Sonic UltraDork
3/31/20 8:38 p.m.

I would appreciate some thoughts and input on how to improve this fuel system for my needs.  

The car is a 2007 Pontiac Solstice that we use for Lemons racing, bought here on GRM (Sale link), and we have run it in one race so far, where it performed quite well.  

The problem we are having is that as the weekend went on, the usable capacity of the fuel tank dropped.  Initially we could run down to well below 1/4 tank showing and it ran great.  By the end of the weekend we were lucky if we could get to 1/3 tank.   As the tank is small and this is an endurance racing, we want to fix this.  Normally I would just get a Holly Hydramat as they are amazing voodoo magic and a pump to go with it, and I still might, but this is an unusual design. 

The stock fuel system is a 12 gallon plastic tank mounted in the trunk, and in that tank is a complete assembly of the pump, sender, etc.  I have deconstructed the whole thing, here are the parts.  First, at the bottom there is this white tank that is the base everything.  Notice the little rubber red spot, that is flexible and will allow fuel to flow up into the pot from the bottom.  That is the only inlet other than pouring into the top. 

The pump itself sits in the bottom of this tub, but it has a strange pickup:

the black circle goes over the red rubber bit, then the normal sock pickup is on the side, like this

From here, the pump output goes through a hose into a metal cylinder that surrounds the pump itself.  Once that is full then it is pushed out through the top of the pump.  In this picture the pump is in the middle, with the U shaped hose going to the cylinder, then the S shaped hose going from the cylinder to the output from the tank at the top. 



My first thought is that I can get an AEM or DeatschWorks fuel pump that have almost identical dimensions but with the correct 11mm offset pickup to use a Hydramat, then just stuff the whole thing in the bottom of this in place of the stock pump and pickup and put it all back together.  Is there anything I'm missing or should do differently?  Holes drilled in the tub? Get the Hydramat out the bottom?  I'm open to ideas.  

Last thing to note is that there was a surprising amount of crud in this tub when I pulled it out.  As this is a plastic tank I can only imagine that it got some dirty fuel some time in its life.  I'm not sure if it was enough to clog up the red rubber valve at the bottom, but it might be.  I'm planning on cleaning the tank the best I can while it is all apart, but not dropping it as that involves dropping the entire rear suspension.   

Thanks for your thoughts!

Robbie MegaDork
4/1/20 12:52 p.m.

Maybe drill some holes in the sides of the tub. On the right and left when installed in the car, if possible about at the level of 1/4 tank of gas. Maybe the front too. But I'd try to understand the correct operation of the pump design first.

My thought is that would allow fuel to slosh in while turning, but not run out the bottom when you need it.

If the car changed during the race though I'd guess that's likely due to dirt or something and not due to design. Don't try to fix dirty with different design!

Is it returnless fuel system? Looks like the pump dumps the return fuel back into its own sump. Is the idea to use the extra pump capacity to keep the inner sump full while not on full throttle? Can you describe the starvation issue a bit? Starving during corner or a bit later?

Robbie MegaDork
4/1/20 12:54 p.m.

Oh wait! Maybe a tiny spec of crud got in the stopper and allowed the full inner sump to DRAIN out with less fuel.

My guess is if you make sure that rubber stopper holds fuel well you will fix your issue entirely.

Robbie MegaDork
4/1/20 1:01 p.m.

If the above is true, this is what I think is happening:

1. If the stopper doesn't seal, then the inner sump can not easily get more full than the tank level around it. That means both the inner sump empties quickly when you get on the gas.

2. If the stopper does seal, then the pump should be able to keep the inner sump just about full most of the time.

I'm really interested to know if someone knows how these are supposed to work!

Sonic UltraDork
4/1/20 1:55 p.m.

Good ideas

There is a return, it empties generally in the area of the cup/pump, but at the top of the tank, so some may splash and not make it.   Some direction of the return fuel to the cup would probably help.  

I like the idea of crud holding the flap open.  Maybe.  

I also want to know what the intent of the original design was, especially the black bit on the pump that goes over the red flap but isn't really the inlet point on the pump.  

Robbie MegaDork
4/1/20 2:03 p.m.

Yeah, I worked on my Saab pump that had a similar thing going on (that I also never fully understood). 

Looking more closely at the pictures, I THINK that black plastic piece may be generating suction at the bottom and big end based on high flow out of the pump to the small end. Maybe to suck gas in the bottom if the big end is uncovered or to circulate if not.

But the big end looks like it might have a hose Barb on it? Where would that go? Maybe someone has already messed with this pump?

Sonic UltraDork
4/2/20 9:32 a.m.

I'm 99% sure nobody has messed with the fuel pump, the car has 53k miles and was completely stock before DaveM got it and he didn't touch the fuel system.  

I also can't figure out how the black thing on the pump works.   There's some sort of Venturi like thing on it, but not sure how the pump can power it.  

bentwrench SuperDork
4/2/20 1:02 p.m.

The canister is like a swirl pot but mounted in the tank. It is there to keep the pump submerged in fuel.

The black business is a Siphon pump, it bleeds off a little high pressure and sprays it through an orifice to create a suction that helps draw fuel into the canister when fuel level is low.

DO NOT drill holes in the canister!!! Low fuel level delivery will be affected/compromised.

Yes, the return fuel should be directed into the canister or it might get pumped dry.


Look at the new NASCAR EFI fuel cells, they have the same setup but engineered for a lot more volume.

Sonic UltraDork
4/3/20 7:18 a.m.

Ok, that makes sense, thanks! 

So it sounds like the crud in the tank is the real culprit here.   Maybe I'll just try to clean everything really well and give it another try before I reinvent the wheel on this one.  At the least I need to replace the filter on the pump pickup.  

dean1484 MegaDork
4/3/20 1:16 p.m.

If all else fails put a second low pressure pump in the tank with a hydromat that pumps fuel in to the pot where the stock one is located.    

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