This 2001 Doge Durango with a 4.7 liter V8 was sent to me from another shop. The truck had come to them with a head gasket leak, which they had already fixed. A new problem had developed though in that the ASD relay fuse in the under hood fuse box would blow sometimes and the engine did not run great. The other shop said that they had checked all of their work and could find no place where they might have shorted out any wiring. To do my job I of course had to go back through every thing that might have been checked. I started by removing the blown 30 amp ASD relay fuse.
I installed a 30 amp circuit breaker in its place and tested the amp load on the circuit by hooking the inductive amp clamp from my tester around one of the jumper wires. I turned the key on and nothing unusual. I cranked the engine and the engine fired up and ran okay but not real good. I monitored amp draw while running and everything seemed okay until the idle speed came down below 1500 rpms. The amps jumped up to about 25 amps, so I gave it a little gas to get the rpms up again and the amps started spiking to 60 + amps. They came back down after getting over 2000 rpms. This was about the strangest thing I had ever seen.
I shut the engine off and checked all of the basic wiring around the injectors and coils. All seemed okay. I checked the diagrams and found that the fuse shown below would eliminate the O2 sensor heaters so I removed it. I found an ignition capacitor on the passenger inner fender and disconnected it. I retested and the same thing happened again.
What in the world could it be? I decided to start checking the coils for amperage draw individually. Hopefully I would find a shorted coil. I removed the tape and separated the wires.
I hooked the inductive amp clamp around one of the wires. It did not matter which one.
I cranked the engine and monitored the amperage draw.
Well I’ll be, 8 amps times 8 cylinders equals 64 amps. That definitely could blow the fuse and could be the explanation of the intermittent high amp draw. Most of the cylinders could be firing at the same time, although they should not be unless the base timing is off. How could the base timing be off there is no distributor and none of the sensors are adjustable? Son of a gun, the timing chains could be off a tooth or two and that could explain the dwell overlap. Yep, engine is an overhead cam design and the chains had to be taken loose to change the head gaskets that were leaking. I have never seen a mechanical adjustment cause an electrical overload on a vehicle before. Now I have!
I called the other shop and broke the bad news to them. They picked the truck up and reset the timing chains and all it well.