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There are many threads out there that talk about doing a Walbro 450 in conjunction with the FPCM but my particular case and my tendency to resist hacking things up too badly, I decided to write this up in case it can help someone else in a similar situation and is willing to spend way too much time on the project. ;-)
The Truck –
2007 Silverado non-Flex Fuel w/ 96” bed (NNBS 1500 W/T 4.8L) RCLB
(As far as I can tell the fuel tank is 34 gallons)
Why do this? –
The stock pump was barely able to keep up when running 11psi boost and fuel pressure dropped down into the 33psi neighborhood despite the commanded voltage from the FPCM being at its max. Once I started running 13psi boost and getting my tune in line, the fuel pressure dropped down to 26psi. AFR was still ok, but slightly unstable and it was clearly time for a bigger pump.
The MU1847 seems to only support up to 550ish HP on gasoline
According to an inquiry made to Walbro the TU464 (drop in unit) can only support around 500 HP since the pump used on it is a 190LPH
My goals –
I want to keep the returnless setup and stock lines/rails/emissions stuff
I want to keep the FPCM intact
I want to use the stock pump assembly with minimal modifications
I want to avoid making holes in the stock bucket to prevent the pump from sucking air when the tank is low (fuel slosh)
There is much debate on whether to drop the tank or remove the bed to work on your pump, but I chose to remove the bed and do the work standing instead of lying on the ground.
I removed the pump assembly and brought it inside to the work bench and that’s where the fun began…
Step 1: Disassemble the stock bucket
I started by removing the fuel level sender, unplugging the sender harness and snipping any wire ties off to make sure it was kept safely out of the way. Unplug the pump harness as well. Now you’ll need to push down on the spring loaded top section and use some needle nose plyers to straighten out the knurl in the bottom of the two metal rods near the bucket so that they slide through and the bucket can be removed. You can now remove the white bucket from the grey lid by pressing in the tabs. Pull the pump and screen out. At this point cut the hose from the pump to the top of the sender unit and get rid of it. You will also find a small ground wire attached to the grey plastic portion of the bucket lid. I carefully removed that and let it go with the harness. Make sure you remove and set aside the pressure relieve valve w/o-ring and plastic retainer. You should now have things fully disassembled.
Step2: Modify the grey bucket lid
Thanks to other threads I knew that the long cylindrical thing was the stock filter so using a hack saw I cut it off flush with the bottom of the lid. You will also need to cut flush the stock mount for the pressure relief valve (see picture). Next, using a hole saw a little larger than the pump diameter, I drilled a hole in the top of the lid (see picture). Finally drill a small hole so that you can thread a long bolt alongside the hole to use as an anchor for clamping the pump in place.
Step3: Install barb fitting into bucket
This is where the venturi/bucket fill portion is dealt with. On the bottom of the bucket you’ll see a small socket where the stock pump would push into via o-ring seal and would pump a small amount of fuel through. By running some tests in a bucket of water with the stock pump determined this was a very small amount but as pressure raises, so does the volume that gets pumped through this orifice. Thread a small barbed nipple into this hole. I slightly heated the brass with a torch and used a socket driver to thread it into the socket somewhat snug. You are now done with the bucket mods (Yes, no holes drilled in the bucket!)
Step4: 4-way Tee fitting
Hopefully this isn’t where people start chucking stones, but here goes. Fabricating this fitting is where I started on the journey but once I got this built, the rest of the project was fairly straight forward and writing it up in this order made more sense to me. For the most part I’ll let the picture do the talking but the general idea is that it has two 5/16” barbs and then has a port for mounting the pressure relief valve and a port to connect 1/8” nylon tubing compression fitting. I purchased stainless fittings on ebay and cut them then TIG welded it up. The portion where the pressure relief goes was simply a ¼ NPT pipe that I drilled out to match the outer diameter of the pressure relief and then welded a washer on it for the plastic clip to snap over and hold the pressure relief on. You may be able to make this with hardware store parts, but it really did not take much time to fabricate with spare parts lying around.
Step5: Mount the pump to the grey bucket lid
Using two worm drive clamps, mount the pump to bolt/screw you threaded into the bucket lid from step2 . Adjust the height so that when the lid is installed on the bucket the screen is pushed firmly down on the bottom of the bucket.
Step6: Plumb the pump
I chose nylon tubing for everything on the pump assembly for a few reasons. To me if you are working with high pressure fuel lines nylon requires no clamps, handles pressure great, resists corrosion, and its relatively cheap considering the alternatives. A little practice (buy plenty extra) and you can form this stuff and perfect your fit onto the various nipples. You’ll notice the loop I made to allow for the slight spring action so that when you install the pump assembly to your tank it can flex some. Making the loop in the 5/16” nylon was done by submersing it in boiling water for a few minutes then slowly making the bend. Keep doing this gradually till you get a nice tight loop. When it comes to pressing the tubing onto the nipples, I used a heat gun to slightly heat the tubing and then some vaseline on the barb itself and then some muscle to push the tubing on. You’ll have to dry-fit all the parts to get the proper lengths for your tubing and take things apart multiple times until you are ready to make the final tubing connections.
Step7: Wiring
Again, I went a bit overboard here but it was par for the course. Using a small flat screwdriver remove the Metri-Pack connectors from the stock harness. Now take two of the Metri-Pack 280 female terminals and solder them into your Walbro supplied harness. (If you already own a crimp tool that is compatible with these connectors you can use that of course). Slide the terminals into the plastic connector and make sure your polarity is correct. On the negative side, make sure you add that small ground wire removed in step 1 and solder that into the connector as well.
I have been running this for the last 2 tanks of gas without issue. I am able to get all the way down to the bottom of the tank (gauge on E and light on with DIC telling me low fuel) and I can still do a full 0-80 pull at WOT with fuel pressure never dropping below 50psi!
*NOTE: The tee I used does not have any backflow preventer so as soon as you key- off, the fuel pressure in the rail will go to 0 as fuel drains back to the tank. When you key-on pressure builds to 60 but fades down to 0 after a few seconds. The moment you crank the pressure comes right back but the only con I’d say is that you have to key on , wait a sec, then crank. From what I understand this is very normal with walbro pumps for years since they don’t have built in backflow prevention valves. In my case the Tee is to blame, but either way I wanted to mention it.
Great write up, but I have a few questions/comments.
-You call it 5/8" line at the top but its actually 5/16", just a typo.
-Is that hose rated for submersion in gasoline/e85?
-Did you upgrade the wiring from the top of the bucket to the FPCM or from the battery/alt to the FPCM? If not I would highly recommend it. I would also use 14ga minimum for the pump, 10 or 12ga being preferred. This pump can draw 20-25amps at high pressure and any voltage drop affects performance.
-My walbro pumps have checkvalves, so not why some do and some dont, but you are right its your pump bleed that makes the pressure go down so quick. Using a checkvalve on your bleed line with a 20-30psi cracking pressure would work to keep the rail pressurized and still operate like you want. Might also get the added benefit of reducing bleed volume.
-And the big one, the way you have your "venturi" isnt quite accurate. Its not a venturi setup, its a pump bleed. You are basically bleeding off main pump flow to keep the bucket full. It will work to keep fuel in the bucket, but you reduced the max output of your pump. The way I understand the FPCM, it actively controls pump voltage to keep the rail pressure at the desired pressure, and the pressure relief only opens at very high pressure (80 or 90psi), so that will basically never open. A true venturi system would use the pump inlet to draw in fuel, but thats obviously harder to do.
I bet if you made a bunch of those fittings you could sell quite a few. The fact is once your typically hobbyist sees "TIG welded", they are out.
-You call it 5/8" line at the top but its actually 5/16", just a typo.
- yes typo! I fixed it above it should in fact be 5/16"
Originally Posted by Atomic
-Is that hose rated for submersion in gasoline/e85?
- Fine question! I have only ever tested it with gasoline and never had a problem on both the 5/16" and 1/8" tubing. I wonder if there is a way to find out the scientific answer? anyone?
Originally Posted by Atomic
-Did you upgrade the wiring from the top of the bucket to the FPCM or from the battery/alt to the FPCM? If not I would highly recommend it. I would also use 14ga minimum for the pump, 10 or 12ga being preferred. This pump can draw 20-25amps at high pressure and any voltage drop affects performance.
- I did not upgrade the wiring but did consider it. I did not run any load tests on the 450 but wow, 20-25amps may demand some heavier gauge wire. Thanks for the tip!
Originally Posted by Atomic
-And the big one, the way you have your "venturi" isnt quite accurate. Its not a venturi setup, its a pump bleed. You are basically bleeding off main pump flow to keep the bucket full. It will work to keep fuel in the bucket, but you reduced the max output of your pump. The way I understand the FPCM, it actively controls pump voltage to keep the rail pressure at the desired pressure, and the pressure relief only opens at very high pressure (80 or 90psi), so that will basically never open. A true venturi system would use the pump inlet to draw in fuel, but thats obviously harder to do.
- Based on the testing i did in my water pale, I call it a venturi because that little tube goes down through the bottom of the bucket and comes back up while drawing gas in as it climbs a long black color plastic mushroom looking thing. When the fuel level in the tank is low (below the heigh of the bucket) this appeared to be drawing liquid up from the outer part of the bucket??? (it was hard to see for sure but I concluded this to be the case?)
I did the same thing with my flex fuel pump bucket, although I took a much simpler route and only used 1 piece of submersible fuel injection hose with a little Dremel action on the bucket lid.
06-02-2016, 12:14 PM
Walbro 450 returnless GMT900 non-Flex w/FPCM stock bucket + venturi
