With an open bypass your fuel will take the path of least resistance which is the return line. The feed hole on the CP-3 is smaller than the return line your using if I'm reading correctly. With a proper high flow bypass valve you'll be able to keep the pressures up quite easily. I ran into the same thing during testing and gave up on the open bypass almost right away.

jm02

Richard

 

So you recomend I go with a bypass valve, and ditch the open bypass? If so, could you school me on the bypass valving?

 

Not a lot too it really. If your running a bypass line at the pump you would simply splice in a high flow bypass such as the Aeromotive or the unit I use in my kits. The Aeromotive would be nice and I believe it's adjustable.

The problem with the small bypass valves that people tried at first was that they just couldn't flow enough volume to keep the pressures down. I have a box full of valves that didn't work (nice little brass paperweights now) due to the flow characteristics not being compatible with our pumps GPH output.

To coin a phrase...

"I found two thousand ways to not make a light bulb"

Richard

 

What did you install? Sorry, but for those of us that are not too well versed, you need to explain more.

Scott

 

SD recommended a fuel pressure regulator (adjustable) at the CP3 to ensure good pressure and flow at the injection pump. A search should find his recommended part pretty easily.

If your pre-filter pressure isn't spiking, then you don't have restriction down stream at the Cat. Agree that your by-pass is too open. The whole point of this mod is to ensure proper pressure/flow at the CP3. The open by-pass seems to be self-defeating.

 

Take a look at my Members picture gallery and you'll see that I have the CP3 gauge mounted on the second 3/16" return line that I added. I am using 1/8" hose barb fittings from the banjo bolts for the 1/4" bypass hose, which is much more restrictive than your AN fittings.

My understanding from reading various posts about the stock CP3 is that it wants a high volume of fuel and will take what it needs. Whether or not that fuel should also be under pressure is somewhat of a gray area. The stock lift pump system puts out around 7psi at idle, but the flow volume drops off considerably upon acceleration. In your case it sounds like the flow volume and PSI are remaining constant, but the PSI's are lower than we've typically seen. I'm not convinced that is bad, as most of us aren't running AN fittings like you did. In my case the Walbro is working harder to provide the flow through a more restrictive delivery system, hence the higher PSI's. But if we put our trucks side by side I'll bet your Walbro is providing more fuel volume to the CP3.

If it were my truck, I wouldn't worry about it. As long as the fuel flow and volume is there and the PSI doesn't drop to zero, the CP3 should be happy. If the truck runs smooth and has decent power then that is the real test.

 

I can't believe the Cat filter is using that much pressure. Either there is something wrong with the filter or the way you plumbed it, or, there is something wrong with your pressure guage/sender at the cp3. What type of sender/guage are you using and can you swap it out temporarily with a mechanical to double check pressures???
My bypass is 5/16" and I've got 20-22psi AT the cp3. The only difference between mine and yours is the 3/8" bypass AND your Cat filter. The Cat filter shouldn't be a 20psi restriction. Something isn't right... where exactly are you taking your pressure readings? They aren't in the pics.

 

I agree that RBM should swap out that digital gauge for a mechanical to make sure it's right.

Tony, correct me if I'm wrong, but aren't you using banjo bolts and hose barbs just like I did? If so, then we have a 1/8" diameter restriction at the banjo bolts that RBM doesn't have. The size of the bypass hose really doesn't matter if the entry and exit points have a much smaller opening. That is the bottleneck, and and the reason why CP3 pressures are higher for you and I than RBM. We are all seeing 20psi+ prefilter at the canister. You are seeing close to that at the CP3, while I have 10-14PSI because of my 3/16" secondary return line to the tank (less restrictive overall). It sounds like RBM has completely removed the restrictions in his bypass line and has taken it to the next level. But we still need to confirm that his CP3 gauge is right.

 

Yes I'm using the tapped banjo bolts. I don't know the size of the openings on the bolts but I do know they are larger than stock for more flow.
When I initially did this fuel mod, I had a 3/16" bypass and the pressure was pegging my fuel guage past 30psi. It was only once I stepped up to 5/16" that it was a more friendly 20-22psi which is the current reading I have everyday...
So in my case, the size of the bypass line made a huge difference.
Also, can you explain to me this 1/8" restriction you are talking about. I don't know what you mean.

 

Well I just by-passed the Cat filter and there was no change at all, I didn't think that a filter that is almost 10 1/2 inches long could be that restrictive, thats a heck of a lot of surface area to flow through.

I'm going to try resticting the return a tad and see how that does.

 

Son of a B! My new fuel pressure sender was bad! I returned it back to stock today so I can make a trip tomorrow and when I hooked it back up, all I was seeing was about 1.5 psi at the CP3. I about freaked then, so I tried swapping the psi senders and it turns out I was really getting around 8.5 psi.

So now I don't really know what I was getting at the CP3 with the Walbro and the 3/8" by-pass. Isn't this a kick in the chops...

If I get some days off next week I will try it again after I run a few things by Gypsyman. We'll see how it turns out then...

 

The 1/8" restriction I meant is the size of the threaded hole where the hose barb attaches to the banjo bolt. From the genosgarage.com website.....

The fitting on the bottom is the standard fitting; the fitting on the top has a built–up hex that is drilled to accept a 1/8 NPT male threaded fuel pressure sensor.

 

Blast Chamber.... gotcha.. 1/8npt. I was thinking you were talking about a 1/8" hole. The hole is larger than that...

RBM - I had a feeling it wasn't the filter... those darned sending units...

 

Wow my dealer would FLIP OUT and void my warranty so quick if he saw that.

Nice work.

 

Finally got around to installing my Walbro pump and fuel pressure gauge. Just as Trik396 stated... 3/16" bypass gave a 30 psi reading (pegged gauge) I replaced it with 1/4" hose and nipples and I now hold pretty steady at 21 psi @ idle... cruising 17 psi, HARD into the go pedal it never went below 11 psi. My gauge is a Autometer Electric model so my sender is located in a "T" attached to the bypass tapped banjo, right on the cp3 inlet.