EMS-Pro with 6AL retards timing with RPM????

[goat racer]

Hey guys!

Scott and I just touched on this while at Bills house a few weeks ago, but I can lock the timing with the ems-pro, and then watch the timing fade back with my timing light as the RPM increases. best I can tell is that it's retarding 3-4 degrees minimum, and I'm not willing to just wing it to 7K to find out how far it really goes.
I have the total set at 34 degrees on the map and I'm sure that it's not seeing more than 30 in reality.

The tech at MSD just told me that there is no way that the 6AL can retard timing. If I remember right, Scott said that a few guys had run into this and there was a fix.

Any takers?

Thanks,
Brian

[TheSilverBuick]

Hmm, I plan on making a bracket and installing a crank trigger wheel sensor this up coming weekend. If I successfully get it working, I'll check to see if mine does it (6AL-2). Right now I account for any timing changes from timing change slack, but after about 1200rpm mine steadies out pretty good. Unfortunately I don't have answers, but I will be watching for it.

[dieselgeek]

First thing I'd check is that, since you have the non-updated tach input, you're not getting the "rounded edge" on your crank sensor's output. This can cause what you're observing with a 36-1 wheel. Got a scope handy? good excuse to spend a few minutes with your dad :-)

Second, make sure you're locking the "fixed angle" when testing so no other variables can affect the timing. I've made that mistake myself a few times.

Third, there is a hidden adjustment in the software (I have to re-figure out how to get to it) that compensates for spark latency. Not sure what the MSD guy was thinking, but it's common with pretty much all EFI systems that digitally control an analog box to get a little bit of latency into the calculation. I will dig up how to make that adjustment, it worked for me once when we had about 3-4 degress of total retard when locking out the timing, as revs climbed.

Also, would be a GREAT idea to ship it to me to have the update performed, or perhaps I can ship out a spare and swap you (minimize downtime).

-Scott

[goat racer]

Hey Scott,

We do have the "rounded edge" output from the crank sensor, and I did have the timing fixed when I checked.
It's definately time for the Jay Brown mods to the box. I'll give you a call here in a bit and we can make some arrengements.

Thanks!

[CDMBill]

As this still a single coil with distributor deal could this be coil saturation latency, or rotor to cap phasing changes? the signal generated at the timing light is reflective of the actual high voltage pulse heading doen the plug wire as read by the timing light so it seems that some of these other factors could cause a RPM retard effect?

I was surprised to find that the 100 octane unleaded we tried on the dyno needed a kick up in total advance from 6000 -7500 relative to the 109 unleaded. I suspect this due to burn rate but it ougth to work on Brian's engine too as chamber is at least as efficient as mine and he has showing higher total advance readings to mae best ET vs. others runnning the same heads (more or less)

[dieselgeek]

Let us know when you get the updated EMS back, and how your timing works after that.