VEMS high AFR on idle

[Bram]

Bram, setting it at 75% will give you a wider amount of numbers to use in the VE table before a big change in fueling occurs.

here is an example:

you are @ 100kpa @ 3000rpm and have VE=95 which gives you a lamda of 1.00

Say you wanted to have there a lamda =1.01 so that you have better fuel economy
You would then alter the VE from 95 to 94 and recheck.
The 94 value could take the lamda to 1.02 !!! So then you wouldnt have a number to use between 95 to 94 to give you the 1.01 lamda that you are after. Of course that can be dealt with in the end with EGO correction, but the point is to be able to have a fueling map that can be very customisable and easily achieve the goals you are after.

By making the reg_fuel @ 75% you get to be able to use more values from 0-255 on the VE table to customise your table. On the other hand, having the 12x12 tables makes it less needed,as vems would have to cover the gaps between the values anyway,but as i said, you will find that you will need to have minor changes done on the VE table sometimes and that can be achieved with an elaborate VE value range.

Mine unforuntelly is not that elaborate at the moment but it does the job. Once i change the injectors i plan to do that

OK, so if I am using the Siemens-Deka 630ccm@3bar injectors I should set the req-fuel parameter to:

630ccm@3bar = 727ccm@4bar FPR

6.49 * ( 2226 / 5 / 727 ) * 0.75) = 2.98

correct?

[A80Avant]

yup!

[Bram]

yup!

hmmmm, currently I got my software where the req_fuel is set to 3.8 so could that cause the lean idle?

[GazzaG60]

no

say you have an idle of 1.25 and your req fuel is 3.8 lowering this figure will make it leaner.

thye req fuel is how long the injector has to be open for stoich. so yours is set to 3.8ms. lowering that dictates the injector is bigger so needs less opening time.

[Bram]

no

say you have an idle of 1.25 and your req fuel is 3.8 lowering this figure will make it leaner.

thye req fuel is how long the injector has to be open for stoich. so yours is set to 3.8ms. lowering that dictates the injector is bigger so needs less opening time.

I will try 3.9 then

[A80Avant]

you can just try 2.9 and raise the VE values on idle rpm until you get lamda=1

[GazzaG60]

all values in ve will be out if you change req_fuel.

it will need extensive changes. if your only just starting its worth doing though. saves lots of changes later.

as Vas says. change the reqfuel then set the ve for idle. use the change in numbers (expect to add 10 or so to ve for that change) as a guide for the rest of the ve chart.

[GazzaG60]

for reference i run similar with the same injectors and similar turbo size. i run around 1.10 at idle 1.05 or so on cruise. still get good idle at 1.15.

[A80Avant]

wow! why so lean @ idle Gary?

[GazzaG60]

petrol aint cheap.

you can dial it out till it starts to pop a little then put a fraction back in.

thing with these cars. well any 4x4 is it drinks too much. i get good returns on the motorway due to miser tuning.

if you set more pressure zones below 100kpa you can fine tune more with the bigger injectors and get much better cruise and still have the zones for boost

[Bram]

for reference i run similar with the same injectors and similar turbo size. i run around 1.10 at idle 1.05 or so on cruise. still get good idle at 1.15.

What do you mean with "I run similar"? same req_fuel parameter as I have (3.8)? Or similar VE parameters on idle?

[A80Avant]

i should do that with the bigger turbo actually.

for now,im getting about the same(maybe slightly better) economy than the motronic on cruising. a bit worse on high boost though.

on idle i have it on lamda=1 and with the use of the isv valve it works like a treat

[Bram]

Yesterday I noticed when starting the car the second time and the engine got warm the EGO kicked in and raised the idle RPM to 1100, where the lambda also showed 1.02 on idle
Now I know this is a closed-loop lambda setting done automatically by the VEMS ECU. I have EGO disabled atm.

Would it be possible that the idle VE values can be set with the VE learning (auto-tune) feature op Megatune?

[Bram]

you can just try 2.9 and raise the VE values on idle rpm until you get lamda=1

you mean 3.9 I guess?

[GazzaG60]

il;l chat with you regarding the idle control as i dont run it still. could never get it to work when driving properly. still gotta fit the diode too.

bram - i have a similar setup. standard bore, wagner setup, sc61, reverse inlet, seimmens injectors, 3" system. those targets work fine with the seimmens