Community Forums

JNSNWT · 09-21-2021, 09:06 PM

I’m considering adding a pressure gauge to my fuel system in an effort to help diagnose problems if and when they occur.

Here’s my understanding of the fuel flow pattern on my engine.
The mechanical transfer pump which is built into the Heui pump pulls fuel from the tank through the primary fuel filter then sends the fuel through the secondary fuel filter and into the common rail inside the cylinder head at about 65 psi. Any excess fuel that was not used by the injectors goes through the fuel pressure regulator located on the back of the cylinder head and into the fuel tank.

If I had a gauge between the secondary filter and the fuel pressure regulator shouldn’t I be able to spot a plugged filter or faulty fuel pressure regulator?

What are your thoughts? Has anyone done this? Is my thinking flawed?

Ted DuPuis · 09-22-2021, 08:34 AM

I'm an engine guy and I love instrumentation. That said, I don't think this is really worth doing. If anything, trying to get software that can see what the computer is thinking would be more useful.

With that said, if the goal is to try to determine if your filters are clogged/clogging, I think I would want to do one immediately after the secondary filter. Not sure what the pressures are in the area where you could get them, but I think past the high pressure fuel pump and to the rail they are very, very high.

donr103 · 09-22-2021, 08:50 AM

I have added fuel pressure gauge to my 2000 workhorse 7.4l.. I am not the first.. many have.. I can't see what you have.. but members here post.. gm does not monitor fuel pressure and can burn up eng.. Google GLOW SHIFT GAUGES.. they will have all you need.. for gas or diesel.. and all fitting.. it took me longer to decide were I wanted to put it.. then install.. tip hit favorite on line store.. for metal cutting hole saw. To make neat hole.. so glad I did it.. all less than 120. Including saw..
Good luck and let us know what you did and maybe better members then me will help you.. oh you tube adding fuel pressure gauge to rv.. KEVIN CAUDILL.. he gave me idea..

Skip426 · 09-22-2021, 08:57 AM

John;
JMHO: I'd say you'll probably feel a plugging filter with your right foot about the same time you'd see a drop on a gauge.

A question . Did Freightliner relocate the secondary filter , off the engine to behind the RR duals beside the primary , as they did on my 99 . Or is your secondary filter still on the motor.

Skip426 · 09-22-2021, 09:08 AM

Quote:

Originally Posted by Ted DuPuis

With that said, if the goal is to try to determine if your filters are clogged/clogging, I think I would want to do one immediately after the secondary filter. Not sure what the pressures are in the area where you could get them, but I think past the high pressure fuel pump and to the rail they are very, very high.

Ted , actual fuel pressure in the system is as John described 65 PSI , it's the oil pressure that the HEUI pump produces and supplied that's 870 >4000 PSI.

Ted DuPuis · 09-22-2021, 02:35 PM

Quote:

Originally Posted by Skip426

Ted , actual fuel pressure in the system is as John described 65 PSI , it's the oil pressure that the HEUI pump produces and supplied that's 870 >4000 PSI.

Thanks for the correction. I was thinking of common rail systems like on my 6.7 Cummins in my Ram, which will see pressures in the 25k PSI range. Learned something about the HEUI fuel pressure. That makes a sensor a lot easier, but I still think probably necessary.

Skip426 · 09-22-2021, 05:54 PM

Quote:

Originally Posted by Ted DuPuis

Thanks for the correction. I was thinking of common rail systems like on my 6.7 Cummins in my Ram, which will see pressures in the 25k PSI range. Learned something about the HEUI fuel pressure. That makes a sensor a lot easier, but I still think probably necessary.

Yes the Cummins HPCR , deserves a lot of respect if you think you have a fuel leak on the pressure side , pages of warnings in the ; Dodge Cummins ; training sessions I took before retiring .

Cat · 09-22-2021, 09:37 PM

Quote:

Originally Posted by JNSNWT

I’m considering adding a pressure gauge to my fuel system in an effort to help diagnose problems if and when they occur.

Here’s my understanding of the fuel flow pattern on my engine.
The mechanical transfer pump which is built into the Heui pump pulls fuel from the tank through the primary fuel filter then sends the fuel through the secondary fuel filter and into the common rail inside the cylinder head at about 65 psi. Any excess fuel that was not used by the injectors goes through the fuel pressure regulator located on the back of the cylinder head and into the fuel tank.

If I had a gauge between the secondary filter and the fuel pressure regulator shouldn’t I be able to spot a plugged filter or faulty fuel pressure regulator?

What are your thoughts? Has anyone done this? Is my thinking flawed?

Yes. The best place is between the secondary fuel filter and the cylinder head fuel rail. The Caterpillar secondary fuel filter base has a straight oring plug installed in it. This 9/16 straight oring plug is the normal location for the fuel pressure fitting. Some already have a quick disconnect test fitting there.
Safe Travels

JNSNWT · 09-23-2021, 01:17 PM

Quote:

Originally Posted by Skip426

A question . Did Freightliner relocate the secondary filter , off the engine to behind the RR duals beside the primary , as they did on my 99 . Or is your secondary filter still on the motor.

On our 2001 3850 Freightliner chassis with CAT engine it only had the primary fuel filter as you describe behind the right rear duels.

I added the secondary fuel filter with hand pump as one of my first modifications.

JNSNWT · 09-23-2021, 01:39 PM

[QUOTE. . Google GLOW SHIFT GAUGES.. [/QUOTE]

Thanks for the tip on the electric gauges they look nice and have good reviews.

I had not considered an electric dash mount gauge. I was just going to put a mechanical gauge between the Secondary fuel filter outlet and cylinder head.

But I guess that gauge would be hard to read while driving down the road and sitting still at idle probably would not be a good indication of a fuel filter starting to plug up.

I watched the YouTube videos you suggested and those all seem to be class C coaches. I have a class A and will need 45 feet of wire between the sending unit and the display gauge. I wonder how much that will throw off the gauge reading? Using 45 feet of wire instead of the supplied 9 foot harness.

Ted DuPuis · 09-24-2021, 07:00 AM

Quote:

Originally Posted by JNSNWT

I watched the YouTube videos you suggested and those all seem to be class C coaches. I have a class A and will need 45 feet of wire between the sending unit and the display gauge. I wonder how much that will throw off the gauge reading? Using 45 feet of wire instead of the supplied 9 foot harness.

The manufacturer should be able to give you this information. I ran an EGT gauge and an oil temp gauge with the 45' or so of wire. For the EGT gauge, an extender box was required. For the oil temp gauge, nothing extra was required. Both seem to read accurately. The EGT is harder for me to verify accuracy of, but the numbers seem plausible. The oil temp gauge I have verified with a thermal gun and works well.

ArtJoyce · 09-24-2021, 07:19 AM

Ii work on my cars and rv. I'm in agreement it's not worth doing it.

I don't have a easy access to a valve to attach a pressure guage. So I added a valve by replacing a bango bolt. Now I just carry my presure guage and I check the pressure every 5k.

JNSNWT · 09-25-2021, 09:45 AM

Quote:

Originally Posted by Ted DuPuis

The manufacturer should be able to give you this information.

I did as you suggested and the manufacturer said I could run up to 100 feet of wire without adverse effect. Just be sure I soldered the connections and put heat shrink insulation over them.

Thanks for the tip.

JNSNWT · 09-25-2021, 09:54 AM

Quote:

Originally Posted by ArtJoyce

Now I just carry my presure guage and I check the pressure every 5k.

My original plan was to install a mechanical pressure gauge that I could check periodically as you are doing but then I realized that a partially plugged filter might be able to pass enough fuel to get a good pressure reading at idle. At WOT the partially plugged filter might be starving the engine.

So I have decided to put an electric gauge on the dash with the instant read out so that if I start losing fuel pressure under heavy load such as going uphill I’ll know it’s time for a new fuel filter.

Thanks for your input