Anyone know the difference between the 1974 vs 75-76 Ljet fuel injection? 1974 had a 6 pin connector on the air flow meter and the 75-76 used a 7 pin connector. The 74 ECU has only one circuit board while the 75-76 has two. Just curious.

The later one has the Temp Sensor II, to adjust for inlet air temp. Hence the additional pin.
More info on this in the thread on this maybe a year ago, in the Originality Forum , 1.8 thread.

Thanks for the reply.

reason for the difference in the pin connector is that the intake air temp sensor is wired separately in the 75s (the extra pin). the temp sensor might also be in a slightly different location within the AFM. not super positive on that, never inspected a 75 AFM but i think that it was slightly repositioned.

also breaks down between calif spec or USA (49 states spec) for each year.

for the 74 L jet its mostly all listed here as to the small differences between calif or USA.

http://www.914world.com/bbs2/index.php?sho...357407&st=0

basically they just used the vacuum advance/retard chamber on the distributor as the main emissions device. the 49 state cars have both chambers connected to the throttle body, the calif cars have only the retard connected. the calif cars run slightly retarded in all steady state throttle (engine vacuum) conditions. the 49 state cars only run retarded at idle. i'm not sure if the throttle bodies were different, the PET catalogue says they were. the calif throttle bodies may have had no port for vac advance cast in, or they may have just had it plugged. never seen a 74 calif up close and original so don't know.
but 74 USA had both ports on the throttle body for distributor hook up.

the throttle bodies were flipped in 75. the USA car got the calif set up with only one port and have seen those. they definitely only had one port in the casting. the 75 calif got the tb with both ports that had been used in 74 USA. the port before the throttle plate was connected to the EGR and operated that. the 75 USA car mimics the 74 calif car.
no use was made of vac advance for the distributor.

the decel valve was changed in 75. its a different design. the 74 used the older decel valve design that was on the D jets.

the distributor is the same for 74 calif and USA and the 75 USA.
had an ignition cut (rev limited) rotor.
the 75 californian did not have the rev limit rotor, instead it had a separate fuel cut off switch at red line.

not sure about the interior of the ECU and circuit boards etc. but its a different ECU.
the 74 L jet is the first application of L jet on any engine. essentially a prototype. the improvements would have been coming fast.
no surprise it was updated in 75. VW almost had exclusive use of L jet that first year it was available. most of those updates in design would have been to do with reliability of the AFM and ECU and redesigning components for that reason along with perhaps ease of manufacture? i don't think the mixture settings etc were altered much if it all - but its possible that in 75 more attention was given to dumping less unburned fuel into the exhaust on deacceleration given calif cars were fitted with cats. interestingly the cats on 914s could not make the statutory 50,000 miles required by CARB and EPA so had to be replaced at 30,000 miles as part of the warranty conditions. that only happened if it was still inside the time limit on the warranty.

aside from "accurate" fuel metering the main emission control devices are external to the ECU and operated "mechanically" - ie the distributor vacuum retard or the EGR (along with a CAT) in 75.

IMHO the 74 USA is the least compromised by its emission set up.
it only runs retarded (and hot) at idle. runs advanced at cruise and engine head temps are lower with better fuel economy.

second would be the 75 calif with the EGR. the EGR offsets the retarded timing at cruise and lets the engine run cooler - lowers cylinder head temps. also has benefit for fuel economy. a more complex and costly device that more or less does the same thing as distributor vac advance but cleans up the exhaust.

last on my list would be the 75 USA and 74 Calif as set up originally.
both run hot at cruise as the ignition timing is retarded.

worth noting:
you can easily de-spec a 74 californian.
either unplug the port on the throttle body or fit a 74 two port tb and hook up the distributor advance. presto. you have a 74 USA L jet. which might have been VW's game in 74. easy conversion of L jet to either region - and flexibility of stocks of cars to sell?

i suspect you could do exactly the same thing with a 75 USA spec car.
fit a twin port throttle body either off a 75 california or a 74 USA and hook up the distributor vac can. not a 100% on that but i don't really think anything in the ECU will stop you from doing that. same would go for the 75 californian. take off the EGR and hook up the advance can. presto = 74 USA spec car. someone who is intimate with the mixture settings on a 75 L jet inside the ECU would know for sure. but i think its entirely doable.

both AFMs have that temp sensor 2 @StarBear .

i can't remember exactly but i think its replaceable or serviceable in the 75 AFM.
non serviceable in the 74 (at least easily). its wired in quite differently in the earlier AFM.
if you look inside your AFM you can see it on the 74s. its a little round bump that pokes down slightly into the air flow on the aircleaner side of the AFM flapper.

the insides of the circuitry on the 75 AFM is a little different in design i believe.
pretty sure that would all be just to improve its operation rather than change anything fundamentally.

I stand corrected. Still, it’s the new pin to Temp II for the later air box, right @wonkipop ?

It could (?) be that my TempII has gone out that’s causing my idle issue but can’t confirm until I set the CO screw on the alternate box that I have, but can’t do that until I get a sample probe bung into the muffler. That’s how things go, eh?

thats right.
i recall @ClayPerrine (L jet guru) said something about the earlier temp sensor in the 001 AFM had electrical interference issues given how it was wired in. so it was separated out to improve its operation - hence extra pin.

i also recall reading somewhere else that the change in design means its possible to replace those air temp sensors in the later AFM units. but not really a 100% on that.
its not like there are any L jets that early in australia on any cars other than obscure private imports like my 914. so not much around to pick one up and take a look at it.

good luck with your testing. hopefully its not your temp sensor. you would have to replace the whole AFM with a rebuilt unit if that is the case.


a bit of further info.
here is the power output curves for the 74 v 75 L jet.
you can see the 75 has to rev just slightly higher to achieve the same rated max horsepower (an eye watering 76hp) as the 74.
same goes for max torque, its a little more significantly higher up the rev band and interestingly developes slightly less max torque. not much of a difference but its there.
but this would be down to both the AFM (and how its calibrated in relation to the flapper) but also i imagine the circuitry or settings in the ECU. just slightly different.
they could have done this for emissions or maybe it was just a tweak for a slightly smoother power delivery. but def different and nothing else would really alter the power curve other than either of those two items.

thinking about it, its probably an improvement in the driving experience when it comes to 75s. i notice that my 74 is pretty peaky and happens fast, not much point really going past 3.5 when accelerating through gears. the 75 would feel like you could stretch it out a bit more i would think. closer match of max torque to max hp.



Click to view attachment

actually i might have to correct myself on what could affect the 75.
i always forget about the exhaust system.
the 75 had those wretched semi reactor heat exchangers.
that could have affected the torque curve as well besides AFM and ECU differences.

My 914 is a 1.8L 75 California car. I purchased a 1974 1.8L engine and trans complete with fuel injection a few years back. I rebuilt the 74 motor to a 2056 with a Mallory Unilite distributor. Given the choice, which year fuel injection set up would you run, 74 or 75? Or, is there no advantage of one over the other?

74 USA (49 states) spec.
but i'm biased.
ie the stock distributor set up. but you don't have that so.........no matter.

any advantage is pretty academic when you look at the power curves etc.
we are only talking 76 magnificent prancing horses when it comes to the stock set up.

and thats the generous measure. the other measure is 73 hp.

the main constriction with L jet is the diameter of the throttle body.
@clayperrine has very sound views on that and how to improve things,
consult him.

Using a 50mm modified throttle body from a Vanagon 2.1. Enlarged the plenum to 50mm also.