Chevy and GMC Duramax Diesel Forum banner

1 - 20 of 25 Posts

·
Registered
Joined
·
34 Posts
Discussion Starter #1
I received and installed a FASS 95 when I replaced my injectors (just about a year ago) FPR crapped out a week later, replaced with a genuine Bosch, no problems since. More recently, my pickup has idled *slightly* rough sometimes (not enough to move the tach needle), and when I unplug the lift pump, it seems to stop. Problem is minimal/gone on high idle. I am thinking it’s a excessive pressure issue. If so, I would like to get a lower psi spring. Research has not brought up definite part #s pertaining to lower pressure. If anyone has some spring #s available to share, it would be much appreciated. If not, I’ll call FASS and iron this out.

Thanks
Ely
 

·
Registered
Joined
·
10,269 Posts
Cut one coil off the spring and go from there. Also Ive used airdog springs in fass n vice versa.
But it should have started when you first did the lift pump. Whens the last time you changed filters?
 

·
Registered
Joined
·
34 Posts
Discussion Starter #3
Thanks for the reply. I’d prefer to not cut the spring but would be willing to if nothing comes up. Didn’t know about the FASS/Airdog spring compatibility! Lift pump filters done about 5k miles ago, CAT one at the engine is due (will be changing this weekend). It is possible that it is a filter I guess. Whether or not it is, I’d still like to back pressure down a bit.

Thanks again
Ely
 

·
Registered
Joined
·
10,269 Posts
Have you put a gauge on it to verify pressure being too high?
 

·
Registered
Joined
·
34 Posts
Discussion Starter #5 (Edited)
Not in recent history. If I remember correctly, it was appropriate for the lift pump- just debating whether that’s too high for an LB7 or not I guess. FASS sells LP’s set up for specific applications, but mine is probably a “universal” one at 16 or so psi. I got it with my injector kit. I’ve been looking around and supposedly an LB7 should be 10 psi or less? I can probably verify actual pressure this weekend.

Edit- permanent fuel pressure gauge is on the to- do list

Thanks
Ely
 

·
Registered
Joined
·
10,269 Posts
Verify pressure then report back. I doubt its at 16psi. It would be loping non stop very noticeably if it was that high. Most fass are from 8 to 12 from the factory.
 

·
Registered
Joined
·
348 Posts
What is your rail pressure and what are your Injector balances looking like? My Fass 150 stays at 10 psi all the time. 16psi would most likely cause a noticeable lope
 

·
LHN...We ARE the Joneses
Joined
·
26,485 Posts
  • Like
Reactions: AlisoBob

·
Registered
Joined
·
34 Posts
Discussion Starter #9
Thanks for the replies.
Every time I have checked rail pressure after FPR replacement, desired vs actual matched closely. Might have changed, will update when possible.
Balance rates are +/- 1.5 or less, I replaced injectors a year ago and have had zero trouble with them.
I had a noticeable lope when I first did injectors due to a failing FPR not liking the lift pump, after replacement it was fine.

The SES light has come on 3 times in about as many months for P0181 (fuel temp range/performance) and is currently on (I’m currently in finals week and don’t have much time until the weekend to check that, and other things)

Thanks
Ely
 

·
Registered
Joined
·
56 Posts
My truck has a slightly erratic idle (not quite a full on "lope"), so I'm thinking it's the AirDog 165 that the PO installed. I'll be picking up a CTS2 to watch everything here soon (especially since they're on sale).
 

·
Registered
Joined
·
34 Posts
Discussion Starter #11
Small update.
Changed the CAT fuel filter at the engine when I did my oil change, drove it afterwards, and the erratic idle didn’t seem to be present, but it was an intermittent deal anyhow. Haven’t been able to get away from home since, so I haven’t driven it past that to see if it the problem has recurred.
I do not currently have access to the scanner to do additional diag, and have been busy with a friends project pickup and have not checked post- filter pressure. Sorry about the lack of current data.

Still would like to see if anyone has FASS spring part #s if possible as well, be it the issue or not.

Thanks again.
Ely
 
  • Like
Reactions: HuckLB7

·
Premium Member
Joined
·
189 Posts
Most pressures I found were 7-10 on idle. My FPR went south 3 days after FASS install as well. First spring cut should be just shy of a full circle for 7lbs on idle (trust worthy gauge)at least on mine it was. Havnt found a specific spring number for Duramax's either. On the 1013 spring for 16lbs on Cummins its really noticably stiffer than the stock Duramax spring. I would like to slap the guy that decided to put that FPR in that spot too! Now that Ive dont it I know the trick of the long torqs head socket but my god man what a pain.
Some guys just put a fuel regulator on the pump, but why if its already got a stock one on the engine. To each there own though Im not going to judge.
 

·
Registered
Joined
·
9 Posts
I did a FASS 95 install exactly a year ago and noticed the loping idle as well. I thought it was the FPR but it seemed to mellow out when the weather warmed up. I called FASS and they directed me to a TSB that the LB7s can exhibit "loping" idle conditions if the pressure is too high. There is a pressure port on the pump itself to check. I still have to test mine to see if the pressure is too high but it looks like FASS is aware of it.
 

·
Registered
Joined
·
81 Posts
Do tou know witch port it is?

02 gmc sierra 2500hd crew cab short bed
3" zone kit
285/70/17 nitto Terra Grapplers
17x9 Raceline 930's
S&B intake
3" turbo horn
PPE boost valve
MBRP 3" downpipe
MBRP 4" exhaust
boost auto tow mirrors (dual function) Edge CTS2 with EAS EGT probe
LED conversion
Fass 90
 

·
LHN...We ARE the Joneses
Joined
·
26,485 Posts
LB7s need 7 psi max
 

·
Registered
Joined
·
486 Posts

·
Registered
Joined
·
81 Posts
Excellent, thank you!

02 gmc sierra 2500hd crew cab short bed
3" zone kit
285/70/17 nitto Terra Grapplers
17x9 Raceline 930's
S&B intake
3" turbo horn
PPE boost valve
MBRP 3" downpipe
MBRP 4" exhaust
boost auto tow mirrors (dual function) Edge CTS2 with EAS EGT probe
LED conversion
Fass 90
 

·
Registered
Joined
·
348 Posts
Do tou know witch port it is?

02 gmc sierra 2500hd crew cab short bed
3" zone kit
285/70/17 nitto Terra Grapplers
17x9 Raceline 930's
S&B intake
3" turbo horn
PPE boost valve
MBRP 3" downpipe
MBRP 4" exhaust
boost auto tow mirrors (dual function) Edge CTS2 with EAS EGT probe
LED conversion
Fass 90
Its 7 labeled in the picture below if you have a 95gph. Can also be found using the install manual off of FASS' website
 

Attachments

·
Registered
Joined
·
81 Posts
Its 7 labeled in the picture below if you have a 95gph. Can also be found using the install manual off of FASS' website
I didn't notice it much in stock form but after I got Tunes it was very noticeable. I've been following This Thread from the beginning but I've missed a few comments. I plan on reading through again thank you for the diagram.

02 gmc sierra 2500hd crew cab short bed
3" zone kit
285/70/17 nitto Terra Grapplers
17x9 Raceline 930's
S&B intake
3" turbo horn
PPE boost valve
MBRP 3" downpipe
MBRP 4" exhaust
boost auto tow mirrors (dual function) Edge CTS2 with EAS EGT probe
LED conversion
Fass 90
 
1 - 20 of 25 Posts
Top