043500QC

Return line size is roughly 5/16. Actually, its a 1/4 metal line, then 5/16 plastic. The return line goes from metal to plastic back to metal on the frame. Problem is Superduty, we can`t get the Swagelok regualtor to adjust down any farther than 8 PSI, and even there, its so far out that the little lock "nut" inside of it won`t thread back in. We up-sized the return line to 3/8 where the plastic line was to try to aliveate some of the return pressure, but that didn`t help any. Any other ideas ? And he`s still pulling down he`s fuel pressure under WOT to around 3-4 PSI.

Superduty

Hmmm.... this is a regulation problem. I had no idea the return line back pressure would be so high. I'm not seeing that on my Ford.

Could you try something ? Instead of plumbing the Swagelock into the return line, temporarily plumb it to a separate line and run it back to the fuel tank. Just stick a hose into the filler hole to test it.

Set the regulator for 15 PSI. It shouldn't be a problem now. Start the engine. Observe or measure the flow coming back from the return line. Then run the engine at WOT (high idle). Measure the flow again. Tell me what it is.

I'd like to know how much fuel is coming through the regulator at idle and at WOT.

I've used those Swagelock regulators before, but never with 8 PSI of backpressure behind them on the return line.

Superduty

I've heard the VP44 has a regulator built into it, set at 14 PSI. What happens if you run the system without the bypass regulator ? Will the VP44 self regulate to 14 PSI ? I guess not because if you over pressure the Swagelok regulator, you see 22 PSI.

Superduty

How is your Walbro wired ? What is the voltage at the pump terminals ?

043500QC

See, I`m thinking it is a regulation problem too. Let me ask you this, what if we went to a larger Swagelok, i.e. the 1/2" version of this one ? Would that allow us to regulate this pressure a little more easily ? The 1/2 version would allow more flow adjustment, correct ?

As for flow, we could have filled a 10 quart pan with fuel an about 30 seconds if we had left the pump on that long.


"I've heard the VP44 has a regulator built into it, set at 14 PSI. What happens if you run the system without the bypass regulator ? Will the VP44 self regulate to 14 PSI ? I guess not because if you over pressure the Swagelok regulator, you see 22 PSI."

Yes, we`ve heard that too. What is the Swagelok pressure preset at ? Do you know, because we pegged his 30PSI pressure gauge the first time we hooked it up (before attempting to set pressure)

"How is your Walbro wired ? What is the voltage at the pump terminals ?"

Stock voltage straight from the truck was around 8.5 volts. I used a 12v/40 amp relay to power the Walbro pump, using the stock wiring to actuate the relay. In other words, I used the stock wiring as a trigger.

Superduty

It sounds like the Swagelok is over flowed, but the backpressure on the return line isn't helping. I think the both of them mess it up.

The Swagelock has to be backed way out to get the pressure down. The body is too small to handle the flow rate.

And the return line restriction drops when the engine goes to WOT. So when the flow slows down the regulator pressure drops and the return line pressure drops and then there is no pressure at the VP44.

I am in discussions with another guy with the same symptoms. He is using a Holley regulator. I'm now wondering how the Holley handles backpressure on the return line.

How much is the Swagelok regulator flowing at idle and how much is it flowing at WOT with the engine idling ?

I need to know these flows to figure out what is going on.

The backpressure on the return line should be nearly the same at idle and at WOT (ie high idle). because the return rate to the tank is nearly the same. The problem seems to be the regulator which is over flowed to handle the regulation properly.

Yeah, these Walbros really pump. What pressure was that at ?

10 quarts = 2.5 gallons per 30 seconds = 5 gallons per minute = 300 GPH.

I really need some concrete flow numbers.

Is there a way to measure the flow at WOT ? Say, using a 5 gallon pail ? I need to know these flows (both of them) to see how much things are changing flow wise at idle versus WOT to size a better regulator.

I think they are set to 25 PSI. Obviously the VP44 isn't regulating the flow to 14 PSI. So much for that theory. We learned something today. That 14 PSI regulator didn't make sense to me. I'm thinking the VP44 is fed by feed pump like the CP3 is.

Here is another question while we are learning. How does your truck start with say 25 PSI of fuel pressure ? Could you test this ? People say the ECM has PWM output to keep fuel pressure down to 7 PSI for easy starting. I think it was to save the lift pump from killing itself trying to feed the VP44 when it wasn't turning.



That sounds good.

043500QC

I`m not sure how we would check those flow rates, at least not "scientifically". Let me ask you these, what would happen if we removed the Swagelok from the return line, and used the larger 1/2" version in the supply line ? Would that be putting too much back pressure on the pump ??? Would the added back pressure from the inline regulator adversly affect the longevity of the pump ?

The truck started fine throughout the pressure range.

I need to add some background info here since dad hasn`t filled out his sign. yet. This setup is on an 02 2500 4wd. He has 100hp injectors, K&N cold air kit, dual 3" exhaust, and an Edge Comp box.

Superduty

"I`m not sure how we would check those flow rates, at least not "scientifically"."

It doesn't have to be really scientific. I won't criticize your methods. Here is what I had in mind.

- plumb the regulator into the bypass, but instead of hooking its output into the return line, hook it to a hose and run it into a pail. Set the regulator pressure to something reasonable, be it 10, 15 or 20 PSI. (You'll need several pails...)

- start the engine in the shop and let it idle. Switch the hose to an empty pail and time how long it takes to fill. That will tell me what the return flow rate is at idle. Shut off the engine.

- get your pails empty and run the test again at high idle, say 2500 RPM. Switch the hose to an empty pail and time how long it takes to fill. This will tell me what the return flow rate is at higher RPMs, and how much fuel the VP44 is taking in. It will give me an idea of how much the flow is changing through the regulator.

Just use a watch to do the timing and estimate the volume of the pails. Nothing fancy. I just need some ballpark numbers.

"Let me ask you these, what would happen if we removed the Swagelok from the return line, and used the larger 1/2" version in the supply line ?"

That is the wrong configuration as far as I can see.

I'm thinking this is strictly a problem with overflowing the regulator, as evidenced by the fact you can't get it adjusted to a low pressure at idle. I **THINK** the return line size will be OK if we had the right regulator in there. I'll give you a better answer if you get me some flow numbers.

"Would that be putting too much back pressure on the pump ??? Would the added back pressure from the inline regulator adversely affect the longevity of the pump ?"

The lift pump needs some pressure relief and putting the regulator in front of the VP44 does not provide that. You'll blow the filter housing lid without some pressure relief.

I think the solution is going to be a larger regulator in the bypass line. I am trying to figure out how much fuel the VP44 is flowing at idle. To me it looks like very little and thus we are over flowing the regulator.


"The truck started fine throughout the pressure range."

Good. That myth is killed.

For those keeping track, we have killed 2 myths in this post.

1) VP44 does not appear to have a 14 PSI pressure relief built into it. The more I read of it, the more it looks like a CP3, minus the ability to feed itself.

2) The VP44 does not need low pressures for easy starting. The reason the ECM lowers the fuel pump voltage during starting is to save the fuel pump. That makes sense given myth #1, ie there is no pressure relief anywhere in the system ie none in the VP44.

043500QC

Ok, I think we can get you some flow numbers, but it might be awhile before we can do this. My shop is about an hours drive from my dads house, so it`s hard for us to do things through the week. He ordered the 1/2" Swagelok today. What affect are we going to have if we totally remove the Swagelok. Would that tell us if it is a big source of the high back pressure ?

I`m not totally convinced we`ve killed the 14psi relief myth. If the relief valve is on the output side of the VP, you would never really know if its relieving the excess pressure, aside from excess flow in the return line. IF thats how it works, and we`re over pressuring the VP relief valve, that might explain the excessive backpressure in the return system(because of the excessive flow in the return line). Or am I totally missing how this works ?

slim51015

What if you just remove the regulater and put a valve in line with the bypass and close the valve until you see say 15 psi.?

BigBlue

I'm gonna argue that one with you. When I had my PE pump the relay for it died and the only way to get it to run was to plug the hot wire directly into the battery. So I'd go and put the wire on the battery and then get in the truck and try to fire it up. When the engine was cold it never had a problem. Once the engine was warm though it was very hard to start with high pressure. The pump was putting out 20psi at idle. Now I don't know if it's just my truck (most likely is) but that was my experience. Once I got the relay working again so it would just run for a brief second before starting and then turn off then I never had that problem again. That was when my truck had 60k miles on the original VP. I'm currently at 92k on the original VP.

Superduty

I'm got an open mind on these myths guys. Tell us what is going on and lets develop some knowledge about how the fuel supply system is supposed to work.

I'll comment more later. I just wanted to let you guys know that if I got the myths wrong, then they are wrong. Lets make them right.

043500QC

The problem I see with that is you would limit your flow to only one setting. If I`m understanding this right, the point of having the regulator is so that there is a more constant fuel pressure throughout the RPM range. By using just a valve, and setting it at idle, you`ll only have one set pressure from idle all the way to WOT. I.E., 15 PSI @ idle may only be 3 PSI at WOT, which isn`t what we`re looking for. By using a regulator, you`ll have a more constant fuel pressure throughout the RPM range because only the excess flow is relieved. At least that`s the way I`m understanding this .?.?.?

Superduty, whats your take on my view of the pressure relief valve on the VP ? Does what I said make sense ?

043500QC

See, we didn`t have that problem on Dads truck. It seemed to start ok with the 30 PSI gauge pegged. We had it straight wired ( to the battery ) the first time we started it. I wasn`t comfortable with the pump only seeing 8.5 volts, so thats why we added the relay. Its so strange how all these trucks seem to be so differant.

slim51015

If you have a valve on the return line restricting flow to maintain 15 psi. at the IP it should maintain 15 psi. at WOT with a high pressure pump.
JMO

I plan on doing this install when I get time I already have the walbro pump. When I do my install I'm going to try to regulate the pressure with a valve in the return/bypass.