chriscook
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| posted on 16/12/06 at 04:47 PM |
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MJLJ and MS sharing signals.....
I am in starting to convert from MJLJ to MegaSquirt-II. Currently I have the MJLJ setup with a TPS (old board style without extra TPS circuit) which
has been mapped on the rolling road and works fine. However, the MS will be mapped using a MAP sensor and I therefore need my ignition map in terms of
MAP and not TPS.
So I decided what would be best to get me started with a reasonable yet safe map would be to log what the map was doing when running on the MJLJ using
the MS2. I have a take off from one inlet tract (running a pair of Dellorto DHLAs) I fitted a vacuum hose to it to go to the MS2. I also spliced into
the TPS signal wire and the PIP wire and took them to the MS2. I can plug my laptop into the MS2 and it tells me whats going on - great I thought I
can go for a drive and record this and work out a new ignition map to start from. However, it seems to stop the MJ working. If I start the car with
the MS disconnected I can see what is happening on the laptop, when I plug the MS in then the runtime display for the MJ stops working but the engine
still runs. If i disconnect the MS then it all start up again. The MS shows believable values if i have the laptop connected to it. The only thing I
haven't tried is using a timing light to see if the timing changes with revs or if it is in the EDIS limp home mode.
I suspect it is because I am trying to share the PIP signal - has anyone any ideas on how I can do this?
Of course it may not make much difference to the MAP vs TPS vs RPM relationship if it is running in limp home and I can still get a reasonable
starting ignition map.
Thanks,
Chris
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Dusty
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| posted on 16/12/06 at 05:01 PM |
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Sorry, can't help with the technical problem but I don't see why you should try to use MAP for load indication when you are running twin
sidedraught carbs. It is difficult to get a steady vacuum signal from four separate inlet tracts. I believe most would use throttlepot for load in
this situation.
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chriscook
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| posted on 16/12/06 at 05:12 PM |
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I am using TPS for load at the moment with my carbs. However, the preferred way to run MS seems to be using MAP to run the injectors and you have to
use the same for the ignition.
This will be easier with the throttle bodies as they have a take off on each body which will give a smoother signal. My current carb inlet manifold
has a tapping into one tract where I can get my temporary vacuum connection from - but it isn't very steady as you say. But for what I am doing
I can smooth it out after it's logged the data and be good enough.
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martyn_16v
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| posted on 16/12/06 at 05:34 PM |
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I'd agree with using tps as the load, map really doesn't like individual throttles (I know, i've found out the wrong way). Using MAP
seems fashionable on the ms boards because most people have plenums.
Resistive sensors don't like being shared. Each ECU has an internal bias resistor in it's input to form a voltage divider with the sensors
resistance to produce the voltage input for the ecu itself. Connecting two units each with their own bias upsets everything, you've now formed a
different voltage divider to the one either is expecting, so they both read wrong. The coil/PIP input isn't quite as straightforward inMS
though, so god only knows what either is actually seeing at the mo.
You could try setting the MS up for single coil ignition instead of EDIS, and taking the rpm input from one of the coil pack inputs instead of PIP?
You'd have to tell MS it was a 2cyl to get the rpm to read right but it should do for logging?
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chriscook
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| posted on 16/12/06 at 07:04 PM |
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The TPS circuit in the MJ doesn't have a bias resistor as it is a potential divider itself. You provide it with 0V, 5V and it outputs a voltage
in between. Provided the resistance from the signal pin on the MS to ground or 5V is sufficiently high then it shouldn't affect it too much.
I could use the clean tacho out from the EDIS as input to the MS I suppose but I'd need to work out what settings to use. But then as I'm
not actually controlling anything it doesn't matter too much provided i don't blow anything up.
Or I could wire up the Vauxhall crank sensor and setup up the missing tooth wheel on the MS.
But I'm not sure it makes a huge difference if its running in limp home or not. Will different advance make much difference to the MAP at
different TPS and RPM sites? Remember this is only for an ignition MAP to start from and I'll keep it conservative at first anyway.
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paulf
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| posted on 16/12/06 at 07:59 PM |
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I am running megasquirt and megajolt together and am using the megajolt tacho output to trigger the megasquirt.
I did try to use the edis tacho output but it did not work correctly ie it was picking up stray signals and at times was firing the injectors without
the engine running.
I am using throttle bodys linked together for the map signal and my megajolt is running on the map signal rather than tps.
I am not sure it would be a good idea to link the two tps sensor signals even though in theory they may work.
The new megajolt software allows data logging but have not tried to use it myself so dont know how well it works.
Maybe you could use the megasquirt to log map and revs on one laptop whilst logging the megajolt on another, you may have to borrow a laptop or you
could use a palm PDA to log the megasquirtas i do .
Paul.
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chriscook
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| posted on 17/12/06 at 10:28 AM |
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The thing is I don't have the MJLJ tacho output wired up. From the info I have found both the PIP and CTO are 12v square waves so I
shouldn't blow anything up trying.... I think.
I don't want to log seperately as a) I only have one rather old laptop and b) I can't be bothered synchronising the data logs.
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martyn_16v
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| posted on 17/12/06 at 11:29 AM |
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quote:
Originally posted by chriscook
The TPS circuit in the MJ doesn't have a bias resistor as it is a potential divider itself.
That's a very good (and rather obvious) point. I'll go and be quiet in the silly corner now  
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chriscook
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| posted on 17/12/06 at 04:38 PM |
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Well I went into work and borrowed a scope. Both the PIP and CTO are square waves at approx battery voltage. Although the pulse width of the CTO is a
lot shorter than the PIP. So I moved the pickup to the CTO and the MS worked fine, also leaving the MJLJ working.
Unfortunately either my serial cable or the serial port on the laptop is dodgy because it keeps stopping and restarting communications while I am
going along - its also dodgy when plugged into MJLJ.
Chris
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paulf
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| posted on 17/12/06 at 10:42 PM |
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Funnily enough have just posted about this in the thread about tacho outputs, my tacho wouldnt work from the tacho output and so I have been using the
PIP signal with no ill effects.
Paul.
quote:
Originally posted by chriscook
The thing is I don't have the MJLJ tacho output wired up. From the info I have found both the PIP and CTO are 12v square waves so I
shouldn't blow anything up trying.... I think.
I don't want to log seperately as a) I only have one rather old laptop and b) I can't be bothered synchronising the data logs.
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