I've been reading some of the threads on these diesel motors?

Something I don't understand is how the fuel system works.
1. There's a sending unit in the tank
2. Fuel pump mounted on the rail
3. Is there a pressure regulator??

What's this stuff about injectors needing oil pressure? What is the part that does this, where is it? Is there still an oil pump in the bottom of the crankcase?

 

Well I can briefly answer the first 3 questions but I do know sort of what the oil to the injectors is for but an expert will throughly explain it to you.
1. Yes the sending unit for the fuel gauge must be in the tank to read the level of the tank.
2. Yes the fuel pump is on the frame rail about right across from the transfer case.
3. Sort of there is a pressure regulator but the fuel pump on the rail is basically a transfer pump up to the fuel bowl but the pump under the hood can be shimmed to create more pressure. Others will chime in on how to exactally to do this.

 

1) Yes, There is a fuel level sending unit in the tank.
2) Yes, the only fuel pump is on the frame rail just north of your fuel tank on the driver's side.
3) Yes, the fuel pressure regulator is on the fuel filter/water separator on top of the engine.

Our injectors use high pressure engine oil to operate. It's technically called a HEUI Injection system that uses high oil pressure pump (called HPOP) that's mounted in front of the fuel filter housing that supplies oil to the injectors to fire them. Here's a link to read: PowerStroke

 

1 and 2 are correct.

3) The pressure is regulated just prior to the fuel bowl on top of the engine.

Yes, fuel pressure is driven by oil pressure provided by the High Pressure Oil Pump which sits right in front of the fuel bowl.

Funny/scary story - one time my oil drain plug came loose and I lost all of my oil driving down the interstate. I pulled over just in time to lose fuel pressure and kill the engine. Thankfully, no further damage was done!

 

Caterpillar developed this kind of injection system.

Here's a place to begin reading about it:
http://www.cat.com/cda/files/87775/7/pehp9526.pdf

When you're done, Google HEUI.

It will teach you all you need to know.

Pop

 

Great link, Pop. I should have walked across the building here and got that document from our Marketing guys.

 

According to the caterpiller .PDF, I'm glad that one of the advantages of HEUI is reduced noise - otherwise I'd think that 7.3s were noisy! ;-)

 

HEUI - Hydraulically operated (via high preassure oil) Electronically controlled (via PCM/IDM) Unitized Injection

 

saw the title and thought of what my wife calls "oiling". The process of collecting WVO and making Biodiesel...

 

Does the sending unit actually send the fuel? Or just the fuel level.

Suppose my truck won't start due to a feul problem, could it be caused by a problem in the sending unit, or is the fuel pump mounted on the frame doing all the work?

 

All sending unit does it tell how much fuel is in the tank. Fuel pump, filter and regulator would probably be the cause. Hope this helps.

 

There is a complicated screen/pickup/return unit for the fuel system attached to the sending unit. That may be where the confusion starts.

If you have a fuel supply problem, it is possible that you have a clogged screen, damaged pickup, or leaking joint in the pickup assembly. The "Hutch" mod addresses these issues. Search for it on this site or at diesel o-rings.com

 

Thanks to springer pop and ponyboychris form pointing to the articles on the HEUI system. It will save me from continuing to take classes from my future 22 year old son in law. He has spent the last few years working for CAT and before that 4 summers working for diesel shop.

 

The sending unit in the tank is nothing more than a straw, and a float type level indicator. (over simplifying of course) The fuel pump on the frame rail sucks fuel trhough this straw and sends it forward to the fuel bowl. the fuel bowl fills and pressurizes and any excess fuel is returned through the fuel pressure regulator to the tank. Inside the fuel bowl the fuel will go through the filter and down the standpipe to two outlets. one outlet feeds the drivers head, and the other feeds the pax head. There is no return from the heads (dead head fuel system) in the heads the fuel is routed to each injector through fuel gallies at about 55psi. Each injector fills and the fuel charge is then intensified to 21,000PSI by high pressure oil (2800-3000PSI @ WOT) and an intensifier piston inside the injector wich is electronically controlled. the fuel travels down the barrel if the injector and is dispersed through a nozzle into a very fine mist which is compressed and ignited by the heat formed from the compression (19.5 to 1) and the resulting explosion is what drives the piston.

NOTE: the only time glow plugs come into play is when the oil temp and ambient temp read below pre set parameters.
Glow plugs do not help in the ignition of the fuel charge during normal driving, only when starting a cold engine, or in extreme climates.


HPO system-
the LPOP (low pressure oil pump) is located behind the harmonic balancer and feeds crankcase oil to the HPOP(high pressure oil pump) resevoir, which is the rectangular piece that is located directly in front of the fuel bowl. The HPOP is actually located under the fuel bowl, and takes oil from the HPO resevoir, increases its pressure, and sends it through oil gallies in the heads to each injector. Each injector fills with high pressure oil and an electronic solenoid is "fired" by the IDM which inturn allows the plunger and intensifier piston inside the injector to push the fuel through the nozzle into the cylinder. the IDM takes a 12v charge and converts it to 120v or 130v(depending upon manufacture date) to fire the injector.

Plese note: the fuel system and the HPO system are two SEPARATE systems that work together.

 

Bob, small typo in your post. The pressure is regulated post fuel bowl just before it heads back to the tank via return line. I just thought I'd point this out in case someone else reads this thread who has a similar question