Lumpy cam Advice needed

[jonfx4com]

I have a 300deg cam and ITB's on a 4pot 2300 8V engine. the entire driving range is compressed between 80KPA and 100KPA and the slightest throttle opening flatlines the MAP at 100KPA. This coupled with a very unstable MAP signal is making it hell to tune.

I have bins at 75KPA, 81 KPA 85KPA 93KPA 95KPA and 100KPA but the "wiggle" on the top of the MAP line is bigger than a single bin even after commoning all 4 vacuum lines into a pot 4" high by 1.6" diameter.

Any advice on how to stabilise MAP would be appreciated as well as general guidance from anyone else who uses MS2 on a very lumpy 4 pot motor. I need all the help I can get here. I have a WB02 but its struggling to keep things running as the moves from one bin to another are very sudden and upredictable. Xtau has helped a little but it's s being triggered by the MAP fluctuations too much. I use a damping factor of 35 and I'm not sure how far I should go with that before it becomes less of a damping and more of a lag. Is AlphaN my only option?

Jon

[fscott]

The first thing you should address is the unstable MAP signal.
Do you have a restrictor and a fuel filter placed in between the throttle bodies and the MAP sensor? This will smooth out the signal a lot. On my bike, which has a fairly aggressive cam (72kpa idle) I wound up connecting all three throttle bodies together and then to a restrictor and then the fuel filter, and finally the MAP sensor. Then in persuit of perfection, I crammed some cottin in between the filter and restrictor, and the result was a perfectly smooth MAP signal.

If the MAP's fluctuating, it makes it really hard to tune.

If, after stabilizing the MAP, you still cannot tune, you might want to consider Alpha-N or Hybrid Alpha-N instead. It's supposed to work better for big lumpy cams like yours.

Fred

[kg6dxn]

I have a similar problem. Lumpy cam with an automatic tranny, with only 5hg's of vacume at idle in drive. I have found alpha-n to work quite well. I have large throttle bodies 2X65mm. In the acell wizard, I set the lowest v/s @ 0.5 w/1.0ms squirt. this made slow throttle take off very smooth. If you leave the engine off with the key on, open the accel wizard. Press the throttle and you can see what your v/s is. I found that I can't open the throttle at 15v/s unless I slam my foot as fast as I can on the pedal. I don't drive like that. In fact with my set up I rarely get above 4v/s, so that is where I set the upper most value. If you have your VE table real close, set the squirt very small, if it bogs go smaller, if it pops go bigger. First use the above technique to find out how fast your throttle opens. I am also running MSnSextra 29q. Megasquirt I V3.0. If you have the same open the settings.ini and change the fueling algorithm to alpha-n and do the same in the advanced features on the megatune dash board. Good Luck! Mike

[Mike Simard]

After you do what you can to physically soften the map signal, if you still have a fluctuation of MAP at a certain condition, you'll have to make those ve bins similar. In other words, if your map bounces around between 92-100 kpa under full throttle, you may want to make the 93, 95 and 100 bin values close to the same. X-tau will also amplify things if you have ve bin changes during supposed steady state conditions. So what does your ve table look like?

[jonfx4com]

Thanks guys. Looks like I have some usefull tips to try over the weekend.

I will let you know how I get on and post some before and after logs.

JonS

[krisr]

More initial ignition timing and a richer idle will help a large cam work at idle.

I have a large cam in my 400" V8 (street car) and stuck to these common principles of combustion.... Here's an example of my timing table where i'm trying to simulate manifold vacuum advance and ported.. It might help you smooth out your vacuum aswell but this is only 1 piece of the puzzle!...

[Karl_Skewes]

Hey man, I hear your pain...

I've spent ages with my new motor, 300 deg cams, 4 throttles, 1600cc..

I've been running map based ITB setups for the past two years, but nothing with as wild a cam. Always 10-20kpa spacing then closing up from 80, ending with 2kpa from 90->102.

I use the dampeners found on carburettors, and drill them out with a one millimetre drill bit if i can't get air to go both ways on it.

My conclusion on this new motor is that A-N is the only way to go.
Or if possible, hybrid A-N with SD below 80kpa. Muythaibxr is currently working on code using dual fuel tables, one for SD and one for AN and cutting over between them... looks really promising.

As for AE... Cycles rather than time seemed to work a little better.. i was just using straight TPS triggered and just dealing with having it go a little richer than I want on accell at times.

[jonfx4com]

Thanks all.
I upgraded to 684 and I added some restrictors to the MAP lines and then damped the hell out of the MAP and EGO signals and it now runs quite well. I'm not confident about what the LC1 is telling me but it seems to be running OK. Just need to do the WUE and XTau as I get a lot of oscillation on EGO correction with throttle movement (see log).

I found an irritating problem with EGO. You can't set a "active below TPS" of more than 100%. Its a colder day than when I set up the TPS and now I get 102% at WOT. This turns off the EGO just when I really dont want EGO to go off in a high speed WOT run with autotune on. May be worth the code masters looking at this. I would suggest that a value of 120% should be allowed to ensure that there is an "misinformed person" proof way of saying I want it to work at all throttle positions.

Jon

[midnightblue]

Hi Jon,

Take a look in your megasquirt-II.ini file and fine the TPSOXLimit entry. I have mine set as follows:

TPSOXLimit = scalar, S16, 590, "%", 0.10000, 0.00000, 0.00, 105.00, 1 ; * ( 2 bytes)

That allows a range of 0-105 kPa, you can adjust as you wish.

Hope that helps. Matt.