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1. 08:25 AM - Re: Bad Tach Readings - Grand Rapids EIS 4000 (Larry & Sandy Sharratt)
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| Subject: | Re: Bad Tach Readings - Grand Rapids EIS 4000 |
I've had a somewhat similar experience with my GRT 4000 with a G3i electronic ignition.
When I first installed the ignition, I got apparently correct tach readings
up to about 2200 or so, then wildly fluctuating above that (the tach pickup
came off the ignition module). After moving the tach pickup back to the
L mag, the EIS readings returned to what seemed to be correct. (The G3i ignition
uses the original - though modified- Slick mags on my O-320).
However, now when I switch the electronic module off, the EIS drops off line completely
with just a row of black squares across the display. When I turn the
module back on, the EIS will come back after switching off and then back on.
I know the obvious answer is to just leave the ignition module on but I would
still like to know what gremlins are running back and forth inside those wires.
Now that spring is returning to the frozen tundra of Minnesota, maybe I'll
get a chance to pursue it.
I realize the causes of our two issues are probably different, just thought I'd
throw it out for discussion.
Larry Sharratt
Waconia MN
Time: 08:25:16 AM PST US
From: Bob Falstad <bobair@me.com>
Subject: AeroElectric-List: Bad Tach Readings - Grand Rapids EIS 4000
Hi,
I have just started flying my GlaStar again after installing a Grand Rapids EIS
4000 and single screen Horizon HX. I've wired my traditional mag P-leads to
tach input 1 (left mag) and tach input 2 (right mag). At first, the "left" mag
and "both" positions showed normal, reasonable, stable RPM indications. During
my runup at 1700 RPM, the "right" mag would fluctuate wildly between 3200
- 3400 RPM. After talking with Greg at GRT, I switched the inputs and the problem
jumped over to the left mag. I then switched the inputs back and, again
at Greg's suggestion, increased the resistor values on the right mag/input 2
to 47K Ohms and then to 100K Ohms. With the 100K Ohm resistor in place of the
original 27K Ohm resistor, the problem abated somewhat. On runup, the right
mag would show a believable RPM for a couple of seconds and then would fluctuate
between 1200 - 1400 RPM.
The pulse per revolution and mag sensitivity settings in the EIS are "1" and "low",
respectively, for each mag.
More recently, the left mag (and consequently, in the "both" mag position) is exhibiting
the same wildly fluctuating behavior - to the point, the tach indications
are useless. This occurs even though the engine is running at a constant
RPM.
An A&P/IA buddy of mine with extensive experience in light GA aircraft thought
that maybe there was a bad ground in the P-leads so we put jumper wires from the
magneto cases to the ground "forest-of-tabs". (The "hot mag" check was fine
even before the jumper wires.) This damped out the RPM swings somewhat but
did not eliminate the problem.
(I'm using a conventional Start/Mag switch with the four shields (from each P-lead
plus the shielded wire to each tach input) crimped on a common ring terminal
attached to the ground lug on the switch. GRT's installation instructions
say it isn't necessary to carry the shield all the way to the EIS box so I didn't.)
Has anyone seen anything similar to this? Any thoughts whether it is in the wiring
or in the EIS itself? Any troubleshooting steps that I can take to try to
identify the root cause of the problem?
Best regards
Bob
GlaStar N248BF
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