D-Jet or L-Jet, Which is best & why? Options

[windforfun]

Which FI system is best & why? I just watched George's video (most of it) & now I'm curious.

[GregAmy]

So you're lookin' for a philosophical discussion, eh? Given that I'm not aware of anyone that has swapped one onto another engine (1.7 and 2L got D-, 1.8L got L-) that's pretty much what this is.

But one can look at subsequent history and see which general design was more widely accepted.

Speaking VEEEEERY generally, the primary difference between D- ("Druck" or pressure) and L- ("Luft" or air) is the primary input to the ECU to determine fuel flow. The D- system uses manifold pressure and TPS to determine load, where the L- uses a flapper to infer air mass.

So which one worked better? Well, lots of manufacturers used both. Volvo, Mercedes, Renault, VW, Porsche, Saab (and likely more) all used L-Jet. Alfa, Datsun, Honda, Peugot, Ford, Isuzu, Subaru, Toyota, ad nausea used L-Jet. In fact, I think the first-gen Miata used L-Jet or something damned close to it (I think my first-gen MR2 does, too).

But the primary downside with L-Jet is the flapper; it restricts airflow. And with improved sensors (that damned MPS), better TPS and temp sensors, and improved ECU computing power, the non-flapper D-Jet designs excelled; you'd be hard-pressed to find any EFI system, even aftermarket, that uses the flapper anymore.

So which general design was better? History says it was probably Druck-based system; that's what most modern cars use. I just replaced my D-Jet with a Microsquirt system that, with the exception of specific sensors and ECU, was pretty much the same concept.

Personally, I was a really big fan of the K-Jetronic "Continuous Injection System" in my Rabbit GTI (K- being "kontinuerlich" or continuous). As long as you kept the fuel tank clean it would run forever (but get rust in the tank and you're fooked).

And...discuss.

GA