Engine/Transmission (1998.5 - 2002) RASP Question

[DieselRam30]

I have a RASP mechanical fuel system on my truck. Lately, I have noticed that my idle pressure has decreased to 7-8 psi as opposed to the 14-15 psi it used to be. I still have ample high rpm pressure. I realize that 7-8 psi may not be that low, but it seems like the truck occasionally mildly stumbles when idling. As soon as I rev the engine a little, the pressure comes up and any stumbling goes away. I have tried shimming it, but that only increases the high rpm pressure, not the idle pressure.



Should I be concerned with the lower idle pressure, and is there anything I can do about it? Thanks in advance.

 

[paulb]

Make absolutely sure that there isn't any foriegn material in the bypass regulator. If there is anything holding the regulator open, then the pressure will be low at an idle, but once the pump is spinning fast enough, it will over come the "leak" through the regulator. Take the regulator apart (pay attention to how it goes back together), and clean it out very throughly with carb cleaner. Lube it with clean fresh diesel when you put it back together, and you should be good to go.



The stumble you feel is probably the stock lift pump kicking in, because the pressure is low enough to trigger the hobbs switch.

 

[BarryG]

I had the same thing happen a couple years ago on mine. And just as Paul above recommended. I took the regulator apart and put it back together per Bill K's recommendation and all was well. I did not notice any chunks in there but from what I understand it really doesnt take much at all (meaning very small stuff) to keep it from sealing tight and bleeding off pressure at idle. I did that 75k ago and all is still fine.

 

[Graphic man]

x3 on that.

 

[Turbo Terry]

x 4 on that good info

 

[rweis]

5 year warrantee. Call DTT. I had mine start dripping after 4 years and they replaced it. In a different thread someone said that BK is working on a new design RASP. I would call DTT after cleaning the regulator.



Bob Weis

 

[DieselRam30]

Thank you for all the responses. I will trying cleaning it out this weekend, and if that doesn't work, I'll give DTT a call.

 

[rweis]

Stefan eluded to this a couple of weeks ago, that someone there (DTT) was working on a new RASP pump system.



I got one of the orgionals, had a little weeping at the front seal after 3 years or so. DTT sent me a new seal kit, did not stop the weeping. Then they sent me a redesigned RASP pump. The redesign had a much longer bearing housing at the pulley shaft end so a more complete packing could be installed. It looked like the same external gear cut and shafts, just a longer packing box.



IF DTT does not come up with a updated system I can make copies of about a year of research of internal and external pumps volumes, pressures, viscosity capability, manufacturer. There are some external gear pumps that would make a really good replacement.



The biggest problem I was finding was a drive system. I think you could use the Boss Pump drive (which is sort of a takeoff of the first design of the RASP pump) and the component parts are available from GDP. The ratio of crankshaft to pump shaft speed is 3:1 for the RASP.



I researched a fractional hp (1/7 hp) dc motor with something like 100,000 hours MTBF. Totally field rebuildable in about an hour, brushes changable from external access, totally sealed bearings, self cooling, harsh environment rated. I was going to direct couple the motor and pump and put a PWM (made by the motor manufacturer) on it to get 1000 shaft speed which was the optimum efficient speed of the pump.



The whole thing was going to be about $300 and should be good for 3,000,000 miles. I wanted something that would easily outlast the truck, i. e. NEVER visit the lp thing ever again.



I did not put the system together. It was fairly long (~ 24"), fairly heavy (~10 #). I have an Industrial Engineer inlaw and he thought probably 200,000 hours MTBF for the motor and never change the pump as it could pump molten lead, it is that tough. Pumping diesel fuel would be no effort at all.



Finding a pump that will do 60 GPH (bypassable to match the VP44 input) at 14 psi is sort of tricky. Many pumps have much higher pressure, much higher GPH. It's acutally is a pretty small pump.



It will be interesting to see what DTT comes up with. I have always been real happy with their products and service. I think you can bet it will be a good pump system.



NOTE: I even put a dynamic balancer on my 02' with the RASP gilmer belt system. Very tight, very close tolerances, but do able. Ads say it can not be done, it can be very carefully.



Bob Weis

 

[PRout]

Bob, thanks for the info. . (sorry, my question was off-topic so i decided to delete it and move it to this new thread: RASP Pump Availability - TDR Roundtable )

I guess we will have to wait and see what DTT comes up with then...

 

[Stefan Kondolay]

Just testing some heat treated versions for wear right now, it will be coming out for sure. I can't stand how loud the electric ones are and my customers have expressed a huge interest, just trying to get the complete set-up for under $500. Hopefully I can get the price down to help everyone out.

 

[rweis]

The RASP still beats every other pumping system. This should be interesting.



Would you consider $$$. $$ plus the old RASP pump to upgrade to the new pump? Just a thought. Each iteration things like this just get better and better.



Bob Weis



DieselRam30 - I use a Kinsler JetCan as the bypass valve because there are several spring combinations and shim combinations available so you can get the exact pressure you want. You might have to take it apart "several" times as you adjust it, but you have total control and can set what ever psi you want.



Stefan Kondolay - There is a new thread about a week old that the Walbro 392 seems to be starting to have a defined life span at about the 2 year point. Not a lot of failures, but some members beginning to have Walbro 392 pump failures.

 

[Stefan Kondolay]

Bob, I can't really post about my pump on that thread, only members like yourself can.

 

[PRout]

Bob, I can't really post about my pump on that thread, only members like yourself can.

Thanks for the update Stefan. I am very interested, even though I said I'm tired of messing with the fuel system, If it would help, I'd like to be a beta tester.

What I have been thinking is using the hobbs switch to only activate an alarm in the cab, and have a manual switch to activate the backup electric pump. Would need some sort of one way bypass line around the mechanical in case it freezes up the electric would become the main supply.

Thanks,
Phil

 

[Graphic man]

Bob, I can't really post about my pump on that thread, only members like yourself can.

keep us posted on the new set-up

 

[rweis]

PRout - the external and internal gear pumps do not let fuel through if they are not pumping. They sort of act like a one way check valve. Vane pumps can pass fuel backwards through themselves.



What I did was put the backup lp on a switch in the cab. You can put the two pumps in parallel in the plumbing system. when the electric is off it will not let the fuel pass through it backwards and the RASP will be doing the pumping. If the RASP should fail turn the electric on and the RASP will not let fuel pass through it backwards when it is in the "off" state.



I have my RASP mounted up front. I have my backup Walbro 392 mounted on the frame by the tank. The feed line has a Y and feeds each one of them. The output of the Walbro joins the VP44 supply line right after the RASP outlet.



I did away with the hobbs switch because first hobbs started leaking and had to be replaced. The second one failed the annual "oh sh. . the RASP failed" operational test because of corrosion on the hobbs terminals. I changed it to a pure on/off switch and I test it a couple of times a year prior to engine start by turning the electric on, fuel psi rises (set at 16 psi at cool temperatures), electric off, fuel psi drops to about 10 psi, crank the engine, RASP pumps normally (set at 16 psi at cool temperatures).



I have fuel psi gauges to verify fuel is being pumped.



Works for me fairly well, very confident with it 93k miles (as I remember about 85k on the RASP (5 1/2 years))



Bob Weis

 

[dieselboy25]

Old thread, but I am having the same issue of low pressure and surging at idle after changing the serpentine belt and breaking the system open.



I pulled what I believe is the by-pass regulator (brass cylinder with aluminum value and spring inside) twice and cleaned/lubed it, but I have not solved the surging issue.



Is there something I am doing wrong cleaning the by-pass regulator or am I removing the wrong one? There is another brass cylinder that is mounted right after the stock lift pump.



Obviously I did not install my system, but I hope to figure this out myself.

Thank you,

Eric