Superduty

"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."

The 1/4 Swagelock is supposed to regulate the flow. It is called a pressure relief, but the spring inside it should move the piston to make it a regulator. I have used it as such before.

The problem here is that the VP44 seems to be taking very little fuel at idle and even with the piston in the Swagelok backed right off, there is still too much pressure. And then when the Swagelock is connected to the rest of the bypass line and then the return line, the pressure climbs even more. (I am speaking about at idle here.)

Then, when the engine goes to WOT, more fuel goes through the VP44 and less through the Swagelok and with the Swagelok backed all the way off, it doesn't tighten up and the fuel just runs right through it.

I *think* the solution is a larger regulator/SwageLok, but I'd like to see some fuel flow readings before I say that for sure.

Sorry if I caused you guys grief with this.

"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 .?.?.?"

Yep, that is the way it is supposed to work. We are using the Swagelok for the regulator. As soon as I see some flows at idle and WOT, I'll comment on a better regulator setup.

I dunno guys. Is there an external relief ? I thought the way people were talking that the fuel went into the inlet on the VP44 and there was a 14 PSI relief between it and the outlet and I assumed that when people were running 20 PSI they had adjusted the relief, if that is possible. Now I hear 04QC3500 gets 30 PSI without any trouble and I ask where is this relief valve ?

Over "pressuring" the VP44 relief valve ? I guess if we can over flow the Swagelok valve then it is possible to over flow the VP44 valve, if it has one. If that is the case it seems as though the pump is getting enough fuel flow to cool properly !

I've got two other "I dunnos" to add here.

1) I am wondering if the "won't start with 30 PSI" is a symptom of the condition of the VP44. Maybe a good one will or won't start with 30 PSI and a bad one won't or will ? Just an idea.

2) It appears as though the Swagelok is capable of doing some pressure control at 15 PSI (ie 25ish PSI when connected to the return line.) What would be the consequences of running the VP44 at that pressure ? It ain't going to hurt the Walbro.

Funny how we run into these over flow/ over pressure situations when we put a good strong pump in the truck. I'm guessing that either the VP44 has a 14 PSI relief in it that was never designed for Walbro type flow OR the lift pump never made enough pressure for the VP44 to need a relief. Either way, it looks like we have some serious flow at the VP44.

J BODY

FWIW I've been over the use of what is being called the "overflow" valve on the VP44 with tech. They stated that the valve was merely there for some resistance to slow the return flow. There was no number in stone as what it was performing this function at. It in no means or function serves the same function as the "overflow" valve on a 12 valve engine with a P pump.

Superduty

Well, apparently it has too much restriction for the Walbro.

Where is the valve located ? Would it happen to be something that could be replaced with another valve or modified to be a pressure regulator ?

J BODY

Valve is similar to the 12 valve. It's part of the banjo bolt where the return line leaves the VP. I have no data to back this up, but I would want the fuel regulated to around 15psi before it gets to the VP. Maybe I'm wrong, but I have a feeling there is a reason behind not wanting a high psi feeding this pump. I have read in the past where some hard start issues arose with aftermarket pumps delivering a higher rate of psi to the VP.

043500QC

Our valve is in the bypass line right now.

We were under the same assumption you are about the pressure remaining constant, but it seems the high restriction of either the 1/4" Swagelok valve or the return lines is cause our pressure to stay too high.

We were shooting for a constant 15psi at the VP.

043500QC

So the "pressure relief" valve is on the return side of the VP then ?

Ok, let me throw this out then. IF the Walbro is over pressuring the VP, and causing this valve to remain open all the time, wouldn`t that be adding more back pressure to the return system ? Basically, you have excessive flow from the VP`s return line, then you`ve got the bypass flow from the inlet side of the VP as well, which I`m gonna say is fairly high also, all feeding into one small 5/16th`ish line. This would explain the high back pressure in the return system, wouldn`t it ?

BTW, dad has changed the return line to a 1/2" line from the T on the back side of the engine all the way down the where the line goes back to the metal 1/4" line.

043500QC

No grief caused man, this is all part of it. When its all said and done, we`ll have alot better fuel system than when we started for alot less than a FASS or RASP. We just gotta get it figured out.

I think the solution is going to be a larger Swakelok too. He ordered a 1/2" version yesterday, so we`ll see.

Superduty

"We were under the same assumption you are about the pressure remaining constant, but it seems the high restriction of either the 1/4" Swagelok valve or the return lines is cause our pressure to stay too high."

Good.

"So the "pressure relief" valve is on the return side of the VP then ? "

I am envisioning the built in pressure relief valve to be that way. I don't know for sure.


"Ok, let me throw this out then. IF the Walbro is over pressuring the VP, and causing this valve to remain open all the time, wouldn`t that be adding more back pressure to the return system ?"

Yes.

"Basically, you have excessive flow from the VP`s return line, then you`ve got the bypass flow from the inlet side of the VP as well, which I`m gonna say is fairly high also, all feeding into one small 5/16th`ish line. This would explain the high back pressure in the return system, wouldn`t it ? "

I don't think so but I might be wrong. He reported fuel pressure down to 4 PSI at WOT. Me thinks the backpressure on the return line is probably about that. I think the backpressure from the return line is causing the already overflowed Swagelok regulator to act even worse, like it is affecting the set point of it.

We will know when they measure the flows and install the 1/2" Swagelok.

We could also find the return line backpressure for sure if the bypass was temporarily installed without any regulator in it.

CTD NUT

I'm at work right now but I am going home soon and will do the flow calculations for 5/16" line at several pressures....I don't remember the equations off the top of my head but I will get them. We can use the cross sectional area of the tubing and the given pressure to determine the flow. I have a feeling that the regulated full flow return style Walbro fuel system is out-flowing this shared return line with the VP44. It will not matter what regulator is used if the return line is not capable of flowing enough fuel without causing a large pressure differential between idle and WOT. As Superduty mentioned, a quick way to determine this is to remove the regulator return line from the original VP return line and temporarily dump it into the fuel filler. If by doing this the large regulator return line pressure differential disappears between idle and WOT, the shared return line is the problem.

CTD NUT

I'm not so certain that I would call the VP overflow valve a pressure relief valve. I would refer to it more as a flow control for the return line. Since it is return fuel flow that cools and lubricates the VP44, regardless of idle or WOT, there does need to be some return pressure at all times. As long as there is any pressure at the VP inlet, there is more fuel being delivered to it than what the engine is consuming. This additional fuel is what cools and lubricates the pump. Since the VP needs constant return flow all the times and regardless of the operating condition, I don't see how there could possibly be a pressure relief valve set at 14 psi that is regulating return pressure. Otherwise, if 14 psi isn't achieved, how could there be proper cooling and lubricating of the pump with return fuel flow? I think we have already demonstrated that the VP is not truely self regulated with a return style system. Otherwise, it would not matter how much pressure we could apply to the inlet - the pressure would remain constant....and we already know that is not the case - the more flow you pump to the VP, the more pressure is at the inlet.....the VP cannot regulate it.

043500QC

Was just talking to dad about this, he`s gonna try to get ya some flow rates this week. I`m thinkin the 1/2" Swagelok will be here today or tomorrow since its only coming from Memphis and they`re usually only 2-3 days from us. We`re gonna try to install the 1/2" first, then see what that does. IF that doesn`t solve this, my next thought is to enlarge the return line to 1/2" hose all the way back to the tank. But, I`m really starting to believe, like you Superduty, that the small Swagelok is the biggest problem right now. We shall see : )

Superduty

CTD NUT: not to discount anything you are doing or saying, but I find it hard to believe that the return line on the 24V ISB would have really different backpressure from the same line on my 3rd gen. I'm seeing 6 PSI backpressure on it, including the stock filter and the CP3 bypass.

The differences between my installation and 04QC3500s is the 1/4" Swagelok, I'm running a smaller bypass line and the post engine part of the return system.

It should be pretty easy to get to the bottom of this.

Thanks for working with me on this.

043500QC

The return system is 1/4" metal line from the return outlet on the VP and the head. It runs into a T fitting at the back of the engine, then goes down roughly 4 inches, then goes to the plastic line, I`m only guessing at it being 5/16th`s. I know its not 3/8" or 1/4" since I had both those size lines here. Anyway, its plastic all the way down to the framerail, then goes back to a 1/4" metal line that runs all the way back to the fuel tank.


BTW, thanks to everyone who is giving us input on this problem. Once we get this figured out, everyone will have a guide to go by for adding the Walbro pump on a VP44 truck.

CTD NUT

I agree......the return line on the 24v ISB is 5/16" and I doubt that there should be much difference between 2nd and 3rd gen return line idle back pressure and it does sound like the 1/4" Swagelock might be out of it's proper operating range.

CTD NUT

1/4" back to the tank?? Are you certain? If that is the case, there could very well be a flow problem that is causing excess pressure. 5/16" line flows 36% more fuel than 1/4" at the same pressure.