Having trouble diagnosing problem with ASD relay on 99 Jeep Grand Cherokee with 4.7. Have determined that relay will stop buzzing when I pull fuse 26 from the PDC. This controls the injectors. Have power at all points on relay that I should when key in on position. Have checked all grounding points and replaced PCM with a remanufactured one. Also tried replacing PCM with a known good PCM out of another grand. Also noticed gauges in cluster not working. Any ideas?
Did you check for any DTC? Battery voltage is ok? Fuse #26 feeds the injectors, but also the coils and gives a power input to the PCM. No gauges indicate a dead PCI data bus. I would start measuring the PCI data bus voltage on pin 2 of the data plug. Normal voltage is about 2V. 0V means a shorted bus, above 6V normally means a problem with one of the components connected to the bus. It is known that a faulty crank sensor can short out the data bus. Don´t know if it could cause the ASD relay to chatter.