today a friend and fellow member of DTR (thumbs) and i met up for a cup of coffee. we were discussing the fuel pressure gauge i got and have yet to install, and a very good point was brought up. when i tap the gauge into the banjo bolt before the fuel filter, obviously it will be reading the pressure thats being put out by the lift pump. if the lift pump FAILS from what i know your truck will still run and operate becasue the vain pump in the injector pump will still pull fuel. NOW if the lift pump fails will the gauge read zero or will it read the pressure that the lift pump is pulling????

 

It would read zero, since the lift pump is sucking on that portion of the fuel system.

 

If only using one gauge, it is preferable to put it in the banjo AFTER the filter, such that the open-ness of the filter can be monitored.

For example, (I am assuming a standard diaphragm lift-pump) with a new filter you are showing a steady 5-PSI, then one day the gauge starts gradually losing pressure, it gets down to 3-PSI and you had better try a fresh filter; if, after the filter swap, the pressure returns to 5-PSI, then you know that a dirty filter was the problem.

On the other hand, with the gauge ahead of the filter, let's say the engine dramatically loses power, yet you still show a good fuel-pressure, you know that the problem lies AFTER the gauge and is most likely the filter; this is fine, but you don't get the advance warning that a post-filter gauge will give.

 

If you had a Compound Gauge it should go from a Positive pressure into a Negative (suction) because the lift pump, fuel lines and fuel should be a restriction as the rotary pump is drawing in the fuel.
How low would be determined by RPM, length of fuel line, viscosity of fuel (WMO)

I think.
Jim

 

A "compound" gauge shows both PRESSURE and VACUUM and are probably more common than plain old fuel-pressure gauges.


Here is a typical example of a compound gauge :

http://store.summitracing.com/partde...5&autoview=sku

Any pressure gauge will work, regardless of whether it says OIL, WATER, BOOST, FUEL, AIR, or whatever; my fuel-pressure gauge says WATER on the face.

What you want is a gauge that shows your expected pressure about 2/3-way, or maybe 1/2-way, across the range.

For example, you wouldn't want a 100-PSI gauge for accurate readings on a system that reaches a maximum of 7-PSI; a gauge with maximum of from 10 to 16 would give a much more easily read indication.


A good rule is for a stock diaphragm-pump, a 10- or 16-PSI gauge is good; for the piston-style lift-pump, a 30-PSI gauge is good; and, if you have one of the 2nd Gen. higher pressure piston-pumps, and wish to read pressure AHEAD of the regulator, a 60-PSI will work.

 

and if you had a piston lift pump that 5PSI reading would be closer to 15PSI.

 

i have a 15 psi gauge on a stock lift pump. i already bought most of the pieces to mount it at the banjo 17mm bolt by the filter but now i understand that if the lift pump fails, the gauge will read zero.

 

Ok two questions then.

Would a good place for the connection to the fuel line be at the banjo bolt on the injector pump? This would read the pressure after the filter and monitor both the filter and lift pump.

The other question is what about an electric gauge. Are these things any good? I know they are much more expensive but I have issues with runnin fuel into the cab around other electrical connections.

 

i have an electric gauge and it works fine.

as far as pressure goes, i was seeing 3psi at idle with my dead lift pump and 0 or possible negative (0-15psi gauge) when driving. and like bear killer said, if you only have one gauge just put it after the filter. that way you know exactly how much you supplying to the injection pump.

 

Where are you tapped into the fuel line for your gauge? Also where did you get the Auto Meter fuel gauge? They ain't cheap but the rest of my gauges are Auto Meter and I want to have them match.

 

You can about take a bath in fuel and go play with matches and not get burned, well, almost(don't try it); it ain't like gasoline.


It is just good common sense to install a cut-off valve at any liquid gauge connection, fuel, oil, etc; should a line rupture, you can shut off the valve at the engine and only lose the function of the gauge.

 

There is no banjo bolt on the injection pump - that thing that looks like a banjo bolt is a restrictor orifice. If you take it out and put a high flow banjo bolt in there it will run realllly bad.

Take out the banjo bolt that has the bleed screw and replace it with the tapped banjo.

I wouldn't spend a lot of money on an electric gauge (Autometer). 24 valve guys go through the sending units for them faster than underwear. I believe Westach sells an inexpensive electric gauge.

 

i got a stewart warner electric gauge for 80 bucks.

 

Thanks guys. I'll try to find them on line now. If I can get one hooked up for about 100 bucks that would be great!!

With the stock fuel setup what kind of pressure should I be seeing before the injection pump. Is 7psi about right? I want to get a gauge with as much deflection as I can.

Does anyone make an electric 270* 0-10 psi?

 

gary to help u out with the parts list, i called nyco and they said 32.05 for the braided line and 2 -4AN fittings on each end. they also stock the 1/8th inch to -4an adapter and needle valves. i didnt get a price on them but im going up there saturday maybe, if u would like to meet me, but i wont buy anything til after i get my rotors : )