ToomTom

GR/GV Fuel System Restrictions [fix included]

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Making this topic so people wont run into the exact same issues @Niran and I experienced. Hopefully this will save people a lot of mucking around.


The Problem

The GV/GR fuel hanger seems to be a significantly restrictive part of the fuel system on late model STI's (MY08 - MY14). Because of this restriction it causes fuel pumps to get hot, cavitate, and eventually fail, causing big issues down the line. The part of the stock hanger which is returning fuel simply cannot flow enough fuel out of it to keep pace with the bypassed amount from regulator. What happens next is rather than the Return line being un-pressurized, it starts building pressure, which affects the performance of the regulator which in turn causes flow/pressure issues down the feed line, which then causes the fuel pump to cavitate. Cavitation link for reference if you don't know what it is. 

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The Solution

This issue can be resolved by using a surge tank setup, or by replacing the fuel hanger with an aftermarket alternative. Radium Engineering hangers have been proven to resolve the issue, as well as the Process West surge tank option. The reason why going to a surge tank solves this issue is because you also change from a high pressure fuel pump, to a low pressure high flow pump which just dumps into the Surge tank. 

Additional Info

  • This may also apply to a select legacy GT's between MY05 and MY07. Someone to confirm, perhaps @Andy_Mac may know, but I believe they use the same hanger.
  • Please note that this discussion is aimed more towards people chasing big power (300kw +) If you are doing simple bolt-on's this may not apply to you so don't worry!


Solution A: Aftermarket Fuel Hanger
The below is for a Radium Fuel Pump Hanger. (20-0380-00, 20-0382-00, 20-0383-00) It is recommended to purchase the plumbing kit for this too.

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Spoiler
  • Note: It is recommended this install be done with a minimal amount of fuel in the tank. This will reduce fuel spills and make installation easier and safer. Draining the tank is recommended.
  1. Remove the rear bench seat that is held in by three clips. The passenger-side receiver clip is shown. Pull the front of the seat up and back at each corner. Lastly, find the center point of the seat, reach underneath and pull straight up. Next, unscrew the four Phillips head screws holding the metal cover plate (shown) in place. Pull the harness and grommet through the hole. Set the metal cover aside and remove the foam. It is recommended to clean the top of the fuel pump housing and the surrounding area as it will likely be very dirty. This will prevent loose dirt from falling into the fuel tank.
     
  2. Squeeze the tabs and unplug the wiring connector on top of the pump housing. Next, remove the fuel hoses, remembering where each routes. First, push the fuel fitting connectors further onto the receiver mating tube. squeeze the 2 plastic tabs. Simultaneously slide the hoses off. Have a rag handy as fuel will instantly leak out of these connections.
     
  3. To remove the fuel level sensor and fuel temperature sender from the OEM fuel pump hanger, first depress the thumb tab and unplug the 4-pin connector from underneath the top plate. Next, pry and pop the fuel temperature sensor probe out of the securing tabs. To remove the fuel level sender, press the thumb tab inwards and simultaneously push the module up and out gently until it unlocks.
     
  4. To install fuel pumps and/or the OEM fuel temperature sensor, the unit must be partially disassembled. Using a 3mm Allen wrench, remove the 4 upper external collector box bolts (2 on each side). Pull up and separate the hanger from the collector box.
     
  5. To install fuel pumps, remove the 3 internal pump hanger bolts using a 4mm Allen wrench. For dual fuel pump applications, remove the “PUMP 2” port plug and replace with the included green bulkhead fitting (lubricate O-ring first). In some instances, it may be necessary to cut the included submersible rubber hose to the specific length. Use the measurements below:
  • * 2.25” (57mm) -> Walbro GSS342
  • * 2.18” (55mm) -> AEM 50-1200 or AEM 50-1000
  • * 2.19” (56mm) -> Walbro F90000262
  • * 1.94” (49mm) -> Walbro F90000267/274 E85
  1. Rotate and align the fuel pump(s) with the cut-outs in the internal pump hanger. Tighten the EFI hose clamps after the alignment is complete. Reinstall the green internal pump hanger bracket. Next, press the filter sock(s) onto each pump inlet and secure with the star washer included with the sock filter.
     
  2. Find the hanging internal fuel pump connector and plug it into the fuel pump. To install the fuel temperature sensor (if equipped), cut the 2 black wires at the white OEM connector allowing as much slack as possible. Strip the wires and crimp the 2 included ring terminals using a standard crimp tool. Secure the ring terminals to the studs underneath the top hanger plate using a 3/8” nut driver. Note: the fuel temperature sensor does not have polarity so wires can be crossed and the readings are unaffected. Wrap 2 zip ties through the Radium hanger bracket and secure the OEM fuel temperature probe to the inner side of the bracket.
     
  3. Reinstall the hanger into the collector box so the supplied fuel level sender connector is outside the box. Route the 2 wires through the opening in the upper side of the collector box.
     
  4. To connect the fuel level sender, cut the 2 wires at the OEM white internal connector allowing as much slack as possible. NOTE: One wire will be black and the other will be either yellow or red. Strip the wires and crimp the 2 included blade terminals using a tool such as Molex 63811-1000. Assemble the included mating connector. Note: the fuel level sender does not have polarity so wires can be crossed and the readings are unaffected.
     
  5. Slide the OEM fuel level sender downwards onto the front of the collector box. Use the included bolt to secure the sender in place and plug it in.
     
  6. Install the OEM rubber gasket to the underside of the mounting flange of the fuel pump hanger top plate. Make sure the rubber nipples are pointing upwards and the gasket is clocked as it only goes in one way.
     
  7. Rotate and insert the float of the hanger assembly into the gas tank first. Then drop the other side in bringing the assembly vertical. Moving the electrical connectors around may be necessary for proper clearance. Install the OEM metal hold-down bracket and tighten all nuts to factory spec in an alternating cross-pattern.
     
  8. Insert a small piece of shrink tube onto each wire, then crimp on the ring terminals included in the kit. Use the 4 smaller ring terminals on the fuel level (and fuel temperature sensor wires if equipped). If powering a single pump using the OEM wiring (check power requirements), crimp the two larger terminals on the pump power and ground wires. NOTE: See the following step for additional details on powering a single pump.
     
  9. If NOT directly powering a pump with the OEM fuel pump controller, solder wires to the pump power wire (Green/Yellow) and route this to a relay. Green/Red wire will not be used.
     
  10. Slide the shrink tube in place then apply heat.
     
  11. Connect the fuel temperature and fuel Level wires to the corresponding terminals on the pump hanger. The sensor wires do not have polarity, so they can be connected to either terminal. OEM Fuel Level Sender (Blue Wire) OEM Fuel Level Sender (Black or Black/Yellow or Black/Red) OEM Fuel Temp Sensor (White/Black Wire) OEM Fuel Temp Sensor (Yellow/Green Wire) Secure the ring terminals to the studs with the included acorn nuts.
     
  12. Locate the 90-degree hose end on one end and no hose end on the opposite end. First, install the 90-deg end to the port marked “CROSSOVER” on the hanger. Run the new hose underneath the sheet metal to the passive (left) side of the gas tank. Next, install the plastic SAE barb fitting into PTFE hose and secure with the included EFI hose clamp (as shown). Lastly, use light oil for O-ring lubrication and install the SAE fitting on the passive side port where the OEM crossover hose was previously attached. When it is fully seated, a click will be felt. Gently tug the hose connection to verify a positive lock has been made.
     
  13. For single fuel pump applications, install the two 90-degree female to female -6AN adapters onto the ports labeled “RETURN” and “PUMP 1”. Orient the 90-degree adapters then install the Radium SAE adapters. Install the OEM plastic fuel lines to the Radium SAE adapter fittings. Make sure they fully “click” into place and are secure. Adjust the positioning of the fittings as needed for optimal hose routing, then tighten all fittings. Make sure the factory plastic fuel lines do not become kinked or routed in a way that causes undo stress on the lines.
     
  14. Reconnect the battery and turn the key to the ON position. Confirm the new fuel pump(s) prime for a few seconds and check for leaks. If no leaks are found, start the vehicle. The engine may run rough for a few seconds until all the air is bled from the fuel system. Recheck for leaks.

 

Source: Radium Engineering

Supporting images to come

 


Solution B: Surge Tank

Process West Anti-Surge Fuel System - https://processwest.com.au/surgetank-08-14

kWKmdlcm.jpg

 

Solution C: Hack Job

Nobody we're aware of has tried this yet, if someone does can you take pictures and post up step by step instructions and ill add it in here.

 

Contributors:   @Dairusire @Andy_Mac

 

Edited by ToomTom
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Ahh I'm an idiot, had my hanger out last night looking for torn hoses. All the covers are still off so I'll pull it again to get some detailed photo’s for comparison. Fairly certain they are the same since pumps and aftermarket hangers are the same for both.

 

The Legacy’s in question will be BL/BP 03-08, not sure if there are any super late ones registered as 09.

 

In semi related news the pump in mine seems ok but the FPCM seems to be intermittently failing to operate which is another issue these cars have due to higher current draws killing the module.

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How does it cause a restriction specifically? I can't fathom it.

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2 minutes ago, Loren said:

How does it cause a restriction specifically? I can't fathom it.

 

My understanding is it can't return enough fuel due to restrictive return line and end orifice so with the pump still spinning it just chops through the fluid rather than pumping which eventually kills it.

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What @Andy_Mac said is right, but to expand on it. 

 

To achieve 300KW+ you need a very high flowing high pressure Fuel pump, this goes up the feed line pressurised and through the rails to the regulator. Regulator then sends fuel back down the return line to tank. 

 

The part of the stock hanger which is returning fuel simply cannot flow enough fuel out of it to keep pace with the bypassed amount from regulator.

What happens next is rather than the Return line being unpressurised, it starts building pressure, which affects the performance of the regulator which in turn causes flow/pressure issues down the feed line, which then causes the fuel pump to cavitate. https://en.wikipedia.org/wiki/Cavitation link for reference if you don't know what it is. 

 

So in short, you modify/replace/change the stock hanger so there is no restriction and thus no pressure issues which could solve your entire problem.

 

The reason why going to a surge tank solves this issue is because you also change from a high pressure fuel pump, to a low pressure high flow pump which just dumps into the Surge tank. 

 

EDITS: Because I'm dyslexic, I'm fixing my grammar and spelling as I spot it. Have to re-read things like this 10,000 times to make sure I've got it all -_-

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@Niran Did your's show issues specifically when on the dyno after a number of runs (heat related), or did it at idle also?

 

It would be interesting to see a test of:

Removing the cradle altogether and just having the hanger (Some of the older models didn't have cradles, mine use to fuel surge under 1/4 tank on track. Keep it above half if it's a street car that goes to the track?).

Keeping the factory cradle but modifying to allow more fuel flow through (again may allow more surge issues but fine for a street car).

Keep factory cradle and route the return out of the cradle

Edited by pl0x

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5 minutes ago, Dairusire said:

So in short, you modify/replace/change the stock hanger so there is no restriction and thus no pressure issues which could solve your entire problem.

Do we know what in the factory hanger creates the restriction?

 

Sounds like a combo of heat and restriction to me

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It sounds like a problem that can be cured in 5 minutes with a hacksaw and a small length of rubber fuel hose.

Edited by Loren
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@Tony might be able to elaborate further. They had a cradle in storage at DTech which they had modified to flow better including adding a second return.

 

Routing the return out of the cradle is what I've been thinking of doing. Just need to have a closer look at it to decide if there will be any negative outcomes from doing that.

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If you read the radium stuff you need to modify the Venturi pump nozzle size or the back pressure creates problems. 

 

The venturi pump is used to pull the fuel from the side of the tank where the electric pump isn’t.  

 

The Venturi pump is just the return line being forced through a small hole to make a jet in parallel to the fuel pickup from the far side of the tank which creates the suction.

 

While I suspected heat initially the Venturi pump system would make most of the fuel returned to the cradle to be from the far side of the tank and therefore likely cooler than expected. 

 

It maybe just just drill the nossle in the factory system bigger.

And maybe add a one way flap or valve to allow more flow to the pump.

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36 minutes ago, Dairusire said:

What @Andy_Mac said is right, but to expand on it. 

 

To achieve 300KW+ you need a very high flowing high pressure Fuel pump, this goes up the feed line pressurised and through the rails to the regulator. Regulator then sends fuel back down the return line to tank. 

 

The part of the stock hanger which is returning fuel simply cannot flow enough fuel out of it to keep pace with the bypassed amount from regulator.

What happens next is rather than the Return line being unpressurised, it starts building pressure, which affects the performance of the regulator which in turn causes flow/pressure issues down the feed line, which then causes the fuel pump to cavitate. https://en.wikipedia.org/wiki/Cavitation link for reference if you don't know what it is. 

 

So in short, you modify/replace/change the stock hanger so there is no restriction and thus no pressure issues which could solve your entire problem.

 

The reason why going to a surge tank solves this issue is because you also change from a high pressure fuel pump, to a low pressure high flow pump which just dumps into the Surge tank. 

 

EDITS: Because I'm dyslexic, I'm fixing my grammar and spelling as I spot it. Have to re-read things like this 10,000 times to make sure I've got it all -_-

 

Great explanation, i have added it to the info at the top

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@pl0x mine munched about 3 fuel pumps. Didn't have as many issues on idle i don't think. Idle is actually a bit funky now with the surge tank setup. But not a biggie. 

 

I think the complexity about modifying the stock cradle is to do with not messing up the venturi that draws fuel from the other side of the tank. Not sure how you solve that when hacking away at it. If you have a solution for that, then hack it up and always keep the tank full - cheap fix 

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10 minutes ago, Niran said:

@pl0x mine munched about 3 fuel pumps. Didn't have as many issues on idle i don't think. Idle is actually a bit funky now with the surge tank setup. But not a biggie. 

 

I think the complexity about modifying the stock cradle is to do with not messing up the venturi that draws fuel from the other side of the tank. Not sure how you solve that when hacking away at it. If you have a solution for that, then hack it up and always keep the tank full - cheap fix 

Hadn't really considered the venturi in my suggested tests above. It would be nice to get some tests on if it is the return line being too restrictive, or heat from returned fuel entering the cradle, or a combo.

You're right though, considering the venturi it gets close to the point of CBF testing and just pay to know a bolt in part is going to solve it.

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Hey guys, from a technical perspective. you aren't describing cavitation as such.

Cavtitation occurs when the pressure on the suction side of the pump drops too low (usually a negative value determined by the pump design) for the pumps given amount of lift. This boils the fluid on the suction side of the pump and the bubbles then collapse on the impeller.

What you guys are describing is more like what I would refer to as dead-heading a pump. This is where the fluid essentially stalls (relative to the impeller) and you get fluid slip on the impeller (like compressor surge).

It sounds like you are driving the pump off the end of its operational curve, and this is driving the current draw up and frying the pump motor.

Can someone measure a dead pumps electrical resistance versus a good pump?

Cavitation would destroy the impeller and maybe the shaft bearings/surfaces. Dead-heading will burn out the motor.



Sent from my SM-G960F using Tapatalk

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Well it’s likely the Venturi nozzle is in line with the the outlet so maybe able to be drilled bigger.

 

Does radium have the sizes written down for the pumps used?

 

Someone with way to much time and a spare fuel regulator could fit a factory pump to the cradle out of the car and see how long it took to empty a bucket from the Venturi second tank side inlet. Then repeat with a bigger pump and it emptied the bucket faster, guess very likely. Then Drill the nozzle size bigger a little bit at a time until it was close to the original time. 

 

Ball valve idea shouldn’t be to hard with plumbing fittings. Just the space to fit it could be an issue.

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Could remove the casing and replace with something like this fuel cell foam

 

https://www.aeromotiveinc.com/product/450-phantom-extension/

 

https://fuelsafe.com/media/catalog/product/cache/1/image/600x600/9df78eab33525d08d6e5fb8d27136e95/i/n/internal_fuel_pump_with_foam_baffeling.jpg

 

Or cut to fit

https://www.harmonracingcells.com/store/c37/Cut-to-Fit_Foam_Blocks.html

 

Edited by Gripless
Can’t link to image as cached by hosting site

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I can see how that thing can cause a restriction now... I didn't know they where completely enclosed. That would cure the terrible surge problems the older cars had. Looks like it could benefit from a lift pump though :)

Edited by Loren

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21 hours ago, Andy_Mac said:

Some pics of the BL/BP cradle for comparison.

Basically identical.

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Would it be possible if someone with a 08-14 Sti could measure the outside diameter of the metal fuel pipes which enter into the engine bay from the firewall.

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