Hi guys,
Just running a sanity check. But how or can you tell the difference between the "Control unit L-jetronic" for a K-100 and a K-75. Background I'm slowly restoring Blue the USD $500. K-100 I picked up last year. And of course I've got a couple of K-75 units laying around as well as the K-100 unit off Blue and I want to make sure I get the right one. And none of them are labeled. Well maybe it's labeled mostly by grease and such but I was meaning is there any physical dimensional or connectors or model labels I should just look at to make sure?

For anyone not familiar with the story, buddy Greg asked me if I was interested in another project bike. And like an idiot I asked how much and details like did it run (it didn't at first). Anyway I went over and met the sellor whose first comment should have warned me off. But he allowed that he wouldn't be selling it - despite that the last time it was licensed (ran) was 2012 - except that he needed to make his bail. Seems some new Indian owners of the building that he was managing came by with some orders and he fell off the wagon and was waving a pistol around and maybe even fired it into the air. And even in the peoples republic of Berkeley the police take exceptions to such behavior and by the time they finished taking all his firearms and tossing him in jail he needed bail money and money to relocate to a more hospitable area. Maybe like Montana, Idaho or Texas? Anyway for a mere $500 his dearly beloved long time K-100 could be mine. He even delivered it as I didn't have any way to get a non-running 500lb bike home. And so it's sat for the past year or two as the pandemic had its way with us. And now after powder coating the frame I'm slowly reassembling the bike. YES, I did get it to run or at least start up before I disassembled it. So that's the true story of Blue.

So Info on the telling the differences in "Control unit L-jetronic" units appreciated.
best regards
J.

AFAIK there is no difference in the case but the label tells the story. The only difference is one extra pin is connected to the third coil. (mental blowout)
Maybe open the case the circuit board may have part numbers on it.

So the stickers have been removed?  I'm not sure, but I would think that there would be a number stamped into the cover somewhere. 

As far as I can tell looking at my wiring diagrams and the operating principals of the Jetronic, the difference is how the external inputs are processed to provide the proper time output to work with the different number of cylinders and the different relationship of the Hall Effects Sensors. The only thing the Engine Control Unit actually does is compute the time the injectors are opened.

http://www.demo.cs.brandeis.edu/postscript.dump/Ltronic/L.html 

(The link doesn't work from the posting, you need to copy and paste the link into your browser. Then go all the way to the bottom and read under "Bread and Butter")

I'm going out on a limb here, but I suspect that you could identify what you need just by trying it.  I doubt that putting the wrong one in the system will hurt anything beyond not having the correct fuel mix to start the engine.  I say this because the inputs and the loads all operate over the same voltage and current ranges, the only difference is in the timing and scaling of the signals within their operating range.  For example, the airflow signal calls for a specific amount of fuel to be injected.  Since there are only three injectors in a K75 vs. the K100, the pulse to the K75 injectors is going to be longer than for a K100.  The ignition control unit is where the signal to the coils is generated.  As near as I can tell, the ignition signal is only used in the engine control module to determine rpm and synchronize the injector timing with the engine speed.

Everything you ever wanted to know about the L-Jetronic:

https://bowlsby.net/914/Classic/zTN_Man15.pdf

Point-Seven-five wrote:Everything you ever wanted to know about the L-Jetronic:

https://bowlsby.net/914/Classic/zTN_Man15.pdf

ooooOOOOOOoooo 

This looks fun!
Thanks :-)

RicK G wrote:AFAIK there is no difference in the case but the label tells the story. The only difference is one extra pin is connected to the third coil.
Maybe open the case the circuit board may have part numbers on it.

Thanks for not calling me an idiot while pointing out the obvious. The sticker on the one unit I've unearthed is "0 280 000 313" I've not found a corresponding parts number on REALOEM's online parts. I note that the REALOEM parts for K75 and K100 differ only in the last 3 digits K100 == 950 and K75==627. But neither number goes with the box I'm looking at.

thanks J.

313 that's the k100. 

To double check, if it smells like gunpowder and tastes like gunpowder, yep that's the k100.

RicK G wrote:AFAIK there is no difference in the case but the label tells the story. The only difference is one extra pin is connected to the third coil.

I think Rick is talking about the ignition control unit that is up front near the steering head under the tank.  Yes, they are different as far as pinouts, but their only connection to the L-Jetronic is from pin #8 which has a red/yellow wire running to pin #1 on the L-Jetronic engine control unit with the rpm signal.

The ignition coils are not connected to the L-Jetronic engine control unit.  The the injectors are connected to the engine control under the seat and the coils are connected to the ignition control under the tank.  As far as the wiring connections to the Engine Control Unit under the seat, they are all identical from the K75 to the K100. 

Since the sensors and injectors, etc are the same on both models, it makes sense to me that the only difference between the two units is in how the inputs are processed internally to generate the injector signal pulse width.  This tells me that you could identify the correct unit by just trying to start the engine with it.  A K75 ECU will make the mixture about 33% too rich to start and run properly whereas the K100 ECU will make the engine start and run as it should. 

Of course, this assumes the engine is capable of running.  If there is a problem with something else like the Hall Sensors or the Air Flow Sensor, neither model ECU will work.

daveyson wrote:313 that's the k100. 

To double check, if it smells like gunpowder and tastes like gunpowder, yep that's the k100.

I don't know about the gunpowder, but that number seems to be a Bosch part number for a K100 ECU.

Does the tag happen to say "3 Zylinder" and be red.  Then it would be for a K75.  It appears that the K100 stickers are black.  Also, the Bosch part number for the K75 looks to be 0 280 000 332.

Point-Seven-five wrote:

Does the tag happen to say "3 Zylinder" and be red.  Then it would be for a K75.  It appears that the K100 stickers are black.  Also, the Bosch part number for the K75 looks to be 0 280 000 332.

Thought of that but the K100 is a '85 and that's before the K75 was introduced so no differentiation.
google search lead me to Beemer Bits:


K100 CONTROL UNIT L-JETRONIC
[13611460950]

K100 CONTROL UNIT L-JETRONIC
BMW Motronic Control Unit from a K100
BMW part number 13611460950, 13 61 1 460 950
Information on unit: Bosch 0 280 000 313, Made in Germany, 4 Zylinder 0280000313

BMW Retail is over $1500.00

So your ECU is for the K100 then.

How about you post photos of the ECU's you have there?

Point-Seven-five wrote:So your ECU is for the K100 then.

How about you post photos of the ECU's you have there?

That was  the issue. They look the same. Apparently the only difference is the number on the box.

Of course they look the same.  They are all L-Jetronic ECU's.  The only difference is probably a couple resistors on one of the circuit boards inside.  That is why they have the stickers on the outside.  The Bosch sticker should be on them as it's a foil backed sticker with a really good adhesive backing. 

I have the impression you have a bunch of ECU's that have the Bosch sticker removed, is that correct?  Or is it that there is no BMW part number visible? 

Looking at photos of K bike ECU's on eBay it looks like there are no labels with BMW numbers on them, you have to go by the Bosch number or the color of the label or the words "3 zylinder" which I think is pretty obvious even if it is in German.  It's possible that there might be a paper inventory tag with the BMW P/N, but after 30+ years, a paper tag might not be there.

Point-Seven-five wrote:
I have the impression you have a bunch of ECU's that have the Bosch sticker removed, is that correct?  Or is it that there is no BMW part number visible? 

Think I have three on the units, one that I inherited of no known provenance, one off my K75 parts bike and then the K100 unit that I'm restoring. Thought I had them sorted with tape on notes of origin. But then when I was pulling parts out to see what needs to be repaired and reconnected in I realized that the one that was with the rest of the K100 parts wasn't marked. And the other two weren't where I thought they should be. But now it's sorted at least as far as having a K100 ecu for the project. The other two will turn up eventually from the safe place I stored them. Where ever that is. I don't remember the details of the other two and question whether I need to search for them at this time. But have you looked at the price tag on ecu's? Think RealOEM was quoting $1,600. USD. That's more than I've paid for two of the bikes combined.

If the k100 or the spare are early models, I think there are some differences. I'm not sure if you mean you don't have labels or the number on the labels are too worn to read. 

Here is an '84 model and an '88 model. 

.

In '84 I don't think K75 models existed so a four cylinder note was probably not made for that reason. So if the number of cylinders is not stated, I'd take that to mean it's four cylinder. See on the '88 model it says four cylinder. The Bosch title is in a different location on the label, plus other differences. 

On the '84 model near the retaining plug says 450, the newer model has 743, not sure that is helpful though.

.


The '84 model (top) has silver coloured screws for the retaining tab on the right. On the '88 they're brass coloured. 

Where I'm pointing on the '88 model,  the rebate is at right angles on the edges, on the '84 they're at 45 degrees.

If the labels are missing but you can see where they were, it's a much bigger label on the k75, well at least with mine. The rebate on the k75 matches the more modern k100 (but the screws have gone silver again So I spose that's no help) 
 

And just to really throw the crowscarers around, BMW used two different types of AMP connector on the FICU. One will clip into both FICU boxes and the other... won't. DAMHIK.

To reduce confusion further still:

The police k100 has a green label with a green circular sticker on the side (police vehicles were green in Germany in the brick days, probably before the EU had somethin to say about it) 

The '84 labeled black has a red circular sticker on the side. 

The k75 labeled red has a green circular paint mark on the side. 

The police k75 labeled blue has the brew that is true.

I think we may now have the definitive visual  differentiation(s).
thanks,
J.

daveyson wrote:The police k100 has a green label with a green circular sticker on the side (police vehicles were green in Germany in the brick days, probably before the EU had somethin to say about it)

So why do the Polizei get something different to the rest of us?

One rumour I've heard is they have more power.

daveyson wrote:One rumour I've heard is they have more power.

Are these un-obtainables? I'd really be interested. Though my buddie, Greg, found that he could substitute Ford fuel injectors for the Bosch variety and get a power boost.

If the rumour is true, it would explain something that has always puzzled me. Low Flying Brick is fitted with K1100 TBs, 6 degrees of advance on the timing and a Polizei FICU. Back-to-back with a standard, freshly-rebuilt K100RS and both running the same bevel drives, LFB took off like a scalded cat and made the standard RS look like a drunken slug. It's said that the assdyno can't detect less than 4bhp difference between two bikes, but LFB gave the impression of running a lot more than 4bhp over the standard RS.

No, I'm not paying for a dyno run even though the nearest one is only twenty miles from here.

Ex police bikes are easy to buy, at least in Oz.

I spose maybe the cop computer allows the injectors to remain open a little bit longer.

Another difference about the cop FICU, it has a metal base, all the others I've got have a plastic base.

Well it's all anecdotal to me and I'm not sure whether it's been dyno'd or not, BUT the info I have is that: "Ford Injectors. F1ZZ 9F​ 593B​, They work best with a better air filter like a K&N and a muffler - like a Staintune." working with a standard ecu ups the power. Course better filter and an improved muffler might in themselves increase the power.

jjefferies wrote:"They work best with a better air filter like a K&N . . ."  Course better filter and an improved muffler might in themselves increase the power.

I haven't seen any testimony here that a K&N is "better" than the OEM filter on 2V Bricks like ours. I wonder what would make it better. It would be difficult to strangle a 2V Brick when its OEM air filter is already the size of a sports bar's TV screen; furthermore, the OEM filter doesn't need oiling.  

For many years the OEM versus 4 hole debate has been going on. I have a mate who's son worked for a company that specialized in injectors. The OEM injectors are designed to spray onto the back of the inlet valves where the fuel further atomises. It also cools the head of the inlet valve. The OEM injector stream angle is designed to be very narrow to accomplish this. The cutaway drawing shows the injector aimed at the back of the valve. No company that sells 4 hole injectors has shown a dyno comparison between the two injector types. The improvement felt after fitting four hole injectors would also be felt if you fitted a clean set of one hole injectors.
See link for K & N comparison. https://ibmwr.org/original/ktech/dyno/index.shtml

MartinW wrote:For many years the OEM versus 4 hole debate has been going on. I have a mate who's son worked for a company that specialized in injectors. The OEM injectors are designed to spray onto the back of the inlet valves where the fuel further atomises. It also cools the head of the inlet valve.

And as a side effect wouldn't that extend the life expectancy of the intake valves?

More than likely.
Regards Martin.

I had an interesting experience with my 84 K100RT.

I picked up a brand new set of 4 hole injectors for small money. They were sold to me as single hole for K100 2v but turned out they were 4 hole. Anyway I took out the original injectors and put these in and yes an immediate improvement which I expected due to them being brand new. Plus an increase in fuel consumption 5-10%. I ran them over 3,000 miles. Then, Will Crean [88] having cleaned my original injectors and identifying one bad one that I replaced with a similar single hole injector, I popped them back into the RT. No noticeable difference from my brand new 4 hole injectors, apart from the fuel consumption reverting to normal. I left the 4 hole injectors in the shed as they can go in the K1100.

My opinion, sure the 4 hole injectors work fine in the 2v engine but no need to do it. Increase in fuel consumption but no increase in performance.

I guess my claim about the colour markings on the sides would be to comical to believe for some readers without a photo. The '88 model doesn't have any colour markings on the sides.




Unfortunately the k100 police label is the same size and location as the k75 one. The cop one doesn't have a tab, but does have deep rebates at the same spot. The one with the blue label is from a 1983 BMW car, surprisingly it has less pins than a brick one. 

Some more differences.






.

Looking at the parts lists, it looks like the police version of the L-Jetronic has something to do with dealing with or preventing interference with the 2-way radio that police use. 

If you look, you will see the L-Jetronic unit listed in both the Fuel Preparation page and the anti-interference kit  listed for use with official(police) models.  Along with the L-Jetronic unit there is a separate part number for an engine wiring harness in that kit.  That special harness appears to have shielding with a ground connection near the injectors. 

Your photo of the police unit with the die cast base confirms that it was designed to coexist in close proximity with a high power RF source.  It's possible that there may be a performance upgrade in the police unit, but the metal case confirms the RF shielding.  With there being no other performance options for the police model like cams or injectors it's quite possible the internals of the police L-Jetronic are the same as the civilian model.

My 92 K100LT is ex police and it has the ABS unit under the seat in what is usually the tool tray and not in the duck tail. It also has a woven mesh earth strap from the gas tank to the frame. I noticed some other differences too over time.

Unlike the K100 which had several iterations of L-jet, the K75 had only one L-Jet throughout it's long life, which was Bosch #0280000332

Just on the injectors, here's a conversation we had quite a few years back about the 4 hole injectors. IMO you're better off getting your old ones cleaned.
https://www.k100-forum.com/t9046-1-hole-vs-4-hole-injectors