1993 Ls400 Running On 4 Cylinders

[kjhwv]

1993 ls 400 with new ecu rebuild, new coil paks, new cranksensor. Everything was fine until about 2 weeks later when the car started running on 4 cylinders. Checked timing belt, it was OK. RPM needle is jumping around, not normal. What feeds the rpm needle? Is it in one of the coils, or does it come from the cam sensor? If yes to either one, what coil or which cam sensor sends the signal? I really need some input on this problem.

[93ls400walt]

If the coils were just replaced I would re check that the connector and coil wire are connected well. Also there are 2 ignighters on the car, passenger side wheel well, could have a bad one. But I have not heard of them ever being a problem.

[kjhwv]

Ok, after a lot of work and changing the cam sensors, we went back to the KISS principal, keep it simple stupid, and started checking things out again. The car ran fine with the covers off the engine but ran very rough when the covers were put back on. My mechanic was checking the wires while the car was running with the covers off and found out the hard way that the drivers side coil wire was arcing. This was detected when he got a good charge of 12 volts DC to his hand. It appears that the plastic covers were shoving the ignition wires down closer to the engine and causing it to arc through the broken insulation. Installed new wiring and now car runs just fine. Thanks for the help. Live and learn.

[landar]

Thanks for the update. BTW, I can guarantee you it was not the 12VDC that gave him a 'charge'...it was more like the 25kv high voltage from the coil.

Another neat "trick" is to mist the wires with a spray bottle of water. If everything(coils, wires) is healthy, nothing should happen other than the wires get wet. But if insulation is bad, you will notice a stumbling engine and arcing. Best to do in low light conditions to see the arcing.

[fsuguy]

Hi,

Glad your problem is resolved. To answer your question about the tach (RPM needle) - according to the circuitry diagram, it is driven by one of the igniters.