ludwick_j

OK, I tried searching, but "fuel pressure check" gets me way too many pages of not really what Iwas looking for information.
My question: what is the best way to check fuel pressure on my 97 12V? Do I need a special adapter? And, where do I check it? Is there a test port on the filter housing? 12-14 psi at idle, correct?
I have a tick and have replaced the rubber lines. I want to check FP before I spend $200 on a lift pump and overflow valve.

plow

To check fuel pressure on 12 valve:

I drill and tap the top of the injection pump banjo bolt to 1/8'' pipe
thread, then install a male x female 1/8'' needle valve with 1/8'' tubing
compression fitting in it. Boost gauge or oil pressure tubing pushed
though some 1/4'' tubing to protect against cuts and kinks to the gauge.
For a gauge you can use a fuel, boost, oil or water pressure gauge, for a 12
valve it must be at least 40 psi, 60 psi is best.

Use no Teflon tape, it doesn't work
with diesel. Instead use anti-seize or Permatex #2. Remember you are
working on the clean side of the filter, keep everything spotless.
Compression fittings with a ferrule that slips over the tubing will leak
if overtightened, finger tight with one half turn of a wrench is plenty.
The ferrule should be replaced if the fitting is ever removed.

If you can tap your manifold for a pyro tapping the banjo bolt is a piece
of cake. Just drill from the inside to keep the hole straight and tap from
the outside. You can also connect to the bleed screw on top of your fuel
filter with the appropriate adapter to tubing if you don't want to tap.
The adaptor is available from TST for $25 they say it is only for temporary use though http://www.tstproducts.com/index.as...WPROD&ProdID=62 .

After the install start your
engine with the needle valve closed then open it slowly till someone in
the cab signals you that it's just reading pressure. If you tighten down
the packing nut under the valve handle the setting can't move. The valve
will control pulsation and buzzing and can also be shut down in the
unlikely event that you have a leak. Without a valve to restrict the flow
the gauge will pulsate so badly that you won't be able to read it in the
short time before it self destructs.

Parts list; 1/8'' needle valve - $2.50 from the hardware store, plastic
oil pressure tubing kit that comes with the compression fittings - under $10
from any auto parts store. 1/4'' tubing for protective sleeve - less than $2.
Gauge is your choice and may come with tubing. The pressure gauges I
use cost around $10 from here http://www.surpluscenter.com/sort.a...es&keyword=NFGA , bringing the total cost to less than $20 and a
couple hours of your time. I think infidel wrote this up I copied it off this board.

ludwick_j

thanks for the info, Plow. So ,there is no test port where I can temporarily check fuel pressure? I didn't really want to install a permanant gage. I was hoping to borrow a fuel pressure tester and scew it into the top of the filter housing to test.

VinDiesel

Yes. The air bleed bolt on top of the outlet banjo on the filter housing. The catch is you need an adapter with a male metric thread (approximately 6mm) like the TST:

http://www.tstproducts.com/index.asp...PROD&ProdID=62

If you're a handy fabricator, you could just obtain a regular metric bolt, braze it to an adapter that gets you to pipe thread, and drill it out. It's the whole time versus money thing.

I might mention that watching the pressure at idle and ~2,000rpm no load will not be the same as actually being able to drive and observe the gauge.
If you permanently mount a gauge, you will always know what the pressure is doing. After you are familiar with "normal" readings, you will know when a filter change is needed or if your lift pump/overflow valve are getting weak. If you would rather not tap the banjo as Plow mentioned, you can also get a tapped banjo from TST (or many other suppliers) as I did.

http://www.tstproducts.com/index.asp...ROD&ProdID=171

It has a taller than stock hex head, providing good thread depth for your 1/8"NPT "snubber" needle valve.

I however replaced the banjo in the filter (the same one we're talking about with the air bleed bolt) instead of the one in the IP inlet. That did away with the air bleed, but you can just leave the spin-on fuel filter a couple of turns loose and pump the primer button to rid the system of most of the air before tightening the filter. The advantage is the filter will have some accumulator effect to soften the pulsations a bit before going through your "snubber" valve. You could take the gauge (or sender) line loose from the valve, if you ever thought you needed to. Another point, if using an electrical gauge, the sender should be mounted remotely from the snubber via a length of fuel hose or grease gun hose or the like. If a mechanical gauge is used, consider a fuel pressure isolator so there's no chance of a leaking line pumping fuel into the cab. Oops, now we've gotten more complicated and expensive and probably to the reasons why you just wanted a temporary setup anyway...

infidel

Quote:

you can also get a tapped banjo from TST (or many other suppliers) as I did.

http://www.tstproducts.com/index.as...PROD&ProdID=171

Warning, these tapped banjos are for 24 valve engine and won't work on a 12. As far as I know no one sells a tapped banjo for a 12 valve, you have to do it yourself.

VinDiesel

'Taint so. 12 x 1.5mm thread is the right size for the discharge port of the spin-on filter housing. Now I'm not sure if the pump inlet is a different size, but the TST banjo fit my '96 perfectly on the filter housing.

infidel

Could be, I've never considered losing the bleed screw, use it too much.
Plus tapping the stock injection pump banjo is so easy and free if you already have the tap. Much more room in the IP area also.

DL1221

Since you’re only supposed to open the needle valve a bit to control the pulsations, are the “normal” readings the same as those published in the service manuals, about 25psi at 2000rpm, or what is normal with this set up?

Also, how do you hook up a “fuel pressure isolator” do you guys run with or without it?

VinDiesel

Yes, same. The pressure is just taken from about a foot away from the IP off the same line.

The isolator is used when a mechanical fuel pressure gauge is mounted inside the cab. Basically just a chamber with a diaphram in it- it is mounted in the engine compartment. There is a port on either side of the diaphram. The fuel pressure line is plumbed in one side, then gauge line out the other. Usually the gauge side is filled with antifreeze mix. That way there is no direct fuel line going into the cab. In case of a leak, it will either be in the engine compartment, or just antifreeze mix in the cab. Much safer than the potential of fuel in the cab.

With that said, diesel is considerably safer than gasoline, BUT do you really want to risk becoming a french fry for the $50-$70 you might spend on the isolator?

Of course, you may just use an electrical gauge and sender. The mechanical is just considered more reliable and accurate. There have also been some folks that have had trouble with their isolators. I figure it's just about like anything else, nothing's perfect.

DL1221

Thanks for the reply. I was thinking of using a mechanical oil pressure gauge to read fuel pressure, good idea? Also, where can I find the isolator?

VinDiesel

Oil pressure gauge would work just fine, especially if you already have one. I'm really picky about the legend on the face, so I want mine to say "fuel pressure".

Here's mine: http://www.dieselmanor.com/isspro/r5..._fuelpress.asp

The Isspro EV (enhanced visiblity) series are a very close match for the factory gauges.

About any of the suppliers of diesel performance gauges have the isolators- Jegs, Summit, Diesel Manor, etc.:

http://www.dieselmanor.com/dm_products/DM-CGI2240.asp

I got a brand new Di-Pricol on ebay for a great deal. Do a search for "fuel isolator".