Coil's Getting No Electricity

[texas_lexus1]

I have a 94 LS400 and i'm getting no electical ignition in the car. I swapped the ignition coils and no spark still i swapped the igniters and still no spark. I got a new ecu for the car and still nothing. does anyone have any ideas of what would have caused this? it was all of a sudden the car ran perfect then nothing...

[steve2006]

Check the CPS and it's wiring this tells the ECU the crank position of the engine and therefore when to provide a spark if it has failed the ECU will not receive this signal and will not give a signal to the igniters/coils to spark the plugs.

Have a look at the topic on the link below from the UK LOC there is a simplified diagram explaining the system.

http://www.lexusownersclub.co.uk/forum/index.php?showtopic=66889&pid=720816&st=0entry720816

One other thing have you pulled the diagnostic codes which may give you a clue as to what is happening?

[texas_lexus1]

I've replaced the cps with my running 92 and still did not work, when i pull the codes i get 13 and 14 sometimes or the light will stay solid.

[RDM]

I assume you've checked every single fuse in the car, correct? You might also want to check the ignition switch itself.

[texas_lexus1]

Yes, I've checked every fuse under the dash and under the hood. Unless, there is another fuse box somewhere I've checked them all; I've also swapped the main engine relay, alternator fuse, ignition relay with my running 92 but none of them fixed the problem. I found somewhere else that the ecu might need to be flashed into relearn mode and it may not be recognizing the key and causing it to not give any spark...does that seem right?

[RDM]

Not on a 1994 model. Key transponders and interfaces weren't offered until the late '90s, and not on Lexus cars until the LS430 I believe. I say the ignition switch because if it's not providing power while the key is on or in start positions the ECU and all controls wouldn't be powered. Though unlikely it's easy to check and rule out.

[texas_lexus1]

How do I check the ignition switch? If it was the ignition switch wouldn't it not crank at all? It does turn over fine, just no spark.

[curiousB]

How do I check the ignition switch? If it was the ignition switch wouldn't it not crank at all? It does turn over fine, just no spark.

Well the wiring to the coil is pretty simple. On the primary side (the 12 volt side) of the coil is attached to the ignition switch. When the car is turned on that side of the coil should be a constant +12 volts. The other side of the primary is switched (pulsed) to ground to create the spark (via the ignitor, an electronic version of what used to be called points in the old fashioned days). So with the key in the on position but not cranking you should have +12V on both sides of the coil primary. Only when you start cranking should you see the voltage drop on the wire of the coil that goes to the ignitor. It should measure something less than 12 volts but don't expect zero because it is pulsed and not steady. If you have a DVM you can make these basic measurements.

[landar]

Something curious about that diagram, curiousb. Seems strange to me that the secondary coil (hi-voltage) would be working against the +12v side rather than ground. Would expect some high frequency spikes on the +12 v side. Of course a good battery would keep things filtered but might not keep the high frequency noise down. Hmmmm...probably some sort of high frequency cap from +12 to ground.

[curiousB]

Something curious about that diagram, curiousb. Seems strange to me that the secondary coil (hi-voltage) would be working against the +12v side rather than ground. Would expect some high frequency spikes on the +12 v side. Of course a good battery would keep things filtered but might not keep the high frequency noise down. Hmmmm...probably some sort of high frequency cap from +12 to ground.

Yes probably a capacitor in the ignitor circuit to ground. Diagram doesn't show the internals of the ignitor but I bet there is one in there. Also as the switch side of the coil is electronic (transistor switch to ground) it is a cleaner edge than mechanical points so not the same switch bounce as the old days.

[Mweezy]

Yes, I've checked every fuse under the dash and under the hood. Unless, there is another fuse box somewhere I've checked them all; I've also swapped the main engine relay, alternator fuse, ignition relay with my running 92 but none of them fixed the problem. I found somewhere else that the ecu might need to be flashed into relearn mode and it may not be recognizing the key and causing it to not give any spark...does that seem right?

Hi, I'm a new 90 LS400 owner and I would like to ask you a little question, but I hope you've got the problem with your car solved by now. My question is: where is the main relay located?

I would truly appreciate it if you can answer me...

Thanks

[steve2006]

Yes, I've checked every fuse under the dash and under the hood. Unless, there is another fuse box somewhere I've checked them all; I've also swapped the main engine relay, alternator fuse, ignition relay with my running 92 but none of them fixed the problem. I found somewhere else that the ecu might need to be flashed into relearn mode and it may not be recognizing the key and causing it to not give any spark...does that seem right?

Hi, I'm a new 90 LS400 owner and I would like to ask you a little question, but I hope you've got the problem with your car solved by now. My question is: where is the main relay located?

I would truly appreciate it if you can answer me...

Thanks

Hi and welcome,the main engine relay is located within the engine bay fuse box just to the rear of the battery,there are 2 slotted bolts to remove on the top cover and all will be revealed once the lid is off,I think the relays are described on the inside of the cover.

[biggest424]

hi billy,

i put the ground wires on manifold and valve cover,but still no start.

i also checked the sensors with my ohmmeter and got good readings.

i then tried the meter on the coil pack wire plugs.i realised when the ignition key was off i got reading but if i turn ignition to on position the meter goes to 000.

should this happen???