Why did the 1.8 engines have L-jet? Options

[VaccaRabite]

Has there ever been a reason Porsche/VW speced L-jet injection for the 1.8 engines instead of D-jet like the 1.7 and 2.0 engines used?

Usually when manufactures do this there are financial reasons for the change. Either they have the same engine on other vehicles they produce, or its just cheaper to use whatever part is being used.

But Porsche didn't use the T4 motor on other cars at the time. And if it was cheaper, they would have done away with Djet on the 1.7 and 2.0. I don't think VW was using l-let at the time for the bus... but maybe?

There has to be a reason that Porsche wanted Ljet on the 1.8.

Zach

[technicalninja]

Two ways to measure load on an engine.
Manifold vacuum- D-jet, also MAP sensor. Can calculate load
Weight of air- maybe more accurate in operation than MAP, L-jet K-jet also MAF sensor.
This actually measures the amount of air being consumed.

All modern stuff I work on has BOTH now...

It's helps to get all of the available data.

This is a NICE quick read regarding Bosch Jetronic overall. I have learned the "death date" of L-jet and it happened exactly as I described...

I also learned that "Mono-Jetronic" exists.

Chevrolet TBI! Ford CFI!
Millions of them...
Only uses a TPS to determine load but totally dependent on O2 control.
Super simple.

https://en.wikipedia.org/wiki/Jetronic

[wonkipop]

Two ways to measure load on an engine.
Manifold vacuum- D-jet, also MAP sensor. Can calculate load
Weight of air- maybe more accurate in operation than MAP, L-jet K-jet also MAF sensor.
This actually measures the amount of air being consumed.

All modern stuff I work on has BOTH now...

It's helps to get all of the available data.

This is a NICE quick read regarding Bosch Jetronic overall. I have learned the "death date" of L-jet and it happened exactly as I described...

I also learned that "Mono-Jetronic" exists.

Chevrolet TBI! Ford CFI!
Millions of them...
Only uses a TPS to determine load but totally dependent on O2 control.
Super simple.

https://en.wikipedia.org/wiki/Jetronic

yes @technicalninja

the old 02 sensor.
the next big thing.
and a massive investment by bosch.
bigger in someways than the whole development behind the earlier efi systems of D jet and L jet.
bosch controlled the patents on that after they finally succeeded.
its made them a fortune.

the lack of a suitable 02 sensor stalled the timeline of the Nixon Clean Air Act.
they were meant to get to a point in 1975 that they did not achieve until the early 80s.
the carmakers and (even bosch) simply could not deliver the technology to make the standards in the time span. The USEPA worked with the carmakers to amend the plan realistically. the 02 sensor was the critical bit needed.

the difference between CARB and USEPA was an agreement reached between the USEPA and carmakers as well to assist with the introduction of technology. more of less split the domestic car market in half and meant in any one year USA and foreign car companies only had to address 50% of the volume of sales to the new standards. the remaining 50% would use the californian stuff the year after in the other 49 states.

L jet evolves. quickly becomes L jet with added suffixes as the 02 sensor kicks in.

not sure when the last airflow meter is done. but i know that 964s had AFMs in the very late 80s. and some domestic sales australian stuff still had them in the 90s on new cars.

in the absence of an 02 sensor L jet is assuming load but its got no feedback.

it was able to do a better (more accurate) job guessing (or assuming) what that was than D jet could. but it still could not make the standards that were aimed for in 1970 for 1975. no one could.

[L-Jet914]

Two ways to measure load on an engine.
Manifold vacuum- D-jet, also MAP sensor. Can calculate load
Weight of air- maybe more accurate in operation than MAP, L-jet K-jet also MAF sensor.
This actually measures the amount of air being consumed.

All modern stuff I work on has BOTH now...

It's helps to get all of the available data.

This is a NICE quick read regarding Bosch Jetronic overall. I have learned the "death date" of L-jet and it happened exactly as I described...

I also learned that "Mono-Jetronic" exists.

Chevrolet TBI! Ford CFI!
Millions of them...
Only uses a TPS to determine load but totally dependent on O2 control.
Super simple.

https://en.wikipedia.org/wiki/Jetronic

yes @technicalninja

the old 02 sensor.
the next big thing.
and a massive investment by bosch.
bigger in someways than the whole development behind the earlier efi systems of D jet and L jet.
bosch controlled the patents on that after they finally succeeded.
its made them a fortune.

the lack of a suitable 02 sensor stalled the timeline of the Nixon Clean Air Act.
they were meant to get to a point in 1975 that they did not achieve until the early 80s.
the carmakers and (even bosch) simply could not deliver the technology to make the standards in the time span. The USEPA worked with the carmakers to amend the plan realistically. the 02 sensor was the critical bit needed.

the difference between CARB and USEPA was an agreement reached between the USEPA and carmakers as well to assist with the introduction of technology. more of less split the domestic car market in half and meant in any one year USA and foreign car companies only had to address 50% of the volume of sales to the new standards. the remaining 50% would use the californian stuff the year after in the other 49 states.

L jet evolves. quickly becomes L jet with added suffixes as the 02 sensor kicks in.

not sure when the last airflow meter is done. but i know that 964s had AFMs in the very late 80s. and some domestic sales australian stuff still had them in the 90s on new cars.

in the absence of an 02 sensor L jet is assuming load but its got no feedback.

it was able to do a better (more accurate) job guessing (or assuming) what that was than D jet could. but it still could not make the standards that were aimed for in 1970 for 1975. no one could.

side track I know Toyota adopted the L-Jet system and improved on the system with their Denso versions and O2 sensors. My 1990 Toyota Corolla LE 5 speed with the 4A-FE engine had a vane air flow meter just like our 1.8L 914s. Toyota used that system up until 1992 on the corollas, 1994 on the Toyota pickup (US) 3VZ and 22R-E, Celica Supra with the 5M-GE, Toyota Supra with the 7M-GE and I can't remember what other models utilized that system.

[wonkipop]

@L-Jet914
yeah - in a similar vane (no pun intended) our workshop 1994 ford falcon ute (aussie ford) that i restored during lockdowns has a straight six with LE-Jetronic fuel injection.
pretty sure its a vane type AFM on it as well. have to check but i seem to recall its there.
fairly contorted plumbing on the fords of that era as they converted and adapted a very old design from the 70s first to cross flow and then to LE fuel injection. the model before it still had a carby with emission strangling. the commercials were the last to get the EFI system.