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Sensory Perception

Making heads or tails of the engine operating system is not a simple job. Often one symptom can be cause by more than one source.

An excellent example of this is the Vehicle Speed Sensor (VSS). The VSS is mounted behind the speedometer in the instrument cluster. It provides electrical pulses to the ECM from the speedometer head. The pulses indicate the road speed. The ECM then uses this information to operate the Idle Air Control motor (IAC), canister purge, and Torque Converter Clutch (TCC). A vehicle driven without the VSS in place may notice poor idle quality; this is not usually associated with the VSS, so not easily diagnosed.

As with most electrical systems, intermittent trouble may be caused by a poor connection, rubbed through wire insulation, or a broken wire inside the insulation. Inspect terminal "A10" for proper mating, damaged terminal, or any other damage. If all checks out OK, then...

*Raise the drive wheel and support by the

axle.

*With engine idling in gear, "scan" should

show MPH above 0. Does it?

YES - code 45 is intermittent. If no additional codes are stored then refer to above paragraph.

NO - Ignition "off" Disconnect VSS buffer and switch ignition "on".

Probe 8 way connecter terminal F with a voltmeter to ground.

Should be 10 volts or more. Is it?

YES - Replace VSS buffer and/or PM generator.

NO - Check ckt 437 for opens or short to ground, including ECM terminal A-10. If ckt is OK, replace ECM.

The latest victim to be discontinued from the GM line up is the 1986-87 Mass Air Flow sensor. ESP Products has been working with an aftermarket manufacturer for the last few months trying to get a replacement MAF sensor up and available. The new circuit board, and body design make it a more durable unit. The circuit board is more accurate and responsive, and as a complete unit the new MAF sensor flows more air, although no horsepower figures have been released at this time. The improved sensor should allow great throttle response through the part throttle range as well as increased top end pull, as a result of the greater air flow capabilities.

Before replacing your MAF sensor, as faulty, be sure the wiring and electrical connector are in working order.


Tech Tips
	*Sensory Perception* Making heads or tails of the engine operating system is not a simple job. Often one symptom can be cause by more than one source. An excellent example of this is the Vehicle Speed Sensor (VSS). The VSS is mounted behind the speedometer in the instrument cluster. It provides electrical pulses to the ECM from the speedometer head. The pulses indicate the road speed. The ECM then uses this information to operate the Idle Air Control motor (IAC), canister purge, and Torque Converter Clutch (TCC). A vehicle driven without the VSS in place may notice poor idle quality; this is not usually associated with the VSS, so not easily diagnosed. As with most electrical systems, intermittent trouble may be caused by a poor connection, rubbed through wire insulation, or a broken wire inside the insulation. Inspect terminal "A10" for proper mating, damaged terminal, or any other damage. If all checks out OK, then... Raise the drive wheel and support by the axle. With engine idling in gear, "scan" should show MPH above 0. Does it? YES - code 45 is intermittent. If no additional codes are stored then refer to above paragraph. NO - Ignition "off" Disconnect VSS buffer and switch ignition "on". Probe 8 way connecter terminal F with a voltmeter to ground. Should be 10 volts or more. Is it? YES - Replace VSS buffer and/or PM generator. NO - Check ckt 437 for opens or short to ground, including ECM terminal A-10. If ckt is OK, replace ECM. The latest victim to be discontinued from the GM line up is the 1986-87 Mass Air Flow sensor. ESP Products has been working with an aftermarket manufacturer for the last few months trying to get a replacement MAF sensor up and available. The new circuit board, and body design make it a more durable unit. The circuit board is more accurate and responsive, and as a complete unit the new MAF sensor flows more air, although no horsepower figures have been released at this time. The improved sensor should allow great throttle response through the part throttle range as well as increased top end pull, as a result of the greater air flow capabilities. Before replacing your MAF sensor, as faulty, be sure the wiring and electrical connector are in working order.