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1994 Honda Civic DX 1.5L SOHC has lost the spark to live

I was intending to check base timing on this 1994 Civic DX 1.5L. The engine was idling fine.

While the engine was idling, I replaced the too-large paper clip in the 2P service check connector, with a smaller one. The moment I inserted the smaller paper clip, the engine BEGAN to die. I ran to the engine and flashed the timing light on the crankshaft timing marks and saw the timing marks near zero, AS THE ENGINE DIED.

The engine would NOT restart (paper clip removed).

I performed the DTC Charts 7, 8, 9 and 15 (at least) several times. All the voltages and ohms are as required. The Ignition Output Signal voltage, at the ICM (Ignition Control Module) terminal #4 is 10-12 volts with the yellow/green wire disconnected from the ICM. This ICM signal wire goes to ECU A21,A22. When the yellow/green wire is connected to the ICM, its voltage goes to 6 volts.

As I understand it, the voltage on this wire should vary from 10 volts to zero volts, over and over, to cause the ICM (Ignition Control Module) to cause the ignition coil to spark while the engine is cranking (and while running). It doesn’t. Why?

The check engine light does not flash to indicate a trouble. When the ignition is turned ON, the bulb check turns the CEL on for a couple of seconds, as normal. No DTC codes will flash when the service check connector is jumpered.

Fuel pressure comes on (35 psi), relays clack under the dash and in the engine bay, fuel injectors click, engine cranks, distributor rotor rotates and points to the correct cap tower (static time is good); but, no spark signal from the ECU.

Replaced the ICM with a new one. Replaced the ECU with a used ECU which was “put on a car and it ran”, and has a 6 month warranty from the recycle warehouse.

The ECU and the Backup fuses are good. The alarm and security system specialist said that the Viper 500+ aftermarket system would be neutralized if I disconnected all its connectors — which I did. No change. Everything works, except there is no spark signal, nor spark.

No, I don’t have the HondaTech scan tool, nor other aftermarket Honda OBD1 scan tool.



What to do? Surely, someone has run into this problem, before, yes?

I’ve been thinking on your problem and this is a tough one. My inclination is that the Backup(Radio) fuse is blown but you say the fuses are good. The other thing would be the power transistor in the ECU but you changed the ECU with a known good one.

As for the wire to the ICU going from 10-0 volts over and over, your meter can’t respond fast enough to see that, you would need an oscilloscope. 6 volts is about right.

I’m thinking coil.

Dang Honda for not publishing ECU voltage pin-out charts. That would help bunches.
I checked the same yellow/green wire, to the ICM/ECU, on a 1992 Honda Accord. The non-running voltage was 10.10 volts. The running voltage was variable between 9.08 volt and 9.16 volt…constantly running up and down .02 to .04 volts.
My previous information/assumption of a large trigger signal voltage is, thus, in error. I think that the trigger signal is millivolts/milliamps. The large 9 volts is just a carrier voltage.
The 6 volts, on the 1994 Civic is probably too low to tigger the ICM.
My multimeter does re-act slowly. I tried the ac setting to see if that would pick up pulsing dc. Didn’t work. An oscilloscope would pick up the signal. Mwah doesn’t have an o’scope.
Ignition coil? Perhaps. An ignition coil can check good with an ohm meter; but, have defects which show up when the voltage builds to thousands of volts at sparking time. Ignition coil: $75. Already spent $160 for ECU, and $70 for ICM. It’s expensive to NOT find the cause of a problem! Lah, lah, lah!

A check of a 1992 Honda accord, with a similar ICM, showed the yellow/green wire, on the ICM #4 terminal, with the key ON/engine off, had 10 vdc. When the engine is running, the voltage goes to about 9 vdc, and varies between 9.08 and 9.16 vdc. Still terminal #4 with the meter set on vac, the voltage starts at 5 vAC (engine running) and over 2 to 3 minuets, goes to 3.20 vac, and stays there as long as the engine is running.
The 1994 Civic values are 11.77 vdc, key ON, engine off. While cranking, it is 9 vdc, and 2 vac. Of course, it doesn’t start.
I’ve not found anywhere on the Internet anything about actually checking the control signals from the ECU to the ICM, how, and what those values should be.

I want to thank every one (keith) who helped me with this problem.
I was able to perform dynamic (in actual use) tests on the components in the distributor by running the Civic distributor on an Accord. The Civic ignition coil would not run the Accord engine. A replacement ignition coil…