Walbro Bypass line

Superduty · 01-31-2006, 12:22 AM

The pump pressures aren't limited unless they have an internal pressure relief. Most don't. So depending on where the pump is running with respect to voltage and restriction, they will develop whatever pressure they do, regardless of what they are rated for. However, when you run them outside their rated pressure, they usually don't last long.

Just so we are clear, this is what I am calling a bypass. When I say the Walbro is supplying the pump 17 PSI with a bypass, I mean we are feeding the pump AND the return line with enough fuel that we see 17 PSI of backpressure.

01-31-2006, 12:32 AM

No good on the link ... Whats the OEM Pressure on the Return line ?

DM

Superduty · 01-31-2006, 12:43 AM

See my gallery for a picture of a bypass.

I dunno what the stock pressure is on the return line. I don't know of anyone else that has ever put a bypass on an injection pump and thus it was irrelevant.

To get that sort of backpressure, we've got 70 GPH flowing past the inlet of the VP44. It doesn't sound like much, but it will feed 700ish HP, depending how much fuel is flowed through the injection pump.

01-31-2006, 12:48 AM

Im cornfused ...LOL 1 st of all .... a Bypass IMO is this

And your bypass regulates the Return line pressure from the Vp44 ?

Superduty · 01-31-2006, 12:53 AM

"And your bypass regulates the Return line pressure from the Vp44 ?"

My bypass provides a path for the fuel to go from the VP44 inlet to the return line without going THROUGH the VP44. Basically the Walbro puts out way too much volume to go through the VP44. The pressure would be about 100 PSI without a bypass. The filter lid would blow.

The original plan was to put a regulator in the bypass, but then we found that the return line provided 17 PSI of backpressure all by itself and decent regulation too because we are flowing so much fuel past the VP44.

01-31-2006, 01:01 AM

Oic .............

Superduty · 01-31-2006, 01:07 AM

Yeah... I didn't expect it to work like that either. But the Walbro flow is very high and it doesn't slow down at 12-15 PSI like other pumps do, so... we need a bypass to get some fuel by the pump and relieve some of the pressure at the inlet.

And if one wants to run a regulator to get really good pressure stability, then you need a second high flow return line because the backpressure of the stock return line is too high.

When 043500QC installed the first Walbro on a second gen, he had the regulator in the bypass line and backed all the way out and still couldn't get the fuel pressure down at idle. Eventually we just threw away the regulator.

And this is all with stock supply lines and filter and suction line.

01-31-2006, 01:08 AM

Where does this line re enter the tank ??

DM

Superduty · 01-31-2006, 01:13 AM

Which line ? The bypass line itself just goes from the injection pump inlet to the injection pump return. See the image in my gallery. Just that little loop of fuel line. The green/blue one. (CP3 people should use a larger line than I did...)

If you are putting a regulator on, the regulator should connect to the injection pump inlet on one end and the other end should connect to the second low restriction return line. I've been told the 2nd gen fuel pickups have 2 return connections, one that is unused. The second return line could connect to that, if it is big enough. Else it could be tee'd into the tank filler vent line ?????

01-31-2006, 01:15 AM

How about a Boost Acuater that closes a valve in the return line to certian levels mimicing boost pressure ? , Posible Monitering with a Fuel Air Mixture gauge

DM

01-31-2006, 01:17 AM

For future referance .... To post a photo from your gallery ...

Go to the photo make it big screen ... Right Click .... Select Copy Image Location ,,, come to the thread ... Click the little Yellow button on the reply window thats a mountain and a sun then right click paste .... then hit OK ..

When you post it will show the photo

DM

Superduty · 01-31-2006, 01:20 AM

No need for it and it is the wrong way to do it anyway.

The right way is to get a high flow regulator and set it for say... 15 PSI and connect it to a return line with 1-2 PSI of backpressure.

The boost compensating regulators compensate 1 PSI of fuel pressure for 1 PSI of boost. So... if the regulator was set for 1 PSI of backpressure (plus 17 PSI from the return) at idle and then boost went to 28 PSI, fuel pressure would go to about 38 PSI because the regulator would go to 28 PSI and the return line would have about 10 PSI. And the Walbro would push it at that pressure too. Bye bye VP44.

Not only that, but finding a boost compensated regulator that would go down to 1 PSI would be hard. Most of them are for EFI cars and they are usually 30 to 80 PSI devices.