Walbro 400 primary pump acting strange, fake? 20b twin pump setup
 

I was hoping that someone may have insight into this strange occurance

I have twin Walbro 400lph in-tank on my 20b FD3S. The pumps are staged. -8 line to the front, into -6 for each rail returning to -6 regulator and factory return back to the tank.

Fuel pressure is easily maintained at 43psi base on the primary pump. Car runs great.

However, I get an hr or two in traffic and the pump starts to whine audibly. If I shut the car off and run the fuel pump by itself, I can hear what sounds like rough growling noises and fuel surging along with a concurrent surging in fuel pressure. Bouncing between 38-43psi.

If the car cools down for an hour, I can return and its smooth as silk for another hour or so.

Does this sound like a fake walbro or damaged pump? Its seems unlikely to me that it may be true vaporlock, as I do have a return system and its hard to boil fuel thats under 43psi of pressure.

This pump worked great in the 13b with factory lines, made 500rwhp for two years. I have run it very low / dry on gas once or twice however.

Thank you for your input,

Zach

I haven't had no issues with my walbro 485 even if I drive the car all day. These pumps seemed pretty robust. I never let the tank go below a 1/4 of a tank. Could possible be a fuel pump giving out especially if the FP is dropping. I would probably verify the wiring for each pump first.

Thanks,

Seems like the pump is going bad. Going to swap it out with a confirmed genuine walbro 400 tonight.

Wiring is 10ga to each pump via 40 amp relay from radioshack

You might want to actually measure the voltage at the pump while the symptom is when it's normal, and when the symptom is happening.

Also, how hot does the fuel get?.

Check your fuel temperature. Your fuel might be getting hot from being pressurized and cycled through the system repeatedly. Especially if you have two pumps pumping way more fuel than is needed it's possible that it's getting pressurized ( heats up), is not needed when it reaches rails, bypassed back yo the tank, increases tank fuel temp and repeats the process... Try same driving style with full tank and with near empty tank see if it take the same amount of time before it acts up. Just my .02 ;)

/\ this

Actually, I'm not using both pumps. Only the primary is running. The secondary is only used over 5psi, so temperature shouldnt be an issue. I do think however that the pump itself may be overheating/dying. I did run it dry accidentally after the build.

When the primary was showing symptom the other day after hours in traffic, I swapped over to the secondary as a test and it ran smoothly, so this should rule out fuel temp / vapor lock

I'm going to swap out the pump today for safe measure. $110 to rest assured that the pump is good. If it still acts up I guess we'll go from there :)

Strangely, I can swap the relay over to the second pump, with the same battery and trigger source and the second pump will run smooth while the primary is acting up. This should rule out voltage to the bulk head / fuel temp. But I will double check the voltage just to be sure.

Only issue left would be the pump itself or wiring in the tank I would think

Yes, pump runs great for 2-3 hrs nice and smooth even fuel pressure no sound. Then suddenly in traffic begins high pitch whine and surging air sound through the regulator with fluttering pressure (lowered).

I had an apexi pump do this on a car after it was run low on fuel for a while. Got super loud. We replaced it an the issue went away. I do recommend checking the voltage at the pump when the issue happens like stated above.

replaced pump and checked voltage; same problem

Test drove the car today. Runs fine for about 30min to an hr then suddenly the fuel pressure starts bouncing rapidly at idle / engine off. If I shut the car off, it will not restart, even with fuel pressure. ZERO signs of firing up. Wait 10-15 mins, flip the pump back on, fires right up!

I'm so confused now.

I've also tried switching pumps in this scenario. Both pumps make the same cavitation sound, yield identical bouncing pressure, and will not fire up the car. The car will remain running smoothly if I do not turn it off.


It sounds like AIR in the lines. How is this happening?


My tank is vented to atmosphere via the charcoal canister vent line, could this cause an issue?

Can too small of return cause the fuel to overheat??? I don't see how that is possible as it ran great with a walbro 400 on factory feed/return on 13b.

I dont Think it has to do with air coming in through the canister or the return line being stock. I have the same setup except with two bosh 044.

I would look to make sure my fuel regulator is working properly. I had the air line to the regulator blocked. The other thing that I would look at is electrical... Does your problem seem to happen when the fans come on or you are somehow loading the electrical system of the car?

Also is the sock (filter) on the pump collapsing where it sucks the fuel?

Cheers

Andrew

i think you are peculating the fuel with too much flow

you could try backing off the main pump some by running it through a ballast resister so it moves less volume
( and using a change over relay you can step back to 13.5 V when both pumps go active )

or you can try a fuel cooler in the return line.

or modding the tank to make the return pip in the opposite corner to the pickups

This makes sense.

First I'm going to install a water temp sender into the pressure regulator gauge port and see if I can measure fuel temps when it aerates.

I like the voltage drop idea

Thanks Andrew,

The socks look fine. We can rule that out because either pump fails during the scenario. Electrical system seems fine. Turning on fans etc doesn't affect the pumps. I have a steady 12v off the relay with the car off. I guess I should check pump voltage while its running.

What do you mean air line blocked? You are referring to the vac port?

Where is the return dumping? I've had cars where it dumps too close to the pickup and aerates the fuel causing similar symptoms.

You should check voltage to the pump while the symptom is occurring. If in fact there is a voltage drop caused by a resistance, the heat generated by the resistance will cause the resistance to go up the longer it runs, increasing the voltage drop, kind of a death spiral scenario. That said, I expect this is not the cause, because it would likely be getting worse every time you run it. But it still should be checked. And it's easy enough to check.

The return is factory and dumping through the metal tube in the tank.

I will check the voltage, however I suspect the cause it too little resistance lol. The pumps are certainly getting adequate power, each is on a relay with 10ga wiring direct from battery in the trunk. I can engage the other pump during the scenario and see 60psi base w same wild aerarion fluttering.

Im putting my money on heat build up from having such a high flowing system. Parallel feeds and a Walbro 400 at full speed is a shit on of fuel to circulate at low loads.

Aeromotive speed controller can modulate pulse width to the pump below 3k rpm and cut the pump speed down so as not to circulate 400lph unnecessarily. This seems most likely the cause. Gotta slow the pump.

Do you have a external inline fuel filter?

Russell 8an 1.5" diameter 3.5" length, 40 micron 130gph rating (walbro 400 is only 100gph at full 400lph)

How about taking the fd3s fuel pump resistor and wiring in between my relay and pump. Then wiring in a second relay triggered by the adaptronic at 3k rpm, and placing thisafter the resistor before the pump to bypass and provide full voltage?

Will reducing the voltage by the factory resistor significantly reduce flow?

Check your filter to make sure is clean.

I have twin 044s running 100 percent of the time with zero issues. I'm with Ihor, I think you return is causing your issue. The return needs to be ran to the floor of the tank, always below the level of fuel.

So would you consider the factory return to be too high in relation to the pickups for these pumps? Attach a hose to the return pipe inside the hanger to extend the length/depth?

Do the pumps making noise even with the Fuel level above half?