Chart C-4H C3I Ignition System Check 3.0L ('85) "N" Series
Ignition System Check Wiring Diagram:
The C3I uses a waste spark method of distribution. In this type of system, the ignition module triggers the #1/4 coil pair resulting in both #1 and #4 spark plugs firing at the same time. #1 cylinder is on the compression stroke at the same time #4 is on the exhaust stroke, resulting in a lower energy requirement to fire #4 spark plug. This leaves the remainder of the high voltage to be used to fire #1 spark plug.
1. If a plug wire is open, the other plug on that coil should still fire at idle. The spark tester tests the ability of the system to produce at least 25,000 volts.
2. No spark on one cylinder may be caused by an open plug wire or secondary winding. Therefore, both wires related to a coil and the secondary winding resistance should be checked. Resistance readings over the upper limit but not infinite will probably not cause a no start but may cause an engine miss under certain conditions.
3. This tests the triggering circuit in the ignition module. A blinking light indicates the module is triggering. The diagram above shows the control wire color for each coil. For example, if testing why #1 plug did not fire, connect the test light between the blue feed wire and the yel/blk control wire while cranking.
4. This test determines whether the ECM is seeing cam and crank sensor signals.
If the test light blinks, the ECM is receiving good cam and crank signals, so the problem is a faulty module connection or module.
5. This test provides the ECM with a substitute Cam and Crank signals. The ECM must see a cam signal first, before it will recognize the crank signal. Therefore, momentarily jumpering the cam signal first, is very important in making an accurate test at this point.
6. Tests to determine whether problem is in cam or crank sensor, Ign. Mod., or power circuits.
CHART C-4H
C3I IGNITION SYSTEM CHECK (Page 1 of 2)
3.0L ('85) "N" SERIES FUEL INJECTION (PORT)
CHART C-4H
C3I IGNITION SYSTEM CHECK (Page 2 of 2)
3.0L ('85) "N" SERIES
Ignition System Check Wiring Diagram:
For timing of spark plug firing, a dual crankshaft sensor "hall effect" switch is used. The cam signal part of this switch sends a signal to the ignition module when cylinder #1 is on the compression stroke. This signal is used to start the correct sequence of coil firing. The engine will still run if the cam signal is lost while running, however, will not restart after shut down and a Code 41 will be stored if the cam signal was lost while running.
The crankshaft sensor also sends a signal to the ignition module and then to the ECM for reference RPM and crankshaft position. There are three windows in a disc which is mounted to the harmonic balancer. These windows pass by the sensor and as each window passes, the next coil is triggered.
7. This voltage is supplied by the module and is pulled low by the sensor each time a window in a rotating disc is aligned with one of the "hall effect" switches. This results in a "crank" or "cam" signal as measured at the ignition module.
8. Checks to see if problem is in ground circuit 952, crank signal circuit 971, Cam signal circuit 972, or ignition module.
Ignition System Diagnosis Chart:
CHART C-4H
C3I IGNITION SYSTEM
CHECK (Page 2 of 2)
3.0L ('85) "N" SERIES FUEL INJECTION (PORT)