2nd Gen Non-Engine/Transmission Fuel Pressure Fluctuation with FASS

[BeefDoc]

I have a 95gph Fass system installed on my truck. I have a Westech fuel pressure gauge (16psi) plumbed into the top of my fuel filter cover. The FASS system has been in the truck for just short of 3yrs (around 4000hrs). For the first 2000hrs or so, my fuel pressure gauge was pegged at 16psi no matter what. For the last 2000hrs 14-15psi at idle 11-13psi pulling at wot. For the last week when the air temp is warm (85+) 10psi at idle 5-8psi pulling at wot. If air temp is less than 70, 14-15psi @ idle 11-13psi pulling. I assume one of these four: 1. Pressure gauge inaccurate. 2. Fuel strainer restricting fuel flow. 3. Pickup tube screen is collapsed. 4. Fuel pump is failing. I have checked the gauge with a mechanical gauge on the scrader valve and feel it is accurate. I have not checked the pickup tube or replaced the strainer. But with the pressure variations noted with temperature changes, I am afraid the pump maybe failing (cooler, thicker fuel will pump better and give me more pressure than warm thinner fuel). I intend to replace fuel strainer here shortly. I have not done the 5 gallon pail test, but am not sure of its value (unless it pegs the gauge to 16psi) because I don't get the pressure drop with higher rpm unless I am pulling the truck hard. Would like some input and advice from you folks please.



Thanks

Matt

 

[LowFly]

I have a 95gph Fass system installed on my truck. I have a Westech fuel pressure gauge (16psi) plumbed into the top of my fuel filter cover. The FASS system has been in the truck for just short of 3yrs (around 4000hrs). For the first 2000hrs or so, my fuel pressure gauge was pegged at 16psi no matter what. For the last 2000hrs 14-15psi at idle 11-13psi pulling at wot. For the last week when the air temp is warm (85+) 10psi at idle 5-8psi pulling at wot. If air temp is less than 70, 14-15psi @ idle 11-13psi pulling. I assume one of these four: 1. Pressure gauge inaccurate. 2. Fuel strainer restricting fuel flow. 3. Pickup tube screen is collapsed. 4. Fuel pump is failing. I have checked the gauge with a mechanical gauge on the scrader valve and feel it is accurate. I have not checked the pickup tube or replaced the strainer. But with the pressure variations noted with temperature changes, I am afraid the pump maybe failing (cooler, thicker fuel will pump better and give me more pressure than warm thinner fuel). I intend to replace fuel strainer here shortly. I have not done the 5 gallon pail test, but am not sure of its value (unless it pegs the gauge to 16psi) because I don't get the pressure drop with higher rpm unless I am pulling the truck hard. Would like some input and advice from you folks please.



Thanks

Matt

OK... first off, do you have the FASS (2 filters) or the HPFP (Just the pump)? That is going to make a difference on how we approach this.



When you checked with a mechanical gauge, did you run the truck down the road and load the engine up? Reason why I ask is we need to get that reading if we can. I see many sending units fail and cause pressure issues all the time and I don’t trust em…. new or old.



Bucket test…. we need to try it…you mentioned that you were going to…so that is good.



Let me know if you got a FASS or HPFP and we can go from there….

 

[BeefDoc]

I just have the HPFP, using the factory filter. I will try tomorrow to get a mechanical gauge rigged so I can test the pressure going down the road. I will keep you informed as I get a few more diagnostics done.



Thanks

Matt

 

[LowFly]

I just have the HPFP, using the factory filter. I will try tomorrow to get a mechanical gauge rigged so I can test the pressure going down the road. I will keep you informed as I get a few more diagnostics done.



Thanks

Matt

Wonderful... . that helps me out tons.



ALSO... check your prestrainer... make sure is a NAPA 3270. If you use a "Filter" it will not work. We use a 144um wire mesh strainer to reduce restriction but protect our pump. Anything tighter will cause issue with pressure under load. Something to check at least... .

 

[BeefDoc]

It's been really busy here lately so it may be a few more days before I can get any decent diagnostic work done with this situation. I have never seen my gauge drop below 5psi so I think it should be safe to drive the truck for the short term. As soon as I have any data/more info, I will relay it to you. I really appreciate your time, advice and patience.



Thanks

Matt

 

[LowFly]

No prob, im not going anywhere! haha... . :-laf

 

[BeefDoc]

I finally got a mechanical gauge hooked into the schrader valve on the pump. The fluction is still somewhat exhistent, but the pressure so far does not drop below 10psi under heavy load. 16psi at idle, 12-14psi moderate load. When new, the pump would not drop below 16psi no matter what. Do I need to do anything with the pump or is this slow loss of pressure common for the age and hours on my pump???



Thanks for the input



Matt

 

[BeefDoc]

I have run the truck for a few weeks now with the mechanical gauge on the scrader valve on the pump and the fluctuation has not changed. Under heavy load, the pressure will not drop below 10psi. Is this a common finding on a pump of this age/hours?? Do I need to do something to keep the pressure higher?? Thanks for your time



Matt

 

[LowFly]

I have run the truck for a few weeks now with the mechanical gauge on the scrader valve on the pump and the fluctuation has not changed. Under heavy load, the pressure will not drop below 10psi. Is this a common finding on a pump of this age/hours?? Do I need to do something to keep the pressure higher?? Thanks for your time



Matt

Sorry Matt... . your 2nd to last post didnt pop in my e-mail.



I have never been a huge fan of reading off the scrader valve due to the restrictoin you get due to the valve itself. Can make the gauge lazy and drop under load. Plus did you bleed the air out of the line between the valve and gauge? If you didnt, this coudl also cause a drop in pressure as well. Not tring to point fingers elsewhere... i just want to make sure all our bases are covered on this.



As for the pump, get me a SN on it and let me run it. We might have a few things we can try depending on the age and such.

 

[BeefDoc]

S/N is 1046, invoice number is 200501042. Any advice or suggestions are always appreciated.



Thanks



Matt

 

[icman95]

I'm looking forward to finding what the cause of your problem is. I have the same kit as you and sometimes during the winter here I encounter almost the same problem. The pressure drops in the same manner your described, sometimes with your numbers, sometimes slightly different, but still of concern. I, too, have the Westach gauge with the electric sending unit and always assumed that the thicker fuel (in winter) was messing with the gauge. My HPFP is only about a year and a half old, so I'd like to think that it is the gauge rather than the pump. One thought was that the hole in the sending unit that sucks in the fuel is so tiny (take a look sometime-it's REALLY SMALL) that the thicker fuel in the winter can't flow in there enough to be measured properly. I have no real basis for this-just a theory. One other theory, assuming it's not the pump, is that the cold weather is somehow affecting the sending unit itself, but it does seem unlikely.



I'd like to think that there is nothing wrong with the pump 1) because it's pretty young, and 2) because in the summer it's ROCK SOLID! I pull my 5er up hills fully loaded and can't get it to go below 13-14psi. Not too shabby.

 

[LowFly]

I'm looking forward to finding what the cause of your problem is. I have the same kit as you and sometimes during the winter here I encounter almost the same problem. The pressure drops in the same manner your described, sometimes with your numbers, sometimes slightly different, but still of concern. I, too, have the Westach gauge with the electric sending unit and always assumed that the thicker fuel (in winter) was messing with the gauge. My HPFP is only about a year and a half old, so I'd like to think that it is the gauge rather than the pump. One thought was that the hole in the sending unit that sucks in the fuel is so tiny (take a look sometime-it's REALLY SMALL) that the thicker fuel in the winter can't flow in there enough to be measured properly. I have no real basis for this-just a theory. One other theory, assuming it's not the pump, is that the cold weather is somehow affecting the sending unit itself, but it does seem unlikely.



I'd like to think that there is nothing wrong with the pump 1) because it's pretty young, and 2) because in the summer it's ROCK SOLID! I pull my 5er up hills fully loaded and can't get it to go below 13-14psi. Not too shabby.

Always start by double checking the gauge. Especally if its an electric. Mechanical with diesel to the gauge is best to check with IMHO.

S/N is 1046, invoice number is 200501042. Any advice or suggestions are always appreciated.



Thanks



Matt

OK... . 8-5-05 i show you got this pump... . you are on the books.



BUT that pump is old enough that there is no wire seal. What you can do is open the top of the pump and check the ball and spring to see if there is any issue with the spring or debris under the ball. Its very simple and the o-ring and gasket can be reused without issue in most cases.



Another thing is you can contact your selling dealer and have them get intouch with me.



I only suggest this to units that predate our wire wnty seal.

 

[SSolderitch]

Last year when I bought the truck, I changed the filter with a paper element fiter, OPS! I still have good pressure. But now, per your sugestion, I went out to buy a prestrainer... like a NAPA 3270. but it was out of stock... so I got a 3253 (same as a 3270-with 120 mesh) and will install it this weekend. However I don't seem to get that 5 second pre start pump run? The pump has gotten quite loud when running. The pump was bought in 05, installed at ADS in va. by the previous owner. (we are both from PA). Could I have sucked something in my pump also? I don't see any wire. Were you offering a rebuild & flow check for a few bucks? local dealer? I won't drive to VA. for that. Advise.

 

[LowFly]

Last year when I bought the truck, I changed the filter with a paper element fiter, OPS! I still have good pressure. But now, per your sugestion, I went out to buy a prestrainer... like a NAPA 3270. but it was out of stock... so I got a 3253 (same as a 3270-with 120 mesh) and will install it this weekend. However I don't seem to get that 5 second pre start pump run? The pump has gotten quite loud when running. The pump was bought in 05, installed at ADS in va. by the previous owner. (we are both from PA). Could I have sucked something in my pump also? I don't see any wire. Were you offering a rebuild & flow check for a few bucks? local dealer? I won't drive to VA. for that. Advise.

If you can part with the pump for a few... i don’t have any issue getting it here and testing it and updating as needed.....



That 120um should be WAY better than your filter you got. See where that gets you when you install it.



As for the 5 second thing, we are a slave to the ECM. IF the ECM doesn’t tell the pump to run, we don’t run. SO might look back and see if you flash the ECM with a tuner (Smarty???) or had some work done at the dealer that might have included a reflash. That is the most common thing that causes that.

 

[SSolderitch]

my pump info: installed Oct 05 at ADT in WV. , SS# 01027. Filter was replaced, pump seems quiter, have to see when hot. Overnight temp high 50's, still not wait light? maybe bad temp sensor? Still no pump prerun cycle? key on twice & starter bump and still nothing? Enging started fine and built 16psi (normal for me) in about 5 seconds. I had no recient ECM reflash as stated in another post. Question: about the part needed to be returned: my pump has the thick block with the fuel line port, then a 1/4" plate, then a thick block with the metal tag, then the motor. What do you need me to sent back? My pump was mounted horizional with a bracket using the 4 bolts on fuel block end (with extra nuts) and a metal strap around the motor. Thanks for the help!

 

[darkhorse]

Those electric sending units are sensitive to weak grounds. I had trouble with mine until I ran the ground direct to the battery. It's worked good since.

 

[icman95]

Good to know. I'll have to look into that if I have more problems.



I realize that the mechanical gauges are a bit more reliable, but a buddy of mine has one and the line in to it leaked once dripping diesel into the cabin. It wasn't too serious, just a bit, but I still would like to avoid running fuel into the passenger area. Just in case. This leaves me with the electric gauge.

 

[LowFly]

my pump info: installed Oct 05 at ADT in WV. , SS# 01027. Filter was replaced, pump seems quiter, have to see when hot. Overnight temp high 50's, still not wait light? maybe bad temp sensor? Still no pump prerun cycle? key on twice & starter bump and still nothing? Enging started fine and built 16psi (normal for me) in about 5 seconds. I had no recient ECM reflash as stated in another post. Question: about the part needed to be returned: my pump has the thick block with the fuel line port, then a 1/4" plate, then a thick block with the metal tag, then the motor. What do you need me to sent back? My pump was mounted horizional with a bracket using the 4 bolts on fuel block end (with extra nuts) and a metal strap around the motor. Thanks for the help!

All I would need was just the pump. BUT some send the pump and bracket which is ok if you wish. All that I ask is that i get a RMA number on it first before you send it so i know what it is when it gets here.



I dont know about the key bump. It should run the pump if the ECM is powering the relay. I might suggest checking with a test light and see if you are getting power on Pin #85 on the relay plug when you bump the key.



https://www.turbodieselregister.com...9-fass-no-workie-wh-1002_wiring_schematic.pdf

 

[LowFly]

Good to know. I'll have to look into that if I have more problems.



I realize that the mechanical gauges are a bit more reliable, but a buddy of mine has one and the line in to it leaked once dripping diesel into the cabin. It wasn't too serious, just a bit, but I still would like to avoid running fuel into the passenger area. Just in case. This leaves me with the electric gauge.

This is very rare and i would say the issues would be directly related to the quality of the items used and install. Not implying anything, just saying...



I have a needle valve plumbed inline with my gauge so if i ever smell diesel in my cab... i can cut off all fuel flow to my gauge... not to mention that i have the thing just cracked opened to snub all the noise from the VP-44.

 

[icman95]

Well, now that's a good idea, Dan. My friend with the leak is an engineer and neither one of us thought of that when discussing why I was getting an electric gauge rather than the same mechanical one he had. Just an overlooked idea.



Thanks.