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Dan has a good point about measuring resistance in a powered circuit -- not so much because the ohmmeter's battery will damage the ECU, but your readings and the operation of the fuel injection will be affected by it. Just measure voltage while it is powered.
Someone from a saab list mentioned ECU remaining powered for a long time after key off, but I seem to recall the main relay dropping out after about 5 seconds, to allow AMM burnoff in LH2.4. I think you'll also find your cold start injector is not being used by the -951 as compared to the -561.
The voltage the ECU supplies to measure the ECT resistance is well regulated to avoid the effect of the variations to the system voltage caused by charge state, accessory loading and temperature changes. If you still see what appear to be variations in the ECT voltage caused by turning on the fan, lights, and so forth, check to see your meter ground is the same as the ECU's ground.
You could watch that more accurately by substituting a fixed resistor at the ECU (value equivalent to warmed up - perhaps a couple hundred ohms) and monitoring the voltage while changing the electrical load environment. The fact that your ECT is grounded through its housing and the aluminum head raises the question of how well grounded is head to firewall, battery to block, alternator to block and body to battery.
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Art Benstein near Baltimore
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