mobythevan Posted January 3, 2009 Share Posted January 3, 2009 I am hooking up an LT1 opti spark to the scope to look at the low res signal before wiring it all up to megasquirt. I have the ignition feed wire to the opti supplied with 12 volts. I have left over the "ref low" wire and the "low res" wire. I cannot see a waveform when cranking the engine. I see the low res wire setting at 12 volts, but it never goes low. Do you guys have any ideas? I assumed that ignition feed gets a 12 volt signal when the key is turned on, so that is what I am giving it. It is a red wire and that is usually a switched 12 volt in a chevy harness. I also assume that ground is occurring inside the opti unit to the engine block. I tried the scope between low res and ref low. I also tried it between low res and engine ground. It doesn't seem like I need to suplly a pullup like the nissan turbo dizzy because low res is already at 12 volts when the opti is powered. I dunno:hs: The opti only has four wires that go to it: high res low res ignition feed reference low Quote Link to comment Share on other sites More sharing options...
randy 77zt Posted January 3, 2009 Share Posted January 3, 2009 i have a gm factory 94 firebird camaro manual but would have to find it at my other shop.are you trying to trigger an ms unit with the opti-spark?i would probably just put 4 magnets in the dampener run a hall effect sensor and use the opti-spark for a dumb distributor.but that is fun in ms-there are a million ways to get something to work-i am working on dis ignition for my z right now. Quote Link to comment Share on other sites More sharing options...
mobythevan Posted January 3, 2009 Author Share Posted January 3, 2009 It seems like the optical wheel would work easily to trigger megasquirt just like the L28et installation, but I can't see a trigger waveform yet. Quote Link to comment Share on other sites More sharing options...
wheelman Posted January 3, 2009 Share Posted January 3, 2009 Moby, According the my wiring diagram pin C (ignition feed from PCM) should get 12 volts, Pin D (Ref low) should be grounded, Pin B is the high res signal and will be 5 volts when a slot is present and Pin A is low res signal and will be 5 volts when a slot is present. This article has some good info but not actual volts at certain pin. http://www.gmhightechperformance.com/tech/0310htp_lt1_ignition_system_understanding_modifying/index.html Not sure you know this but it should be possible to trigger the MS using the rising edges of the low res signal just like a standard optical distributor. If you can't get it to work using 12 volts for power try dropping it to 5. The light sensors produce a standard 5 volt TTL output signal, maybe the circuit wants a 5 volt input. Wheelman Quote Link to comment Share on other sites More sharing options...
mobythevan Posted January 4, 2009 Author Share Posted January 4, 2009 OK, thanks for the info. I will try tomorrow. Quote Link to comment Share on other sites More sharing options...
Matt Cramer Posted January 5, 2009 Share Posted January 5, 2009 The Optispark pretty much is an 8 cylinder version of the L28ET distributor, from what I've heard. You'd ground the Reference Low and wire the Low Res signal to the MS. Please let us know how this works out. Quote Link to comment Share on other sites More sharing options...
deja Posted January 5, 2009 Share Posted January 5, 2009 Here's the schematic from the GM manual for a 95 Fbody. Quote Link to comment Share on other sites More sharing options...
wheelman Posted January 5, 2009 Share Posted January 5, 2009 The Optispark pretty much is an 8 cylinder version of the L28ET distributor, from what I've heard. You'd ground the Reference Low and wire the Low Res signal to the MS. Please let us know how this works out. Matt, I think the only real difference is the low res slots of the optispark are not all the same size so you have to be sure to trigger off the correct edge. I've looked at this a couple times but haven't made the leap to MS my LT1 yet. It's hard to argue with a car that runs as good as it does with the factory PCM and a custom tune, plus I have TunerCat. Wheelman Quote Link to comment Share on other sites More sharing options...
mobythevan Posted January 5, 2009 Author Share Posted January 5, 2009 I think the only real difference is the low res slots of the optispark are not all the same size so you have to be sure to trigger off the correct edge That is why I wanted to scop it before connecting up to megasquirt, just to be 110% sure which edge. I haven't got back to the garage to try again, but if it doesn't work I am going to pull the unit off so I can play with it on the bench instead of cranking the starter. Quote Link to comment Share on other sites More sharing options...
dts300z Posted January 5, 2009 Share Posted January 5, 2009 I had an old opti laying around so I took it apart and set it up on TDC and took various pictures. Anyways hope that helps. It looks like the largest window is #1 and is is open for approximately 21 camshaft degrees. Quote Link to comment Share on other sites More sharing options...
Matt Cramer Posted January 6, 2009 Share Posted January 6, 2009 That is why I wanted to scop it before connecting up to megasquirt, just to be 110% sure which edge. I haven't got back to the garage to try again, but if it doesn't work I am going to pull the unit off so I can play with it on the bench instead of cranking the starter. The 240SX has the same type of setup with unequal length slits, and we've found the 280ZX mods work for it. Quote Link to comment Share on other sites More sharing options...
mobythevan Posted January 22, 2009 Author Share Posted January 22, 2009 Well, anyone who has worked much with megasquirt can understand where I am at now. With everything connected on the first opti spark I can see the high res signal on the scope but not low res. Grabbed a second optispark from my friends engine and hooked it up, same thing, see high res but no low res. Took the second optispark to the bench and wired a custom connector to run from my 12 volt power supply I use for the stim board. We figured maybe the wire harness on the engine had a problem. Turn the opti by hand to confirm and see the same thing. High res OK, no low res signal. I have seen some strange things so far with all my megasquirt setups and this one is right up there. What do you guys think? Both optisparks are bad with the same sympton, seems odd My test setup supplies 12 volts to ignition feed, grounds reference low signal. High and Low res are connected directly to scope probes, the probes are grounded to reference low. I also reversed the scope probes which yielded the same results. If I can't think of something else to try I guess we will either put magnets on the damper or an EDIS trigger wheel, but I would rather stay with the simplest setup of using the optical wheel in the optispark. Quote Link to comment Share on other sites More sharing options...
wheelman Posted January 23, 2009 Share Posted January 23, 2009 Moby, Here is a link to an article posted not long ago on the DIYAutoTune web site that describes how to use Megasquirt with an LT1. http://www.diyautotune.com/tech_articles/how_to_megasquirt_your_chevy_lt1_lt4_l99.htm Hope this helps. How fast were you rotating the wheel while trying to watch it on the scope and did you have your scope set to trigger or just show the trace? Wheelman Quote Link to comment Share on other sites More sharing options...
Matt Cramer Posted January 23, 2009 Share Posted January 23, 2009 What sort of pull up are you using on the low res side? Quote Link to comment Share on other sites More sharing options...
mobythevan Posted January 23, 2009 Author Share Posted January 23, 2009 No pull up Matt, that was something I tried with the first unit when I didn't see anything. I did not try that with the second unit. One of my buddies says he searched a lot and the low res failure seems to be common so he wants to try taping the hi res slots to get a low res type signal. Matt, I notice in your writeup on the diyautotune site a pullup is used on the v3 mainboard. I am using the v2.2 mainboard so the references didn't make since to me for the pullup. Are you putting a pullup on the low res signal?? I did go through various scope triggers and settings. I also spun the dizzy at slower speeds by hand, but hi res functioned fine for my time scale and I got many pulses on the screen. Maybe the units have debri or rust blcoking the low res opto detecter? More experimenting to come. Quote Link to comment Share on other sites More sharing options...
Matt Cramer Posted January 23, 2009 Share Posted January 23, 2009 The missing pull-up on the V2.2 is an oversight - I'll see if I can get this fixed soon. Quote Link to comment Share on other sites More sharing options...
mobythevan Posted January 23, 2009 Author Share Posted January 23, 2009 The missing pull-up on the V2.2 is an oversight - I'll see if I can get this fixed soon. So I should add a 1k pullup to 12 volts on the low res signal at pin 24? Quote Link to comment Share on other sites More sharing options...
mobythevan Posted January 24, 2009 Author Share Posted January 24, 2009 Well, I feel like a noob:mrgreen:. I guess I just didn't have everything connected correctly at the same time in my tests. With the pullup resistor now the low res functions fine on the scope. It is curious to me that the hi res does not need a pull up to function. I could only guess that it is different circuitry for the higher frequency toggle rate. Thanks for the help guys. Quote Link to comment Share on other sites More sharing options...
wheelman Posted January 25, 2009 Share Posted January 25, 2009 I want to make sure I understand what you're saying. You put a pull up to 12volts on the low res line and now you get a signal on the scope. If I'm right that means it reads 12v when a slot is not present and drops to zero when a slot is present, correct? So to trigger off the trailing edge of the slot you need to set megasquirt up to trigger on the rising edge of the signal trace, or is the signal inverted in the hall sensor configuration? See, now you got me confused. Wheelman Quote Link to comment Share on other sites More sharing options...
mobythevan Posted January 25, 2009 Author Share Posted January 25, 2009 At this point I am as confused as you. The easiest way to determine the correct edge since I am having a hard time spinning the opti by hand to get a good picture on the scope is going to be using the either edge option in 029y4 code. I plan to grab the timing light, make a temporary mark on the damper and crank the engine using rising edge then falling edge and see which one gives the correct stable trigger. If I had a second person to help I could hook a drill to the opti and get a good scope plot with the pullup, but this will be easier at this point. My test setup requires too many hands to support the opti unit and crank it, plus get the correct time base set on the scope. At this point I can just see that the trigger is working, but I haven't zoomed out to catch all 8 slots on screen at once. EDIT: I wasn't correct on the rising falling selectable trigger, that is only for second trigger setups. The main tach input has to be set up in hardware for rising or falling edge. My setup is working correctly with it wired and set up just like the L28ET installation sticky. I am now having trouble controlling the LT1 ignition module so I think I will just hook up an old HEI 4 pin module to control the coil and call it a day. Quote Link to comment Share on other sites More sharing options...
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