Jump to content

Acceleration Wizard

V8 Freak

Recommended Posts


I've done quite a lot of reading over the last few days and still don't believe I've seen, recognised or found the answer to my question....

I would like to understand what "v/sec" refers to in the help files.... How do I calculate what it is / can be ?

"TPSdot Threshold

This is the threshold in %/sec (v/sec in some older code versions) below which no acceleration enrichment will occur (you can move the throttle from idle to full open without acceleration enrichment, if you open it slowly enough). A typical value is 15%/sec. "

I understand the idea of 15%/sec and it's relationship to pushing the throttle pedal down faster than 15% of total travel per sec would introduce an additional injection of fuel.. (Sublect to other parameters being met.)

But what does v/sec refer to pleeeeze......


Link to comment
Share on other sites

At a guess, MS will be looking at the voltage it gets from the middle of the throttle position potentiometer (TPS), this may well swing between say 0 and 5v full deflection. I'm pretty sure its a 5v reference but I'm sure someone will correct me if I'm wrong.

MS can then calculate the rate this voltage changes over time, which directly related to how quicky your boot stamps on the pedal.

v/sec valves will differ slightly from %/sec values, in that 100% in the above example would equal 5 volts.

So, potentially

100% / sec would be equivilant to 5 v / sec

50 % / sec would be equivilant to 2.5 v / sec


To get an idea of values, you could put a mulimeter set to measure voltage between MS pin 19, TPS earth, and pin 22, TPS signal (Green and red wires, according to wiring diagrams on here) and see what happens to the voltage over the full range of pedal movement.

MS may well have the ability to adjust the range of the pot used, its quite possible that full deflection of the pedal only uses 4v worth of range on the pot, so you could scale 100% = 4v, rather than 100% = 5v.

Of course, someone who actually has a bit more in depth knowledge of MS will have a far better idea than me!

Link to comment
Share on other sites

It is in volts/sec which is the speed you're mashing the pedal at - this is the sort-of equivalent to an accelerator pump on a carb.

The TPS does range from 0-5v although it may well sit above 0v when closed and may never reach 5v when fully open. The volts/second speed can be greater than 5v, if you mash it from zero to the floor in half a second then it can be changing at 10v/sec (5v/0.5s = 10v/s, see?)

You don't need to worry what the actual volts are, you just need to worry about what values appear in the wizard when you mash the pedal, and how the car reacts when you do it. I've never really got a good handle on tuning the accel, Bill explained it to me once and added "Too much is very similar to too little" so I'm none the wiser :rolleyes: might be worth a ganer at the MSEFI forums / megamanual to see if there's any good advice there.

Link to comment
Share on other sites

Cheers John....

I have been reading them there forums for a few days and losing the will to read more... The usual comment is "Play with the settings til you get what you want."

I've got the idea of the v/sec now.. And now understand why 2.2 v/sec is working for me and eliminated my bunny hopping when pottering around town or on lanes...

I'm guessing each is now a setting for degrees of mashing.... So if I never smash the throttle down at the equiv of 15v/sec I don't need an equivalent additional injection in milliseconds....

And I suppose, that if my TPSdot is at 2.2 v/sec it's pointless having an adder value below that setting as well ! (Which clealy would demonstrate some of the examples given on the support forums were not thought through !)

I'm going to try lowering TPSdot and see where the hopping comes back in and also see if TunerStudio is able to show me what levels of v/sec I'm getting when I do mash the pedal... (I believe it does..)

I'm now wondering if there is a way to look at the logs to see how effective the adders are as you stab the throttle / accelerate in a progressive fashion !

All fun for another night.

I'll report back on how I'm doing.


Link to comment
Share on other sites


I think you've basically got it - although I think MS does interpolate between the different values from 0 to 15v/s to give a smooth progression. Effectively you're drawing the shape of a curve. If you never hit 15v/s then you can lower it a bit.

I had a problem with the Series being quite bouncy, so it was always triggering at the low value (2.2v/s) over every bump, which also forces it open-loop. I think going MAPdot fixed it although I can't remember what I ended up with. I know I need to go back to it and do it properly one day... :rolleyes:

Any feedback/insights you have from doing this would be good, as it's often neglected and seldom understood.

Link to comment
Share on other sites

Answer 1st is :

TPSDot: The rate of change of the TPSADC/Sec but converted on the display of MegaTune to Volts/sec the volts of the TPS go from about .5 volts at idle to about 4.5 volts at full throttle so 4 Volts/sec means the throttle is moving at a rate on going from no throttle to full throttle in one sec. MS2 works with percent/sec.

Now some explaination and homework : :rofl: ......

From the very helpfull whiitlebeast on MSefi.com :

One of the best infos I have read on this subject - enjoy :D

I am trying to put together a general tuning guide for AE and Megasquirt Below is what I have come up with so far. This applies to several versions of Megasquirt.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *


There is a lot of confusion regarding the tuning of Acceleration Enrichment in the MegaSquirt family of programs. Over the last two years I have been involved, to a varying degree, in several of these ways to control AE. It is far easier to tune AE if you under the underling causes and effects.

There are a few that we have to consider. (Hang with me here)

1) You may remember from high school physics that water will boil at close to room temperature if you pull enough vacuum on it. Conversely, if you apply pressure you can raise the boiling temp up to 250F or more.

2) Water on the driveway always evaporated faster on a windy day than it does on a calm day.

3) Water on the driveway always evaporated faster on a hot day than it does on a cool day.

4) If you leave a cold glass of beer on the counter water droplets form on the side of the glass, apparently water from nowhere.

5) Cold air has more oxygen molecules per cubic foot that hot air.

6) A VE table as we in the MegaSquirt world is designed to balance the amount of fuel delivered from the injectors with the air flow. The internal math of the MegaSquirt estimates this airflow and in turn calculates the matching injector pulse width. This airflow calculation is based on intake air temperature, RPM, intake manifold absolute pressure (KPA), and RPM.

7) An intake manifold often has hot water in it. This manifold is attached to hot things and is being blown on by constantly changing amounts of hot air coming off of the radiator and from the exhaust system.

8 ) An intake manifold has a constantly changing amount of air properties and the amount of fuel that can condense on the walls.

9) Fuel in the intake constantly collects on the inside walls of the intake.

10) The amount (thickness) of this layer of fuel is constantly changing.

11) The earlier the fuel is injected in the intake airflow, the more area of the intake wall can get wet.

12) Back pressure on the exhaust, weather caused buy high atmospheric pressure at the end of the exhaust system or by trying to flow too much exhaust through the system causes the motor to need less fuel.

13) The injector delivers fuel only after it has opened. The injector opening time consists of about the first 1.0 millisecond of the pulse width. So if MT reports 10 ms pw1 the injector is only supplying fuel for about 9 ms. This is a big deal if you have a cruse pw of say 4ms and your AE added pw is 6ms. The amount of fuel delivered goes from (4-1) or 3ms of fuel to (4-1)+6 or 9ms or three times the fuel. Plenty of fuel to put out the fire.

14) Way too much fuel feels just like way too little fuel from the driver’s seat.

15) Fuel collecting in the walls and floor of the intake behaves much like the water examples above.

A few definitions.

MAP: Manifold air pressure. The units are KPA. The important part to remember is 100 KPA is close to amount of air the world has at sea level. At 6000 ft elevation you have 80% air or 80 KPA. 15 psi of boost amounts to about 200% air of 200 KPA. Most manifolds have on a steady state motor about 40 KPA at idle and 95 KPA at full throttle assuming normally aspirated.

MAPDot: The calculation of the change of MAP/sec An indication of how fast the MAP is changing. Extra and base BG code uses KPA/Sec where MS2 uses percent/sec MAPDot is normaly a better indication of a need for tempary additional fuel than TPS related schemes.

TPSADC: The location of the Throttle Position Sensor as the Squirt sees it.

TPSDot: The rate of change of the TPSADC/Sec but converted on the display of MegaTune to Volts/sec the volts of the TPS go from about .5 volts at idle to about 4.5 volts at full throttle so 4 Volts/sec means the throttle is moving at a rate on going from no throttle to full throttle in one sec. MS2 works with percent/sec.

AE driven fuel percent Gauge: This gauge displays the percent of added fuel taking into account the opening time of the injector. This little advertised is extremely valuable to put into perspective just how much fuel is being added at any given time. The opening time is assumed to be 1ms and is adjustable in the MsnsExtra.ini

TPS Threshold: The value of the TPSDot that activates the AE event

MAP Threshold: The value of the MAPDot that activates the AE event

Note: MS2 allows a mix of MAP and TPS threshold All versions of Extra are all of one or the there, pick one.

So how does all this pull together as it relates to tuning the motor?

Remember that the VE table is designed to deliver the correct amount of fuel at steady state and normally will not be designed to cover for extra fuel required during these transition times in the fuel requirements caused by all these rules stated above. Any motor that is properly tuned to give a stable AFR at steady will have a huge demand for added fuel if the motor is exposed to more pressure in the intake. At low RPM the manifold AMP may jump from 45 KPA to 99 KPA in a very short amount of time. The added fuel is going to wetting the manifold up to the amount of fuel that can now coat it given the newfound pressure in the intake. Any time the opposite happens, fuel has to be pulled from the normal amount fuel required. This is referred to as the Decel setting. 90 is 90% of the normal amount of delivered fuel. The other 10% comes from the fuel that was on the walls of the intake and are now evaporating off the walls caused by the huge decrease in MAP pressure. At high RPM the motor may be running 90 kpa and a punch from ½ throttle to full throttle may only raise the manifold MAP from 90 KPA to 95 KPA. This is a relatively small change in MAP and as such very little AE is required. As you can see from this MAPDot may be a better gauge of the required amount of added fuel. But what do you do if your cam makes it so that you have virtually no workable MAP change to work with and TPSDot does not seem to be a workable solution. What about this thing called decay and where do I ever start on tuning this thing.

Over the last year, several ways to tune AE have evolved.

1) The original BG method: based purely on the rate of change of the TPSDot or the MAPDot. The AE, once activated can remain on for a certain amount of time (or in some versions of code) for a number of ignition cycles. The advantage of engine cycles is that at 4000 RPM the AE time is ½ of the amount of time that AE is active at 2000 RPM. The wider the powerband and the more high strung the motor is the more difficult this method gets to tune both the high RPM and the low RPM requirements. ITB’s make this method almost useless. 5000 RPM v8s with an automatic is doable. All existing codes to date

2) The RPM based AE method: With this method, the RPM of the motor is constantly taken into account. There 4 separate RPM values that can be set. Below the lowest RPM setting the max AE is controlled by the lowest ms cell. Between the lowest RPM cell and the highest RPM cell a linear interpolation happens between the two closest RPM cells. Above the highest RPM the highest RPM ms value is used. Only one threshold is in effect when using the AE scheme, depending on the choice of MAPDot or TPSDot. The AE table on the AE wizard is ignored. Note: This option is on Extra 026h8 and Extra 029M and later. All other versions have known issues.

3) Hybrid BG/RPM based: This is "normal AE/ Non x-tau" option in the MS2 v2.64 and later code. This method is a combination of the two above schemes. The terminology in the this graph and the terminology used on the final release of this scheme may change but the basic idea is that there is the ability to have large AE events at low RPM and less as RPM raises. The base settings would be set at low RPM and taper off to zero AE at some high RPM. This method has advantages and disadvantages compared to the RPM based logic used in the Extra code. I feel it is a huge improvement to the original B&G code. By setting both RPM values higher than your redline the result will be AE just like the original B&G code. Very promising.

Please not that the red lines that go from the upper left to the lower right of the graph are not necessarily linear but to draw them that way is too confusing.

4) X-Tau: This method is by far the most elaborate and potentially difficult to understand and tune but very promising. The just of the scheme is that virtually all of the inputs listed above are in the algorithm. It takes into account the airflow of the air in the intake (based on RPM), the pressure in the intake (MAP), the temp of the intake walls (coolant temp and air temp) and fudge factors for all of the other stuff. My fear is the numbers of variables involved and if we will ever be able to get a handle on the setup. This will be in the 2.62 and later codes yet to be released. This is used buy many OEM motors.

Tuning the Extra RPM Based AE

Tuning is a fairly simple procedure. As with all MS installs, the very first thing to do is sort out ALL input signals to the Squirt. IAT, CLT, RPM, MAF if installed, TPS and MAP signals must be all very stable. The goal of all of these AE methods is to have a very flat AFR during all transitions of the throttle. Once perfected, the motor will be very smooth throughout the entire power band including throttle stabs, shifts and throttle roll-ons. I always try to run MAPDot if I have a reasonable idle MAP to work with.

This all assumes that you have a tuned VE map. If using RPM based AE, start by setting the lowest of the four bins close to the RPM that your motor idles at. Say 800 RPM. The next cell to set is the highest RPM bin. This is the highest that you are likely to ever activate AE, say 80% of your redline. This should be close to the RPM that your motor drops to after a 3-4 shift. The two other RPM settings should be evenly spaced from the two extremes. For our example 800, 2000, 3000 and 4500 RPM. The second RPM number is where your motor will most likely need the greatest amount of AE in terms of total ms and percent on the AE Driven Fuel Percent gauge. I normally tune the base AE settings by getting on a stim and temporarily set the AE time to 2 sec and the decay to No Decay. Note that you will need to guess the MAP at say 85 KPA for this test. I use a syringe to apply 85 KPA to the Squirt. Play with the ms of AE numbers until from the lowest RPM thru the second RPM setting get close to a flat 150% AE through this range. The 150% is just a guess on my part but it is a place to start. Now go to the third RPM with the stim and set the third ms of AE to get about 115% Next go to the highest RPM and set the highest ms to get about 103% on the gauge. Set the AE time to .7 sec and the decay back on. If you do not own a stim then the numbers can be guessed at. Now start data logging, drive the car locked in second gear and put the motor at 2000 RPM, stab the throttle and have a friend watch the o2 gauge and the AE driven Fuel Percent. Play with the time and ms of the second RPM cell till you get good throttle response and most likely the best response will be when the o2 remains close to about stoch or a little richer. Lean holes are never the correct answer. Now try applying the throttle with a lighter stab. This ends up a compromise. Once a balance is set go to the third RPM and play with just the ms of the third cell to get good response. The highest RPM cell will be for high RPM (redline) shifts. Last go to idle and tune the ms of the lowest cell to get a reasonable off idle response from the motor. Note that as the RPM climbs, the AE will get stepped down by either the timer and the decay function or slammed down by the rising RPM.

See pages 101 thru 120 of 591 on... http://fordfuelinjection.com/files/GUFB.pdf for lots more light reading on the subject.

Have fun tuning.


OK, having waded through this - try this now :


ACEL is the most complicated and least easy concept to both grasp and resolve

I would be extremely interested to see how this pans out :)

Link to comment
Share on other sites


That looks like more waffle and wibble the likes of which I've been reading for a few days now....

John has about the right level of feedback for me.. Nice short words I can understand and ask questions about....

I'm not keen to go for a degree on acceleration tuning right now, especially as I have the Janet and John version of how it's done implanted in my small brain...

So I'll keep it simple ! :)


Link to comment
Share on other sites

Tuning the acceleration enrichment is best done with a WB O2 sensor………. Understanding the settings is easy ………… but its better to understand what the end result should be.

Go along at a steady speed / throttle setting and poke the go pedal …………. Observe the log for the lambda and it should always be slightly rich on the acceleration and revert back to stoich ………. It should never go lean. Normally when the settings are wrong, as the go pedal is poked the lambda leans off badly and then reverts to slightly rich ……… in other words you need to inject more fuel in relation to the speed at which the pedal is poked.

Its hard to go very wrong the other way with the lambda going soot rich and then reverting back to slightly rich ………… when this happens you can get false readings due to the cooling effect of the ‘rich’ gases on the sensor.

Hope this helps............

Link to comment
Share on other sites

Cheers Ian...

Am I right in my understanding then that I'm unlikely to be able to really check / detect the rich and then stoich with narrowband, or will the resultant voltage changes be enough ?

If not, I'm wondering if a WB 02 sensor would be an investment and then share it with Nige for him to help nail others acceleration programming.... (With a potential small charitable contribution to the forum or for Nige's time for each use perhaps ?)


Link to comment
Share on other sites

Yes, you can do it with a NB but it takes longer because is not so accurate ………. a NB can only tell you its rich but not exactly how rich ………. similarly a NB can tell you its lean, but not exactly how lean.

Pete (Bowie 69) has borrowed my WB ………… you can always use that one ……. Sort it out amongst yourselves ………..I am in no rush to get it back …….. it wont work on a 70hp outboard :rolleyes:

Link to comment
Share on other sites

I'll drop Pete a note, but may invest so the forum and the Megasquirt department have another to borrow/use as required. Your offer is very kind, thanks.

I'll try some logging at the weekend and see how my current settings look...

One thing I am sure of is that I'm above the 70hp threshold:)


Link to comment
Share on other sites

I have a WB too (LC1) that you can borrow

But you need to understand (well somewaht I still don't fully :P ) ACEL ENR hence the above post

From WEEKS of trawling it was the most educational AE post I read :) (and I read and studied loads many

of which said Blah Blah black science - difficuly Blah Blah help blah blah) I was there already :rofl:

And I still reckon I'm only 60% at best truly comfortable with this very compex subject

And to add Stray T F away from X-Tag or whatever it is called, you'll regret it big time !!!!!!!


Link to comment
Share on other sites

The short, short version is:

Start off with low values / zero.

Poke the pedal and watch the EGO.

If it goes lean when you poke it, richen that bucket of the accel thing up a bit and try again.

Once it starts to go rich when you poke it, you're close.

Once it feels pretty good, leave it alone.

If you go too far, it will dump so much fuel down you drown the O2 sensor and it will read lean.

Link to comment
Share on other sites


Looks like TunerStudio has it all built in.... The acceleration wizard looks at TPSdot (or really v/sec plot) KPa and plots AFR live, so could potentially do it all on one screen.. Just need to be in driving seat and watching the screen now ! :)

Gonna see if anyone has done any writing on this nice and helpful screen...


Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Create New...

Important Information

We use cookies to ensure you get the best experience. By using our website you agree to our Cookie Policy