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PitBull

Which MAP limit mode to use?

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I'm running methanol injection on my engine so I currently have the MAP limit mode set to "Ignition" since I figure if I use fuel cut, with the methanol keeps flowing the engine may experience a dangerously lean condition.

However, I have on occasion hit the MAP limit in 1st or 2nd gear and in one instance it resulted in a very loud bang out the exhaust, presumably because the unburned fuel ignited somewhere in the exhaust.  It was loud enough that it worries me that it could damage something so I'd like to prevent it from happening again.

I notice the MAP limit mode "Rotary" says that it limits fuel and ignition.  Is there any reason this mode shouldn't be used with a piston engine?  It seems that cutting ignition AND fuel would be best for my situation.  I am using sequential fuel injection mode.

 

 

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I'm running methanol injection on my engine so I currently have the MAP limit mode set to "Ignition" since I figure if I use fuel cut, with the methanol keeps flowing the engine may experience a dangerously lean condition.

How would the fuel keep flowing if the injectors are turned off?  What sort of engine do you have and are the injectors in the ports in a fairly normal position? 

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The rotary cut mode cuts the injection and ignition outputs in a particular order to suit a rotary engine. It is hard to say what the effect would be on a 4 stroke engine, there is the possibility that a fuel and ignition event could occur or overlap, this could be a risk to the engine.

Scott.

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Hello, sorry I didn't get back to this until now...

Adam:  What I meant is that if I use fuel cut, the fuel injectors will shut off and the gasoline will be cut nearly instantaneously.  However, since the methanol nozzles are probably about 2 feet before the throttle body, even shutting off the nozzles upon hitting MAP limit will leave a certain amount of methanol in the intake tract.  I don't know if that amount would be enough to cause a lean condition and possibly detonation or preignition. 

I do realize that if it is an extremely lean mixture, it would just misfire, rather than cause detonation.  At maximum injection, the methanol is accounting for approximately 30% of the total fuel, so if the gas were shut off but that amount of methanol remained, perhaps that would not be enough to cause any issues?

The more I think about it, maybe it would still be better for me to use fuel cut, rather than ignition cut.  I definitely won't try the Rotary setting after your warning, Scott.

 

 

 

 

Edited by PitBull

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I still dont think you have provided enough info about your setup.  It sounds like fuel cut might be a bad idea for you but we need more info.  Are your methanol "nozzles" actually normal injectors or are you talking about a water/meth type nozzle?  If they are in fact injectors, then what injection mode are you using - sequential/staged or sequential/auxiliary?

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The nozzles are Aquamist water/meth nozzles, but it has a fast-acting valve just before the nozzles that cuts the flow off very quickly (though not as quickly as a fuel injector of course).  So it would mainly be the wetting of the intake pipe that would be providing the methanol once the cut hit.

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Adamw, he is most likely using a Aquamist HSF2/3/4 system. 

I have used tons of the alky/meth injection systems and have never had an issue with what style of rev limiter I used.

It sounds to me like his rev limiter is just set up to  be pretty aggressive.  If he tones it down and does more of a "OEM" style rev limit it will reduce the bangs he is referring to.

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Yes, I have an Aquamist HSF4 system which varies the methanol flow using a "fast acting" solenoid valve and constant pump pressure.  But it gets fed a PWM signal from an Aux output on Link ECU, rather than tapping into one of the fuel injectors.  This allows me to control methanol flow independent of the fuel flow.  I have the Link set up so if it hits MAP limit, it turns off the PWM signal to the Aquamist, which causes it to quit injecting pretty quickly.  Much faster than if it was just relying on variable pump pressure to control flow.

 

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If it was connected to an injector driver then using fuel cut would be fine, but Definately do not use fuel cut if your auxilary injection is controlled using a GP PWM signal.

An aux output signal is a relatively low priority output and is not scheduled or timed to any engine cycle event.  That means it is likely when injectors are cut there will be some engine cycles that will continue to get a partial fuel dose from the auxiliary injection. How many cycles will depend on RPM and other variables but I suspect at high RPM it could be significant.  I strongly advise this is a bad idea. 

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Okay that's good information to have.  My Storm only has 4 injector drivers so I have to use a GP output.  If I upgrade someday I'd definitely switch it over to use an injector driver...

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Okay that's good information to have.  My Storm only has 4 injector drivers so I have to use a GP output.  If I upgrade someday I'd definitely switch it over to use an injector driver...

Maybe I was not clear or you have misunderstood me.  Just switching to an injector driver that is still using the GP PWN function will not be any better.  This is still an auxiliary function that and is not sequenced to any engine event.  I assume the HSF4 would normally be spliced into one of the existing fuel injectors so it is timed very closely to the normal injection event, if you do this then fuel cut would work as expected and be relatively safe.  

If you want it controlled independently from the normal injectors then the only other way you can do it is to change to group/staged injection, have two drivers controlling your normal injectors (paired up) then one of the other remaining (secondary) drivers controls your pump/valve.  You then use the secondary injection table for your meth volume. 

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Ok, I understand better now about the difference between using GP output and injection.  I'm pretty certain of the answer already (no), but can an Aux output be utilized in group/staged injection?

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