gmctd

That's very good input, and agrees with Paul's assessment - how specifically did the bypass valve fail? Were you able to analyze it in detail?

Philabuster

I shook the pump in my hand and could hear the check ball rattling around like a paint can. In order to get to the bypass valve, one must cut open the metal crimp that connects the pump and the motor--essentially destroying the pump.

I have thought about trying to block off the bypass channel by filling the port on the output side with epoxy so the pump cannot bypass fuel at all and use an external regulator, but at that point, might as well go with a proven $100 Walbro. Interesting to note that the Walbro pumps consume only 6 amps at 70 gal/hr @ 20 psi.

Even for a stock truck, getting rid of the Carter seems to be imperative to maintain *some* reliability--well, as much reliability as the VP44 will allow.

gmctd

No prob - that's the second posted failure mode for the Carter - would have been nice to disect several handfulls of the warranty failures

Philabuster

OK,

I need to think this statement through a little better.

I am in process of installing a Walbro and decided to mount the regulator in between the stock fuel filter and the VP44. The problem I found with having the regulator there is the filter sees at least 5X the flow than originally designed AND it is under higher pressure because the regulator will keep a constant pressure at the VP inlet, but the filter will cause a measurable restriction and the pump will increase the filter inlet pressure as the filter gets dirty. If the pressure differential is too great, it will cause all kinds of messes.

My stock filter housing was leaking recently at the water drain valve. I tightened up the torx screws and the problem went away. Fast forward to my Walbro install (15 psi at the VP44 inlet) and the leak resurfaced and was almost gushing out of the drain handle area. The small o-rings on the plastic dump valve were flat and need replacement, but I am sending a tremendous ammount of fuel through there now and something let go.

I am going to relocate the pressure regulator back before the fuel filter to ease the flow rate going through it and just monitor the fuel pressure like everyone else does. This will drop the pressure a little, but more importantly, reduce the flow volume going through the filter back to normal levels.

I may just replace the leaky stock filter assembly with a Racor unit I have sitting here.

The AIRDOG would have been much simpler to install and I probably should have gone that route.

high country

why not just trigger the lift pump off of a hobbs switch? then you have pressure whe nyou need it none when you dont and it is all so simple?

PaulDaisy

I agree, and said before that careful design would be necessary to avoid blowing a lid off of the filter housing. The filter will create a restriction, and the higher the flow, the larger the pressure drop will be across it. But what I expected was, as the filter becomes dirty and more restrictive, that's when the pressure gradient across it may become high enough to blow it up or cause leaks everywhere. I didn't expect that simply the excess flow would cause that by itself.
I think that your system (with bypass regulator between FF and VP44) would work great if you added a PWM controller (or simply a rheostat) to reduce the flow from the Walbro to less than 5x that of the stocker thereby reducing the pressure in the filter housing. And, consider this: even though Bent_Valves active-feedback PWM system is nice, it is not a must have especially if your bypass regulator does the actual pressure control. It would be enough to simply slow down the Walbro to keep flows in check and reduce pressure gradient across the FF and reduce aeration via excessive re-circulation. I would think you'd need a pressure gauge on the FF housing help understand what that pressure gradient actually is.
-P

slim51015

I've been running a walbro with the bypass between the FF and IP for two years now. I never had a problem with the FF. I change the filter between 5-7000 miles along with the oil.
I run an open bypass into the stock return line. My average pressure is 15 psi.

Philabuster

I removed the stock FF and in it's place, I installed a Racor 690R1210 fuel filter/water separator complete with a 200 watt heater and a water in fuel sensor, except I am using a 2 micron R90S filter element. The heater plug was the same, but I had to splice on a new connector for the WIF sensor. I also added a small FP gage on the FF inlet and I now have a FP on the gage pillar which reads at the VP44 inlet. This will allow me to monitor the pressure differential across the filter--especially because it is a 2 micron.

I relocated the pressure regulator before the filter to avoid any further issues, but I really don't need to worry about leaks from the Racor because it doesn't have any tiny o-rings to blow out. The install turned out nice. Pics to come.

As far as the Walbro goes, it is running at full speed right now. Instead of a PWM or a rheostat, how about wiring in a resistor from a vehicle heater fan motor to cut the voltage in half? I might give that a try with my spare Walbro wired to a 6 volt golf cart battery and see how that works.

Truck is back up and idles fine. Road testing is next.

gmctd

Can you temporarily tap the output of the Walbro to monitor the pre-regulator pressure? If that's a gearotor pump it can pump way in excess of 100psig, not even good in a 15psi Diesel fuel system.

Racor is good to 30psi, and the Fleetguard\Cummins should be in the same range, which is why most a\m systems place the regulator before the filter head.

PaulDaisy

Phil,
Do you have pictures of the Racor installation? You think you could post some for others who might want to follow your path? I am interested, for one.
Thanks! This is great information! I saw a smaller unit (Racor 490) elsewhere for about $120, and Ebay seems to have them for bids for less. The replacement elements are about $20, right?
-P

Philabuster

I traded my friend some stuff for the Racor and filters, which he originally bought new off eBay. I made my set-up from a Vulcan big line FP relocate kit, little extra fuel line and a their FP regulator. I have a cleanable 140 micron screen before the Walbro and a Draw Straw also from Vulcan. The Walbro 392 was purchased from eBay.

I have about 200 miles racked up on my Walbro and the 2 micron Racor set-up. Everything seems to run great. Idle FP is 14psi, cruise is 13psi, and full power is 11psi. Again, I relocated the regulator before the fuel filter and not at the VP44 inlet as originally intended.

This gauge monitors FP before filter, while the in-cab Dipricol monitors FP at the VP44 inlet. I plan to replace this gauge with a bottom mount style connected with a 45* elbow (to clear the oil dipstick) so I can check FP without crawling on top of the engine.


I ran out of fittings so I used 3/8" line from the FF to the IP.