degree increments

[alfa boxer]

Would it be possible to alter the next firmware.so we could have say 10.5 11.0 11.5 of a degree to really smooth things out? many thanks for all the help over the last year mjlj works a treet now.

[MartinM]

Interesting.

The specs for EDIS that I've found (which controls the actual advance calculations) are:
SAW Pulsewidth (usec) = 1536 - (25.6 x (desired spark advance in degrees))
Range: 64 - 1792us (57.5° BTDC to 10° ATDC)
Resolution: 4us (5/32nd of a degree)

So first impressions would seem to suggest that sub-degree resolution is possible

However, doing the math(s) shows that only 5, 10, 15, 20 etc degree advances are accurate anyway as they are the only ones that result in a whole number of usec - all other advance values are not multiples of 4 usec

Code: Select all

1	1510.4
2	1484.8
3	1459.2
4	1433.6
5	1408
6	1382.4
7	1356.8
8	1331.2
9	1305.6
10	1280
11	1254.4
12	1228.8
13	1203.2
14	1177.6
15	1152
16	1126.4
17	1100.8
18	1075.2
19	1049.6
20	1024
etc

So sub degree advances don't seem very simple to get spot on...

Do you see that there would be discernible differences if there was sub-degree capability?

[alfa boxer]

Yes i have a very light road car, and it would help surging below say 3000 rpm for town driving although i know we all like the performance gains acheived with the work done on the mjlj so far. It would be the iceing on the cake . cheers Lee

[brentp]

I believe the MJLJ firmware could support the addition of .5 degree steps, but it's not a trivial change.

The Ford EDIS module uses the SAW pulse (the ignition advance signal from the MJLJ) to gate an internal clock which in part sets the inter-tooth period for firing the plugs. It seems that the frequency of this clock is static, so the precision and accuracy will vary based on RPM.

Thanks for the feedback,

[alfa boxer]

This would greatly improve low down drivability for us. at least you didnt say no,not possible. I think it would emulate the original distributor better at low rpm s Thanks Lee

[Oliver Sedlacek]

No distributor will maintain consistent timing to 0.5 degree accuracy, so I don't think would improve running smoothness to have 0.5 degree resolution.

[alfa boxer]

The map i have is as good as it gets with the current firmware, the engine is a Alfa 1.7 16v boxer moter with twin 40 idf carbs fitted, i am not the first to do this ,as the carbs have more character than fuel injection, fitted as standard to this engine. I have to disagree regarding smaller increments for light throttle use, all of the current maps that i have looked at for my engine have quite low amounts of advance up to 2400 rpm, and they do have smaller increments, ie emerald ecu. Also when refitting the dizzy it seems smoother up to that point! I know that these ecu's are at the top dollar price wise, I just thought that it would be a great for every one to have this option. ps this is not a complaint just a sugestion.

Thanks Lee

[Oliver Sedlacek]

I still don't think resolution is particularly a problem. For example, on the map shown, if you changed from linear interpolation to cubic, you would easily alter the timing by more than 0.5 degrees at points off the grid. What you probably want to do is to have more grid points where the timing changes quickly. You can do that with the megajolt by adjusting the bin points. If the map is good and it's not running so well, then you may have some other problem with your megajolt.

[aarc240]

Looking over that map you posted, I would scrap the top 5 bin points and use them down where it matters.

You're not running a Formula One engine, nor are you using fuel injection, nor are you using a carefully and precisely blended racing fuel, so a variation of 0.75 degrees just isn't going to matter. Or it certainly won't unless you like running close to the grenade point!

Change your mapping strategy to use interpolation to better advantage at the top end with two (or three maximum) BINs from 4000 up.
Again, only two BINs for idle and something like 1300 RPM.
Use the rest to give good control in the region where you are experiencing surging.

The idea of 0.5 steps sounds fine in the sales literature but in anything short of an extreme racing engine in a very carefully controlled environment, it is just that - SALES PITCH

btw, I have 3 BINs at 3800, 5200 and 7500 on a supercharged six cylinder that runs in the 'OMG it's going to blow' territory and found no advantage with my earlier maps that wasted more control up there. From idle up there are BINs at 800, 1400 and 2200. The extra BINs and control between 2200 and 3800 stopped an issue with blowing head gaskets apart every time I jumped on the gas in the mid range.

[merlin]

Hi this is a bit of topic but the map showen abouve is In some program called IAW are you using this program to design and control you Mega Jolt and is it any different to Bernts software
Regards,
Paul.

[alfa boxer]

Hi Paul, the above map is something that i posted,i received it from a friend with a programable ignition system. and is in no way conected or used by megajolt. it was just to show incremental changes between 1000-2500rpm. Regards Lee