Fuel injector pulsewidth signal for Tiptronic

[PeepPaadam]

Installed VEMS plug and play to Porsche 964 Tiptronic, works fine but Tiptronic is in limp home mode due to the missing fuel injector pulsewidth signal. 

I connected the P259 pin 4 (ch0, with pullup) to the corresponding pin (pin 32 on Motronic 55pin connector) and configured boost gauge output hoping it will settle for just some kind of square wave signal but Tiptronic is still in limp mode.

Any tips how to proceed with this? I think fuel injector load output signal would be useful for many cars, even Audis use this to calculate fuel consumption, many Porsches etc. With display you can just ignore it but with tiptronic it ruins the driving -> cannot be ignored...

[MWfire]

Why do you don't connect to one injector outputs?

[VEMS]

Hello Peep,

Please produce some scope measurements of the stock ecu having both one injector signal on one probe (ch1) and the pin32 mot55 signal on the other probe (ch2), and take a few (clearly marked by filename) scopeshots @ idle rpm, 3000, 5000 rpm.

Without proper measurements its hard to know whats needed at all.

Best regards, Dave

[MWfire]

Did you try to use sec pwn?

[jrussell]

Configure one fuel injector channel to use two outputs. Add a pull-up to 5v or 12v (whatever the tiptronic controller prefers to see) and it will pulse both outputs at the same time. One firing an injector, the other signalling the tiptronic controller. The one downside to this is you use a high current output for such a simple task, but gets the job done.


At the red arrow, I selected a second output for the injector0 channel.

[PeepPaadam]

Tried the injector output and still in limp mode, scoped the output both with Motronic and VEMS, VEMS obviously has shorter pw because of bigger injectors that are tuned properly, couldn't get higher with Motronic than 1100rpm because with bigger injectors mixture became too rich.

Seems that we would need to configure boost_alt or some other output so that it would feed the pw of original injector despite the use of bigger injectors. Original injectors are Bosch 0 280 150 731: 201cc/min @ 43.5 psi (3 bar), however, factory FPR is 3.8bar so that makes them 226cc. 6cyl engine.

Here's Motronic load signal:


And here's VEMS load signal:


There's also output from Tiptronic to Motronic that is called "ignition timing change" which is used to request retard on gearchange (factory has it 5V on Motronic side that is pulled down during request). I would think I can connect it to VEMS input and configure ignition retard? Any tips how it would be best to configure?

[VEMS]

Hello Peep,


I see some scopeshots, however not in the proposed format, your shots do not provide enough information to determine the relation between the stock injection signal and the magic signal.
If you follow the instructions to the letter that would save you and me a lot of time. Reminder you of what's needed:

Please produce some scope measurements of the stock ecu having both one injector signal on one probe (ch1) and the pin32 mot55 signal on the other probe (ch2), and take a few (clearly marked by filename) scopeshots @ idle rpm, 3000, 5000 rpm.

Thanks! Best regards, Dave

[PeepPaadam]

First of all, the scope shots were done by customer, the car is in another country (Finland to be correct) and secondly I already mentioned that it is not possible to rev the engine more because of bigger injectors and Motronic injectos too much fuel into engine (currently injectors are 680cc).
Motronic outputs exactly the same pulsewidth as its injector pulsewidth and since there's no other signal that is fed from Motronic to Tiptronic TCU, this must be the issue.
I don't know if the output pulsewidth has to be very accurate compared to factory injection pulse because with cold engine pulsewidth is longer etc and I am not sure it can be replicated with VEMS if separate output is used other than injector one (which is of no help due to bigger injector).

Nevermind, I will experiment myself, if that screenshot is not enough. Next move will be probably to put in original injectors and see if it will work with VEMS.

Thanks anyway.

[PeepPaadam]

I got the Motronic load vs injector signal scope shots of 1000, 3000 and 5000rpm. Scope was only single channel, hopefully these shots are of any help.

Injector output at 1000rpm:


Load output at 1000rpm:



Injector output at 3000rpm:


Load output at 3000rpm:


Injector output at 5000rpm:


Load output at 5000rpm:

[VEMS]

Hello Peep,

Nice scopeshots, thanks! It seems the magic signal just mirrors the injector signal of a single injector, it should work in the way Jason suggested.

Best regards, Dave

[PeepPaadam]

We tried that but sadly it doesn't. Car has 550cc injectors instead of original 226cc and the TCU does not like shorter pulsewidth, it expects the longer pulsewidth of smaller injector.

We tried it without pullup though, 1kohm to 12v should be ok? Also we have all the injector outputs occupied (idle motor and resonance valve in the intake), we just connected it to cyl1 output (EC36 pin 7). If we add a pullup, would that be ok?

[jrussell]

we just connected it to cyl1 output (EC36 pin 7). If we add a pullup, would that be ok?

If there's an injector on that channel, the injector is the pull-up since it has 12v on the other side of it.

[PeepPaadam]

Duh, of course

I will ask the customer to try once more to verify, hope it will work. If not, the boost gauge or boost alt output would need to be modified in a manner that it shows factory injector output signal...