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I am fine tuning my Ford V8 w/ Borla EightStack individual throttle bodies. The design is such that the Injectors are above the throttle blades so initial flow and priming pulses are somewhat blocked.
I've tried priming pulse as high as 200ms and cranking compensation at +300% and the engine still cranks for 5-7 seconds before it fires.
Is this the best it is going to be or does anyone have ideas on how to improve the cold start characteristics. ECU is a Performance Electronics, priming pulses trigger on first rpm
Suggestions or ideas?
Cold starts with injectors above the throttle plate is going to be difficult.
Is it possible to add additional injectors post throttle plate just for starting? Only other option is having the throttle at WOT when doing a pre crank prime to ensure the fuel makes it down instead of sitting on the plate then attempting to start it.
I tue a methanol fuelled V8 that runs itb's with the injectors above the throttle plates. This engine runs a Motec M800 and there is a feature in the Motec that provides a pre crank prime pulse of fuel above a certain throttle position. We've used that feature above 80% throttle and found that 2-3 applications of full throttle and then cranking with around 25% throttle allows the engine to start crisply and quickly even in cold weather (which is hard at best with methanol). I'd see if you have the option of replicating this technique and see how it works for you.
As Andre suggested, the Fuel Stopped Injection function on the Mx00 family of ECU's is designed for this usage (done for the V8 Supercars) in that it allows for the tuner to configure a setting that allows for the injector to spray past the open throttle butterflies (hence why you have a large number for the throttle opening to trigger it) and wet the inlet runner, creating the fuel film needed for the engine to start. Once the runners are wet, when the engine is then cranked with the throttle in the idle position, the lower pressure in the inlet tract post throttle plates allows for the fuel to flash to vapour and transfer into the cylinders when the inlet opens, thus promoting combustion.
You obviously need to have the fuel pump running at this point as well, to provide pressure for the injectors to operate, it is amazing how many people don't do so though.
Unfortunately, my ECU doesn't have this "stopped Injection" feature of the Motec units. I am talking to them to see if it can be added. Their system (Performance Electronics) sends the priming pulse either at power on or at first RPM. Holding the throttle plates open for this doesn't make for the most pleasurable starting experience. Really gets everyone's attention when it catches ;-)
To those familiar with the "Stopped Injection", does this create any issues when the engine is already flooded? My system turns off the injectors if the TPS is over 95% and the engine isn't running, as a way to clear the flooded condition. The stopped injection feature would only add more fuel to an already bad condition? How do they deal with that?
Stopped injection is the ideal function to fix your issues, but there are other ways you can get a similar result. The priming pulse may have a similar affect if you can make it big enough and ensure it happens when the throttles are open. You could also try making a significant increase in the fuel table values around the cranking rpm at large TPS values to inject more fuel than normal. This is a band aid obviously and you'd need to be a little cautious about your throttle opening when the engine does start.
The stopped injection pulse is only used when the engine is stationary and the tps exceeds the set point in the software so it won't have any impact during cranking.