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Old 12-29-2019, 08:42 AM   #1
marcusj2001
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Default Megasquirt tuning help

Hi, This is my first post so sorry if it is in the wrong place.

The car is a Volvo 740 with Megasquirt 2 v3.

Engine: b230ft with
90+ turbo manifold
ebay t3t4 turbo
Kl racing t2 cam
stock compression ratio 8.7:1
bigger intercooler
1226cc injectors
3 inch exhaust with one muffler and 200 cell cat
95 oktan for winter and E85 for summer.

The problem i'am having is that when cursing down hill lightly pushing the throttle the engine misfires or something. I have tried adding and retarding timing noting seems to help. At around 40-20 kpa. AFR, VE and ignition tables


[IMG][/IMG]


Last edited by marcusj2001; 12-29-2019 at 09:15 AM..
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Old 12-29-2019, 04:31 PM   #2
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Have you tried setting up "Over-Run Fuel Cut" under the Fuel Settings menu?
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Old 12-29-2019, 04:48 PM   #3
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I have not tested "Over-run fuel cut". Can it help?
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Old 12-29-2019, 05:48 PM   #4
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Can do you a datalog of the issue?

Is the car an auto or manual?
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Old 12-30-2019, 02:08 AM   #5
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Your fuel table is really rough and has some bizarre numbers in some cells. Look at it in 3D view and it's like WTF?

Your AFR table is too lean (almost all of it) (1/2 point and more in some areas).

Your spark table has too much advance from 1700 up on the bottom half, and too much retard on the top half.
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Old 12-30-2019, 07:10 AM   #6
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here is a log picture i don't now how to post a entire log. it's not so notseble in the log but the AFR goes from 14.5 to 15.5 when it happens and the car jerks a bit. Ignition table with less timing below 2000 rpm. The ve table does that when i have Auto Tune on and it just takes all the fuel away when i let go of the throttle after a pull. So i go in and add fuel after the auto tune is done as you can see in the picture.

I'm afraid of knock at higher rpm and high boost (20 psi/1.4 bar) that's why the timing is so conservative. Right now on 95 oktan.

The car is a manual.

How does a good AFR table look i have lead it out to get good fuel economy?






[IMG][/IMG]
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Old 12-30-2019, 09:46 AM   #7
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Ok, first.. most 8v VE tables will be dropping off not going up after about 5400rpms. after 6 they start dropping off quite hard unless you've got some special sauce type of setup. Even on pump gas 7 degrees up top is probably not enough, but that's a separate issue. timing table looks fine except 1350 to 2050, looks like it's coming in too fast. The raw numbers aren't all that bad for an 8v. generally it will be all in and only gradually increasing by ~3k.

post a whole datalog, think it has to be a zip file or maybe a dropbox link.
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Old 12-30-2019, 09:58 AM   #8
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Here's the log, I think it works


https://www.dropbox.com/s/rwq3xm1o43...28.31.zip?dl=0
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Old 12-30-2019, 10:44 AM   #9
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first thing that jumps out is TPSdot threshhold is too low and your AE settings are fairly aggressive. on very slight tip in your PW is going up almost 50%

set your tpsdot threshhold to like 75, and then for your accel enrich adders drop them by half, and see if that helps
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Old 12-30-2019, 11:19 AM   #10
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Okey. Will try that. Is the AFR table good / bad?
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Old 12-30-2019, 11:25 AM   #11
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afr table is targets for it to hit. it's alright I reckon if thats what you want
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Old 12-30-2019, 11:28 AM   #12
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Okey good so i don't blow the engine
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Old 12-30-2019, 02:07 PM   #13
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This is the spark table from my project, I think yours is going to make the turbo glow like a lava lamp.

I don't make the whole AFR table lean, lean it in the Cruise Bubble, give it what it wants for power and idle.



I can export these files to you if you make a post over on the MSExtra forum

http://www.msextra.com/forums/viewforum.php?f=101

That did not work, PM email address and I will send that way

Last edited by Dirty Rick; 12-30-2019 at 02:16 PM..
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Old 12-30-2019, 02:36 PM   #14
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PM sent

What mpg do you get?
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Old 01-01-2020, 12:07 PM   #15
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Tested it today. it works really well thank you Dirty rick
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Old 01-01-2020, 02:45 PM   #16
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Those tables are not a finished product and will likely need some tweaking. (Tweaking not wholesale changes)

If you look at your tables and the ones I sent you you will see the differences and that may give you some insight.
I feel you were overthinking the afr and spark tables.
For good mileage, you will see in my tables what I call a "cruise bubble" about 4 cells in the low load area at cruise rpm.
Leaning the other areas will torture the motor and actually make the motor inefficient and use more throttle than needed.
The same with the spark table, excessive advance will likely ping and not be as efficient, exacerbated by the need for more throttle.
Excessive retard of the spark in boost will make the manifold and turbo glow brightly and eventually crack both.

So keep this in mind when you work on your VE table, when you increase the throttle you want the car to go.
When you are in a steady state at cruise (where you spend most of your time) you can squeeze it to optimize mileage.
In a light load steady state you can add advance (mimicking vacuum advance) as I have done and the motor will tolerate a higher AFR.
As soon as the load moves out of those areas you need to go back to either idle strategy or power strategy to keep the motor happy.
It is also best to keep the tables fairly smooth, anywhere there are large steps will make the motors response less smooth in transition.

It seems like every time I drive the car I find another little tweak it needs and over time the changes will diminish.
Just don't over-do it, make small changes in one area and see how it changes the motors behavior.
Over time as you become more familiar with the system you will get more "in tune" with what is happening.
Don't forget not everything is corrected inside Tuner Studio, you have to see that all the outside hardware is complementary.

Last edited by Dirty Rick; 01-01-2020 at 02:58 PM..
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Old 01-03-2020, 06:28 AM   #17
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Yeah I was overthinking it, But now i'm thinking i'm starting to get a hag over it. The ve table is stating to look like something now and like you said I added a bit of timing at light load and it helped. It also made some of the compressor surge go away in 5th gear to.
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Old 01-03-2020, 10:40 AM   #18
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it's easy to do. there's a lot to take in initially when learning this stuff, so take your time and feel the system out. save it to a different filename before you make changes in case something doesn't work out, and most of all, have fun with it.. it can be very rewarding.
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