How to calculate a baseline for IJPU

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How to calculate a baseline for IJPU

Postby eMTea on Mon Sep 30, 2019 5:39 am


After figuring out trigger setup, we got the car to start.

It stops after 2sec, and we've tried almost everything, adding fuel, in small and big amounts. Leaning out, nothing seems to help, to keep it running.
I guess it only runs on the priming pulses we give it by throttle blip through "Stopped Injection".

BMW S14B23, stroked and bored, 2900ccm.
NA rallycross motor from Köhler Racing,
high compression, big custom cams, custom pistons, staged injection.
approx 385hp @ E100. (Prevoiusly ran M48)

How do I proceed to get the right amount of fuel, to at least keep running.
I copied IJPU, fuel main table, cranking corrections, post start corrections, etc from the M48 to the M84, but it seems to be way lean. But if I add fuel, there is no difference. Event when double the IJPU (from 20 to 40mS) and adding fuel in main table.

Is there someone here who can compare these 2 maps for me, to see where I'm off?
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Re: How to calculate a baseline for IJPU

Postby SDean on Mon Sep 30, 2019 9:24 am


Can you please post the M84 map, and logging of the engine start process thanks.
Stephen Dean
MoTeC Research Centre Melbourne, Australia
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Re: How to calculate a baseline for IJPU

Postby Vlad on Mon Nov 25, 2019 5:32 pm

What i usually do, is set my IJPU and fuel table, so that after the calculation, i have aprox 1.5-2.5 ms PW at idle...I saw that that is a pretty good way to start fuel mapping, and have the engine idling ok'ish...not stalling... Also, be sure to set your lambda on fast heat mode, for this part of the tuning.
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Re: How to calculate a baseline for IJPU

Postby stevesingo on Tue Nov 26, 2019 3:32 am

Can you not manually convert you M48 values?

What injector flow rate at your operating pressure?

Fellow s14 runner with M800. :D

I'm running 627cc/min (429g/min) Bosch EV14 at 3bar sequentially.

In general set up>fuel: Injector scaling is 5ms

Idle values in table are 46 which corresponds to 5/100*46=2.3ms or 0.016g of gasolene.

This equates to Lambda 0.95 for me.
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Re: How to calculate a baseline for IJPU

Postby super7 on Tue Nov 26, 2019 6:16 am

Is it running?

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