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Thinking the ecu is bad but want to be sure. Have a no start but does crank. I attempted to begin with a 5v reference check but not to confident in the test. Took the cam, crank, and COP ignition coils and all have 3 wires each. I assumed these wires are ground, power, and signal. I got 12volts of power for each feed and good ground, and no signal voltage. Is this enough to say bad computer? 12v to high for sensors? Shouldn’t it be 5?
Thanks for the reply, I’m very new to this. I have no spark, soi felt the need to start there before compression and fuel. (Installed a new fuel pump before this) haven’t checked compression or fuel pressure. The spark plug wells and COP coils were filled with oil. I was going to replace them but wanted to test the coil. It’s a three pin. The harness gives a 12 constant power and the ground is good. Nothing from signal and no flash when probed with a test light and engine cranking. It used to have some codes a year ago but I gave Up at that time. so I’m not sure if that erases codes overtime.now it has no codes but cranks . Any way I can “ be the signal” to makes sure the coil on plug works?
The signal from the PCM to the coil is very weak, and won't show up with a test light (incandescent, LED or otherwise). Best choice for verifying signal is with a scope.
This SD video demonstrates how to 'be the computer' with these coils:
I understand why you're not worried about injector pulse, fuel, or compression just yet, since you don't have spark. However, knowing if you have those other things can help you get a better idea of where you're headed with your diagnosis. For example, missing spark but not injection pulse might suggest the cam/crank signals are OK. Missing both might suggest an input problem.
update: I did have a voltage reading on my signal wire for the coil ( COP type). as suggested i was not able to pick it up with a test light due to low voltage. Used a multimeter and this signal wire had a voltage reading of 9mv in the on pos. when cranking it went to 45mv. These readings seem low for a signal. Should i expect to see a higher voltage? if so possible reasons; short or ECU? also have not gone around to getting a scope yet
Sal209120 wrote: update: I did have a voltage reading on my signal wire for the coil ( COP type). as suggested i was not able to pick it up with a test light due to low voltage. Used a multimeter and this signal wire had a voltage reading of 9mv in the on pos. when cranking it went to 45mv. These readings seem low for a signal. Should i expect to see a higher voltage? if so possible reasons; short or ECU? also have not gone around to getting a scope yet
That 45mv cranking might be your DMM averaging trigger pulses in with the base ~0 v. If your DMM has a bar graph manually rangeing to 6v and watching the bar graph might show pulses. This works with my Flukes, as a quick and dirty test, but they're fairly fast refresh at 40 Hz.
Dang I have no graph on my basic Multimeter. Any product you recommend I try to see this pulse? I hope the signal is there and it’s just a bad ignition coil. But then all 6 coils would be bad, which I’m hoping for but not likely. This car does have 160k miles and the spark plugs never seemed to be Changed so I hope they are all bad and ecu is fine. Thanks again
Sal209120 wrote: Dang I have no graph on my basic Multimeter. Any product you recommend I try to see this pulse? I hope the signal is there and it’s just a bad ignition coil. But then all 6 coils would be bad, which I’m hoping for but not likely. This car does have 160k miles and the spark plugs never seemed to be Changed so I hope they are all bad and ecu is fine. Thanks again
I may try to experiment with this tomorrow on my Sentra. Let you know what I find.
I finally got around to trying this on my Sentra. Different YMM, of course, but the principle should still apply.
Short answer is yes! You can use a DMM to check for signal on the coil wire. First, a shakycam of my meter on the #1 coil control wire with the engine idling:
