[Monkey Wrench]

there is a solid state relay available that has LED's that indicate, I believe fuel pump power and power to the ECU ( or DME) I dont think it does anything to verify if you have ignition pulse, yes there are other ways to verify ignition pulse.
here is what the solid state relay LED's can show:
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Ignition SW – (Yellow) Input signal to power up fuel injection system and enable fuel pump control.
Fuel Inj. Power – (Red) Output indicating the fuel injection system is powered up.
Ctl. Fuel Pump – (Blue) Input signal indicating the DME has commanded the fuel pump on.
Fuel Pump – (Green) Output indicating the fuel pump is powered up.
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verifying ignition pulse at the primary "proves or disproves " that the engine sensors are working, at least somewhat, the DME is performing its job of supplying a pulse to the power stage and the power stage is functioning and sending the pulse so far as the ignition coil primary.

troubleshooting a no start issue requires breaking the problem down, isolating probable causes, so going straight to weather or not the pulse exists is just basically helping isolate the problem.

hooking up an LED straight to the primary coil shows weather these parts are functioning , at at a glance , in real time. this is basically just "jumping to the chase" it is not a replacement for other checks and observations , they are still all valid.


If you found that there is no pulse then you can divide the problem further and check that the DME has power, whether it is properly grounded , if there is a voltage drop on the hot wire, if engine sensors are functioning , if the sensors are providing a pulse to the DME, if the DME is providing a pulse to the powerstage and if the power stage is working. You can involve an oscilloscope.

verifying a pulse to the primary does not provide info on weather you have fuel being injected or if there is a problem with the secondary or cap or plug leads or plugs.

Its merely a way of breaking the problem down more quickly than for example, looking for an engine sensor malfunction by employing an oscilloscope to to verify weather or not an engine sensor has a valid response to find out if this is the cause of a no start situation.

you would still want to do the above if the ignition has no pulse, and sure a signal could be flaky or intermittent. a scope may help see that or isolate it. Its possible but not normal to monitor a scope when driving, you might need an inverter to power it is it runs on 110

the LED is a lot easier to keep your eye on real time , when driving or upon encountering a no start situation. It is a lot more simple. it does not replace what a scope can show you.

an LED may show a intermittent problem of a missing pulse while driving, for example. if you observed an intermittent pulse at the primary perhaps coupled by an engine intermittent. you'd of course still need to delve into the actual cause. Then yes, you may need to break out the O-scope to properly prove the cause.

so lets just say for example you have a bad wire from a sensor, its creating an intermittent issue, so for this example, that's the actual cause. the result is that the car stalls or starts missing, its running very rough.

checking with a scope in this state may verify the sensor works fine, because it is when you checked it, but when the engine torques, when driving, it is pulling on a wire so then it is causing a intermittent pulse att eh primary coil. the problem is nothing to do with the coil, but you can see theresult of the issue there and so you have narrowed down the possibility of it being , for example , an interittent fuel pump.

by the way, the LED on the solid state relay wont tell you the pump is intermittent either, it merely verifies the contacts of the relay are trying to send power to the pump, it won't produce any info about dead or intermittent pump , or an issue of a bad lead from the relay to the pump.

basic troubleshooting normally involves breaking the problem down into sizable chunks. eliminating possibilities , zoning in to narrow down possibilities in order to isolate and prove the issue.

Yes there are other approaches and some different techniques which are also valid.

in essence checking if the primary has a pulse and seeing that it does would lead me to checking if it has fuel , maybe trying quick start to prove if its a lack of fuel issue and not a no spark issue.

the LED will not show if I have my plug wires mixed up or if I have forgotten to install the rotor in the distributor, or if I have a loose plug or coil lead. those are symptoms that come "after" the coil. its only a basic check that verifies the system prior to the coil is functioning, at least well enough to produce an ignition pulse.