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L-jet vs. D-jet

Hi all,

What are the main differencies between L-jet and D-jet EFI ?
Old 04-04-2005, 12:51 PM
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I don't know much about D-Jet.

L-Jet is used on the 914 1.8 engines. It has only a few sensors that the computer uses to determine fuel mixture. The main sensor is the Air Flow Meter, this measures incoming air and adjusts the amount of fuel accordingly. Because this is the primary sensor, L-Jet is very sensitive to vaccum leaks. You cannot have any vaccum leaks - with leaks, the engine is getting more air (unmeasured air) than the meter is measuring and won't adjust the fuel properly.

The other sensors are the throttle position sensor which senses full-throttle and adds more fuel to compensate for the engine load. There is a head temperture sensor that lets the computer know the temp and leans or richens the mixture for a hot or cold engine. Lastly, there's one more sensor (I can't remember the name). This thing controls the cold start valve that injects additional fuel when the engine is cold. I believe that D-Jet engines have these last 3 sensors as well.

I have L-Jet on my 1.8 and when tuned properly, the engine runs very well - consistantly.

Vern
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Last edited by Tidybuoy; 04-04-2005 at 02:25 PM..
Old 04-04-2005, 01:20 PM
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D-jet system is explained in lots of detail on the following web-site:
http://members.rennlist.com/pbanders .

It uses a weird electromechanical device to measure the air pressure in the intake manifold, and it "assumes" that the amount of pressure (or vacuum) is related to the amount of air going into the engine.

It also uses a TPS to find when the throttle is at idle (and also to provice acceleration enrichment), a CHT to enrich the mixture when cold, an intake air temp sensor to slightly richen the mixture for colder intake air, and some stuff to help the engine start and idle when it is cold.

--DD
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Old 04-04-2005, 01:45 PM
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Anybody know if it is possible to use the L-jet with a 2.0 liter engine? If you were to do so, how much horsepower would you have? Just curious. Steve
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Old 04-04-2005, 02:17 PM
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I believe the current L-Jet is calibrated for the 1.8. I would think that if you used it on the 2.0 it would have to be re-calibrated somehow (which is way over my head).

If is was a simple bolt-on, I would think that everyone with 2.0FI would be doing it.
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Old 04-04-2005, 02:26 PM
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I gathered together a lot of information about the different systems on my web page .
Old 04-04-2005, 03:20 PM
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Quote:
Originally posted by Tidybuoy
I believe the current L-Jet is calibrated for the 1.8. I would think that if you used it on the 2.0 it would have to be re-calibrated somehow (which is way over my head).

If is was a simple bolt-on, I would think that everyone with 2.0FI would be doing it.
The 1.8 L-Jet works perfectly fine on a 2.0 motor, I had no problems at all, my 2.0 was basicly stock except for the higher compression pistons (eurospec).

The L-Jet FI has gotten a bad rap from a few owners/mechanics that did not understand it too well. It's sorta like a modern version of the CIS injection......neither system likes vac. leaks, so you have to make sure everything is sealed up nice and tight.
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Old 04-04-2005, 03:30 PM
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Actually, now that I think about it, the 2.0 could probably use the L-jet setup as long as it had 2.0 injectors which probably spray slightly more fuel.

As far a L-Jet problems. I've had very few problems. Once I cured all my vaccum leaks, my car has run problem free for several years.
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Last edited by Tidybuoy; 04-04-2005 at 04:49 PM..
Old 04-04-2005, 03:53 PM
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The injectors may not be swappable. They will fit and plug in just fine, but I have heard that there are major electrical differences between the D-jet and L-jet injectors and that Very Expensive Things could be damaged if you tried to mix them up.

Mike's L-jet 2.0 seemed to run fine. However, I would have really liked to see a WBO2 (wideband O2) meter readout, particularly at high RPMs and loads (throttle settings). I would be afraid the car would run lean that way.

Even if the mixture were find, the car would very possibly lose a little bit of HP (1-5?) because of the restriction of the 1.8's "barn door" air flow meter and the more convoluted path for air to get out to the cylinders.

But all of the above is just guess-work. We'd have to find someone who adapted 1.8 L-jet onto a 2.0 and get him to dyno his car and plug a WBO2 in to find out the real answers. (And we can't exactly do that with Mike's car, can we?? )

--DD
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Old 04-05-2005, 01:20 PM
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The MAF sensor method of measuring engine load seems really simple and elegant. I wonder who thought that up.

Quote:
When the engine is running, an electrical current is used to heat a thin wire or film in the sensor. The current flowing through the wire/film is regulated to maintain a constant temperature above that of the intake air temperature. The amount of current required to heat the wire is the basis of the engine load signal.
Old 04-05-2005, 01:52 PM
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I have driven both and either will work fine. I have noticed that the Djet seems to have better throttle response......

Geoff
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Old 04-05-2005, 05:33 PM
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L jet was installed on 2.0 912E's,
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Old 04-05-2005, 06:33 PM
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If ( when ) my SIX blows up, my good running 2.0 FOUR gets a hot cam and Webers. Period.

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Old 04-05-2005, 09:40 PM
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better buuy those webers quick.....

1200 a pair now...
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Old 04-05-2005, 10:00 PM
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It's only money......
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Old 04-07-2005, 04:13 PM
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Quote:
Originally posted by Acox914
L jet was installed on 2.0 912E's,
Yes, and some of those systems have 2.1 Vanagon EFI components but dont tell anyone...
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Old 04-08-2005, 02:56 PM
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yep, and if your 2.1 is a four it started life in the very pedestrian 411/412... so what. The L-Jet was technically more advanced than the D-Jet, but an example of how sometimes the older technology can be more robust than the first generation of something new. Some elements of each can be found in modern systems.
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Old 04-09-2005, 04:56 AM
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ya missed it (the point) by a mile. Carry on...
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Old 04-10-2005, 07:21 AM
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I put 1.8 injectors in my 1.7 d-jet this afternoon. it did not run well. it would start quickly, rev then die but never idle. I liked my L-Jet car. I like my d-jet car. I liked them both more than carbs. they are smoother, better milage, and easier to start up in teh AM. I like teh Edelbrock carb on my V8 914 although I would prefer multi port FI.
the 2.0 buses were L-jet with tuqoise 1.8 injectors, same p/n
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Old 04-11-2005, 11:21 PM
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I have been told that swapping L-jet and D-jet injectors can damage expensive parts. I don't know exactly what swap will damage things (and it may have been a "scare tactic" on the part of Bosch's service department) but I'd be careful when swapping injectors around...

--DD
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Old 04-13-2005, 10:14 AM
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