Gotta Whopping 10 PSI Fuel Pressure!

[mikepvg]

OK, After checking for the obvious things like fuel line kinks,leaks, pre-filter screen, filter etc. .
What is the easiest way to determine if Lift Pump or IP Over-Flow Valve is bad?

I obtained fuel pressure of 10psi to an incredible 14psi WOT #ad

I believe gauge installation is correct because I'm getting 4-5psi unloaded @55mph & 20psi WOT when I switch back to boost port.

Only symptom that lead me to check fuel pressure is a stumble @ 2200 rpm.

I would like to "pressure" you guys for an answer! #ad

Mike



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94 2500HD 5sp 4. 10LSD 4X4 RWAL w/GearVendor OD, K&N Oval w/ Pre-Filter, Straight Exhaust, Geno's Fumotovalve, AW-Direct Idle Controller, DiPricol Boost, Mag-Hytec Rear, 124K miles. NRA Member. V1.

 

[Timinator]

Could you constrict the fuel return line to see if pressure builds? If it builds up to 20-25, then the lift pump is probably OK, meaning it is the overflow valve that is the culprit. If pressure does not build, then the lift pump is weak. How does that sound?

 

[illflem]

Good advice Tim,vice grips work well. Only other thing to check would the screen in the tank module, I would only do it if the prefilter screen was dirty when you checked it. 10 to 1 your lift pump is ok.

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95' 25004X4,AT,Driftwood,Banks Stinger,Warn fender flairs and running boards(work truck)
95 3500,5 speed 3:54,BD E-brake,Driftwood,Banks&Psycotty,34,000 GCVW apple and tractor hauler(works harder truck)

 

[Red Rocket]

I checked my overflow valve 2 weeks ago, its easy to check, but contact me for the details if you plan to do it, I can save you time with the mistakes i made.

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1998 2500, 12 valves, SLT, auto, 3. 54, 285/75-16, TST 230/605, t/c switch, DiPricol EGT/boost guages,K&N,camper special, 65,000 miles(2/01),
12 ton goosneck!
'01 Polaris EDGE-X 600

 

[drawson]

Red Rocket, don't leave us in supense, tell us all about it. i am thinking mine might be loosing some pressure also.

 

[Red Rocket]

Ok, heres how it's done. Hope you like to read!

The valve is located on the fuel pump, as you look toward the firewall, it is on the close left highest corner of the pump. you can search for more detail on finding it if you need to. It has a banjo line coming off of it. This looks almost like a ball joint socket, with a bolt going thru it. There are pictures here, but I dont remember where. do a search for them.

Take these precautions,
Stuff ALL of the crevices the small washers or the spring itself could fall into. Make sure you have lots of lights, and a magnet.

heres how it comes out, piece by piece, and anyone who knows of any other way, please add it to the thread.

small bolt that pressurizes the spring,

two TINY washers,

cone shaped spring,

ball valve,(b-b)

main assembly.

Now, I had mine apart, and did it according to others, and the threads I read, but I found that if you take out the whole assembly at once, ie. remove the banjo connection from the pump, you eliminate the chance of losing the small parts. So if you want to, loosen the larger part first, but be careful no to lose the rubber washers that seal the banjo. You will have to do some adjusting of the line to get it out, but it works. Then separate the rest on a tool bench, or somewhere that you wont lose anything. The spring is supposed to measure . 500, mine was 3/32 to 1/8 inch short of that, and crooked too.

note: in a jam, a pen spring will make the engine run, say to move the truck to search for a lost spring, thats why i advise taking the whole valve off, instead of piece by piece.

Anyone can do this, just don't lose anything. I hope this explains well enough, and I notice an idle improvement on my truck.
good luck!

I forgot to mention, I couldn't find a new spring, so I precision adjusted the old one... hehe.


[This message has been edited by RedRocket (edited 03-29-2001). ]

 

[Rammin On]

Here us a picture of the overflow valve disassembled. I have tweaked the springs in these things and have found that they don't last very long at all ... .

#ad


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'95 2500 Stretch 4X4, Auto, 3. 54, 265/75/16, white. TST #5 250/635 plate, 215/230 injectors, Pschotty Air, Cummins chrome, BD Valve Body, Pro-torque LS convertor, BD pressure-loc, mystery switch, JRE 4" turbo to tailpipe w/ monster tip, BD exhaust brake, ISSPRO boost and pyro, Grover air horns, Pioneer CD system, Galaxy 99 CB w/ 400 linear, nerf bars, Rancho 9000's, 8K tag-a-long RV ... Life is Good!

 

[mikepvg]

Redrocket
Thanks for the heads up!
Didn't realize it is comprised of all these looseable little pieces. I'll take the necessary precautions this w/e when I work on it.

Mike
#ad

 

[pcorssmit]

In case anyone was wondering, the overflow valve IS a warranty item.

Pete

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'97 2500 CC 4X4 5spd Sport
'83 K5 Blazer 350 TBI (ex 6. 2), 39. 5 TSLs, 3" lift, Dana 60/GM 14 blt, Detroits

 

[drawson]

I just checked my fuel pressure. I was getting 7 at idle and 18. 5 at WOT. I took the overflow valve aparts after removing it from the engine(thanks RedRocket) the spring was short and bent over at angle.
I straitened it out and found myself two shims like the OE ones and installed them. I now have 9. 5 at Idle and 22 at WOT

I going to make a new spring using some of my gunsmithing spring stock this weekend. What pressure relm is ideal for HP?

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EAT'M UP
97 2500 Club 4X4 3. 54, Forrest Green/Driftwood, LSD 5 speed, & Psychotty Air System, TST #11, 370 HP injectors, timing at 16 deg. , 16CM2 housing, AFC spring kit, TST EGT gauge & 0-60 boost gauge in A Pillar, Cat-be-gone, 4" Dynomax Bullet muffler, Crome 4" turn down, 2 Electric Fans, One inside/ One out front, AmsOil Through out, Geno's trans filter kit, AmsOil Bypass system, Lund Winter front, Leer Cab Level Shell Driftwood , 255/85R16, South Bend's Hypo Clutch*NRA/USPSA member and proud of it*

 

[Rammin On]

The general concensus is ... . 21 - 23 psi . . however the '95 FSM states 25 psi to be the minimum pressure ... so ... anyone know the real scoop?

 

[Andy Redmond]

A good lift pump, clean filter and good/like new overflow valve will net 23-30 psi at idle after the filter.

Your overflow valve still sounds bad, you should have far more than 10 psi at idle. You gained a little and it sounds like its been tinkered with before if the spring was bent.

Good luck

 

[Red Rocket]

My spring was also bent crooked, and I know it has never been taken apart. Sorry, but I have no clue what my fuel pressures are or were, all I know is that it idles better.

 

[drawson]

My over flow valve spring was also bent/cocked to one side and it had never been out it was still covered with the OE paint.

 

[pcorssmit]

From the '97 manual:

"Presssure should be 117-152 kPa (17-22 psi) at idle speed. Pressure of 172-207 (25-30 psi) should be seen after raising engine speed to its rated rpm (2,500 rpm) with no load. "

This is with the engine warm.

The torque spec on the banjo bolt is 18 ft. lbs.

Pete

 

[Missouri Mule]

Rammin on,
As I recall the 96 shop manual states 20 psi minimum on outlet side(supply to injector pump from filter).
That is 25 psi minimum to intake(supply line from tank to filter).
5 psi maximum difference from intake to outlet. Which would make 20 psi the lowest allowed.

I would think that those who have 96 to 94 having the spin on filter would have same specs for psi(fuel).

------------------
Bill Thomas
Missouri Mule - 96 Wht 4X4 ST CC,5 spd, 3. 54, 8 ft bed, 1 ft high cheater boards.
99 Freightliner bl/wht FL60 ISB-5. 9 24v,215 hp,520 tq,6 spd, 3. 59 nsr,16 ft box, 19. 5 tires,Wt/gvw 11,000/23000

[This message has been edited by Missouri Mule (edited 03-31-2001). ]

 

[mikepvg]

Interesting that my overflow valve looks nothing like the above pic. It does not come apart & was for sure defective.
My idle pressure, outlet side, is a good 24PSI now.
BUT @ 2000rpm pressure does not go up to the 28-36spec.
Took apart pre-filter & no clogging. All lines look OK.

So what do you all think? Bad lift pump or should I start getting into the tank & check p/u there?
Mike

 

[mikepvg]

What? Waiting for days & NO suggestions that @ 2000rpm I'm not generating the 28-36psi spec? Opinions?????????????
#ad

 

[illflem]

I wouldn't worry about it. 22 psi is where mine runs almost all the time, only time it will go higher is when coasting downhill.

 

[mikepvg]

illflem
Upon test drive after getting psi up from 10 to 24, stumble @ 2200rpm vanished. So I'm thinking more is better & TST stated I should have 28-36 @ 2000rpm, therefore I'm looking for the additional pressure to see if I can get a better/stronger response above 2200. I want to be sure I got it right before I put in a torque plate, otherwise I may be missing some additional power w/o knowing it & you know that would be totally tragic to leave HP just lurking around! #ad

Mike



[This message has been edited by mikepvg (edited 04-02-2001). ]