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fuel pressure too low ?

3K views 29 replies 7 participants last post by  illflem 
#1 ·
i finally got a 1/8 pt needlevalve so i could install a fuel pressure gauge. i already had a snubber valve but when i received it the instructions said i also needed a fuel isolator.wtf ? so i just screwed the needlevalve onto the snubber valve. would using that setup affect my readings? after i got everything back together she fired right up but was only showing 7psi at idle. so i cleaned the prefilter and installed a new fuel filture and now it idles at 10 psi.i run it pretty hard down my driveway in 2nd and it did'nt get over 15psi.
so i guess i have 2 ?s first in that setup giving an accurate reading?
and if it is, is it safe to drive till i figuire out the problem?

thanks, kelly
 
#4 ·
yep, she's wide open.

i was thinking about going to the stealership and picking up a new ofv and see what that does.
 
#3 ·
you shouldnt need a needle valve with a properly size snubber.

Are you usnig an isolator? an improperly bled isolator will give low readings


i wouldnt call ~10psi safe, your actually severely into the danger zone. if your just granny driving around you reduce the risk of fuel starvation/cavitation damage, but its not the best thing you could do for it.
 
#5 ·
no i don't have an isolator. well i guess i'll park it cause i don't know how to drive one easy.lol so what's my next step? i was thinking ofv?
 
#6 ·
Clean the prefilter first and see what happens.
Pinch the rubber return line that passes behind the fuel filter with pliers with the engine idling.
FP gauge should shoot up to at least 60 psi.
If it doesn't your lift pump is bad.
If it does shoot up then your OFV is bad.
Only $25 for one here> Overflow
 
#7 ·
thanks bill, i just ordered that ofv and i'll try pinching that line tomorrow.

thanks again,kelly
 
#10 ·
yea around that area...its kind of a beotch to get to. you may also want to entertain the idea that there is something wrong with your gauge...i think my fp gauge is currently on the outs. readings seem to change and change often and to radically. pull the snubber and just run the needle valve and see what happens. also what kind of line are you running to the gauge? braided? was it clear before you hooked it up? nothing living in it, stuck in it? and what brand is the gauge?
 
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#11 ·
the gauge is an issapro and i did buy it used. the line i used was new 1/8 poly and i did have to put a union in the middle because it was too short. the gauge reads pretty consistant so i'm thinking it's ok. i went ahead and ordered a new ofv and a new lift (transfer) pump today.
now what's the easy way to install that pump it looks tight down there?

thanks, kelly
 
#12 ·
drop out the starter. some say you can do it without doing so but it is tight down there and even though its only two bolts it was a bear for me to get them started even with the starter off. i would just try one before doing the other. ofv first if that fixes your problem save yourself the trouble and just keep the lift pump lieing around for when in another 200k miles it does actually quit on you haha.
 
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#13 ·
Buy a pair of studs with nuts to replace the stock lift pump bolts and the job will be a hundred times easier.
Size is 8mm x 30mm x 1.25 pitch. Most auto parts carry them.

If The OFV or pump doesn't fix it you could still have a flow restriction such as a clogged pre or tank filter or a kinked supply line.
 
#14 ·
i already cleaned the prefilter and it was pretty nasty. on the tank filter do you have to drop the tank? after seeing how bad the prefilter was i'm gonna go ahead and clean the tank filter too.

thanks, kelly
 
#15 ·
If the prefilter is really bad it's safe to assume the tank filter is too since they're both about the same mesh.
You can drop the tank or tilt up the bed to get at the filter but it would be wise to flush out the tank at the same time which requires dropping the tank.

If the truck has spent it's life in FL the tank is probably gunked up with diesel algae.
The algae thrives in warm coastal climates.
This means after it's flushed you should use an algaecide with most every fill up.
ALGAE-X is the most common one carried at marine shops. The stuff is very concentrated, one gallon will treat several thousand gallons of fuel.
 
#18 ·
well i dropped the tank and cleaned that filter ( it was'nt that bad) and that did'nt help. so i then removed the snubber valve thinking maybe that was bad and tapped my banjo bolt and went with just the needlevalve. that improved the pressure to about 12# at idle and about 20# going down the road.
the most improvement i got was when i replaced the ofv and that did'nt last long, so any chance i may have bought a bad ofv? is that common?
and i have used two different gauges and they were both reading the same. any ideas?
 
#19 ·
People here have reported getting bad OF valves before.
If you bought it from Larry B or the fellow on ebay they will gladly send you a new one.
I know Larry doesn't even ask for the old one back.
 
#20 ·
i bought this one from larry. i'll do the pinch test tomorrow and see what happens before i call him.
thanks, kelly
 
#21 ·
when you say dangerzone, what do you mean? will low fuelpresure wreck the ip? or does it just kill performance?
 
#22 ·
Danger zones:

Low FP, 17psi or less, can starve the injection pump of fuel needed to lube and cool the top end = rapid pump wear.

High fuel pressure, 45psi +, can blow out internal IP seals and even crack open your fuel filter.
 
#23 ·
oh goodie, looks like while i fix the HG, i got a LP to replace along with an OFV to be safe :D
 
#25 ·
I used one for several years.
I highly doubt there is any gauge that can't be used with diesel fuel.
Just make sure to use a gauge snubber or a needle valve almost closed or the gauge will pulsate so bad you can't read it in the short time before it self destructs.

Needle valve installed on injection pump
 
#26 ·
sounds like you might have a leaking line, whether its supply or return. check or replace your rubber return line from the injection pump back to the metal line and the rubber supply line from your metal line to the filter housing, also check your sending unit for cracked lines in it ive seen that cause low fuel pressure and cause a truck to cut out and smoke every few seconds its just sucking air and most gauges are dampened so you dont see the needle bounce it shows a steady pressure but a low pressure
 
#27 ·
yes i am showing low fuel pressure (a little better after i dropped the tank and then removed the snubber valve and went with just the needle valve) but the truck runs great and starts as soon as you bump the key. even after sitting a few days. but i'm gonna try another ofv and if that does'nt cure it i 'll go ahead and change all the fuel lines.
thanks kelly
 
#28 ·
i had the wife watching the fuel pressure gauge as i reached under the wheel well and pinched the return line right at the tank and she said the gauge jumped up to about 60#.
i'll be calling larry in the morning and have him send me another ofv. hopefully this will fix it.
 
#29 ·
well i called larry and told him what was going on and two days later a new ofv was in my mailbox. he's a helluva nice guy and i will definitly buy from him again.

after i installed the new ofv my fuel pressure jumped up to about 22# at idle and 25# going done the road. not as high as i've read some people have but are well within factory specs.

thanks for everybody's help. kelly
 
#30 ·
Larry actually gave the business to his high school aged daughters a few years back and just helps them when they need.
The kids have hung in there and do an excellent job.
Good enough that Larry spends most of the winter in Mexico.
 
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