[Diy_efi] Testing an inductance coil.

[Joe Boucher]

This system is really simple.  The one component I don't know how to test is
this coil around the spark plug wire.

Do I use the voltmeter and do a simple resistance test from one terminal to
the other?  Do I set the spark plug wire with the coil on the wire, on a
working engine, and see if I can detect a voltage with the across the coil
with the voltmeter?  Will I damage the frequency function of the multimeter
if I use it on the coil while an engine is running?

Keep it simple.

Joe

-----Original Message-----
From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]On
Behalf Of hugh at sol.co.uk
Sent: Tuesday, August 16, 2005 2:44 AM
To: diy_efi at diy-efi.org
Subject: RE: [Diy_efi] FW: [fangle] Testing an inductance coil.


Joe,

Most EFI systems control the earth side of the circuit, so your injectors
should have 12 volts when not firing.

Original Message:
-----------------
From: Joe Boucher boucherj at prodigy.net
Date: Mon, 15 Aug 2005 21:25:06 -0500
To: diy_efi at diy-efi.org
Subject: [Diy_efi] FW: [fangle] Testing an inductance coil.


What I want to test is an inductance coil.  I purchased an analog AirSensors
EFI unit over a year ago[Joe Boucher]  at a swap meet .  The kid told me the
entire kit was there.  However, the temp sensor was missing.  A week ago I
found a source for the part.  So, I started testing.

There are some LED's in the box indicating if certain functions are working.
The only inputs are the mass air flow sensor, temperature, ignition on, tach
signal from coil, and an inductance coil wrapped around the second firing
spark plug wire.  Outputs are fuel pump power, an optional fast idle signal,
and the four injectors.

I'm not sure if the inductance coil wrapped around the wire is working.  All
the LED's went out, but the injectors didn't fire when I hooked up the tach
and inductance lead to the Camaro.  The coil has to be oriented properly to
the wire and I think it was correct.  Didn't have time (and the idea) to try
swapping the coil.  The diagnostic trees in the manual list the coil has a
requirement for firing.  I think.  It's not a great manual.

I want to test the coil.  All I have is a multi-meter.  It does have a
frequency function.  I used it to test the tach signal.  There was a
frequency that increased and decreased with engine speed from the tach
signal.  Can I use the frequency meter to see if there is a signal [Joe
Boucher] from the spark plug coil without destroying the millimeter?  Or
should I set the meter to AC and 20K volts and see if there is a signal?

The injectors are fired like most with the ground bring controlled to pulse
the injector.  While the unit was "on", there was not 12 volts at either of
the lines into one of the injector plugs.  One initially showed a signal but
the voltage quickly decreased to 0.  That doesn't seem good.  I will admit
the connection to the 12 volt power source was suspect, so I will do a
better job for the next test.

My plan is to try the test again, see if the inductance coil is working, try
flipping the coil, and see if there is voltage at the injectors.  If not,
the next step is to open the box and see if I can spot where the magic smoke
has escaped.

Thanks for any help.

Joe


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