Engine/Transmission (1998.5 - 2002) Fass Failure?

[BMote]

I am having problems with fuel pressure. Fass pump will start up, and build pressure (16#) then after 5 secs pressure slowly drops to 0 and stays there with pump running. I have taken both lines off pump and put temp 3/8 line to 5 gal pail, pump will push lots of fuel. Put pickup line back on pump, still moves lots of fuel. This would rule out a faulty pickup line screen, I believe. Taken line off at fuel filter feed point and still moves a lot of fuel. Put guage back on system, and pressure drops to 0!!!!! It would appear that I can't hold pressure. What goes on here is baffling me. Any clues where to go next?





2001 W250 Fass 90 , auto, skyjacker4" lift, 4" :-laf exhaust, brush guard,

 

[Cummins724]

Sounds like a bad gauge if the flow is there until the gauge is on.

 

[JLabossiere]

It sounds like the relief valve on the pump to the return line is faulty. May have a bad spring in it or the valve has something holding it from seating. It only takes 5 minutes to check it out. Hope that helps cure the problem.

 

[JStrosnider]

Have you completely bled the air from the fuel line feeding your guage (manual guage I assume)??? I had a similar problem when I changed my fuel filters the last time. . I think I spent about 15 minutes trying to bleed the air from my gauge and pump. . When the pump would turn on it would go to 20 psi then drop to 0 with the pump running... It took me several try's to successfully bleed the air from my guage and pump but when I did all was well... However I have a manual gauge with a diaphram hookup to my guage... Not sure if you have the same set up or not but if you do it's worth a shot...

 

[BMote]

What is 5 min check on the relief valve setting? Doi I have to take pump off vehicle and take apart?

I have bled all air from system and have run a separate guage with same results.

 

[JLabossiere]

You just have to remove the return line fitting from the pump housing. The spring and valve is behind it. You won't even have to remove the pump to do this. Sometime's when the pump is being installed it get's crap in it and either get's stuck in the pump or in the pressure relief valve or just taken out by the filter.

Your pump is turning and you have flow but no pressure,it's probably something stuck in the relief valve. This is usually pretty rare to happen but it does happen.

DPP also has a trouble shooting chart for the FASS pump at their web site. www.dieselpp.com

 

[bbodammer]

not sure how your gauge is hooked up, but i had the same problem and it was the isolater under the hood. pulled of the top line, added more antifreeze, and pressure is back to normal. always hoping for an easy fix

 

[BMote]

So much for easy to get at. Took pump off truck, dismantle to get at spring and ball in interior middle of pump. 4 -1/4 bolts take off motor. o ring on top, plate sits on pump housing, spring just sits on top of ball in middle of in and out ports. Cleaned all parts, re-assemble and test, still no pressure. Now what do I do? I'm getting a little frustrated about now.

 

[JLabossiere]

Sorry to hear that, I didn't realize you only had the pump and not the fuel-air separator system also. On the filter system the spring and ball is behind the return line fitting, hell a of a lot easier to get at. The only thing I can think of is take it back and exchange for another one or get your money back. You had a lot more patience with this then I would of had. Sorry I couldn't be anymore help with this.

This sound like a pump I had rebuilt at work once, pumped great under no pressure back to tank bottom. But switch it to the stabilizer system under pressure it would die. Found out later when the millwrights checked it out, that when it was rebuilt they forgot to put the half moon key back in on the impeller shaft. No load, the friction between the shaft and impeller would turn it, but as soon as you put it under load the impeller would stop and the shaft would spin in the impeller.

Joel

 

[OL RATLR]

Sounds like a bad gauge if the flow is there until the gauge is on.

Hook you up a mechanical gauge to it and see what happens.

 

[BMote]

I have guage inside after isolator, which will indicate pressure upon startup (16#), then after 2 secs slowly drops to 0. Also, have put mechanical guage on injector pump fitting with same results. Biggest problem here, I'm in Toronto working, 500 miles away from my home and workshop, and don't know where to get help down here.

Anyone in this area help me out here.

 

[BMote]

Joel



Thanks for input, and insight. Got me thinking on right track anyway. Pump gears are driven by half moon shaft, no chance of key missing, ball itself is black plastic and spring is intact. Plate is dowelled so really can't put together wrong. I would try to hook up pressure guage at fass pump port, but don't have fittings to connect guage there.

 

[JLabossiere]

Glad to help a little. Keep trying different thing's, something will klick and it will work.

 

[LowFly]

I have guage inside after isolator, which will indicate pressure upon startup (16#), then after 2 secs slowly drops to 0. Also, have put mechanical guage on injector pump fitting with same results. Biggest problem here, I'm in Toronto working, 500 miles away from my home and workshop, and don't know where to get help down here.

Anyone in this area help me out here.

Get rid of the isolator or rebleed it and seal all pipe fittings with Thread sealant. I bet you that is your issues. By-pass it and see what your pressure does. We see TONS of issues like this.....

 

[OL RATLR]

Get rid of the isolator or rebleed it and seal all pipe fittings with Thread sealant. I bet you that is your issues. By-pass it and see what your pressure does. We see TONS of issues like this.....

The key words is " NO ISOLATOR " Oo.

 

[LowFly]

The key words is " NO ISOLATOR " Oo.

I got's me a Needle valve in my ride.....

 

[Cummins724]

Get rid of the isolator or rebleed it and seal all pipe fittings with Thread sealant. I bet you that is your issues. By-pass it and see what your pressure does. We see TONS of issues like this.....

My brother had the same thing happen on his truck. When he installed a isolator on his 04. 5. It was air bubbles in the line. I agree with Diesel Dan... . Eliminate/bleed the isolator & that should solve it.

 

[BMote]

Hey Dan.

This is not a new install, setup has worked flawlessly for 6 months, Suddenly I lose pressure. I've made no changes to create a problem. I have put pressure guage on injector pump (Schrader fitting) and both guages will indicate 16# on start then after 2 secs drop slowly to 0. I tried to by-pass isolator valve and ran fuel line directly to filter can. Still no pressure indicated on other guage. If I put pressure guage right on pump port after removing pipe plug, will or should this give me a 16# reading?

 

[LowFly]

Hey Dan.

This is not a new install, setup has worked flawlessly for 6 months, Suddenly I lose pressure. I've made no changes to create a problem. I have put pressure guage on injector pump (Schrader fitting) and both guages will indicate 16# on start then after 2 secs drop slowly to 0. I tried to by-pass isolator valve and ran fuel line directly to filter can. Still no pressure indicated on other guage. If I put pressure guage right on pump port after removing pipe plug, will or should this give me a 16# reading?

Yes..... you should see a 16# reading at the FASS if that is your pressure.



OK... . i was under the understanding that you had not tested you pressure with another known good gauge. Here are some suggestions:



-Try the 5 Gallon bucket test. See if you have a restriction. This could be a sign of something that is plugged up. (I just saw you tried this)



-Block off the return line going back to the tank. See what your pressure reads. (NOTE: If you have a 95 GPH OR SN: 3862 and before, slowly block it off and have a friend check the pressure..... you may be able to run it up to 45-100+ PSI depending on what spring you have in your T-block. Dont go much past 30 PSI for testing. The 150 GPH pumps are fine... they are hobbled to about 25 PSI. Just pinch it off 100% with these pumps. ) See if the pressure holds.



-Change any filters.



-Might have some trash in the Check Ball seat in the T-block. The fuel does go through the Water Sep first... but i have seen weirder things happen. This would cause the High pressure bypass to bleed off (if the trash is big enough) and reduce top end pressure. Do not cut any seal wire if you have one on your pump. If you have an older unit without the wire... you can take the four horizontal bolts holding the pump on to the T-block and remove the pump and motor. Carefully remove the wareplate. Under this is the spring and check ball. Clean out and reinstall. 110 in/lbs torque for all 7/16" bolts.



-Trash in the return check ball. BUT this is very unlikely since this is only receiving filter fuel 100% of the time.



I still don’t like that isolator... . even if it is not the issue... i would still take it out..... it will be come an issue down the road someday. This just fits the description of a bad isolator. See if that helps.

 

[BMote]

Final Chapter

Took 2 days off, went away and came back fresh. . Started at beginning again. Cleaned pump, removed all fittings, re-taped and connected, bleed isolator, re-charged isolator to guage line with antifreeze and whatever or wichever was cause, it is corrected. Now .

have my 16# pressure back and a smile on face.

Thanks to all for inputs.