Modifying A L-jetronic-ecu ...

[Dandu 0]

Hi,

 

has anybody ever tried to adjust the fuel injection time via modification of the ECU (L-Jetronic)?

 

Cheers Dandu

[welshpug 1,626]

yes, but its much easier and better to fit the original Motronic that has the correct maps for the engine.

[Dandu 0]

Hi welshpug,

 

I like the Jetronic albeit it has some disadvantages. On the other hand I don't want to exchange the whole control system in order to adjust the fuel injection cycle. Bytheway I feel pretty familiar with the motronic 1.3 ... the curves for spark advance, fuel injection etc.

 

And now I only want to know how to convince the L-Jetronic-ECU to increase the fuel injection. I suppose, there are curves for idle, pot and wot as well. But where?

 

Just to give some background. I replaced the throttle body, and I realized, that I can't comply with the needs of fuel via AFM, FuelPressureRegulator or anything else precisely.

 

Can you help me?

 

Bye Dandu

[jim21070 2]

Hi Dandu,

 

The old way to do what you need to do was to use an auxillary "piggyback" ECU that would intercept the injector outputs from the L-Jet ECU and artifically extend them by the required amount before passing them on to the injectors. The problem is that these were a bit "flat" in that they extended generally a fixed amount under all conditions. No reason why an intellegent auxillary ECU should not be able to take account of idle, WOT and lean cruise though with a bit of electronics.

 

I've no idea how available these ECUs are nowadays. Have not seen them advertised for years... Do you know an electronics genius near you to design and build one for you...

[Dandu 0]

Hi Jim,

 

much thanks for your comment. But I actually can not derive any advantages from a "piggyback" ecu. I'm in need to adjust the injection differently. No constant increase/decrease.

 

But I hope, there is a chance to modifiy the ECU itself.

 

Bye Dandu

[DamirGTI 327]

Hi !

 

Which injectors are you using ? (read the numbers from the injectors ..)

 

Damir

[Dandu 0]

@Damir,

 

the ones you prefer too: 762. Nice to hear from you again.

 

@Jim,

I figured out some piggyback controllers, that seem to be able to adjust the signals in a variable way. Insofar they are still an option. You've mentioned the possibility of their existence ... thus forget my former comment. And much thanks.

 

But I actually feel pretty overwhelmed. Is there anybody, who can recommend one?

 

Bye Dandu

[DamirGTI 327]

Hi !

 

Well if you can't adjust the mixture rich enough to suit for your engine specs. , i would not spend money on expensive aftermarket ECU-s (if you have not done some serious engine modifications ..)- try to find some bigger injectors on scrappy from some other car and see if that helps + with a little playing with fuel pressure ..

 

These yellow - 762 injectors haves 214cc flow , try with 240cc (701 injectors) , of maybe 270cc injectors and see if that helps you can find a lot of various injectors at scrappy yards and very cheap just check before you buy them that they operate at same resistance 14 to 16 Ohms ..

 

As sad Motronic ECU is much better solution for modifying than Jetronic ECU , Jetronic is just simple analogue base EFi system you can try to make DIY superchips mod. with two variable resistors on Jetronic ECU and see if you can do something with that to richen up the mixture to requested level ... but i can advice you that you first try with a little bit bigger injectors and adjust the fuel pressure more or less as because this option is a lot cheaper ..

 

This is one interesting site if you wish to read more about Air/Fuel ratios , injectors etc. (it's for Opel/Vauxhall cars but there's a lot of interesting infos. for various engine adjusting modifying stuff ..worth to look at ! ) :

http://www.max-boost.co.uk/max-boost/fuell...BiggerInjectors

 

And injectors flow tables :

http://www.max-boost.co.uk/max-boost/resou...-basic-info.xls

http://users.erols.com/srweiss/tableifc.htm

 

Cheers !

Damir

[Dandu 0]

Hi Damir,

 

once again it has been a pleasure to read your answer. At first I'll go the route with the 2 variable resistors. Let me explain, why.

 

You surely remember my project, do you? I recently replaced my 8v-throttle body with a bigger one from a 3.5L-BMW. The same happened for the AFM. With a little help from heaven above ... I'm already able to get more air involved into the combustion. The only problem is the adjustment of the fuel consumption. Fiddling with the AFM (spring) enables me to find an optimum for idle, pot or wot. Setting up the perfect mixture at:

 

1. idle results in a rich mixture in pot and wot.

2. pot results in a lean idle and a rich wot.

3. wot results in a lean idle and pot.

 

I can't imagine, in which way bigger injectors or a fuel pressure regulator might help. That means, back to the ECU ...

 

After I recently opened it up, I gave up instantly to reprogram any kind of chip. Thus the piggyback idea came back to my mind. Researching the web gave me some ideas of a likely ... but expensive ... solution. It might be possible, that I've to reconsider that, but at first I'd like to build up my own simple "piggyback" system. Consisting of some variable resistors, that influence the resistance (coming from the AFM) at idle and wot. Relays, actuated by the throttle switch, will help to affect the signal at the right time. Everything is preceded by a correct AFM-setup for partial open throttle.

 

I'll keep you up to date.

 

Bye Dandu

[Hilgie 16 2 Cars]

This site explains how the Jetronic ECU works and shows the required modification to adjust rev limiter and/or injection time.

 

http://www.205gti.com/bosch/mods.htm

[Dandu 0]

What a magnificent link. Thanks, Hilgie.

 

Cheers Dandu

[Hilgie 16 2 Cars]

http://www.205gti.com/bosch/ is the main site.

 

other resources:

- Technical Instruction L-Jetronic - # VDT-U 33 En - Robert Bosch GmbH

- Bosch Fuel Injection and Engine Management - Charles O. Probst, SAE - Robert Bently Publishers #GFIB; ISBN 0-8376-0300-5

[Dandu 0]

Hi Hilgie,

 

much thanks again. I feel familiar with the url: www.205gti.com/bosch, but the topic "L-Jet modifications Removing the rev-limiter and other stuff" hasn't drawn my attention yet. Very strange.

 

Bye Dandu

[Dandu 0]

Hi,

 

just to give an impression of my very simple piggyback system (influencing the AFM-voltages at idle and wot):

 

 

If someone is able to figure out any kind of mistake ... I'd appreciate his comment. Thanks in advance.

 

Bye Dandu

[Dandu 0]

Hi,

 

just to report my experiences. I've managed to set up my simple piggyback-system. The final version is a bit different from the version above. Some major faults had to be corrected. And now ... it's running.

 

The AFM (that means the spring) is adjusted to deliver the "proper" amount of fuel at WOT. In dependence of the TPS-signal additional variable resistors are actuated at POT and IDLE. The current configuration is as follows:

 

IDLE: 0,92 Lambda

POT: 1 Lambda

WOT: 0,87 Lambda.

 

At a first glance it seems to be ok, but there is a small problem. At WideOpenThrottle the Lambda-value is jumping. The scenario is as follows: Driving along in 4th gear steady at 3500 rpm, smashing down the gas pedal, the pointer passes 4000 rpm -> Lambda 0,87, 5000 rpm -> Lambda 0,87, suddenly Lambda goes down to 0,70, as quick as it came it goes up to 0,84 again and doesn't change as long as the pointer goes to the limiter. Why does the engine seems to overfuel for a moment? Does it have to do with the inner sanctum of the AFM (the design of the sliding board)?

 

Bye Dandu

 

P.S. Hey Damir, did you experience the same at higher revs? Bytheway .. your recommendation to buy a wide-band oxygen sensor was very helpful. Much thanks again!

[DamirGTI 327]

Hello mate !

 

Yes it's good/fine at WOT but it's a bit too rich at idle and mid range you will waist big amounts of fuel at idle and mid range ...

 

I can tweak/adjust fueling when ever i wish and im doing this via fuel pressure regulator and by fitting-refitting modified ECU - when i wish to race i fit modified ECU when i go for a long trip i fit standard non modified ECU .. but i use this car as a daily drive so this is important to me , if yours is for racing only then it's not of such importance ..

 

First with just internally modified engine (headjob , high CR etc.) and running with standard fuel system ECU injectors fuel pressure etc. i was having problems with drop of lambda values/volt readings at WOT just as you have described , it was reasonably good at mid range but when i was pressing the pedal harder speeding up from 4500-5000 to 6000 lambda/volts was suddenly starting to fall down from 0.82 at 5000 down to 0.80 - 0.79 - 0.78 as i was speeding up to full load 6000-6300rmp ... so it was a must to do something to correct that before i wreck the engine because anything below 0.80mv at WOT is considerable as dangerous for the engine and especially if engine goes increasingly lean (values drooping.)at WOT - this is no good ! ..

 

At idle it will be best around 0.85 (or less if you can set it less , it does not need to run rich at idle !)

At mid range around 0.88

At full load - WOT from 0.86 to 0.87 is fine if it does not have high tendency of falling back down on WOT like from that 0.87 value down beyond 0.80mv , it will switch a bit from say 0.84 to 0.85 - 0.86 - 0.87 at WOT so don't worry ! the lambda values/volts wont stay still all the time on 0.87mv at WOT (when you stick/hold the revs at lets say 5000 or 6000..they will swing a bit up and down..) or at any rev range it will always switch up and down a little bit in fact at WOT this readings can go as high as 0.90 (especially when you pres the pedal really hard on mid range (4000) it's good if you then notice that from this moment values quick increase to 0.90mv - this is sing of a good setup !) and even more then that for the best power but not more then 0.92 - 0.93 me thinks (also you must reset/adjust the ignition timing for different mixtures otherwise you will just waist fuel - lots of unburned fuel will be lost out from the engine via exhaust and waisted fuel energy because of the wrong/incorrect spark timing ..)

 

Anyhow i've set my fueling so that it rises almost linear when i accelerate hard from mid to high revs , without drops in readings

Try adjusting/playing some more

and what color the plugs are ? for idle fueling check them after switching from steady/idle and for WOT plug reading you must run the engine at full throttle driving on the road (or on race track which is better solution ..)and then switch off the engine at WOT and cruise down with the car until you stop without the engine running - then pull the plugs out for WOT mixture examination ...

 

hope this helps !

Damir

[Dandu 0]

Hi Damir,

 

you've got the point: I'm still in the need to change a bit - let's say: play a little with the equipment. According my feelings ... the car setup is fine. Neither idle, pot or wot makes me nervous. The car is very responsive and fast. I dare to sum up: it was worth to change the throttle body.

 

But today - quite accidentaly - I figured out, that my injector nozzles do not seem to be the same at all. Recently I had to replace one of them. I checked the Bosch-Nr. 762, and considered the nozzle to be appropriate. Today I saw a small number imprinted above the Bosch-Nr. Suddenly I got to know, that I replaced the injector nozzle 762 - 841 with a 762 - 056 or 051. Do you know the difference? I don't consider a difference to be present. Otherwise I should experience a lack in power. Today I've been able to rev up the car easily into limiter at 5th gear.

 

Cheers Dandu ... and much thanks for your elaborate response, Damir!

Edited August 27, 2007 by Dandu

[Dandu 0]

Hi Damir,

 

you've got the point: I'm still in the need to change a bit - let's say: play a little with the equipment. According my feelings ... the car setup is fine. Neither idle, pot or wot makes me nervous. The car is very responsive and fast. I dare to sum up: it was worth to change the throttle body.

 

But today - quite accidentaly - I figured out, that my injector nozzles do not seem to be the same at all. Recently I had to replace one of them. I checked the Bosch-Nr. 762, and considered the nozzle to be appropriate. Today I saw a small number imprinted above the Bosch-Nr. Suddenly I got to know, that I replaced the injector nozzle 762 - 841 with a 762 - 056 or 051. Do you know the difference? I don't consider a difference to be present. Otherwise I should experience a lack in power. Today I've been able to rev up the car easily into limiter at 5th gear.

 

Cheers Dandu ... and much thanks for your elaborate response, Damir!

 

I've just taken a look at the replaced nozzle - the nr. above the Bosch-nr. is 063. The others ... 841. Bye Dandu

[Dandu 0]

I talked to my bosch-dealer. He told me not to be worried. These numbers might stay in relation to the date or location of fabrication. The nozzles are the same.

 

Bye Dandu

[DamirGTI 327]

Hi !

 

Just something i wish to ask you - did you check injectors for flow ? what i mean are they clean , is the spray pattern good ? if one (or more of them) are not clean or the spray pattern/flow isn't balanced up to +-5% tolerance to each injector it will be a bit pointless to spend time and trying to adjust the right mixture because just one bad or clogged injector can mess up your readings badly and you will just turn around in circles scratching your head why you can't get this right and why you have strange/incorrect mixture readings and you've done everything right as it's should be done ?...

 

If you are not sure about that - get them checked to someone who haves ultrasonic cleaning/flow checking machine (like your Bosch dealer ..) , and first before cleaning check each injector for cc. flow and spray pattern and if one or more of them are out of tolerance zone clean them ultrasonically , after cleaning check again for spray pattern and flow cc. of each injector , and if they are still not in the tolerance zone clean them once again until all injectors are balanced to reach same flow cc. and good spray pattern +-5% is acceptable , but the best scenario will be if they all reach same cc. flow and nice strong spray pattern after cleaning .. this will be of benefit for correct mixture adjusting , better fuel consumption and more engine power/response !

 

Cheers !

Damir

 

(how much did you pay for an wideband lambda sensor ? and which brand did you chose/buy ?)

[Dandu 0]

Hi Damir,

 

you're right. It should be very useful to check them. With a little luck I'll be able to do it at the garage of a friend soon. In the meantime I'll try not to overdo it. Although I've to admit that car feels very quick now. It seems like the 3.5L-BMW-throttle-body-transplantion was efffective and useful. Thus I'm not intensively worried.

 

The wideband-oxygen-sensor has been imported from the USA - innovate motorsports:

 

http://www.innovatemotorsports.com/products/lm1.php - The Basic Kit.

 

Price: 350$ + 90$ (shipping) + 80 Euro (customs duty). Let's say, it has been a lot.

 

Much thanks for your help, Damir. You took part in the success of my project too.

 

Cheers Dandu