I was just wondering why did the 6.9 and the 7.3 idi have injection pumps but converted to heui injection on the 1994.5 and up to the 6.ohs ?

 

Ford had Nothing to do with it. The HEUI design was a joint effort by Caterpillar and International. And it was Very advanced in 1994 And is still used today

 

HEUI was necessary to provide the elevated pressure required for direct injection into the cylinder. This is the key thing that makes a "PowerStroke" what it is. The older diesels are called "IDI" which stands for Indirect Injection. This means the fuel is not shot directly into the cylinder, it goes into a "precup" in the head.

 

The HEUI system still uses a pump that's used to raise the fuel pressure to 20,000 psi or higher to work with the HEUI.

I had three Kenworth T-300's with 3126E Cat engines… I quizzed the Cat factory reps several times on why the IHC injectors (which would work in my Cats) cost less than $300.00 each but the cat injectors were over $700.00… all I heard were crickets.


HEUI Injectors

 

? The fuel pump on a OBS 7.3 only makes around 60 psi.

The oil pressure in the injector is what makes the pressure needed for direct injection.

 

The high pressure oil pump supplies oil to the HEUI injectors… different than the engine oil pump.

 

Knew that, but the way you posted seem to say it was a HPFP.

 

Basically it was to meet emission standards.

 

they didn't have a choice.the ip's on our old granddad idi's is designed to pop open injectors at less than 2,000 psi.something with a lot more kick is required for direct injection.

 

They could have and probably should have used a rotary pump. There are plenty of rotary pumps available for direct injected use; which don't have hard start issues, expensive injectors, glow plugs, etc. Rotary pumps offer better fuel economy also.

Heui is reliable and proven, but it's over complicated, expensive, and unnecessary.

 

Why does DI need more injector pressure than IDI?

 

http://en.wikipedia.org/wiki/Indirect_injection

 

Because the injector has to overcome cylinder pressure to actually inject fuel. If the cylinder pressure is 3k psi, and the injector only puts out 2500 psi of fuel, the fuel isn't going to find it's way into the cylinder (probably flow backwards..). I'm not sure what actual cylinder pressures are, but I know they're up there..

 

A PSD has a lower compression ratio than an IDI, and an IDI with 450psi compression is pretty good. There's no way the cylinder pressure is that high...
The IDI injector also has to overcome cylinder pressure, unless you're saying that the pressure in the pre-cup is less than the pressure in the cylinder...

 

He's referring to cylinder pressures while the engine is firing, not just compression psi