I need someone to clear something up for me. Being the dizzy on my LXI is vaccum advanced is it possible to use retard or advance timming electronicly?
I need someone to clear something up for me. Being the dizzy on my LXI is vaccum advanced is it possible to use retard or advance timming electronicly?
Originally Posted by stephensimmons
No it isn't. The timing is still done mechanically with the diaphragm for vacuum advance and springs/weights for mechanical advance. This is one of the major benefits of OBD1 or standalone ECU conversions.
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I kinda figured that and thank you.
the only way ive seen is to use an ignition box like MSD btm etc on the stock ecu. Even so, youre still using the vacuum and mechanical advance as a basis for the btm which is sketchy at best, so the best way to go is to go obd 1 and gain full control over the spark timing through maps, instead of springs and vacuum pots.
429whp 362wtq A20 TURBO. A20T>*
So I too am trying to figure this out. I am currently building my very own DXI. I am currently trying to plan my Megasquirt wiring harness. If there is no way to for the stock ECU to control spark, why are there three, count 'em three different outputs from this distributor? I believe y'all, specially since I can't seem to find any inputs into the distributor coming from the ECU but... why would a fuel only ECU need all this data about crank and cam positions? If I just wanted to run fuel through the Megasquirt for now, could I just use the TDC signal, and call it a day? From what I am reading here, my timing should be fine with this distributor if I just keep the one vacuum advance line hooked into un-ported vacuum right? Capping the cold advance off?
Thanks for the help, and I hope I am not hi-jacking this thread too much.
have a great one...
I've had my MS running for over 2 years now and I just recently figured this one out. The stock ECU uses the crank and cam position to determine the timing for the fuel injection. The stock injection is sequential, meaning that it fires each injector once per engine cycle, and follows the order that the cylinders fire in. Up until quite recently Megasquirt has been a batch fire only system, where the injectors fire multiple times per cycle and fire in groups instead of individually. Batch fire is simpler because it doesn't have to know the exact timing of the cylinders. All it needs is a tach signal. And for the most part it works just as well as sequential injection. Where it doesn't do as well though is at idle and low RPMs. Sequential injection has the edge here because you can tailor the injector timing to fire when the intake valves are closed. This ends up working better because when the fuel hits the hot valves it vaporizes and makes for a more homogeneous mixture. It also helps to cool the valves. It's more complicated though because now it needs to know the angle of the crank and also which cycle the cam is on. So these are the extra signals coming from the distributor.
The baffling part, is why Honda didn't also use this information to control spark as well? The information is there, they just needed to use it. The only thing I can figure is that the ECU didn't have quite enough capability, and maybe the more capable electronics were too expensive. IDK.
For the MS there are several options (may depend on your particular ECU version). You can use the negative side of the coil (or the TDC signal) for a tach signal and run fuel only. The distributor will work as normal with the vacuum and mechanical advance. When (if) you get to controlling timing as well you should be able to use the TDC signal (but not the coil negative) and run a distributor-less wasted spark setup. If you're using a MS2 with the MS2-Extra code it's also possible to add the cam signal and run COPs (one coil per plug) and sequential injection. Generally when you get to that point you want to use a toothed crank wheel for better accuracy, but I believe it's possible to do it with the TDC and cam signals from the stock distributor. At the moment I'm in the process of modifying my MS2 to do sequential injection with COP ignition. It does require some fairly intense modification to the ECU but if you have some knowledge of electronics and can use a soldering iron it's not super difficult.
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They did use it to control spark already in 84 I think, but only in the JDM B20A's. The rest of the world only got vacuum advance.
Thanks guys, I have already read alot about sequential fuel injection... I just had no idea that Honda was into this already with the A20... I will be running a MS2 with a version 3.0 main board. I only plan to use it for injection at this point, since it looks like I would have to upgrade to a newer dist. to use it for timing. Also, I will probably have my hands full trying to get my car running as is, without adding more modifications to the current factory setup. So my car up until tomorrow or the next day has been a carbed DX, what will I need to do if anything to use the distributor that is currently in this LXI motor to get it to fire my plugs? Do I only need to hook up the wires that go to the coil and call her a day? and then you recommend running from the TDC for my Tach signal for my MS? I was unsure what would give me the best signal-easiest to wire. But this sounds like it would give a good result, and could only help toward a latter upgrade.
Thanks y'all for your time... have a great one
Last edited by cougar97536; 03-10-2010 at 02:36 AM.
I have been thinking on upgrading ignition to an EDIS setup using Megajolt because of the problems with mechanical distributors and getting parts for them is... well, difficult.
I do not want to do the OBD-1 conversion as I use the car as daily driver and it seems a more intensive work than an EDIS upgrade anyway.
Thanks for confirming that the sensors in the lower part of the distributor are for EFI operation. I thought that when I first saw them (I replaced leaking seal) and I was about to go reading to find out... no need for it now thanks to you guys
So if I go the EDIS/megajolt route I will need to keep the old dizzy in place, right?
If it ain't broke... I fix it!
Pretty much if you want to control the ignition with the MS you will just get rid of the distributor. You could still use it by locking out the mechanical and vacuum advance and using the MS to fire the stock coil, but one of the advantages of the MS is being able to switch to a completely electronic crank fired ignition.
Doing fuel only first does reduce the number of variables to deal with. Originally I was going to do the same but in the end I decided to just go for the complete conversion and get it over with. Not that anything I do is ever truly *done*.
It needs to fire the coil and connect to the blue wire for the tach and fuel pump relay. That should be it.
Yep, that's exactly right. I'm 99% sure the TDC signal is from a VR type sensor, so you would use that circuit for the tach input on the MS2.
With EDIS/Megajolt you lose the distributor completely. EDIS uses a toothed wheel mounted to the crank pulley to determine crank position and fires one of the two coils based on that position. Each coil is connected to two cylinders that always fire at the same time, hence the name "wasted spark". One of the plugs will fire during the exhaust stroke and that spark is literally wasted. It is totally independent of any stock ignition parts. It's also more accurate because the position isn't affected by the slop in the timing belt.
The down side to the EDIS conversion is that you have to remove the AC compressor and modify the crank pulley.
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Thank you sir for all the info. I just finished assembling my MS. I am now trying to find the time to tear into my car and start the install of the new engine, fuel tank and lines, and all that FUN wiring that is ahead of me. Taking the entire interior apart is FUN....!!! Why couldn't they have run those fuel lines under the car? Would have made my life a lot easier...
Anyway, thanks again y'all for your time
Dose anyone know if i can buy the weights and springs for for the advance in my dizzy? Mine some how managed to come apart and could be fixed if i could get them.
Doesn't appear they are available separately from Honda. You best bet is to get another distributor from a junkyard for parts.
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