed hole for the little flapper






Little flapper


 

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The GTO bucket inlet uses fuel flow from the FPR bypass to create a small jet aimed at the inlet hole to aid filling.

What does the 8.1 bucket use?
 

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Discussion Starter #4
The GTO bucket inlet uses fuel flow from the FPR bypass to create a small jet aimed at the inlet hole to aid filling.

What does the 8.1 bucket use?
That’s null and void if the bucket is empty and has no fuel to bypass. The 8.1 bucket is the same (well it’s different but it shoots excess fuel inside itself like the gto). Think about it, if I suck the bucket dry and the fuel pump isn’t picking up fuel, it cannot circulate it back. I did just go drive the car....more on my thoughts in a minute.....


The gto tank has no sump. It has no slosh baffles either. So I got in my truck (you guys are gonna think I’m crazy but I don’t care....it makes sense) and had to pick up a new strainer. Old one was dirty. Why not. So anyways, I was thinking. I wish I knew what the fuel slosh looked like. I was thinking about getting a clear container and doing some testing to see where the extra inlet would be best placed. Then I saw it. A 1/3 full poweraide in my cup holder. This is the part where you are gonna think I’m crazy. So I stopped, layer the bottle flat on its side and nailed the gas pedal and watched what the liquid did. How it sloshed to the rear. The place I had decided one seemed to be about ideal. So I proceeded. I actually made those holes bigger in the final result. And then I popped in the little flapper and put it back together.


Put half a tank of gas. Usually has issues around this area so I keep it higher. I made some hits. I did some logs. Fueling was richer and more stable. Not leaning out on the top end but actually getting richer. And oddly the car pulled noticeably harder than it ever has. That poor 4l60 was probably being stressed to the max. I’m gonna have to turn the boost down. I’m seeing 14lbs on the 2-3 shift at 4800-5200rpm and levels off to 12.9psi. More than I feel comfortable with.

So honestly I think I made a move in the right direction. I’ll find out as I run the fuel lower. And report back. I think if this fixes my issue, it’ll be a more elegant mod than rigging up the 8.1 bucket. If it don’t fix it, I’ll do what I gotta do.
 

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Discussion Starter #6
I wasn't trying to make any point, just curious as i've never messed with the 8.1 bucket.
Hey no worries. I was having this discussion with someone else earlier too and he thought my issue would be fuel line size. Which can’t be the case since the fine line gets no bigger when I put over half a tank in it. The only thing that changes is it ensures the fuel pump is completely covered in fuel so it can’t run out of fuel.

I do think this mod helped. But I’ll have to see how low I can let the tank go now.
 

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Discussion Starter #7
Ehh. Experiment failed. Leaned out on me again below half tank. Time to to buy a used gto pump assembly and build me a custom pump. It does feed the fuel pump better when I got over half a talk tho. But the fuel slosh from acceleration just is too much. O well. I tried. Lol
 

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Put a gauge on your fuel rail to monitor fuel pressure. And for that matter, if you intend to keep testing with the potential to lean out, maybe there's a way to install a Hobbs switch that would trigger on low pressure to maybe restrict boost or timing or both?

I'll throw your thread off topic for a bit. I know you said the GTO bucket issue is well documented, but I don't see anything on the forum about it. Granted, I haven't searched, and maybe it's just because my relatively new status hasn't allowed me to see everything on the forum yet... but I don't see it in the fuel system forum.

Fbodies use the stock bucket and pump out more than 600WHP. When they do it with a stock fuel system, all they do is account for pressure drop with VE through a pull. During normal operation, fuel is pulled from the bucket and returned to the bucket. Naturally, the engine consumes fuel, so not as much is returned as is supplied. The deficit is met by allowing fuel to push into the bucket through the flap at the bottom, which isn't spring loaded or anything, it should open freely. The motive force there is just the liquid head in the fuel tank, but that seems to be fine for so many OEM applications with pumps in tanks. If there was no liquid volume in a fuel bucket, that's an issue.

There's so much to go into there, but I honestly believe your issue is driven mostly by your use of the stock 3/8" fuel line. If you watch HCI Fbodies on the dyno and watch fuel pressure, you'll see they make 450WHP and the curve looks nice, but the fuel pressure drops as they get up to the top. Many will never know there'e an issue, because the tuner can compensate with VE.

I'll bet you cash that if you put a digital fuel pressure gauge on your rail and changed nothing but the supply line size, you'll see a serious improvement in fuel pressure stability. Change the return to 3/8" and move the regulator to the fuel rail, and you'll think your gauge is broken because it won't move.
 

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Alright, a quick Google search, and yes I see the threads on the bucket issue. So yeah, I would expect you've improved some by switching to the 8.1 bucket. However, I'd also wager that your current remaining lean issue is due to supply side restriction.
 

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Discussion Starter #10
Alright, a quick Google search, and yes I see the threads on the bucket issue. So yeah, I would expect you've improved some by switching to the 8.1 bucket. However, I'd also wager that your current remaining lean issue is due to supply side restriction.

It’s not. I know that without a doubt. I’ve put a gauge on it. The fuel pressure stays constant when the tank is over half full, keeping the bucket submerged in fuel so it has a constant supply. I have logs both ways. Fuel level high and low. If it was a flow restriction then fuel level would make zero difference. As soon as I get around right under a half tank, fuel pressure will drop like a rock under higher boost and it will go lean to 15 and 16:1. I can run it hard no problem as long as I keep the tank full. Think about it. If it were fuel line causing the issue, it would do it all the time. My afr is a constant 10.8-11.2 at high boost with a high fuel level. Does not lean out at all.
 

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One thing to remember, if you put holes in the rear facing part of the bucket, because that is where the fuel goes under hard acceleration, the fuel in the bucket, due to the G forces will exit those holes draining the bucket
 

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It’s not. I know that without a doubt. I’ve put a gauge on it. The fuel pressure stays constant when the tank is over half full, keeping the bucket submerged in fuel so it has a constant supply. I have logs both ways. Fuel level high and low. If it was a flow restriction then fuel level would make zero difference. As soon as I get around right under a half tank, fuel pressure will drop like a rock under higher boost and it will go lean to 15 and 16:1. I can run it hard no problem as long as I keep the tank full. Think about it. If it were fuel line causing the issue, it would do it all the time. My afr is a constant 10.8-11.2 at high boost with a high fuel level. Does not lean out at all.
If you have a digital fuel pressure gauge that you're logging your pulls against, why didn't you mention you had that data? Did I miss you mention it somewhere?

Even still, your VE can compensate for a drop in pressure without you even knowing it. Your VE would be derived from data you gathered while logging. Your AFR is constant because your VE already "accounts for" the drop in fuel pressure, just like it does on those HCI Fbodies on the dyno that show a rock solid AFR all the way up (while the fuel pressure drops to 45PSI at the top end). So if your AFR showed 12.0 vs target of 11.0 at 6400RPM, your corrective action would be to increase VE for that cell and you wouldn't be addressing the fuel pressure issue, but you'd see a better AFR delivered at a lower fuel pressure. Then, you dial up the boost and have the same issue pop up... add VE, done.

There aren't many more components left in your fuel system left before you get to the supply line and regulator.
 

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Discussion Starter #13
One thing to remember, if you put holes in the rear facing part of the bucket, because that is where the fuel goes under hard acceleration, the fuel in the bucket, due to the G forces will exit those holes draining the bucket
True. i did put the little flapper valve in it tho. gas pushing to get out would shut it. But maybe not. Doesnt matter, I ordered all the stuff to do the 8.1 bucket.
 

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Discussion Starter #14 (Edited)
If you have a digital fuel pressure gauge that you're logging your pulls against, why didn't you mention you had that data? Did I miss you mention it somewhere?

Even still, your VE can compensate for a drop in pressure without you even knowing it. Your VE would be derived from data you gathered while logging. Your AFR is constant because your VE already "accounts for" the drop in fuel pressure, just like it does on those HCI Fbodies on the dyno that show a rock solid AFR all the way up (while the fuel pressure drops to 45PSI at the top end). So if your AFR showed 12.0 vs target of 11.0 at 6400RPM, your corrective action would be to increase VE for that cell and you wouldn't be addressing the fuel pressure issue, but you'd see a better AFR delivered at a lower fuel pressure. Then, you dial up the boost and have the same issue pop up... add VE, done.

There aren't many more components left in your fuel system left before you get to the supply line and regulator.
i dont have a digital gauge, I had a remote mounted (on my windshield lol) manual gauge.

I'm not following what your saying about the VE. I do not see anywhwere on the car where my fuel pressure can be read to the ecm. So I'm not sure how it would know to compensate. And really, what good does it do to increase injector pulse if the bucket is sucked dry and theres no fuel to push?

Basically i know what my problem is, well I'm 99.9% positive from process of elimination....i do appreciate any and all input too.


I will eventually go to a return system and likely build an aluminum tank with a sump in it, but for now, baby steps as that is all i have time for.


I do plan on adding a back wall to the tank with a flap to catch fuel from sloshing back and riding up the back wall of the tank. more on that in the next post.....
 

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Discussion Starter #15
Ok, if you look down in a gto tank, there is a "wall" spot welded in place towards the rear of the tank, right next to what would be the rear of the fuel pump. (i'll take pics next time I pull it out....maybe this weekend if parts make it). That stupid wall has a bunch of 3/4"ish holes in it....whaich seem counter intuitive to me. Im going to make a plate that i can pop rivet in place that has a shelf to stop the fuel from rising up the back wall and escaping the pump.
 

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I'm not following what your saying about the VE. I do not see anywhwere on the car where my fuel pressure can be read to the ecm. So I'm not sure how it would know to compensate. And really, what good does it do to increase injector pulse if the bucket is sucked dry and theres no fuel to push?
it wouldn't, it assumes that the load conditions and RPM that the fuel drop starts happening is consistent. which, i'm sure it probably tends not to be.

I do plan on adding a back wall to the tank with a flap to catch fuel from sloshing back and riding up the back wall of the tank. more on that in the next post.....
i'm having a hard time visualizing how fuel slosh would keep the points where the bucket draws fuel from being submerged.

i had another thought today, but i don't know how relevant it is.

i was wondering if the weight of the fuel, and thus the pressure at the point where the pump is drawing the fuel in, is having any effect on your issue. lower the bucket fuel level, and less pressure at the bottom of the bucket where the fuel is being drawn in through the sock.

now the pressure is more dependent on the height of the fuel than anything, iirc my high school physics. if your bucket can't stay full, even though ther sock is submerged still, the pump can't do the same amount of work to the fluid as if the bucket was full.
 

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Discussion Starter #17
Ok. I really need to draw this out. I don’t have autocad so I’ll just hand draw it. But before I do, I’ll explain a few things and I think you’ll understand.

I know you’ve seen the fuel tank before. It’s a large rectangle. The fuel pump is on top right smack dab in the middle of the tank. Now if you accelerate fast enough and the fuel level is low enough, all the fuel rushes to the back of the tank, uncovering the bottom of the pump. What we have working against us is the tank is sideways, so all that rear wall area is where the fuel will rush to, unsubmerging the pump. Once it sucks the fuel out of the tiny bucket reservoir, your done. That bucket is a makeshift sump. Now think about how fast and engine with 650+hp will empty that thing. Pretty quick. If I were to move the pump up against the wall of the tank, my mind tells me that it would put in in the area the fuel is rushing to, no? Now imagine if I make my own three sided wall close to the pump, basically acting like a catch, I imagine it would trap fuel right there.
 

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Ok. I really need to draw this out. I don’t have autocad so I’ll just hand draw it. But before I do, I’ll explain a few things and I think you’ll understand.

I know you’ve seen the fuel tank before. It’s a large rectangle. The fuel pump is on top right smack dab in the middle of the tank. Now if you accelerate fast enough and the fuel level is low enough, all the fuel rushes to the back of the tank, uncovering the bottom of the pump. What we have working against us is the tank is sideways, so all that rear wall area is where the fuel will rush to, unsubmerging the pump. Once it sucks the fuel out of the tiny bucket reservoir, your done. That bucket is a makeshift sump. Now think about how fast and engine with 650+hp will empty that thing. Pretty quick. If I were to move the pump up against the wall of the tank, my mind tells me that it would put in in the area the fuel is rushing to, no? Now imagine if I make my own three sided wall close to the pump, basically acting like a catch, I imagine it would trap fuel right there.
i get what you're saying, i just don't think fuel slosh is the reason for your bucket not getting filled. you start having this issue below half a tank, not near empty.

this stuff has all been done before, and there are a ton of stuff on this site about what people have done to deal with the same exact issue you are having.

fairly sure the 8.1 setup uses a venturi fed by the FPR return like the GTO had. have you thought about feeding the venturi using a separate fuel pump and not the FPR return? this is a pretty common solution to keeping the bucket full. One pump feeds the engine, one feeds the venturi.
 

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it wouldn't, it assumes that the load conditions and RPM that the fuel drop starts happening is consistent. which, i'm sure it probably tends not to be.
Yes, mostly. If you have 58PSI at all times because you have a garden hose for a supply and return line, and you tune for AFR, your adjusted VE table will reflect it. Similarly, if you have 58PSI through a crazy straw that drops to 45PSI as your demand increases through a pull, and you tune for AFR, your VE table will reflect it.

So while fuel pressure is not specifically accounted for with a sensor in OEM configuration, fuel pressure definitely has an impact on your VE tables. When it gets dangerous is when you tune on a dyno in the 1:1 gear, but then you go pull in the 1:1 gear where a pull takes a different amount of time due to external conditions. Fuel pressure doesn't drop exclusively with engine RPM, it drops with time when pressure drop through the line is a factor.

Good luck on your project!
 

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Discussion Starter #20
i get what you're saying, i just don't think fuel slosh is the reason for your bucket not getting filled. you start having this issue below half a tank, not near empty.

this stuff has all been done before, and there are a ton of stuff on this site about what people have done to deal with the same exact issue you are having.

fairly sure the 8.1 setup uses a venturi fed by the FPR return like the GTO had. have you thought about feeding the venturi using a separate fuel pump and not the FPR return? this is a pretty common solution to keeping the bucket full. One pump feeds the engine, one feeds the venturi.
I read this before leaving work this morning and thought about it the whole way to work. This actually isnt a bad idea. I could mount a stock fuel pump and sock near the rear wall and feed the bucket with it. I'll try the 8.1 bucket first. see how that goes.
 
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