Engine/Transmission (1998.5 - 2002) What is too much Fuel Pressure

[MichaelRyan]

Hello,

I used to subscribe and am back.

I put in the Glacier walbro 392 system last September and the truck has never run better. It purrs now and seems to run better and throttle response is more linear. Stats Better, Much easier to start after fuel filter replacement.

Well, You can tell I like it.

My FP was down to about 12 at 90000 miles and WOT 6.

My questions is this! How much pressure is too much. I am running 18 psi no matter what maybe down to 17 WOT.

Any help appreciated.



Mike Ryan

 

[16919]

Thats not toooooo high... if it were me I would try to keep it around 15 or so. That is what I heard from Blue Chip. . they seem to know what they are talking about. Supposedly you can damage the seals above 15 or so. Mine stays 14-16 at idle 13-15 cruising and 11-13 at wot.....

 

[Ncostello]

People have ran 7psi pusher pumps in series with the OEM for 22 psi for long periods with success. That used to be the fix.

 

[JR2]

I know of people who have run 20 for a long time, on some trucks its fine on others it make them hard to start. I would shoot for 15-16 and call it good.

 

[rweis]

I am pretty sure 13. 5 psi is calibration pressure. Generally it is thought that +-3 psi is ok.



I think there are 2 issues to deal with.



1. Too much psi (20 + ?????) will cause turbulence in the internal intermediate pump when it fills the input cavity for its pressureization. Too little psi may not fill the intermediate pump cavity completely.



2. There is a metal diaphram between the VP44 low pressure side and the high pressure side. I think the acceptable deflection of the diaphram is . 5mm. This diaphram has seals on it and too much or too little pressure cause the seals to distort.



I think it is generally thought that + - 3 psi (10. 5 - 16. 5) is ok and will give the most optimum intermediate pump fuel charge and not distort the diaphram beyond its . 5mm flex limit.



I do know that when input fuel temp is less than about 40* you gain about 2 psi of pressure(over what it is at 80*). When input fuel temps gets to about 60* you gain only about 1 psi of pressure(over what it is at 80*). When input fuel temps get over about 100* you will lose 1 psi of pressure (of what it was at 80*). When the input fuel temp goes over 120* you are going to lose another (ie 2 # down from what it was at 80*) 1 psi of pressure. I do not let my input fuel get over 120* (Bosch limit is 160*). I have been full time monitoring input fuel temps for 2 years.



I set mine at 15 psi and take the +2 to -2 psi swing. The + side only last for me about 30 minutes at 2000 rpm. I live in warm FL, have 4 fuel coolers on the return fuel, dump the fuel back into the tank at the tank vent line.



I think that a stock truck fuel system will heat the fuel fairly quickly to 80* or so because DC dumps the cooling fuel (after it comes out of the VP44 and is hotter than tank fuel) right back into the same cannister area as the fuel pickup area is. Winter not a bad idea because it warms the fuel , summer I really question the sanity of it because I think the "cooling fuel" gets WAY to hot and it contiributes a lot to VP44 failure in the summer time.



Bob Weis

 

[JKinney]

You can go to glaciers web site and find a scematic of the fuel regulator. Then take it apart and take one of the spring shims out and try that, that might get you down to 15 and 14 wot.

 

[ChrisWilliams]

Hey Bob, does the fuel heater run all the time? I see my pressure drop a pound or two after it warms up good and was wondering about the fuel heater. Maybe hook it up to a thermostat if it's not already.

 

[rweis]

ChrisWilliams -



What you are seeing is the heating of the fuel by the VP44. The "fuel heater" in the fuel filter (which is a different actual heater) is on a thermostat. THe VP44 heats fuel because fo the heat generated by the VP44 doing it's thing (rotating and pressurizing fuel).



The amount of heat the VP44 generates is DIRECTLY proportional to the rpm of the VP44 (which is 1/2 engine rpm) and the load the truck is carrying.



Gary suggested that the load had something to do with it a couple of years ago when I first started watching fuel temperature. I could not see how the VP44 would know there was a load. Gary was right! I can see rpm, because the VP44 mechanism is a rotating pump and it pressurizes fuel every rotation. But, it also depends on the load of the truck.



What you are seeing is the heating of the fuel by the VP44 probably. IF you have a temp sensing IR gun, take the temp of a fuel line before engine start and after you see the pressure drop. It will be different. I find about 90* is when the first psi drop occurs, the second drop about 120*. I do not know what happens when the fuel goes above 120*.



I generally keep my fuel to OAT + (10 to 12)* with the coolers.



Bob Weis

 

[mhenon]

Hello,

I used to subscribe and am back.

I put in the Glacier walbro 392 system last September and the truck has never run better. It purrs now and seems to run better and throttle response is more linear. Stats Better, Much easier to start after fuel filter replacement.

Well, You can tell I like it.

My FP was down to about 12 at 90000 miles and WOT 6.

My questions is this! How much pressure is too much. I am running 18 psi no matter what maybe down to 17 WOT.

Any help appreciated.



Mike Ryan

The Glacier system has the fuel bypass already included. All you need to do is remove the washer in the bypass and install a thinner washer. This will get your pressure down a little. I actually ground down my final washer until I got exactly 13. 5psi at normal cruise. Now the engine idles at 14. 5psi and WOT gets down to 12psi. This may be over-kill but you can play with those washers to get whatever pressure you like.

Mike

 

[DAWG-1]

Fuel Coolers

Hi Bob Weis,

What fuel coolers are you using? I am going to do another fuel system overhaul, at the tank. I plan on changing supply to -8 and the return line to -6. I figure I have enough fittings to install a fuel cooler with -6 ftgs. Thanks, Sam.

 

[rweis]

DAWG-1 What fuel coolers are you using?



Multi part answer:



I tried a couple of different one's: Summit DER 13225, Summit DER 13221, Derale 13252, H7B from Tru-Cool. The Summit one's are for frame mounting (a little easier to mount on the inside of the frame) and have AN-6 fittings. The Derale 13252 was an experiment with a finned tube cooler. The H7B I had from a different project.



Basically I wanted to fill the available linear frame space with fuel coolers. If you do a search, I think now the Duramax's and the PS's both have factory fuel coolers. Dieselsite.com has a flat plate fuel cooler for PS's that would work fine.



I live in FL and even when it is cold (40*) out I still see a 10* fuel temp rise. If you lived in the cold areas of the country you might think about a bypass of at least some of the coolers for the winter months (ie gelling problem). Fuel additive?



I tried forced air blowing on the coolers and found at normal driving speeds air turbulence under the truck works just as well. The hotter the differential of the fuel temp to the OAT temp the better the coolers cool. Sitting in traffic with no air flow around the coolers the fuel temps will rise some, but as soon as you get under way again it comes right down again.



As part of the fuel cooling experiment (to save the VP44) Gary and I also blow OAT air (240 cfm) on the VP44 with a boat bilge blower, especially after shutdown to keep the engine heat soak off the Vp44, but that is another whole concept. But we also found above 40 mph ram air from the bilge blower floods so much air onto the VP44 that it very very substancially reduces the heat the VP44 generates.



I also put a heavy duty thermal heat blanket between my VP44 and the engine block to keep the engine block heat off the VP44.



I also run the fuel return line into the tank filler vent line, and use a DrawStraw for fuel pickup, and use a RASP lp with fuel bypass (same concept as the Walbro installs (fuel bypass concept works really well, I do not cool the bypass fuel - only the VP44 return fuel).



Bob Weis

 

[ChrisWilliams]

Bob, you have done your homework and have some good info. I knew I was getting heat from the VP44, but wasn't sure about the actual fuel heater. I hoped it was on a thermostat. I may add a fuel cooler when I re-engineer my fuel system after my first lift pump goes out. I will need a bypass for when I go to the cold country. I definitely see a drop in fuel pressure and it seems like a drop in power also. Especially after towing the boat a few miles. Of course, the OAT is usually fairly warm and humid as well. Thanks!