View Full Version : Digital 6 Plus - Breaking Up At 5800 Rpm

07-23-2005, 09:56 PM

I just looked at the long post regardng the digital 6 and wanted to provide some additional info. I have a good wires going straight from my the Digital 6 to the positive and negative battery leads. One other thing to add that could be my problem is that I beleive my wires going from teh MSD box to the distributor run right beside a 2 guage wire going to my alternator. I am assuming this could be potentially causing the problem.

Turbocharged Mustang running 20 psi making in the range of 800 hp. Running FAST fuel injection with stock distributor, TFI, and Digital 6 with an HVC II Coil (Blue).

When the car hits 5800-6000 rpm's the car starts to break up and struggles to pull through that rpm. According to the datalog the A/F looks fine when the it reaches 6000, then starts to go real rich. I am thinking it is because the iginition is not firing consitenly enough to burn the fuel.

Here is a link to the datalog.


You can car that the pulls smoothly until 6000 or so, then the RPM's just bounce around 5800-6000 with the car beginging to go rich. The tune is correct as the a/f is find when it first reaches the cells in the VE table.

Any suggestions or observations would be appreciated.

bill jones
07-24-2005, 10:59 AM
-looking at the chart you hit 27# of boost at something like 5800rpm.
-That boost pressure is trying to kill the spark and the boost also seriously affects the ability of the fuel to evaporate.
-First thing I'd do is to shorten the sparkplug gap and second thing I'd do is OHM the plug and coil wires and get plug wires on there that are less than 50 OHMs per foot.
-Third thing I'd investigate is the "distallation curve" of the fuel you are using.
-You need fuel that requires the least amount of heat to evaporate the fuel at the various points on the distallation curve yet still has the octane rating you need.
-I'd also be looking at what's happening inside the distributor by cutting a window into the cap so that you can view the rotor index at 6000rpm and when you have the engine under boost.
-When the boost happens you probably have some sort of spark retard and for that retard to work you end up with the rotor index becoming compromised somewhere, and it needs to be dead nuts during the max power/high boost situation.
-I'd be curious about running the stock TFI and consider change the digital 6 out for a stacker #7000 so that you have the benefits of both the inductive spark duration AND the CD spark power.

07-24-2005, 12:42 PM
Just wondering what kind of performance you were getting with a stock ignition, if that was hooked up before? Don't use trick plugs - set the stock plug to .035 and open up slowly until you get a little roughness.
Why are you running a #2 wire on your alternator? Isn't that a little overkill? I wonder if the alternator's output terminal can physically handle that large wire.

If you are running a mag pickup trigger, temporarily route some spare wire away from other engine wireing to see if you are getting trigger interference. If you are running the white wire (high level) trigger, there would most likely NOT be an interference problem.

From your datalog, you show 36 degrees of timing advance at 3200 rpm, but only 16 degrees at 6000 rpm. What is controlling your timing? It seems you would be better off using a Digital 7 programmable ignition with data aquisition to allow the strongest spark and programmable timing for each cylinder.

07-25-2005, 10:05 AM
Yeah, sounds like not enough ignition for the amount of boost that is present. You might want to think about stepping up to a 7 series ignition.

07-25-2005, 10:26 AM
The 27psi was just a spike due to a problem with my C02 controlled wastegate setup. Fast is controlling the timing and it is only 16* up top because this is a street tune for pump gas. I normally run 22* or so on race gas up top. Plug gap is at .26. Wires are brandnew MSD's.

07-25-2005, 12:30 PM
You still might want to think about upgrading that ignition. The amount of boost is still a little much for that unit.