Random_badger Posted November 24, 2014 Share Posted November 24, 2014 Hello, This is my first post on here so please be gentle and admins, by all means move delete as appropriate. Like a lot of people starting with megasquirt I've been through Nigels (HFH's) comprehensive posting as req'd to try and get round various issues. Having finally got my 3.9 started and running with base maps (again provided by Nigel) and the installation effectively 'finished' i've been having the following issues whilst trialling: 1. Flat at WOT and feeling bogged down in the middle rpms 2. Lag from idle before picking up revs 3. Significant lag at idle and throttle is blipped (almost an impulse step) 4. Slow response to regain revs when starting large electrical loads (fans) I spoke to a mechanic friend of mine and his opinion was a lack of advance in the ignition (issue 1) and a poor ignition map for the others. Initial test was to up the trim angle to force in more advance across the range, not a very refined method i'll admit, but results sat in the garage was an instant improvement in response whilst up to temperature (away from dreaded zone of warm up enrichment). So with the evidence of my ears and a small amount of knowledge (dangerous i know) I set out to re-write a starting point map that would work, and yet remain safe and not damage the engine. So my brief had 4 requirements: 1. Find a way of modelling a known distibutor, but not a lucas if possible. 2. Generate a new table that would be "safe" 3. Be able to model both vacuum and mechanical advance. 4. Manually adjust to put a "Valley" outside the bottom of my known rev range to assist in stablising the idle The starting point was to try and find a generator that would allow me to understand what it was generating and how it was doing it, and allow me to model a known working solution within the 12x12 map. As a mechanical engineer I decided it was easier to use someone elses solution and reverse engineer understanding than make my own. Luckily after a few hours of searching i came across this thread on another forum: http://www.msextra.com/forums/viewtopic.php?f=94&t=29033 which contained the following spreadsheet (of unknown origin i'll admit please do not follow if you are concerned about the security implications of unknown excel spreadsheets): http://home.comcast.net/~whaussmann/MS_MGBGT/MGB_Ignition_map.xls This will generate a table based on both a vacuum advance and up to 2 spring rates for mechanical advance (not quite as refined as a 12x12 table, but please remember I am trying to create something that works and refine in the future). This allows the modelling of a magnecor type dual spring distributor with vacuum (fulfilling the requirement of a "known" solution). This can then produce a mechanical response (advance) that will look something like the two stage graphs at the bottom of the following link. This can be adjusted to fulfil what appears to be a fairly standard "bring in quite a lot of advance early" approach (the spreadsheet can only do linear response, but you could manually input figures to give a more refined match): http://www.britishv8.org/Articles/Curving-Rover-Dizzy.htm So as a compromise between the various curves i chose to have the initial spring coming in between 900 and 1700 rpm with an advance of 15 degrees and the second spring operating from 1800 to 3300 rpm with a advance of 10 degrees. This gives a total of 25 degrees of mechanical advance across the rev range with it all in by 3300 rpm. The next challenge was to find the characteristics of a vacuum system that would work on this engine, a few more hours and another tank of juice on the e-cigarette yielded: http://www.distributordoctor.com/vacuum_units.html This gave me the data needed to produce a vacuum response of 5 inHg start 17inHg with a total vacuum advance of 8 degrees across the range. The final stage was to input the static advance, the book says 2-3 degrees for a 3.9 high compression, so I used 6, as it looks better at 0 vacuum and i can adjust as required. Once the table had been generated i adjusted the 500rpm bin to be 800rpm bin +1 degree, uploaded to the ecu. The result, a stable idle at 750rpm and 35-40 kPa, no lag on revving and a big grin in anticipation of the next competion. Having looked around this forum, I have concerns about this as it appears to have a lot of advance, similar in areas to Nige's 'extreme' tables. However, having looked into the theory I think this is quite an accurate modelling of a magnecor distibutor (with the advance limited towards the top end) fitted with a Lucas vacuum advance module (admittedly one for an MGBGT) and represents what would be happening on a dizzy driven ignition system. Hopefully someone may find this useful. Comments please... 1 Quote Link to comment Share on other sites More sharing options...
Hybrid_From_Hell Posted November 25, 2014 Share Posted November 25, 2014 Coooo Gotta Love this forum....and Megasquirt !For someone "Just getting into MS" you've done a fab bit of investigative work, and Thumbs up for whatever comes from this !I need to take some of what you have siad and spend some time reviewing and adding to it, but a Cracking 1st Post on LR4x4 and Cracking Starton MS Knowledge Thats what LR4x4 AND Megasquirt are both about !Nige Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted November 25, 2014 Share Posted November 25, 2014 Have to say, mighty impressed Your spark map is not too far off what I run, and I will give it a go for sure, certainly you have the background and clear explanation that makes it all make sense I suspect that the 3-6 degrees change you put in at idle is what has made the map look more 'extreme', but honestly for a 3.9 it looks fine to me. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted November 25, 2014 Share Posted November 25, 2014 I haven't the time to analyse the answer but the approach sounds dangerously logical. Ignition tuning is a relatively riskier business than fuelling and it's harder to measure without things like knock sensors. Quote Link to comment Share on other sites More sharing options...
Random_badger Posted November 25, 2014 Author Share Posted November 25, 2014 Fridge Freezer, I thought a sensible approach would be a 'performance' dist based map, as this would give a characteristic that would be safe for the engine. Working on the principle that any of us could go out and buy one and bolt it on. To be honest until i'd looked into the ignition mapping i wasnt aware of the amount of damage that could occur with it being too advanced, one of the reasons i've stuck with a known working map prior to starting this process. It has been an eye opener and one hell of a learning curve, I bought the kit second hand but unused from ebay, plus a few bits from Nigel. Since throwing all the parts into the engine bay I've had capacitor failures, resistor failures and have had to replace the injector controller dual inverter chip thingy. That was a few weeks of head scratching, turns out that age and not being used had not done the components on the board any favours, but thats probably a topic for a different thread . The support and resources available on the forum have been useful and can provide good starting points and i thought i'd put this together to bring all the various questions on ignition mapping and starting out as a bit of a how to, it remains to be seen if this works in the field or quarry. To be honest I didn't think i'd find myself line checking the PCB to diagnose an integrated circuit failures in order to get the injectors to fire on a 25+ year old engine!! I would do it again tomorrow, as i have learnt so much in the last 18 months on engine management. Hopefully Santa will bring me a wideband sensor kit and then it'll be research into AFR tables and all the other good stuff associated with that Quote Link to comment Share on other sites More sharing options...
Random_badger Posted January 17, 2015 Author Share Posted January 17, 2015 Time for an update...Few trials now and a few more mods to the map. The engine is running much better, no lag, good pickup and plenty of power. A bit more reading mainly "how to tune your V8" type books and have now wound the advance at idle up to 10 degrees, upped the valley to 2 degrees (definate improvement when the fans auto start, not megasquirt controlled, yet.) whilst keeping the maximum advance the same. As well as having the fuel cut on overrun I thought i'd retard the ignition in this region as well (only sat here this evening I've realised that this does nothing!!) Seems to have sorted most of the issues i've had with it. Next step is to build an extension loom to get everything waterproof for logging in winter in cumbria in a windowless trials vehicle.... Quote Link to comment Share on other sites More sharing options...
kevindawes Posted January 19, 2015 Share Posted January 19, 2015 Interesting thread for sure R_B, interested in seeing your last table - the file link in the last post doesn't seem to work for me, would you please mind reposting? Quote Link to comment Share on other sites More sharing options...
Badders Posted January 20, 2015 Share Posted January 20, 2015 I'm with Kevin above... this is really interesting! I need to spend some time looking at what all this means , I too have one of Nige's set ups and she pops and bangs a bit, I don't have any timing marks on my engine so it's difficult to time up, I think I did a pretty good job on assembly but I played with the trim this morning and it runs a bit smoother with a couple of degrees in. Thanks Random_badger Stu Quote Link to comment Share on other sites More sharing options...
Random_badger Posted January 25, 2015 Author Share Posted January 25, 2015 I seem to be having problems uploading screenshots since changing to Linux, not sure why.... 5 mins of thought and realised that it's not the software, its the idiot operating it... Quote Link to comment Share on other sites More sharing options...
kevindawes Posted January 25, 2015 Share Posted January 25, 2015 Thanks R_B Quote Link to comment Share on other sites More sharing options...
TSD Posted February 12, 2015 Share Posted February 12, 2015 The approach you've taken is the right one in my view, but I'm not sure I agree with the spreadsheet. In the most common dizzy installs, the vacuum take-off is above the throttle plate when the throttle is closed. So at idle, the vac advance has no effect, but as the throttle plate opens measured vacuum at the dizzy rises rapidly, then tails off slowly down to wide open throttle. The added ignition advance mirrors the vacuum. Megasquirt installs use manifold vacuum, so the reading is maximum, not zero, when the throttle is closed. The overall effect can be tuned to be the same or similar, but the spreadsheet tries to emulate the action of a mechanical dizzy, so best to model the real world effects from the off. I have a very simple spreadsheet (which the PC says I wrote back in 2003 - WTF did the time go?) which just has four MS tables added together. The first models the advance from the first dizzy spring from idle to 2500rpm as a straight line. The second models the action of the second spring only, from 2500 to 4400, then flat to the redline The third table adds a slug of additional advance in the mid vacuum range, the model the vacuum advance. The fourth table is simply the sum of all the other tables, and is the total advance at any point. It's very primitive, but then so is a shagged out 30yo distributor. It certainly worked well enough that I never tuned it very far from that point. Quote Link to comment Share on other sites More sharing options...
AncientGeek Posted February 19, 2015 Share Posted February 19, 2015 35 bdc at WOT? Doesn't it ping? Quote Link to comment Share on other sites More sharing options...
Recommended Posts
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.