Alternative Fuel Injectors

[scarceller]

Rick,

I looked at the article for L584 and that sure looks a lot like what is in the Carrera DME. I tend to agree.

Originally Posted by rick-l

Here is an obsolete part that explains how the peak and hold works. (not the one in the DME)
L584 data sheet source

10 ohms wouldn't make much sense. If you have six, one ohm injectors in parallel the 10 ohm current sense would dwarf the injectors. It would also limit the peak current to under an amp and a half (0.23 amps per injector).

[scarceller]

Rick,

I measured that R409 resistor you are indead correct it is .1 ohm marked +/- 10%

Also the IC 0127 has this marking on it as well 8440

[rick-l]

Originally Posted by scarceller

Also the IC 0127 has this marking on it as well 8440

Made during the 40th week of the year 1984.

[dfink]

OK I have to at least give up my argument unless (or until) I find more information. There are indeed only 4 wires on the fuel injection connector.

[scarceller]

dfink,

I did a bit of reading last night in a book titled "Bosch Fuel Injection & Engine Management" and the type of system you are thinking of is called a 'Sequential Injection' system, this is the type that fires each injector separately and timed to the intake valve. Timed to the intake valve means some relationship to the intake valve opening but does not mean the injector fires right when it opens, they warn about this myth. Each engine is diffrent and can vary as to when the injector opens on a engine by engine bases.

Here is the opening sentence in that section of the book:
"Sequential Injection means delivering fuel seprately from each injector in sequence - in firing order"

It then goes on to say that such Motronic systems do exist and are know as 'Motronic ML.3" but the 84-89 Carrera does not use sequential injection system.

Stop beating yourself up. You are correct that such systems exist but it's not the one in our cars.

By the way that is an excellent book.

Originally Posted by dfink

OK I have to at least give up my argument unless (or until) I find more information. There are indeed only 4 wires on the fuel injection connector.

[safe]

If the system is sequential or batch fired (all at once) doesn't really matter form a performance view, its more an emission and fuel economy thing.

At high rpm a sequential system fires its injectors almost constantly to supply the engine with enough fuel.
At part throttle the injectors can be timed better with the valve and get a better combustion.

[scarceller]

I scanned 2 pages from the "Bosch Fuel Injection & Engine Management" book. The sections 'Fuel Injectors' and 'Fuel Metering & Pulse Time' are worth a read.

I found the later section 'Fuel Metering & Pulse Time' very interesting, had to read it and look at the pie chart pics a few times before it sank in. But after understanding this I now see how a system such as the one in our cars could become fuel starved at the higher RPMs. The bottom line is that at the higher RPMs the engine is spinning so fast that the injectors don't have as much time to open. In my car I have moved my red-line up to 6800RPMs and after about 6600 RPMs my mixture goes lean, I have bumped my WOT fuel map in the chip way up between 6600-6800 RPMs but it has 0 effect. I'm starting to think I may now understand why. Possibly the injectors are just fully open and can't keep up.

[scarceller]

Safe,

But our 84-89 Carrera cars are not Sequential correct?

Thanks.

Originally Posted by safe

If the system is sequential or batch fired (all at once) doesn't really matter form a performance view, its more an emission and fuel economy thing.

At high rpm a sequential system fires its injectors almost constantly to supply the engine with enough fuel.
At part throttle the injectors can be timed better with the valve and get a better combustion.

[Lorenfb]

"In this case you can not consider that there are 6 injectors in parallel because only one circuit at a time is being activated. Also because of the short frequency you would never see anywhere near that type of current draw."

Guess again, please!

"But of course you would only draw that much current if you applied a solid ground to one side and 12v to the other."

So, a soild ground and a pulsed ground produce different peak currents, right?

"But of course the signal is pulsed duty cycle so the current would never be that high for long."

Do what?

"My bet is it is a 10ohm 1watt resistor."

Another bad guess!

"Common sense dictates that you can not send a single pulse. If you did there would fuel going into every cylinder nearly all the time."

Whose common sense?

"But after understanding this I now see how a system such as the one in our cars could become fuel starved at the higher RPMs."

Really? So the Bosch engineers should have consulted the Pelican 911 Forum for
validation and design review of the '84-'89 911 DME ECM, right?

[scarceller]

Loren,

I'm glad you are here!

I know you repair these DMEs all the time. And we here are learning. So please help us learn.

Here are the questions, we could use answers please:

Is the 84 - 89 Carrera sequential injection or batch?

Above I scanned 2 pages from a Bosch book and I was just trying to say that according to the book you COULD run out of time to inject enough fuel at high RPMs. I'm 100% certain that the Prosche engineers would have never designed this system wrong. But in my car I'm far from stock, I have webcams 20/21 and non stock intake as well as SSIs with 2in2out exhaust. And then on top of this I moved the red line up to 6800. So my point is maybe by moving the red-line up and all the other changes I just moved outside the Porsche engineered specs. Could that be possible? It's just a question. What I do know is that my WBo2 system tells me I'm going slightly lean after 6600RPM and far more lean between 6700 and 6800 and pushing the WOT map up has no effect. What's your thoughts?

Is the circuit that drives the injectors a current limiting circuit?

Are the injectors in parallel (batch mode)?

Finally,
That 10ohm resistor I confirmed to be .1 ohm, I was wrong. But I took the time to go measure it as I do not like to guess. When I looked at the schematic the resistor was marked as component R409 with value R10 so I took the R10 to mean 10 ohm but I see I was wrong, it means .1 ohm.

Would love to hear your answers to these questions for those of us trying to learn

Thanks in advance.

Originally Posted by Lorenfb

"In this case you can not consider that there are 6 injectors in parallel because only one circuit at a time is being activated. Also because of the short frequency you would never see anywhere near that type of current draw."

Guess again, please!

"But of course you would only draw that much current if you applied a solid ground to one side and 12v to the other."

So, a soild ground and a pulsed ground produce different peak currents, right?

"But of course the signal is pulsed duty cycle so the current would never be that high for long."

Do what?

"My bet is it is a 10ohm 1watt resistor."

Another bad guess!

"Common sense dictates that you can not send a single pulse. If you did there would fuel going into every cylinder nearly all the time."

Whose common sense?

"But after understanding this I now see how a system such as the one in our cars could become fuel starved at the higher RPMs."

Really? So the Bosch engineers should have consulted the Pelican 911 Forum for
validation and design review of the '84-'89 911 DME ECM, right?

[Lorenfb]

"Is the 84 - 89 Carrera sequential injection or batch?"

Batch (all at once)

"I was just trying to say that according to the book you COULD run out of time to inject enough fuel at high RPMs."

At probably >7500-8000 RPMs
It's just a function of pulse width and fuel pressure.
The injector firing rate is 1/3 the spark rate, i.e. all injectors fire once per revolution of
the crank. So at 6000 RPMs (sparks at 3.3ms), the max pulse width possible is 10ms.
Sequential allows for a max pulse width at 6000 RPMs of 20ms as is the case for
both the 964 and 993 (and later). The key benefit, though, is better emissions control.

"And then on top of this I moved the red line up to 6800."

Not a problem!

[scarceller]

Loren,

Thanks a bunch,

I'm glad to here I should have plenty of injector head room at 6800RPM, must be something else going on. I did not dig in to deep on this yet. Since I'm still tuning the 5225RPM to 6500RPM AFR at this time.

Originally Posted by Lorenfb

"Is the 84 - 89 Carrera sequential injection or batch?"

Batch (all at once)

"I was just trying to say that according to the book you COULD run out of time to inject enough fuel at high RPMs."

At probably >7500-8000 RPMs
It's just a function of pulse width and fuel pressure.
The injector firing rate is 1/3 the spark rate, i.e. all injectors fire once per revolution of
the crank. So at 6000 RPMs (sparks at 3.3ms), the max pulse width possible is 10ms.
Sequential allows for a max pulse width at 6000 RPMs of 20ms as is the case for
both the 964 and 993 (and later). The key benefit, though, is better emissions control.

"And then on top of this I moved the red line up to 6800."

Not a problem!

[Peter Kelly]

Originally Posted by scarceller

I'm glad to here I should have plenty of injector head room at 6800RPM, must be something else going on. I did not dig in to deep on this yet. Since I'm still tuning the 5225RPM to 6500RPM AFR at this time.

Hi,

I have an EPROM emulator permanently connected to my DME (89 Carrera) with stock injectors and regulator and I have no problem getting enough fuel into the motor at 6800, so if you are going lean with max WOT trim values you must have a fuel system problem. My Fuel P runs 35 PSI at WOT and high revs.

-Peter

[scarceller]

Hi Peter,

Would you mind sharing your WOT fuel map? Just curious what it looks like.

Originally Posted by Peter Kelly

Hi,

I have an EPROM emulator permanently connected to my DME (89 Carrera) with stock injectors and regulator and I have no problem getting enough fuel into the motor at 6800, so if you are going lean with max WOT trim values you must have a fuel system problem. My Fuel P runs 35 PSI at WOT and high revs.

-Peter

[dfink]

I guess I never gave much thought to how the injection actually works. Hell they might as well have done like chevy and stuck one big injector after the throttle body. Crap save some money and just stuff one big injector on each side. I am now sad and have lost respect for my porsch. (notice missing "e")
"Common sense" was not thinking correctly. I had in my brain the fuel was injected into the cylinder instead of the manifold. (i know this is incorrect but stuck in brain anyhow) visions of washed cylinders.

Perhaps a nice garden mister would work.
My vision of syncronized perfection down the crapper........
I am now going to go cry.....
I did however learn something.

[rick-l]

Originally Posted by scarceller

Hi Peter,

Would you mind sharing your WOT fuel map? Just curious what it looks like.

scarceller
You have perused FR Eilk's site correct?

[scarceller]

Rick,

I'm Sal.

Yes I have seen that site - I also have just about every stock stock chip binary file for the 84-89 Carrera plus a few aftermarket chips.

I was just curious what the WOT fuel curve looks like that Peter has since it sounds like he tuned it for his specific car.

I burn chips for my car all the time, I have been fine tuning my Fuel Maps for a few months now with lots of good results.

All this work pertains to this thread because my goal is to get my WOT map at 13.1 AFR (+/- .1) across the RPM range with the stock 158 injectors. Then I have some test injectors that are not 158s but are low-impeadance and very close to the 158s but much cheaper. The goal is to then install the test ones and look at the results of the WBo2 AFR readings and compare.

You get the idea. Get a good baseline with the 158s then plug in the possible alternative injectors and see if they work.

See here for the test injectors and how they look:
Alternative Fuel Injectors

Originally Posted by rick-l

scarceller
You have perused FR Eilk's site correct?

[ischmitz]

So Loren, it seems like you know really a lot on how the injector stage works on the ML3.1Motronic. Could you shed some light on the S400 chip. As mentioned here and elsewhere it's got to be some sort of peak and hold driver with dual output controlling the darlington output stage and the flyback/dump stage.

What do people do when this IC goes bad. Is there a replacement available today?

Thanks,
Ingo

[ischmitz]

hm Loren, no answer so far - does that mean you don't know or you don't want to tell us?

[rick-l]

Loren could be in time out.

Hurray for Schneider's Autohaus!!