The check engine light on my 1994, 4.0L, 4WD, automatic transmission, 61k miles Explorer has been intermittently lighting (every couple of weeks, for several seconds) for the past three months. No loss in drivability has been noted, even when pulling a 2200 lb boat and trailer with the Check Engine light on for 30 seconds at 55 mph.

Checking the codes by counting the light flashes I have a stored CID fault (cylinder identification).

Checking my Ford service/shop manuals (printed by Helm) I find conflicting causes/sensors.

In the Emission Diagnosis Manual a CAMshaft position sensor is listed for the 4.0L as the signal that provides cylinder ID. A crankshaft position sensor is listed for the 2.3L, 4-cyl.

In the Powertrain Service Manual a CRANKshaft position sensor is listed for the 4.0L and the text states that a camshaft sensor is only used on the 2.3L, 4-cyl for California.

Looking at my engine it would appear that I have both. On the rear, center of the engine I find a device that looks like the top of a camshaft position sensor, down to the color codes of the three wires coming out of it. On engine front at the harmonic balancer I have a crankshaft position sensor.

Any ideas on which might be the cause of a CID fault, how to diagnosis, etc?

The CRANK sensor is external and lists for $62 at NAPA. Simple bolt on. The CAM sensor apparently needs to be aligned when replaced (probably like a distributor?) and is located on the rear of the engine, darn close to the firewall, cramped quarters. NAPA did not list a cam sensor. I have not checked a Ford dealership for advice or parts.

Thanks for any insight and help.

Michael