Engine/Transmission (1994 - 1998) fuel pressure

[shendren]

thanks to illflem, i got my fuel pressure guage set up. i cracked open the needle valve and read 20psi. (cold engine) then turned the needle valve off. i will just turn it on when i need to check it. i left the guage under the hood.



drove around town all day and smelled a little fuel so i check one of my fittings was leaking a little. so i tightened it back up and checked the pressure again and it wouldn't go past 15psi. (warm engine)... .....



what's up?



liquid filled 0-60psi guage... .....



thanks for the help... .....



scott.

 

[ronco]

shendren,



I watched a mechanic while he tested my fuel pressure Monday. The gauge was connected to the top of the fuel filter housing with 24 inches of rubber line. At idle, the gauge was showing every pulse of the lift pump. There was a 10 PSI swing between min. and max. fuel pressure. My fuel pressure was also showing an average of 15 PSI (which is low). If your fuel pressure gauge is "damped" to prevent the fluctuations I saw, you will get a more accurate reading (the needle valve will provide damping). If your gauge is reading low, talk to your mechanic about an adjustment.





Ronco

 

[shendren]

my reading was dampened by a needle valve provided by bill fleming. i also used a liquid filled guage. NO pulsations at all. what kind of "adjustment" should be made? does this indicate a return valve going bad?... ... the truck runs fine... ... .

 

[shendren]

btw,



those are idle pressures above... ...



thanks. scott.

 

[illflem]

I'm assuming the needle valve is open enough.

15 psi at idle is too low, problem is probably the OF valve. Your truck will still run fine but even though our 12 valves aren't as dependent on fuel for lubrication and cooling as a 24 they still require some. You won't have as much cooling/lubing flow though the return line with low pressure. Your mpgs can also suffer for a reason I don't understand. Good idea to have the pressure up to specs, I consider 18 psi to be the minimum at idle especially if the gauge is under the hood and you can't see what it's doing under load.



The high pressure you had initially was probably due to air compressing in the line. With the needle valve shut almost all the way each lift pump pulsation can go though the valve but not leak back because the next pulse is coming. Once the line is full of fuel, which doesn't take long it will read correctly because fuel doesn't compress like air does.



What leaked Scott?

 

[shendren]

thanks bill. i'll order an overflow valve from piers. my leak was at the plastic tubing ferrule cap. your setup worked fine.



the ferrule i bought at the local auto store was not one i have seen. the ferrule does not go inside the tube the ferrule is cone shaped and the tube goes thru it.



any suggestions?

 

[illflem]

Better price here-

Precision Diesel Injection and Turbo Inc.

Marty Tompkins

toll free 888-734-7349

$20 + $5 shipping and handling.

Does over the phone with a credit card.



Some auto parts sell cone shaped ferrules, others oval ones. Both go on the outside of the tubing. Best to use the type that came with the fitting.

Most compression fitting leaks come from being over tightened. Tighten by hand then one half to one turn with a wrench is plenty.

 

[shendren]

$25 sounds cheap. is it a bosch?

 

[illflem]

No, but it's German and appears to be high quality

 

[krs]

"$20 + $5 shipping and handling"



OUCH!!



(just got one from you-know-who)

 

[MLee]

gauge

where are you guys getting your liquid filled gauges? what store? I've looked in the hardware stores around here, and have ask the clerks if the have them. they just scratch there head. they don't know. I know about Bill's gauge, and have not been able to locate one.



Marv.

 

[shendren]

i got mine from the local grainer store. it wa $8.

 

[krs]

http://www.use-enco.com/CGI/INSRHM

has them too.

 

[illflem]

I use the5HK52

60lb gauge from Grainger.

Grainger says that you must be a business to buy from them but with just a little fibbing you can set up a credit card account right over the internet.

Main thing they will ask for is a tax number, just use your SSN instead.

Do it here https://www.grainger.com/Grainger/wwg/registrationRender.shtml?regType=C

 

[shendren]

yep, that's exactly what i used... ... .

 

[MLee]

gage

THANKS TO ALL that was a great help. i've read Bills post about this gage for some time. we have a store here, will see if they sell over the counter.

Marv.

 

[bluthndr]

how do I connect it?

How and where do I plumb the gauge in to check my lift pump???

 

[shendren]

you should plumb it at the inlet to the INJECTION pump. right after the fuel filter. email bill for the set-up... ... .

 

[akline]

I had some problems with a shudder/bucking feeling being transmitted through the driveline on my truck and traced it to the fuel overflow valve with a broken spring. I simply stretched the spring to compensate and it works great. If 20 psi is better than 10, why not 50? Just wondering... more info about my experience-



I copied this from another thread where I was asking for help with the missing problem the truck had-some of it doesn't apply here.



One thing I would check is the fuel overflow valve in the return line banjo fitting on the front passenger side corner of the fuel pump. This valve controls how much pressure is maintained inside the injection pump of what is delivered from the lift pump. If this valve is bypassing too much fuel it causes the injection pump to have to 'suck' the fuel out of the tank and it is not designed to do that-hence the reason for a lift pump. The smaller nut on the end will allow you to take the guts out of the valve-a small spring, a cradle for the ball(between the spring and ball), and a small ball. There also was a small washer that I found while working on this, I am not quite sure if it came from there or not. Right now it is not in there, if it was, I think it was under the spring where the spring sits on the bolt that holds it in the valve. These parts are easily lost(trust me, I know:mad I had to pull the guts out to get enough room to get it out between the injection pump and the intake manifold, then I could take out the banjo bolt, which contains the seat that the ball seals against. Mine had a broken spring, the problems caused were discussed in detail under 12 valve engine/trans: bucking problem. I simply stretched the spring to compensate for the broken part, I may get a new valve eventually(about $50). Use a 1/4" NPT tee fitting with an air guage on it, and use some teflon tape and very gently thread the assembled valve about a half turn into one side of the tee(the threads DO NOT match), and use a rubber tip blow gun to slowly apply air pressure to check what pressure the valve will hold and whether it leaks (you will probably get a bit of leakage where the valve threads into the tee-I want to figure out the thread size and tap out a tee for this purpose) I am told the pressure inside the pump is to be around 20 psi, I am not exactly sure what this translates to in air pressure while testing the valve, but mine is holding about 35 psi of air, and you could simply blow through it when I first took it off. I was around 25 psi, but that didn't completely fix my problem, so I stretched the spring a bit more. Hopefully my whole schpiel is helpful, I have spent TWO YEARS trying to find this problem on my truck, and am very happy to tell someone else what I found!

 

[illflem]

Originally posted by akline

If 20 psi is better than 10, why not 50?

Any higher than the rated 35 psi max just creates more work/wear for the lift pump, wear on the barely open overflow valve, more potential for leaks (split filter) or an internal rupture of your fuel filter allowing all the crud though.

You have absolutely nothing to gain with pressures higher than the design specs.



I would consider your spring fix to be very short lived, best to spring $25 on a new overflow valve especially if you aren't running a fuel pressure gauge and are basically guessing at the pressure.