accel enrichment, decel enrichment

[ovlov760]

I pretty much don't use accel enrichment. I tuned with the VE map only... which I assume is ok. I still don't have good understanding of how the triggering of the accel enrichment works. I know it has something to do with the TPS position and MAP? How do you know what a good TPS position for it to kick in is? and how much actual enrichment are you getting? ms/vs?? I'm even more clueless about Mapdot.

With decel enrichment I read somewhere at a bigger number is less enrichment and somewhere else it was the opposite. Which is correct? I definitely need more because the car goes way lean on decel lately. I set it to 100% and then 130% and got no difference.

[Matt Dupuis]

If your car runs fine without accel enrichment, you don't HAVE to use it. But there are a few things you must understand first.

First is to properly calibrate your TPS. This is important for two reasons - first is because it controls your accel enrichment, second is because it controls your flood clear. See the MT notes on calibrating your TPS.

Second is that your TPS provides Megasquirt with a variable voltage signal that increases towards WOT and decreases towards closed throttle.

Acceleration enrichment is based on how quickly your TPS moves, or how quickly your MAP changes. These are called TPSdot and MAPdot respectively. With the TPSdot, this rate of change is measured in v/s, or volts per second. If your TPS goes from providing MS with a .5 volt signal and ramps up to a 2.5 volt signal in .50 seconds, it's moved 2.0 volts in 1/2 second, or 4.0 v/s. MAPdot works in much the same way, but instead of volts it uses kPa.

Another adjustment that's important is the threshold below which MS ignores the accel enrichment command. If you set your TPSdot to 1.0ms, it won't calculate any enrichment if you move the pedal slower than that, but above this point it calculates it normally. Ditto for the MAPdot. Setting it too low can cause repeated and random acceleration triggers, which kills fuel economy and driveability, and setting it too high can make your car dead on light tip in but really hammer on fast throttle openings.

I believe you've now also got the ability to cancel out acceleration enrichment above a certain manifold pressure, which is really useful for MAPdot and boost, 'cause I used to get random enrichments under boost at a MAPdot threshold that was even a bit too high for normal driving. If I had the ability to kill accel under boost, I'd have set the threshold lower and had better power & driveability, but I've never really liked MAPdot anyway...

I've also never used the decel enleanment either. 100% means no correction, 0% means no fuel, but two things to remember here - one is that your threshold must be set low enough that you're shutting the throttle faster than the threshold, and that the enleanment only lasts for a few tenths of a second, not the entire time you're decelrating. Some with turbos have said that they need enrichment, or higher than 100% values, or else they get slight detonation upon rapidly closing the throttle on boost. I've never found this, and generally I prefer the overrun fuel cut.

As for choosing the appropriate rate and squirt bins, it's really a matter of trial and error, which you shouldn't be afraid of since everyone knows you don't install a fully programmable EMS onto your car because you want it to run well, right away. Datalog, logview, tune, datalog, logview, tune... that's how I get 'er dun.

[the poi]

( glad you're back doopoo :) )

[kyle242gt]

Bah :grrr: you may be glad, but he didn't leave much left to type on the subject :-D When you goan spill the details of your new setup, Matt?

When DLing for MST3K (worked great BTW) I turned off accel enrichment. I didn't notice much in the way of drivability problems, except for initial tip-in and low-speed launch. Then, the lack of AE made the engine stumble.

Looking at my DLs, I found I ran rich on decel, so I set DE to 80%, it seems to have helped a LOT. I previously ran it at ZERO, thinking I'd use it like a preemptive overrun fuel cut. Bad idea; any time I let off the gas, it would buck for a second. Ick, took me a day to figure out. :oops:

[Matt Dupuis]

You mean this?

http://members.shaw.ca/UglyDuck2/videos/Movie_00_(100_1771).mpg

[ovlov760]

If your car runs fine without accel enrichment, you don't HAVE to use it. But there are a few things you must understand first.

First is to properly calibrate your TPS. This is important for two reasons - first is because it controls your accel enrichment, second is because it controls your flood clear. See the MT notes on calibrating your TPS.

Second is that your TPS provides Megasquirt with a variable voltage signal that increases towards WOT and decreases towards closed throttle.

Acceleration enrichment is based on how quickly your TPS moves, or how quickly your MAP changes. These are called TPSdot and MAPdot respectively. With the TPSdot, this rate of change is measured in v/s, or volts per second. If your TPS goes from providing MS with a .5 volt signal and ramps up to a 2.5 volt signal in .50 seconds, it's moved 2.0 volts in 1/2 second, or 4.0 v/s. MAPdot works in much the same way, but instead of volts it uses kPa.

Another adjustment that's important is the threshold below which MS ignores the accel enrichment command. If you set your TPSdot to 1.0ms, it won't calculate any enrichment if you move the pedal slower than that, but above this point it calculates it normally. Ditto for the MAPdot. Setting it too low can cause repeated and random acceleration triggers, which kills fuel economy and driveability, and setting it too high can make your car dead on light tip in but really hammer on fast throttle openings.

I believe you've now also got the ability to cancel out acceleration enrichment above a certain manifold pressure, which is really useful for MAPdot and boost, 'cause I used to get random enrichments under boost at a MAPdot threshold that was even a bit too high for normal driving. If I had the ability to kill accel under boost, I'd have set the threshold lower and had better power & driveability, but I've never really liked MAPdot anyway...

I've also never used the decel enleanment either. 100% means no correction, 0% means no fuel, but two things to remember here - one is that your threshold must be set low enough that you're shutting the throttle faster than the threshold, and that the enleanment only lasts for a few tenths of a second, not the entire time you're decelrating. Some with turbos have said that they need enrichment, or higher than 100% values, or else they get slight detonation upon rapidly closing the throttle on boost. I've never found this, and generally I prefer the overrun fuel cut.

As for choosing the appropriate rate and squirt bins, it's really a matter of trial and error, which you shouldn't be afraid of since everyone knows you don't install a fully programmable EMS onto your car because you want it to run well, right away. Datalog, logview, tune, datalog, logview, tune... that's how I get 'er dun.
Thanks for all that. Clears some stuff up. My TPSdot threshold is at 2.0 or 1.95 depending on if MS complains about one or the other and makes it change. Still messing with decel since i'm going lean and getting lots of popping out the exhaust lately.

[Matt Dupuis]

Yeah, MS rounds whatever you put in to some goofy number... Anyway, 2.0/1.95 is really quite high for TPSdot - I usually got away with 0.6-0.8, whatever that rounded to. It all depends, of course, on your TPS itself...

[740ATL]

sorry, I have nothing to add to this, but Matt, I'm glad you're back. I've always enjoyed reading your posts!

Mike

[The Aspirator]

For accel I don't usually need any enrichment on light tip in of throttle unless it stumbles, but my car definately likes some more fuel when I hit the gas faster and faster. Say you're cruising at 3000rpm, if you floor it FAST does it ping? AE should cure that. My decel is set to 100%, I get a teeeny bit of popping every once in a while, but I like it. My brother is using mapdot and his car pops like crazy on decel, he absolutely loves it cause it sounds badass.

Cold accel enrich is another thing. My car stumbles alot for the first minute after startup, so I'll have to mess with those settings more until I get it down pat.

John