Lift pump press. question

MMLMM

MMLMM

Tunergeek
Mar 2, 2008
4,086
2
38
43
Reno, NV
www.dyncal.com
Buddy has an LB7, and on a big tune hes getting a "popping" type sound and a "loss of fuel" feel.

His lift pump is at 15psi Idling, and at WOT it drops to 6-7psi, could that be part of the problem.

On a low tune the symptoms are not there and pressure is up to 11psi at WOT

Hes is running a Jegs billet elec. pump. (120gph)
 
2500HeavyDuty

2500HeavyDuty

Book 'em, Danno!
Feb 14, 2008
2,209
1
0
Katy, Tx
www.myspace.com
hmm maybe a bad fpr, i have a similar problem on my truck, i idle at 10 psi and drop down to 1 psi under WOT and thats with an airdog 150 too. Mine has been bad since last summer when i had a loepy idle and awful tacking noise coming from my passenger side.

im going to increase my pressure to 15 psi and see if that will cure my problem, but airdog told me that normal psi should be around 10:confused:
 
ripmf666

ripmf666

Active member
Sep 20, 2006
15,123
14
38
47
Wentzville Mo
I thought you couldnt run high pressure from your lift pump thru the ecm on those trucks with the ecm having the fuel running thru them?
 
JoshH

JoshH

Daggum farm truck
Staff member
Vendor/Sponsor
Feb 14, 2007
13,716
779
113
Texas!!!
Yeah, the LB7 and LLY run fuel through the FICM. Supposedly, anything over 12 psi running through there can cause weird idle issues.
 
fishsmith

fishsmith

Active member
May 14, 2008
1,402
0
36
42
Monroe, LA
On a hot tune mine does the same thing. I thought it may be fuel filter related but I put a new one on it and it still does it. I have dual tts lift pumps by the way. It used to do it only on the monster tune but now it seems to be getting worse. I have been starting to think that it may be the fpr. Logging the truck it seems to hold rail pressure though.
 
mytmousemalibu

mytmousemalibu

Cut your ride, sissy!
Apr 12, 2008
2,230
0
0
Kansas
Are you guys sure your not having an injector/ combustion rattle? Mine does some times, especially after i stand on it, which i belive is from low rail pressure. I have an injector issue right now, one of them will intermittantly leak and when it does it rattles. It rattled when all of my prevoius failures happend. A dirty fuel filter seems to exacerbate the rattle. I am not running a lift pump.
 
fishsmith

fishsmith

Active member
May 14, 2008
1,402
0
36
42
Monroe, LA
I just had injectors replaced so I don't think that is it. At least on mine. I know it happened once before and I changed fuel filter and it seemed to fix it but that was before I had the lift pumps, now I change the fuel filter and it doesn't seem to help at all.
 
NWTDIESEL

NWTDIESEL

On a Time Out
May 8, 2008
1,405
0
0
ATS Extreme trans
I ran the FASS 150 that is preset at 15-17psi. I dont get any kind of lope at idle. The FICA can take 21-22psi before it will crack. One thing i did have to do was upgrade a few parts on my filter housing to take the psi.

I have ran a lift pump since 30,000 miles. I firmly believe that the lift pump has kept my cp3 in awesome shape and would recomend everybody to run one even if you have a small tune. Your cp3 will last alot longer.
 
RENODMAX

RENODMAX

Dead Wrong
Mar 4, 2008
3,602
0
0
I get just a tiny tiny lope when im slowing down like coming to a stop sign with the PPE pump set at 12 psi. Nothing horrendous that would shake the truck, just chugs a tiny bit. I think the problem your buddy is having Mike is going to be along the lines of what everyone else has already pointed out.
 
MMLMM

MMLMM

Tunergeek
Mar 2, 2008
4,086
2
38
43
Reno, NV
www.dyncal.com
RENODMAX said:
I get just a tiny tiny lope when im slowing down like coming to a stop sign with the PPE pump set at 12 psi. Nothing horrendous that would shake the truck, just chugs a tiny bit. I think the problem your buddy is having Mike is going to be along the lines of what everyone else has already pointed out.
Click to expand...

lol, which is...? (theres a few ideas)

I am thinking FPR or bad lift pump.

Anyone know what psi it should show at WOT with a good sized tune
 
RENODMAX

RENODMAX

Dead Wrong
Mar 4, 2008
3,602
0
0
MMLMM said:
lol, which is...? (theres a few ideas)

I am thinking FPR or bad lift pump.

Anyone know what psi it should show at WOT with a good sized tune
Click to expand...

Id think FPR if the pumps good. How old is the pump? Did he run it dry, etc. Easy way to tell is just to see what PSI the pumps running at idle. All the ones I have ever seen die wont hold whatever theyre supposed to at idle.
 
MMLMM

MMLMM

Tunergeek
Mar 2, 2008
4,086
2
38
43
Reno, NV
www.dyncal.com
RENODMAX said:
Id check FPR if its alright at idle and is a new pump.
Click to expand...

Thats the thing, its not a brand new pump, and I dont think its a great pump, especially running this ULSD thru it, its also for gas, that may be part of it. the other thought was his bypass was not shutting all the way and pushing some to the tank as well....
 
NWTDIESEL

NWTDIESEL

On a Time Out
May 8, 2008
1,405
0
0
ATS Extreme trans
MMLMM said:
Thats the thing, its not a brand new pump, and I dont think its a great pump, especially running this ULSD thru it, its also for gas, that may be part of it. the other thought was his bypass was not shutting all the way and pushing some to the tank as well....
Click to expand...

Thats why i dont have a bypass! I just carry a few parts to do a bypass if the pump fails. The check valve he used is for water line so maybe the rubber is eatn away???????????? He does use Diesel additive and that $hit is pretty potent.
 
You must log in or register to reply here.
Top Bottom