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 Post subject: Ignition Advance
PostPosted: Thu Nov 06, 2014 12:01 pm 
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Anyone actually done it while using LPG?
We all know using dual fuel means at best a compromise. But has anyone used those ignition advance piggy backs with some success?


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 Post subject: Re: Ignition Advance
PostPosted: Thu Nov 06, 2014 12:10 pm 
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Yes, it does make a tiny difference on LPG

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 Post subject: Re: Ignition Advance
PostPosted: Thu Nov 06, 2014 1:17 pm 
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Hi Scotty,

Is this the kind of thing that goes between the sensor and the ignition amp on an old distrubutor system?

Only asking as I looked at those from AEB only to find that a dongle and expensive software was necessary to configure them.

Currently looking to make a PIC solution to replace the original ignition amp on mine.
More to do with wanting to dump the distributor than getting the extra advance for me - but the abilty to start/idle at 'petrol' timings then advance for LPG sounds good. I was also concerned that it would be possible for the mix to still be burning when the exhaust valve opened (if the spark was not advanced).

Let me know if you find anything useful about.... I still don't know how I should retard (or not advance so much) when the engine is under load, assuming I can just use a basic vaccuum sensor.

Keith


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 Post subject: Re: Ignition Advance
PostPosted: Thu Nov 06, 2014 3:30 pm 
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I was more along the lines of more modern maps.

You see most people can download a bit of software and start tweaking their own maps I guess. But the issue is that realistically you should have two maps for a dual fuel engine.

One for petrol 95 octane and then one for lpg.
Obviously only on the road tuning would be sufficient. But you could effectively have your own petrol map. Then a separate more advance lpg map. Not sure how much more it would be worth over the cost mind.

I was just interested in knowing if anyone had actually done it.


Or even if you could have one map but mapped for say 99 octane or 100 octane for petrol then just make sure you always buy that petrol. That would come close to the lpg octane rating.


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 Post subject: Re: Ignition Advance
PostPosted: Fri Nov 07, 2014 9:36 am 
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Location: South end of North Yorkshire
Quite a few cars have ECUs that hold two (or more) complete maps for ignition and fuel, with a 'sport mode' switch or similar to select which one. I know it's not uncommon to remap some Gen IV Subaru Legacy ECUs to have a very aggressive 100RON map for performance/track use and and more conservative map for normal driving on 95RON petrol.

You're right, it would maybe be useful to switch to a different map for LPG use, but it wouldn't be as easy to do it with the 'universal' kits that we currently use. Either the LPG ECU needs some way of telling the petrol ECU to switch maps (assuming it supports multiple maps), or it'd have to pretty much take over the whole petrol side of things, which is very unlikely.

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 Post subject: Re: Ignition Advance
PostPosted: Fri Nov 07, 2014 2:26 pm 
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Scotty,

Are you looking to;
Use an entirely separate map for lpg?
Or
Just to add some extra advance to the standard (petrol) map at speeds above idle?

Keith


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 Post subject: Re: Ignition Advance
PostPosted: Sat Nov 08, 2014 1:09 am 
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No personal experience, but I recall reading on a plausible sounding website that the amount of extra advance that an LPG fuelled engine benefits from is more at lower rpm. At higher rpm the situation was reversed, so the add-on devices which retard the whole advance curve a set amount won't increase the maximum power, but may help lower down the rev range.

Would be interesting to see more rolling road figures to back this up, or otherwise.

EDIT - here is the link:
http://www.acl.com.au/web/acl00056.nsf/ ... enDocument

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 Post subject: Re: Ignition Advance
PostPosted: Sat Nov 08, 2014 10:54 am 
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Which isn't what Robert has found with his system, +3 degrees seems to give an increase right through the rev range. See his most recent post on here viewtopic.php?f=32&t=8781&start=60, lots of dyno time spent there.....

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 Post subject: Re: Ignition Advance
PostPosted: Sat Nov 08, 2014 11:42 am 
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I guess I was looking at a complete seperate map I think would be best.


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 Post subject: Re: Ignition Advance
PostPosted: Sun Nov 09, 2014 10:23 am 
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Gilbertd wrote:
Which isn't what Robert has found with his system, +3 degrees seems to give an increase right through the rev range. See his most recent post on here viewtopic.php?f=32&t=8781&start=60, lots of dyno time spent there.....



yes your right there gilbert ,35 runs in a day and lots of partial runs meant a tired robert!

main thing i discovered is some lpg engines make a big jump in power with only a degree or two of advance .


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 Post subject: Re: Ignition Advance
PostPosted: Mon Nov 10, 2014 10:45 am 
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So get mapping my car!
It would be interesting to find out how much advance I could get away with.

Shame I can't change the cams to give me a slight bit of advance. As the twin sparks have adjustment ton the cams.


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 Post subject: Re: Ignition Advance
PostPosted: Sun Nov 29, 2015 9:34 am 
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something to bear in mind is , on my engine , it was turbocharged as well as lpg . that +3 degrees was on top of a map that was advanced at bottom end ,and retarded at top end compared to petrol . i estimate i am around 5 degrees advanced over petrol up to 2500 ,and then at top end i think i am around 1 to 3 degrees retarded compared to a petrol map .

regards
robert


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 Post subject: Re: Ignition Advance
PostPosted: Sun Nov 29, 2015 3:02 pm 
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mat_fenwick wrote:
No personal experience, but I recall reading on a plausible sounding website that the amount of extra advance that an LPG fuelled engine benefits from is more at lower rpm. At higher rpm the situation was reversed, so the add-on devices which retard the whole advance curve a set amount won't increase the maximum power, but may help lower down the rev range.


None of us will have much experience on this. I've read similar on websites where a lot of dyno time has been spent on Yank V8 engines.
We might expect more advance to be beneficial across the entire rpm/load range and generally that may be correct but there may be a lot of exceptions, might be better off with less generalisation and more testing on specific engines.

Ignition advance processors are available that advance timing only below certain rpm by a few degrees out of the box or which advance timing across the entire rpm range by a few degrees out of the box, some of these are custom programmable if you have the facility (in terms of AEB that would mean AEB's special interface).

Some are designed to be used between cam/crank sensor and it's wiring - Interesting in finding out exactly how these work... Thinking since cam/crank wheels have missing teeth to ID TDC etc would think it far easier to design a generic retard processor than generic advance processor, as to give accurate advance signal of such missing teeth etc the processor must anticipate such gaps occurring and the only way to do that would be if the processor learned the full 360 degree design of the wheel...? Have wondered if in some cases processors (which don't learn wheel design) may give different advance for different cylinders - imagine if missing teeth were just before TDC for cylinder 1 and advance processor didn't accurately advance lack of signal for missing teeth but then did advance the following toothed section on the run up to the next cylinder firing (3 in this example if engine has 1342 order), in this case cyl 1 wouldn't be advanced but other cylinders would, meanwhile petrol ECU might see increasing rpm signal between 1 and 3, decreasing rpm signal between 2 and 1, the warbling could adversely effect fuelling and ignition timing to the point of outweighing/over-riding benefits anticipated from the advance the unit is supposed to deliver (petrol ECU adjusting fuelling and ignition timing itself when it sees the engine speed change - enrichment and advance for acceleration and vice/versa).

Simon

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 Post subject: Re: Ignition Advance
PostPosted: Sun Nov 29, 2015 4:19 pm 
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We used to ft a lot of them back in the day. Just standard timing advance processors. You could select them with dip switches 5/15/30 as I remember and a little trimmer on top. They are still available I'm sure. And they just fed the 'raw' signal back to the Ecu as I remember ?


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 Post subject: Re: Ignition Advance
PostPosted: Sun Nov 29, 2015 8:37 pm 
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I have a few here but without dip switches, I know the type you mean though.

Just thinking out loud really! It is the signal bit that interests me, if it returned unprocessed raw signal there wouldn't be any effect to timing... Relatively simple to create a delayed signal (|which would retard ignition) even for sensor wheels that have missing teeth / Where sensor wheels don't have missing teeth would also be simple to effect an advanced signal using a similar type delay / Where wheels do have missing teeth delay wouldn't work to advance timing unless delay was almost 360degrees of wheel rotation...

Full group injection engines and wasted spark ignition systems only really need to know crank position (missing tooth on crank sensor wheel would do) while engines with sequential injection and/or individual channel ignition need to know cam position (missing tooth on cam sensor wheel). The only way I can see an appropriately timed simple delay working is if petrol ECU picks up missing teeth on cam wheel then counts crank wheel pulses (on crank wheel which doesn't have teeth missing) to determine engine position from that point (for ignition purpose use), with processor fitted to crank wheel - but the thing is crank sensor wouldn't be able to have teeth missing for positional info.. A simple delay method processor would only really work on wheels without teeth missing, a much more advanced processor (that learned wheel design) would be needed for use on wheels with missing teeth because a 360degree delay would be very difficult to implement properly, where 'properly' means not be a fudge where slight gains from a bit more advance would be outweighed by inaccuracies in timing and/or fuelling, particularly when rpm isn't constant.

Incidentally, I recently changed the crank sensor on a 4L Grand Cherokee, a real pita of a job on those!

Simon

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 Post subject: Re: Ignition Advance
PostPosted: Fri Dec 04, 2015 1:03 am 
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The 4L Jeep CPS change is easy if you have arms that are 9ft long and have about 18 joints in each and a third arm to pull the new cable up through the inlet manifold! I accidentally dropped the connector while repositioning the cable during some recent maintenance work on my Cherokee and that was a right pain!

Back to the thread but still on the subject of the Cherokee, it has a "Power/Comfort" switch which in terms most people use is "Sports/Economy" and i've found it makes a real difference while running on gas because it advances the timing slightly and delays upshifts on the auto box. Even on 98 RON unleaded it doesn't make as much difference as it does on gas. Further up someone else mentioned the Sport/Economy modes and the Jeep really proves the point. That said in Economy (Comfort) mode, i've recently seen 24mpg on gas which i thought was pretty impressive for something weighing nearly 2 tonnes with the aerodynamics of a breeze block, a 50 year old design engine and an auto box! :D

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 Post subject: Re: Ignition Advance
PostPosted: Wed Dec 09, 2015 12:06 am 
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I've looked into building a programmable ignition curve on distributor motors and I expect one day I'll get round to trying it.

Jaycar (Aus) used to sell a kit for building one but it doesn't seem to be available any more.

The easiest way is to clamp the advance plate with too much advance and then build in some delay. The delay then has to be pegged to the rpm to keep the timing steady because the delay needs to get shorter as the revs go up. But of course you need it to know the rpm anyway so that's just an extra bit of software.

Implementing the advance curve can be done in various ways and that's where it gets most tricky - I kind of like the idea of setting some fixed points and have the software draw the curve as straight lines between them.

Once that's all sorted out it would be quite easy to set up a bunch of different curves and switch between them.

Vacuum advance could be referenced from a MAP sensor.


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 Post subject: Re: Ignition Advance
PostPosted: Wed Dec 09, 2015 4:12 pm 
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LairdScooby wrote:
The 4L Jeep CPS change is easy if you have arms that are 9ft long and have about 18 joints in each and a third arm to pull the new cable up through the inlet manifold! I accidentally dropped the connector while repositioning the cable during some recent maintenance work on my Cherokee and that was a right pain!
My findings too! I used multiple 1/4" wobble extensions to 7/16" socket to un/re-fasten, taped a length of wire to new plug to pull it around back of engine to rhd side plug connection. I'd previously sorted the old Tartarini Tech 99 LPG system, dodgy wiring to petrol pump, fitted an OBDuFix to keep trims in shape (and prevent cruise being disabled and poor drive-ability on petrol for a while after running on gas), swapped in another cruise unit and another radiator fan control unit on same vehicle so I swapped CrankPS at customer premises (wouldn't run) for a very low price.. and got caught doing 37mph where 30zone started hundreds of yards from the 20 houses customer town consisted of on way :(

Jeep 4L's are no slouch but might as well have one of the much more pokey V8s (bit dearer to buy though and no chance of good results from a mixer system except on straight 6 version - though I have seen mixers fitted on Jeep V8's! :roll: ), the 4.7 gives very similar mpg to straight 6.

Oldskool wrote:
Implementing the advance curve can be done in various ways and that's where it gets most tricky - I kind of like the idea of setting some fixed points and have the software draw the curve as straight lines between them.
Yeh, you'd just need in effect a table in memory with rpm on one axis and vacuum on the other, fill in the cells, program to interpolate between cells... bit like mapping various fuel systems only for ignition. Figures in cells needn't be actual advance figures, just a number for length of delay.

Simon

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 Post subject: Re: Ignition Advance
PostPosted: Thu Dec 10, 2015 10:38 pm 
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Yeah something like that would allow for lots of tweaking. The way I set up my old American stuff the mechanical advance curve is just three straight lines like this (ignore the dots):
................ ______
.............. /
...... ____/

So I guess to specify that in a table might only require three values (initial advance, rpm for the ramp to start, and rpm at max advance)

As usual - too many projects !

BTW I just noticed when I post it tells me the maximum post content is 60,000 characters.

It's almost like they saw you coming :D

Steve


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 Post subject: Re: Ignition Advance
PostPosted: Fri Dec 11, 2015 7:35 pm 
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His might be of use to someone with an oldschool gas system.

I have a 3.8 XK engined Jaguar that ran with a distributor tuned to the car, warm days it would start on gas but not in the winter. I fitted an aftermarket ECU and wrote two maps, one each for petrol and gas (with advise from a good Jaguar engineer). I have fitted my gas system with a manual change over switch to keep both systems independant when touring.

So I have two switches one above the other and both are switches to run on either gas or petrol (one for the fuel one for the ignition map).

I'm aware that I should not run on gas until the engine is warm, but it starts easily on gas whatever the weather and changing from standard spark plugs ( to suit the two ECU's) to Iridium means that they nolonger die after 18 months.

Brian


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