Mark; Tracy;
I’d like to explore this
further. Mark S wrote:
After reading Bob
Darrah’s post last week where he noticed a big improvement after
separating the leads to his coils I gave it a try on my 20B. It made a
big difference, but was most noticeable in the lower rpm range. I was
only able to separate the wires down near the coils, and then only by a small
amount, but it made a substantial improvement. My question for Tracy is,
can I leave the grounds and +14v wires bundled together and only separate the
trigger leads, or do I need to separate all the wires? Also, if I were to
use 3 individual shielded wires and ground the shields, could I then bundle the
trigger leads together with the rest of the coil wires?
On a side note, after
separating the coil leads, it took a much leaner mixture to get it to run
smooth. Before, the best it would idle was about 1200rpm, now it will
idle nicely at 900 rpm, not that I want to do that, but it shows that the improvement
isn’t all in my head.
Clarify for me which leads you
separated; the control leads from pins 3, 20, and 21 (C-pins) from each
other? I find that below about 1400-1500 rpm the engine begins the
occasional miss, and gets progressively rougher as rpm decreases.
I’ve been thinking that it seemed more ignition related then mixture
related.
I have the C-pin leads and the
B–pins ground bundled together from the box to the firewall penetration
(a few feet). These bundles are separate for each set of coils (lead,
trail). From the firewall to coils (a few more feet) the power lead
(pin-D) joins the bundle. The A-pins are all grounded at the coil mount.
Tracy wrote:
1. How long is
the wiring harness between EC2 and coils?
About 6 ft for the trailing and 10 ft
for the leading.
2. How is the
power ground to the coils (A terminals) routed? (hopefully not in the same harness, if so,
there is your problem).
3. Same question
as 2. on the power terminals.
Does this say that the power lead
(D-pins) should not be bundled with the C or B pin leads? If so, is this
just as true if the lead and trailing bundles are separate.
4. I would be
surprised if this turned out to be the problem but if coupling between the
control lines themselves (C pins) turns out to be the problem, use either
twisted pairs or shielded wires to drive the B & C lines to
each coil. I would lean toward twisted pairs.
I ran a common B-pin ground for each
set; bundled with the C-pin leads but not twisted. Twisted pairs would
mean adding more wires – or would twisting 3 control leads with one
ground to as well?
5. Are there any
other lines routed along with the coil harness (injector drives, etc)?
The coil bundles run with the injector
drive bundles from the near the firewall to the top of the engine, maybe 4 ft
or so; and run with other wires for a foot or so. One objective is to
minimize firewall penetrations, another is to maintain separation between sets
of injectors and sets of coils for true redundancy, and another is to separate
noisy wires from quiet wires; so further separating isn’t a simple
matter.
Al