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Discussion Starter · #1 ·
Hi all, new here. I have a Titan XD w/ the Cummins Turbo Diesel, around 76k miles. I replaced the lift pump with a FASS unit a few months ago due to a nagging fuel leak (lift pump itself, not the filter). The truck has been performing awesome since, about a month now. Or at least I thought, that thought changed once I hooked up for the first time to pull my RV with the family. I made it about 80 miles or so when I had a low pressure warning followed by power reduced and a CEL. I pulled off, let it sit, and took off again. 20 miles later the same happened. So I turned around and made the long ride back home in 20 minute increments.

Once home, I made a jack and coke to calm myself as I was pretty annoyed. Then I grabbed my scanner and pulled a p0087- low fuel rail pressure fault. That is the only fault present.

I would have thought low pressure pump as indicated by so many in other posts, but it didn't seem feasible for a new FASS unit to have this issue.

I pulled the main filter (on the engine) this morning, only thing that looks weird is the big o-ring is stretched and will not sit in its groove anymore, so I will be replacing.

FACTS:
-I DID fill the truck the day before at the same store as I usually do, as well as filled the DEF tank for the trip (i put it in the right hole). looking at my primary filter, no crystals or debris of any kind.
-Issue began over 1/2 tank of fuel
-Once off the main highways (70mph) and at slower speeds (45mph) the problem was less frequent.
-Only happens WHILE towing- RV wet is probably 4500lbs

Thoughts?
 

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I’ve never come across an otherwise bone stock with a FASS setups before.

Did the truck feel underpowered or sluggish, as far as drivability?

I would be curious if you’re getting too high of fuel rail pressure. I know the code says ‘low’, however, the the truck even have a ‘high’ pressure CEL or code?

Not sure. I need to re-read and think a little longer.
 

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Discussion Starter · #3 · (Edited)
No, it felt great (no sluggishness or underpowered, no soot from over fueling) until the warning would pop up, then she would basically chug and/or stall out. Pulled over and let her rest a minute then on our way again for about 20 miles.

for reference:
 

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This truck is particularly sensitive to misalignment of the o-ring seal on the filter/housing. Even a small fold, kink or misalignment may result in a pressure leak pulling air and/or reducing fuel pressure often resulting in low pressure warning/alarm somewhere along the fuel delivery system. Fuel may not leak out from the seal when not in operation however when increased suction occurs during operation the seal isn't sufficient to keep the system from pulling in air.

If the pump (s) failed the fault would be persistent not wait until under heavy load. The fact that the fault didn't trigger until sustained heavy load (thus long term high fuel demand) seems to indicate a inflow restriction or deficiency. Another source of this fuel starvation can be blocked or restricted vents into the fuel tank (frequently a bad gas tank cap). After driving for a period at high consumption the vent can't pass enough air into the tank and a vacuum develops, pump can't pull enough fuel and voila, low fuel pressure.



Sent from my SM-N960U using Tapatalk
 

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Discussion Starter · #5 ·
Thanks! I replaced the main filter (on the engine) that had the wonky o ring. I will probably hook the trailer to it again this weekend and just drive on the bypass loop around Charlotte for a couple of hours (70mph speed limit, 1.5 hour full loop) to see how it does. The filter cover was really cranked down tight, thinking that could have messed up the o ring. Installed to spec with white lithium grease. Fingers crossed.
 

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That under hood filter can be trouble if the rubber fitting on the bottom gets torn too. Might check it as well. (I learned the hard way)
 

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I always get a bit anxious when changing my filters because of the o-ring. I keep a small jar of K-Y jelly... oops, I mean petroleum jelly :cool: in my tool box to coat the o-ring with prior to tightening down the housing to lessen the chance of a tear.
 

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I always get a bit anxious when changing my filters because of the o-ring. I keep a small jar of K-Y jelly... oops, I mean petroleum jelly :cool: in my tool box to coat the o-ring with prior to tightening down the housing to lessen the chance of a tear.
I agree. Vaseline on the threads and the o-ring helps with getting the housing turned all the way in for a good seal.
 

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Discussion Starter · #10 ·
Update- So far 2 tanks of fuel with no issue. Planning to tow this weekend and see what she does. Also, with the fass installation I had to tap into a fuse for power and the one I had tapped into actually made the pump run for about 30 seconds after the truck was shut off. I found a different fuse to tap off of that doesn’t stay powered after the ignition is shut off. Not sure if that contributed to the problem or not, but at the very least I think it is better this way.
 

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Discussion Starter · #11 ·
Hey all! Bad news, loaded up and drove at highway speed 70-80mph) finally and it failed again at 80ish miles. Fault code P0087- fuel rail/system pressure too low. Any other thought? This only happens at highway speed with a load/while towing. I have driven it for hours on end at highway speed unloaded with no issues whatsoever.
 

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Hey all! Bad news, loaded up and drove at highway speed 70-80mph) finally and it failed again at 80ish miles. Fault code P0087- fuel rail/system pressure too low. Any other thought? This only happens at highway speed with a load/while towing. I have driven it for hours on end at highway speed unloaded with no issues whatsoever.
Tune and delete that thing!

LOL

But seriously, I wonder if the fuel pressure is too HIGH. Can any technicians on hear confirm if there is even a high fuel pressure code?

there is no way that truck is getting underfueled with the FASS.
 

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Discussion Starter · #13 ·
Tune and delete that thing!

LOL

But seriously, I wonder if the fuel pressure is too HIGH. Can any technicians on hear confirm if there is even a high fuel pressure code?

there is no way that truck is getting underfueled with the FASS.
Lol!
Just what I need, more tunes and fun. My wife would kill me, I already have a project car (a Subaru I am building for over landing etc, so this truck has to be able to tow for when it breaks down lol).

I felt the same way though- no way this thing is actually low on the low pressure side. I think my bigger fear is the high pressure pump is failing after long periods of high load, ie 80mph pulling a 5k lb trailer. But that could be way off.

the p0087 is the only code theta I know is throwing. 🤷🏽‍♂️
 

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Hey all! Bad news, loaded up and drove at highway speed 70-80mph) finally and it failed again at 80ish miles. Fault code P0087- fuel rail/system pressure too low. Any other thought? This only happens at highway speed with a load/while towing. I have driven it for hours on end at highway speed unloaded with no issues whatsoever.
It could be a few things but with that code and intermittent drivability issues it is possible the low side fuel system is not supplying enough fuel to the high pressure side under heavy loads. It is also possible that the high pressure pump could be starting to fail. If it was things like injectors or a bad pressure sensor it would typically happen under all driving conditions.



Tune and delete that thing!

LOL

But seriously, I wonder if the fuel pressure is too HIGH. Can any technicians on hear confirm if there is even a high fuel pressure code?

there is no way that truck is getting underfueled with the FASS.
P0088 is for fuel rail pressure too high.

A malfunctioning FASS system could definitely cause a low pressure condition on the high side.
 

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Discussion Starter · #16 ·
I ordered new fass filters today. @realbored do you have a recommendation on what type of fuel pressure gauge I should use to test after the low pressure pump? I used one while working on bmw fuel systems years ago but these lines are massive in comparison.
 

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I ordered new fass filters today. @realbored do you have a recommendation on what type of fuel pressure gauge I should use to test after the low pressure pump? I used one while working on bmw fuel systems years ago but these lines are massive in comparison.
You can use a regular gauge with the correct fittings to check the low pressure system. The high pressure system need to be checked with a scanner because of the pressures. You need to check the commanded pressure and the actual pressure to make sure that they are the same.
 

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Discussion Starter · #18 ·
Ok- spoke with fass and they recommended watching fuel pressure like real bored says and make sure it doesn’t dip under 75psi. If it does replace filters and try again. So I got new filters and will just proactively replace before the next drive tomorrow. Also borrowed my buddy’s apollo d8 snap on scanner and can live view low fuel pressure and high fuel pressure real vs commanded. Going to figure this b**** out this weekend.
On a kind of positive note, she still pulls strong at slower speeds. Towed my Subaru toy car home last night. Just replaced both cylinder heads and she goes and spins a bearing on me 20 miles later. 🤦🏽
46382
 

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Discussion Starter · #19 ·
Went for the drive today- low pressure fluctuated between 71-81psi until she failed, when it dropped to 15psi. High pressure real pressure vs commanded stayed reasonably close so I think this is for sure a prematurely failing fass unit. Disappointing considering how much they cost.
 

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Discussion Starter · #20 ·
@realbored .... I replaced the main filter again on the engine- saw some trash in it, and drove again. That’s 3 new filters this week (both fass and a factory primary filter on the engine). The other day when it failed it was in the 90s. Today it was in the low 80s and I made it about 100 miles. The fuel pressures (low and high) don’t seem to drop until the stall happens, like there is no taper it just stalls and that’s when the pressure drops. I was watching my egr gauge and it stayed pretty high today as well. I am really starting to wonder if this is a temp issue, like egr related? I had read somewhere on this forum that a failing egr system would/could cause de fuel? With no other faults or warnings?
 
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