Drivability is now excellent with the exception of one condition. If I stab the throttle and release quickly, the engine goes lean and dies.Under all other conditions things are now rock solid. I do not understand how to tune the enricment Wizzard graph that would allow increasing fuel under rapid decel.

The driving situation would be if you hit the throttle to start up, and saw something that made you quickly change your mind (such as someone running a red light) and quickly hit the brake. The engine will die under those situations. Best practice now is to drive with both feet, and be alert.

Thanks, Sam

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I have not used the wizard you describe. Could be the decel fuel setting is too low. Try raising that. Should be a window for enrichments that just lists parameters and is not a "wizard".

Lou

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Home of Slant6-powered fun machines

On the old MS I, there were four rates of tps movement that could be adjusted independently. Matt tells me there is a graph with movable points somewhere in the tune file. I have not found this yet, and am hoping someone can point me towards it, and maybe explain the abreviations used. It is some range of motion per millescond kind of thing.

Matt has repeatedly suggested I download the latest Tuner Studio firmware, but a big part of me is fearful I will end up with a tune program that will not work at all. When I upgraded my iPad, some things worked worse.

Sam

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Sam - I don't mean to be picky about semantics but downloading the latest Tunerstudio is separate from downloading the latest Megasquirt firmware. Tunerstudio is the software that resides on your laptop. Firmware is the software that's physically inside the megasquirt itself.

That being said - if you backup your current tuning file there's really no harm in upgrading either Tunerstudio or MS firmware as you can revert to whatever you had before if need be.

If Matt suggested you do it more then once then you need to heed his words. I don't blame you for being shy about it with what you've gone through with that car, but if you were that worried about it you'd have gone back to a carb

Hi Pierre, Don't worry about offending me with education. This stuff is just a bit above my paygrade. Those kinds of distinctions are what I need. However, I think my confusion on these issued resulted in my perhaps using the wrong language in my initial post. At this point I am unclear as to whether Matt was suggesting upgrade to the tuning software, or a change in the Megasquirt firmware. Perhaps it was both. But your post will help me going forward in knowing how to talk about it.

I would not have this fuel injection system working at all if Lou had not helped with the first MS I install. I did the MS II install alone, but not without a number of hiccups.

Sam

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TunerStudio is the program in the laptop. It displays the acceleration enrichment as a curve where the older MegaTune that it replaced displayed it as a chart.

The firmware in the ECU is independent of the software on the laptop. Upgrading TunerStudio will not change any of the settings in the MegaSquirt.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

This sounds to me like it would be in the part of the table that controls fuel delivery at closed throttle and RPMs somewhere above idle.

I don't have any direct experience with Megasquirt but I know it is typical for fuel injection systems to cut off fuel delivery when the throttle is closed on deceleration when the motor is above some threshold RPM. The fix might be to increase fuel at 0% throttle at all RPMs or increase the threshold RPM where fuel cut happens.

Or it might be related to fuel delivery at high manifold vacuum. In any case I would be looking in the fuel tables and not in accel enrichment.

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The fuel table is working very well under every circumstance except that quick stab and release. If there is a table that cuts fuel proprtionaly to how quickly the trottle is released, I want to find it. I do have the over fuel cut-off enabled at high vacuum. Without that it would run rich when coasting down at 0 throttle, and die from too much fuel. I am pretty sure the release after a quick stab does not create high enough vacuum to trigger the fuel cut off. It is something to look at though. Maybe there is an rpm threshold for that that needs to be raised a bit.

I think I have seen a graph for accel enrichment related to how fast the TPS moves, but cannot recall seeing one for decell cut related to speed of TPS movement. 😕 thanks for your comments.

Sam

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Try turning off the Enhanced Acceleration Enrichment until the VE table is spot-on everywhere. A bad spot in the VE table can make EAE go crazy when you lift the throttle.

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"Mad Scientist" Matt Cramer

'66 Dart - turbocharged 225

My blog - Mad Scientist Matt's Lair

How about a dashpot so it can't close too quickly..............

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

That might work. I have considered it. I fooled around with the fuel table for half an hour today to no avail. I richened up the cells everywhere around the area the pointer moved into when it went lean, and I could still kill it with a sudden stab and release. I am sure the gas mikeage will be compromised. It ran fine the way it was, except.........it seems wrong to make the fueling richer than it needs to be for this one condition. There should be a trim table for this, but has eluded me so far.

I could NOT find a graph for various TPS movement rates on decel. There is one for TPS movement on accell. I did create a data log of an event where it dies, if I did it right, and will send that to Matt on Monday.

I do have a timing bump up set where timing is advanced coming off idle. I wonder if the death spiral is timing related, as the timing would drop off 10 degrees when rpm drops back to idle. I will look for that table soon and see what conditions are adjustable.

Sam

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Do you have a IAC valve?


Here's my thought; as soon as you give it some gas, the IACV closes.


You take your foot off the gas, the IACV doesn't open up again quickly enough. The engine dying isn't from being too lean, but too low of an rpm (it only appears to be lean for some reason)


Slowing down the initial closing of the IACV (somehow) might fix the problem. (just like a dashpot would do)

If you can't slow it down, there might be an adjustment for minimum IACV valve closing.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

BTW, I get the same symptoms with my BBS


But I think it's because it goes too rich...........

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

I had an IAC valve but took it off because it quit working reliable. That is on the list of things to fix.
Sam

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I woke up this morning wondering if the just-replaced bad battery played a role in causing this behavior. I have not tested the theory yet but am eager to try it now with a know, good battery.

Sam

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