msd digital 6 plus

[tuffxf]

G,day,
I have a sbf powered bracket car with a 6al, ran finefor 6 yrs, hundredss of passes.
Bought a digital 6 plus to step it up a bit, used the correct coil, used the optional shielded trigger wire, had 14.4v supply volts, zero resistance on the earth wire back to the batt neg terminal.
All the wiring was as seperated as posible from each other.
With a msd tester it worked fine up the rpm limit which was very close to where it was set.
Went to largest meeting of the year, first pass misfiring in the burnout and at the top of each gear from about 5000 rpm up.
Fattened the carb, lifted the rev limiter, nothing made any difference, a mate had an old 6al, threw it in and run perfect, still in there.
Sent the msd back to the agent here in Aust, tested it ok, sent to another place ok?
It honestly beats me! the batt is in the boot, the ignition was not wired all the way back to the battery but positive went to the hot stud on the starter solenoid, this is fed with big dia welding cable, earth wire went to the frame, batt neg in the boot is earthed to the frame, maybe not correct? can't detect any voltage drop or high resistance but.
Maybe going back to the batt would shield the unit from picking up interference with the engine running, i believe that it is picking up interference when the eng is running? not sure.
There is a pigtail of unshielded cable from the pigtail in the dizzy?
If you check the ac output out of the alternator it is near perfect so it beats me!
I wondered if the pickup in the dizzy is not suitable as it is a ford bosch one, but the engine ran fine on an engine dyno with a digital 7 ign and exactly the same dizzy and cap and leads, so rotor phasing shouldn't be an issue?
They seem to be very finicky, i went to the digital to try to mirror the magnetic compensation circuitry of the digital 7 and keep the timing identical up top as i heard that the analog msd's retard slightly at high rpm.
Anyone have any ideas or experience with these things?
Thanks very much!
Paul

[tuffxf]

G,day Pat,
Thanks for that! it was back in June when i took it off, i can't remember if i tried that or not, i don't think i did.
Cheers
Paul

[tuffxf]

G,day Pat,
What do you think about the above ign? there seems to be some issues when you google them?
Cheers

[1320racer]

made the same swap back in '07, going from a 6AL which was trouble free for thousands of pass, to a Digital 6 Plus which wouldn't rev pass 3100 RPM without banging and backfiring.

Pulled only the box out and reinstalled the 6AL and all was normal.

After trying 2 more Digital 6 boxes and changing every part of the ignition system except one, I finally found the culprit...the magnetic pickup in the MSD billet distributor which not only wasn't an issue with the 6AL box, it was also less than 2 years old.

Swap it out, reinstalling the 14 year old pickup it replaced and never had a problem again and it's still in service today.

BTW, the only step up with this box over the 6AL is the retard functions. There is no on track performance gain to be had. It wasn't worth .01 in my car.

[Terry Cain]

"the batt is in the boot" Huh? Just kidding with ya.
I suggest playing with pickup. The digital's are way more sensitive.

[rallye bob]

Originally Posted by Techwest Racing Services

tuffxf

One thing to look at since the MSD 6al works in the car. It is possible the mag tigger wires may need to be reversed. When you move from an analog box to a Digital box sometimes the purple & green wires need to be swapped.

This solved my "misfire" issues, after switching from an analog, box to a digital, but after you swap the purple & green wires (polarity) you will have to reset your timing, as it will change considerably.....
This is from a MSD Tech: " Changing the connections so that the Black/Orange connects with the Green and Black/Purple connects with the Violet will change the polarity. This may throw the timing off by about 20°.
With an analog unit (i.e. 6A, 6AL, 7AL, etc) the connection you want is with the most retarded timing. On a Digital unit (i.e. Digital-6 or -7 Plus, etc) the connection you want is with the most advanced timing".
The wire connecter for the purple & green wire is "keyed" so you will have to remove the pins in the connecter, and swap them...... Good luck.

[Sean Marconette]

Pick up polarity is reversed. Had the same thing happen on mine.