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Timing Chain Being Off One Tooth
Can Cause Ignition Coils Not to Fire

Posted 1/16/2001
By Paul Kujawa

“Since the problem occurred right after the water pump was replaced, I wondered if the camshaft and crankshaft position sensor signals were out of phase with each other, since the timing chain must be taken off to replace the water pump.”

Vehicle: 1996 Nissan Maxima. VQ30DE

Symptom: Misfires. No spark from the coils for cylinders No. 2 and No. 3. The cam timing is off a tooth.

The problem began with a leaking water pump. After the water pump was replaced, ignition coils No. 2 and No. 3 did not fire.

This Nissan's engine is equipped with a distributorless ignition system (DIS), with a separate power transistor mounted with each one of the six coils. This gives each cylinder one coil and one power transistor. A separate signal from the powertrain control module (PCM) to the base of each of the power transistors turns the power transistors on and off. The power transistors pulse coil negative to ground, based on those signals from the computer.

The technician verified that the signals from the PCM to the base of the power transistors for the other four working cylinders were good. He found no signal from the PCM to the base of the power transistors for cylinders No. 2 and No. 3 at the power transistors. The harness was checked for opens and shorts between the computer and those two coils' power transistors. The signals at the PCM were checked as well. The technician tried running new wires between the PCM and the power transistors, and also tried new coil/power transistor assemblies for those two cylinders, as well as a used PCM. There were still no signals from the PCM to the base of those two power transistors. The camshaft position sensor (phase) and crankshaft position sensor (reference) signals were both scope-checked and had nice, consistent sine wave type patterns with proper amplitude for both signals.

Since the problem occurred right after the water pump was replaced, I wondered if the camshaft and crankshaft position sensor signals were out of phase with each other, since the timing chain must be taken off to replace the water pump. This engine has a main timing chain and two camshaft timing chains. The camshaft timing chains go around the smaller intake and exhaust camshaft sprockets. The main timing chain goes around the crankshaft sprocket, and then up around two larger camshaft sprockets that mount on the end of the intake camshafts, outside of the smaller intake camshaft sprockets that the camshaft timing chains go around. The main timing chain is the one that needs to be removed to replace the water pump.

When I asked the technician to check the engine mechanical cam timing, he found the timing chain was off one tooth. He corrected the cam timing and the two coils started firing once again.

So if you get a couple of coils with no spark and there are no signals to the base of their power transistors, make sure the timing chain is not off a tooth.

Paul Kujawa [an error occurred while processing this directive]


On '93-'97 Chrysler, LH Body:
Signal Wire at 5 Volts Indicated Open in Sensor

Posted 2/7/2001
By Tom Vadnais

“If the signal wire is at 5 volts, there is an open in the sensor and it needs to be replaced.”
Vehicles: 1993 through 1997 Chrysler, LH body.

Engines: 3.3L and 3.5 L.

Symptom/Problem: 5 volts seen on the O2 sensor circuit accompanied by a code 21 (02 sensor shorted to voltage). The powertrain control module (PCM) has detected an open circuit in the 02 sensor.

Text & Fix: Measure the voltage on all four wires at the O2 sensor. There should be two ground wires that have no more than 50mv with the vehicle running and the sensor connected: one wire with battery voltage for the heater; and the signal wire, which should be switching from approximately 0.2 to 0.8 volts. If the signal wire is at 5 volts, there is an open in the sensor and it needs to be replaced.

Background: In 1990, Chrysler changed the design of its PCM, and went to a single board engine controller (SBEC). One change that was noticed with this transformation was that the 02 sensor went to 5 volts when open-circuited. The purpose of this voltage is to monitor an open circuit or a heater failure. If, when running with the engine coolant temperature sensor at approximately 176 degrees Fahrenheit and the O2 sensor voltage above 1.2 volts for over 2.5 seconds, a code 21 (O2 sensor shorted to voltage) will set. This is somewhat deceiving since the voltage will go high open circuit or with a heater or ground failure. The voltage is really low current. When monitoring the circuit, if the sensor is disconnected, the voltage will immediately go to 0.5 volt and then will slowly climb to nearly 5 volts either on a scan tool or DVOM. This is a normal condition and not a problem with the PCM.

Note: On the Jeep truck engine controller (1996 and newer) this 5-volt reference is also used to run the heater test. With the engine at idle immediately after a cold start...and with engine coolant temperature sensor less than 147 degrees Fahrenheit ... and with the battery temp sensor within 27 degrees Fahrenheit of the coolant temperature sensor reading...if the 02 sensor voltage stays above 3 volts for 30 to 90 seconds, then the heater failure code will set.

Vadnais [an error occurred while processing this directive]

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© 2001 IDENTIFIX. All Rights Reserved.


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