Porsche produced the 914 1.8 for two years (74-75) with two different FI. Every time I talk to someone regarding the l-let, they are quick to point out two things. First, the l-jet is the best FI for the 914 (also the basis for all future FI, used on the 912 2.0L, AFC vs MPC, etc) and it hates vacuum leaks! Which is great? But does not address the fundamental lack of information for Porsche 1974 and 1975 914 regarding their l-jetronic fuel injection system.

I have searched high and low for information regarding l-jet. It has been hell trying to get basic information that in the d-jet world widely documented considered simple and widely available. I dedicate this thread to the “Full Disclosure” -- l-jet revealed!

I am hopeful that we can put together a thread that can actually help 1.8 owners

The glove has been thrown…

Regards,

James

I will watch this thread with interest!

If you look at the top of the page, in the 914info page.
Click on other 914 sites.

guess what you find.

Three awesome sites.

This one is all for L-jet

http://manuals.type4.org/ljet/

Also, get the Bosch FI book.
It is really a great manual and it explains Bosch FI very well.

Rich

Yes, I agree, but if you really look at it.. It is not specific to the 914. That is what I am hoping we can address. Is the very specific application of the l-jet to the 74-75 914. Like the Porsche 914 l-jet version is an open-loop not a closed loop...

The goal is to keep the thread specific to the 914 not other implementations of l-jet

Hey James, be sure to review the L-Jet documents I have on my website if you have not seen them:

http://members.rennlist.com/914_collectibles/RareDocs.htm

I would not go so far as to say either L-Jet or D-Jet was 'better', I think they are both good and have their own strengths and weaknesses. L-Jet was a more developed system and improved over D-Jet in several ways, but a D-jet was a good system.

L-Jet characteristics that come to my mind:

*Fewer components which were to make a simpler system, but those components were more complex.

*The hardware design was significantly better over D-Jet and upgraded variations are still used in modern cars = spring loaded wire terminals, no reliance on a fragile rubber boot for protecting the connector wires and connections, but the harnesses are 2x as complicated as D-Jet harnesses.

*The double relay component replaces some of the function of the standard 914 relay board.

If I recall correctly, L-Jet uses a air flow meter that is really measuring he position of the flapper door in the AFM itself on a potentiometer. It also uses a throttle position switch much like D-Jet. It measures cylinder head temperature. The injectors fire for a percentage of time and that percentage goes up as the need for fuel as measured by the flapper door, the throttle, and the head temp dictates. The L-Jet on 280Z cars has dropping resisters to bring the voltage down to what is needed to fire the injectors. I am not sure if the VW Porsche L-Jet does.

I don't believe one is superior to the other. With the possible exception of the fact that we don't seem to be able to get berylium to rebuild the MPS on the D-Jet. The L-Jet seems to be easier to get rebuilt...

I hate them both. More patient men will disagree.

Once upon a time, Alfred used to maintain a bunch of l-jet information.

His site is gone, but can still be accessed through archive.org.

Use this link:

http://web.archive.org/web/20050913031343/...nk/earlyefi.htm

I'm impressed this is an excellent repository of Ljet information. I happen to be working on an L jet right now. Unfortunately I have several ECUs and I've mixed them up so, can anyone tell me the numbers for L jet ECUs?

ConeDodger - you are correct on the operation of the "barn door" air flow measuring. This is the same as the 944 and 944 turbos. One substantial upgrade for the turbo is the elimination of this unit with a mass airflow sensor. It's supposed to be about 8% gain in HP.

i looked in the PET and found illustration 901-05 listing 2 ECU's:

for engine numbers up to EC0 037 551 the ECU is 022.906.021G
for engine numbers from EC0 037 552 the ECU is 473.906.021

my guess is the 022. is 74 and the 473. is 75

If you're technically minded, this is the book to get. It covers a ton of technical information about Motronic, L-Jetronic, LH-Jetronic, LH-Motronic, D-Jetronic, K-Jetronic, KE-Jetronic, and KE-Motronic.

Great stuff.

I hear the same modification is available for my '84 3.2 911. But the fact that I have to do smog here in California and the fact that I have been threatened with great bodily harm or death if I modify anything on this 55K mile car has kept me from doing it. I hear it smooths out the idle and really wakes things up!

Challe was nice enough to ponit me toward this link
http://www.pelicanparts.com/914/technical_...4_18FI_diag.htm

Switching over to a MAF setup on Motronic (for 80s carerras and 944s) and MAF for AFC on the 914 are very different. Even though the systems are VERY similar, they are just that - similar.

I found a place that could make me a MAF sensor and the interpreter box - for only $800 and the cost of them scrapping an ECU and AFS. It would work great on 914s because they're not closed-loop controlled by an O2 system, and most have no smog limitations throughout the country.

L-jet works good and it evolved into most of the systems used today. Manifold pressure wasn"t where it was at and Bosch evolved. The flapper box works good but has lag. Backfiring through the intake damages the flapper box. Flappers were later replaced by hotwires to measure airflow and they eliminated lag and backfirng issues.

I have a later version called Digifant on my 1986 wasserboxer Vanagon and it is bulletproof. Looks just like the one on my teener.

Ken

Going back to why L-jet is open and JH jet is a closed loop.

I think its an emmission issue given the timing.
EFI was forced evolution by the EPA...take a look at carbs from the 70's through the 80's
By the end, the carbs had 20 vacuum lines running off of them and were impossible to diagnose, it was a rats nest of sensors etc.

L jet was simple, and it cleaned up the mess of lines, and lowered the emissions.
the evolution to LHjet, with a lambda sensor was a natural evolution to keep up with the progressing laws of the time.
I think that LH jet was used by the japanese cars for years.

Rich

Wouldn't the l-jet on the t4 VW buses be basically the same as the 914 l-jet? May want to check the VW forums for more information, thesamba, shoptalkforums, etc.

I'm reading that Bosch book right now to try to understand the l-jet in my Bus better.

What triggers the injection event in ljet? I haven't gotten very far in the book yet!

-Chris

yes, its basically the same, some part numbers are different. I would think you could run the bus Ljet in a 914 but you would have to set up the airfilter.

the L-jet in my '81 Vanagon is "the same" as the L-jet in my 74 914.

i think the injection is triggered off the distributor. this makes me wonder and ask the question about how the ignition/injector systems are affected if you use a Pertronix, pointless ignition. obviously, it works but if the injectors are triggered off the points closing, and there are no points to close..... aarrrrrrrggggggghhhhh!

Ljet at least doesn't have the trigger wheel in the distributor like Djet, I was happy to find this out when I started poking around my new bus because it allows you to run a mallory (at least more easily than djet). That doesn't mean that the injection event isn't still timed off the distributor in some way, but how . . . dunno.

Definitely really digging fi though over the dells in my Beetle. One thing that bugs me about this old fi though is it doesn't have the limp home abilities that carbs do.

Yes, the L-jet ECU receives engine speed information from the ignition signal. That's why the injection harness has a terminal that connects to the switched side of the coil. Amaze your friends with this bit of ancient injection trivia -- because every coil pulse looks the same as any other coil pulse, the L-jet ECU is UNABLE to track engine position. It only knows the SPEED of the engine. Since the ECU doesn't do, indeed CAN'T do, injection phasing, your mallory will work just fine.

Modern ECUs rely on a crankshaft signal that is modulated in some way (for example, with extra or missing teeth) so that the ECU can deduce crankshaft position as well as speed.

Be careful though, as some later versions of L-jetronic (not digifant) used on VWs, Audis and other euro cars do have a TDC sensor.

The throttle position switch on an L-Jet system is not like the D-Jet. It only has 2 switches, one for idle, and one for WOT. On the 912E they eliminated the idle switch. And the L_jet on the 914 uses a set of dropping resistors.




The LH-Jetronic system was used on most Volvos. It is almost idenitcal to the L-Jet system on a 914, with the exception of a Hot wire Mass air flow sensor, and an O2 sensor for feedback.





The L-Jet system uses a circuit in the ECU that is identical to a tachometer. It listens to the pulse on the negative side of the coil and fires ALL 4 injectors on EVERY OTHER pulse. So half the time the fuel is being fired at the back of the closed valve. But the injector dwell is half of what it would be on a sequentially injected car.

L-jet is the second generation of EFI. D-Jet came first. L-Jet was the evolutionary base for LH-Jet, digifant, and Motronic. D-Jet was the evolutionary base for some of the GM Delco systems that use a MAP sensor to determine engine load.

I have been chasing this surging rich idle problem on my 75 1.8. I removed the intake system and replaced all gaskets, hoses, Time Temp sensor, Cylinder Head Temp Sensor, Cold Start valve, and checked the specs for all the components and everything check out. When the engine is cold, it starts right up and once warm idles almost perfectly. However, after I have driven the car (operating temp) and stopped for a few minutes and start the car. The idle surges from a very low to a somewhat normal idle speed. The idle is “rough/shakes car” -- get some gas and it goes just fine. Also, no matter how low the idle goes when surging it does not stall! The other thing that really bugs me is that the engine runs perfectly above idle (cruising at 80 down 280 is a dream it just purrs…).

I am left with the Air Flow Sensor, wiring harness and ecu as the last questionable parts (theoretically).


I don't think it is a short as it only occurs at idle and not at speed on rough roads. I am thinking Air Flow Sensor but the resistance was within spec.



Any suggestions would be greatly appreciated!



Regards,



James

Verify that the ECU is the correct year. A 75 ECU will plug into a 74 Harness, and it will not run. A 74 ECU will plug into a 75 harness and run, but it will have the symptoms you describe.

BTDT!!!

It's been my experience that you either tune for idle or you tune for driveability.
I've never been able to satisfy both.

Check the intake for vacuum leaks yet? Sometimes the big black bellows/tube from the air filter to the intake will have a crack on the underside that seals OK till things expand when warmed up. Also removing the oil filler cap will kill the idle, so a low idle is almost always a vac leak, high idle is almost always the Aux Air Valve not closing. (Pinch/plug the hose to prove if its closing all the way.)

Have you checked/monitored your fuel pressure?

The fuel pressure checks out,no vacum leaks, etc. ClayPerrine, BTDT has an interesting idea re ecu. Obviously getting a new air flow meter will not fix incorrect ecu. So I am going to check the ecu. Anyone know what the proper ecu part number is for a 1975 1.8L california car. Also, where would the part number be located on the ecu?

Thanks for the help.

James

Actually, I have (Well Betty has) a 74 1.8 that idles perfect and pulls strongly. It also has great drivability.





The part number will be on the label. You can check PET for the correct part number. Be careful, some of the 75 cars were built with 74 FI components. They used them until they ran out, then switched over.

There was also (supposedly) an altitude compensator in the L-Jet system. I have seen documentation on it in the factory manual, but I have never seen one in person.

Clay,

I am totally inspired by your 74 ecu connected to a 75 harness. That is so cool, actually brilliant. Give the PO track record with the FI that would be PAR for the course!

Thinking totally outside the box! Awesome!

Still

James

Something must have been wrong then. When tuned properly, they idle fine and run good up to 4500 with a stock cam.

Naa.. not thinking outside the box. It is just 20+ years of working on them. You learn the quirks after a while. Plus, back in the 80s, I went to the factory training course for VW on L-Jet.

Ok so I started to remove the ecu to see what I had, but as soon as I moved the charcoal canister I saw what I think is the parts number label. As the ecu is in my 1975 1.8 CA, I am hoping that this ecu also belongs in a 1975 914 1.8L California car. Does anyone know the correct part number for the ecu?

I am still beating my head over this one...


Regards,

James


Here is the pic with label roated and enlarged.

Click to view attachment

dont know a whole lot about the part numbers but my '74 ecu always had a black label with white lettering not orange with black like your picture. dont know if that makes a difference or not. but at least you didnt blow 2 ecu's with impatience, a dead battery, and a car starter/charger like i did. waiting for ecu #3 to come in the mail

Here is a clip from PET...

Click to view attachment


Basically this means that is the correct 914 1.8 ECU. It may be the wrong one for your car. The >>EC0 037 551 means that the listed ECU is used with everything up until that motor number. After that number uses the second one.

Someone could have switched it out. That looks like a replacement parts label.

Ok, let’s make this a little more interesting. The engine in my car does not have an engine number. Everyone has basically said that this is a replacement case. Some where along the line something bad happened to the engine case. But was repaired meaning it received a new case… Therefore it does not have an engine number. Thus I cannot determine the engine number to ascertain the ecu that is required for my car? What should I do from here? I guess the question becomes… What is the defining characteristic for a 1.8 that defines the ecu? Does anyone have any ideas?



Regards,

James

How many contacts are on the harness connector to your AFM?

If 6 then its a 1974 system.
If 7 then its a 1975 system.

While very accurate.. it is not technically correct. The switchover didn't happen until after the 75 was released. Early 75 cars had 74 L-Jet systems on it.

But the info about the air flow meter pins are correct. If it has 6 pins, then it needs the early ECU. If it has 7 pins, then it needs the late ECU.


Is that confusing enough for you??