Split second makes a translation box that allows you to use a MAF with the L-Jet brain. It translates the voltage of the MAF to a voltage that the L-Jet recognizes. I was helping to tune one that was set up like this on a twin turbo 928. It would have been great if it had data logging but the one I was working with didn't so you had to tune in real time. What a pain in the rear.

It sounds like you may be more well versed in electronics than I am. There is no flappy, I think you may be refering to the AFM since it has a little flapper in it. When you say pulse duration, are you reffering to injector pulse duration? As I understand it the AFM varies its voltage signal to the computer depending on how the much it is open or closed. Could you or someone else elaborate.

Thanks. This thread is going great.

 

I've been thinking about going that route, except it does nothing to "fix" the ignition problem. The easiest solution I can see is using the S4 EZK - so I might as well use the S4 LH.

 

No offense, but wouldn't it be cheaper and WAAAAAAYYYY easier to just go to an S4? BTW, I have Tim's EZK from Jack.

 

Cheaper? In my case not even close.
Easier? That is a matter of opinion. If I end up with 500rwhp in a car that is 300+ pounds lighter than your car.......What was the question again?
Don't bring up the brakes & suspension argument since my 79 is already upgraded to S4 specs (and is even lighter). The S brakes are more than enough for a street car (on my 81).

This is why I said 9ish PSI is as far as I would go with an L-Jet car. Anything beyond this would require furthur modifications that IMO may not be worth the effort.
If you can upgrade the exhaust, bolt on a supercharger and get 350+rwhp out of an otherwise stock OB - that is worth the effort and cheaper than an S4.

 

I keep hearing upgrade to the Lh ect if it was that simple I would put it on my 86. No knock sensors seems to be the sticking point, on a small block or Buick V-6 I have remapped and added Meth and produced 24 Lb's of boost with no knock. So it seems a little more involved than explained to me on these cars. From what I am reading plenty of fuel "up to a point but the Plugs blow out at some point of boost. So if the 350 Hp cut off due to these factors.

 

Enzo-
Do you have any idea what is happening when the stock ignition box seems to be giving out on you? I just wonder if it is something that can be a) reproduced on a bench, and b) possibly fixed with a change in coil or plug or something. I've always felt that the big weakness is that it is not tied into the injection and thus cannot take advantage of knowledge of throttle postion, mixture, etc.
Fabio-
Sorry, I guess the S4 crowd has another use for the word 'flappy'. I was talking about he 'barn door' in the AFM. So, the way it works is that the AFM has a variable resistor which gives a resistnace reading which represents the position of the barn door and thus the amount of air going through it. The other primary sensors are resistive also, the air inlet temperature sensor (also in the AFM, typicall) and the head temp sensor (I may actually be measuring coolent temp on this car, I forget). There is also the oxy sensor giving feedback on the actual mixture produced, but I am not quite sure how that looks electrically.
The ignition system sends a trigger pulse to the injection system every time it fires a plug. The L jet brain takes the measurements it makes from the AFM and other sensors and turns it into a injection pulse that fires the injectors. The injectors are solonods so they are either open or closed, so the only variable is how long they are open. This means the computation that the L Jet brain does is to figure out how long the injection pulse should be based on the sensor readings it makes. I've never reverse engineered an Ljet, but I did a little of this with the earlier Djet and it was a pretty simple anlog pulse shaper. One big difference is that the Djet had seperate double trigger points for the injection so it fired half of its injectors each time, while the Ljet fires them all together.

 

So; is it possible to control the Inj pluse by maybe externally controlling it? Seems if you could control that, your fuel issue could be addressed a little more accurately.

 

What do you mean by externally controlling it?

Seems like there are basically 3 options for getting more fuel:
1. Increase the fuel pressure or injector size (or number of injectors) so that within the stock pulse duration more fuel goes in.
2. Fool the L-jet into increasing the pulse duration.
3. Use a different system to control the fuel pulse duration.

By external control do you mean #3, basically scrapping the L-jet "brain" for an aftermarket controller?

 

I never tried to reproduce the ignition issue on the bench, there was no need since it was very obvious the car was missing due to an issue with the ignition. The exact cause of the ignition could be debated. I've had issues with multiple Bosch ignition boxes, so IMO replacing that unit with something else is a good idea as a starting point. MSD boxes are cheap.
In case you missed the post, closing the gap on the plugs eliminated the miss. As far as I know this points to a weak system. Porsche switched to a duel coil setup with the EuroS and 32V cars so even they knew this system was not "up-to-suff" for more power.
The close gap is not a long term solution since it now doesn’t run very well when cold.
Under boost these systems are maxed out. Maybe you could increase the resistance of the Temp II sensor a bit to increase the injector pulse until you max out the injector.
As for larger injectors – I’m confident in saying the stock sensors will not have enough range to run the car properly under “normal” day to day driving. Too much fuel will be going in for the system to compensate for. Going from 24lb to 42lb injectors will add way more fuel under normal load for the system to compensate for. Increasing static fuel pressure was more than the stock system could handle causing the car to run rich at idle / cruise.
I know of other projects (non 928) with the Bosch L-jet system who have tried with little success.
If I’m wrong then cool, where do we buy larger injectors for this system? I haven’t looked so I’m not sure what is out there.
The temp II sensor directly controls the pulse width of the injector. A few of us have tested this with good success to add fuel. If there was such a device to simply add electrical resistance as boost is increased, you could probably fuel an L-Jet car with stock fuel pressure up quite a few PSI. I have no idea if such a device exists. Would be cool to play with.
In theory yes. If you can somehow increase the resistance of the Temp II sensor as boost increases. How high? I have no idea.

 

There are lots of way of modifying the Temp II resistnace based on boost. The first questions to answer would be:
-What does the signal coming to your boost gauge look like, electrically, and
-How much granularity would we need in the modification of the Temp II resistance? I would almost certainly suggest doing it in discreet steps, if possible. Creating electronically controlled resistance is a bit tricky unless you either know something about the circuit that is reading the resistance or are willing to do it with some granularity.

On the ignition side, I think it must get harder and harder for a plug to make a spark as the pressure in the combustion chamber climbs. Probably a shorter gap makes it easier. I wonder a couple of things here: what kind of pressure does the combustion chamber see at Enzo boost levels, and would it be possible the make a clear chamber that you could thread a plug into that would take that kind of pressure. If you had that you could play with different combinations of plug, coid, box, etc and see what is happeing without having to road test each time. Plus you could be real sure spark is the problem. I am thinking you could take a block of clear polycarb, drill a hole in it, tap one side to hook to your compressor and tap the other side for a spark plug. Then you can pick a pressure and crank your motor and see what your spark is doing. It might have to be a metal chamber with a polycarb window.....