[urq] EFI + MAC-14 maxing ataround 5k RPM

[Cody Forbes]

> So we think it might be ignition after all.  I guess I'm not seeing
> where the ignition signal drops out.  I do see the pulse width spike
> when the RPM drops.  Are you looking at the log from today?  

I'm not expecting a signal issue here, I'm thinking it's a problem downstream. Something like coil, plug wires, stuff like that.


> 
> Cody, is there someway to turn on the ignition pulse graph line in
> the logfile? 

The screen shot you posted on the MSExtra forum shows the RPM signal line, unless I'm mistaken.


> 
> I remain sceptical at this point about the ignition part, even though
> it was my original speculation.  The more I have looked at the
> ignition the more it looks correct and even an improvement over
> stock.  Unless I'm getting some parasitic draw on coil primary or
> losing current to coil output, but I don't see that.  I do have the
> coil driving the tachometer - would that be more of an effect on the
> MAC-14 than it was on the MAC-02?      

Well one way to find out is disconnect that wiring and use the tach on the MS main screen just for the test. I sorta doubt it, but you never know what signal noise there could be.


> 
> How can we see what is happening to the coil primary?  How can you
> see if spark is dying at high RPMs?  Anything else to look at? 

Scope. With a scope you could watch the coil>distributor lead looking for any falter in the pattern, and you could watch each plug wire individually looking for an irregular pattern. I've got a big Sun diagnostic rig with a scope, but I think it would be a tight fit in the trunk of my Audi, plus I'm booked for the next 3 weekends.


> 
> Also, remember - although the log shows ignition (timing advance,
> etc.) it is not being used.  I have been contemplating installing 5
> window hall and using MS for ignition as well.  I just figured AUDI
> probably does this a little better.   

You don't want to use a 5 window hall for ignition on an engine like this. Slop in the timing belt, slop in the distibutor drive, slop in the distributor shaft bushings, and the small innacuracy of the hall sensor will all add up to a ton of slop in your signal (relatively speaking - I wouldn't want it to bounce +/- 3 degrees at 30psi of boost!). I'm currently working with some guys to get a board made up that will convert our flywheel sensors into a signal useable by the MS (it can't read more then about 60 teeth on a pickup, our ring gear has 135). Until this board gets done you are right that you can not match the accuracy and quality of the stock ignition system.

-Cody Forbes
http://www.5000tq.com
'87 5ktq - Fast.
'87 5ktq QLCC'd plus some
'86 5ktqCD
'86 5k
'86 5k