Spark inverted NO with MSD 6a

[oskarax]

Hi!

Everywhere I look it says that when you run with a msd 6a with you megasquirt 1 you MUST change spark to inverted YES.

My problem is that I HAVE to set it to NO for my engine to run. If I choose YES my timing gets really retarded and the engine runs very poorly.

My timing when inverted NO is chosen, is all over the place and it's almost impossible to get it matched up with the trigger angle.

I've seen that in some cases you might get problems with msd 6 and need to take a wire and run from d14 to IGN. Not sure what that's supposed to do or if it will fix my problem. I haven't tried it yet. On diy autotune it says:

"Note that some variations of the MSD box do not work well with BIP373s. We’ve seen this primarily crop up with a few Digital 6 variants. They only trigger if their signal is pulled down to nearly zero volts, and BIP373s do not pull the signal down quite as far as some other ignition outputs. If this occurs, you can substitute a different switching transistor such as a TIP120"

I do not know what that means either or if that is my problem. This is out of my comfort zone so please treat me like a beginner on this one. I haven't built the megasquirt so I can't answer many questions about that I'm afraid....

Oskar

[Matt Cramer]

[oskarax]

I'm really not sure what a datalog would be to any help?

I will try to upload a msq then.

[oskarax]

Note that the engine isnt tuned yet.

[slow_hemi6]

We are a bit limited by not knowing what hardware your build has.
Basically what the MSD white wire input wants is a trigger that mimics a set of points. ie one that is grounding when no spark is required and then releasing that ground at the point of spark.
The spark setting you select is with regards to the cpu's output pin. The types of switching hardware and combinations of switching hardware after this can cause their own inversions of that signal. That is something that the builder will have done and you are not, at this point, aware of. But you can say that only one spark output condition will trigger the MSD correctly and accurately. So go with the condition that works. MSD white wire requires around 100 to 200mA so you definitely need a switching transistor as part of your builds output. You cant over dwell a MSD box so you can't really hurt the MSD trying each condition. The manual's recommended settings only apply to the recommended hardware builds found in the manual.

[Six_Shooter]

If your Q16 is a BIP373, you'll likely have issues as DIYAutotune suggests.

What DIY is saying is that the signal provided by the BIP373 never actually gets to 0V, it will only get down to a couple or few volts, for sake of argument let's say that the BIP373 only pulls down to 3 volts, enough to trigger a coil, but not near enough to 0V to trigger an MSD box.

You have a couple options, replace your Q16 with a TIP 120, which will be a direct replacement, unsolder the BIP373 and replace with the TIP120, or move the ignition trigger to D14, in which you will need to make a couple modifications to that circuit. Remove the LED, and add a 1K ohm resistor as a pull up. If you look in the MS2 manual (I haven't looked at an MS1 manual to nkow if it has the same info), for the HEI ignition modifications, but only for D14, the rest will not apply. The same info may be covered in the CDI box section, but I again haven't looked at that specifically, but know that the D14 modifications will work to trigger an MSD box.

[Matt Cramer]

I see you're running a total trigger angle of 102.5 degrees. What sort of distributor are you running here?