No Spark

Have you checked for fuel pressure? You can also check for battery voltage on the dark green / orange wire in the coil pack, one of the injectors, or the small wires on the back of the alternator. Holler back with your findings.

I can't remember if the Neon uses a separate fuel pump relay, but regardless, if you don't have voltage to the dark green / orange wire in the coil pack, you don't have fuel pressure either. With a separate fuel pump relay, it is turned on along with the automatic shutdown (ASD) relay. Some models only use the automatic shutdown relay. In that case it runs the fuel pump along with the coil pack, injectors, and alternator.

Here's where it gets misleading. Use your test light or voltmeter to measure the voltage on the dark green / orange wire in the coil pack or on any of the injectors. You WILL see voltage there for just one second as soon as you turn on the ignition switch, then it will go away. You will likely hear the hum of the fuel pump too for that one second. That's where the apparent fuel pressure is coming from. If you don't have voltage for that one second, we gotta go in a different direction.

What you will most likely find next is that voltage does not come back during engine cranking. That's why there is no spark and the fuel pump will not be running. The Engine Computer has not turned the ASD relay back on in response to engine rotation. To clarify what I'm trying to say, you must test for voltage on the dark green / orange wire while cranking the engine. The computer turns on the ASD relay when it sees engine rotation, (cranking or running).

When the computer doesn't turn the ASD relay on during cranking, it is because of a lack of pulses from the crankshaft position sensor or the camshaft position sensor. Most of the problems are caused by the camshaft sensor. The Check Engine light should also be on and there will be a diagnostic fault code stored in the computer's memory related to which sensor isn't working. If you get a code related to "cam and crank sync", the computer has shut the engine down to protect the valves due to a jumped timing belt. If the timing marks look like they're lined up correctly, pull the cam sprocket off and check for a sheared off dowel pin. That only pertains to the single overhead cam engine.

Caradiodoc

Wiring rarely causes a problem so before you tear harnesses apart, back-probe the connector pins and look for 5.0 volts on one pin and 0.2 volts on another. If you find them, and since you have new sensor installed, you'll save yourself a lot of time by reading any fault codes.

Caradiodoc

Hello,

I would check to see if the system has power to the injectors and ignition coil, there are a couple of fuses that need to checked as well as well as the auto shut down relay. I would also disconnect he oxygen sensors to see if that helps.

Here are some guides and engine wiring diagrams that will help you trouble shoot the problem and get the car running again.

https://www.2carpros.com/articles/how-to-check-a-car-fuse

and

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

and

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Please run some tests and get back to us so we can continue helping you.

Best, Ken

You need to test the CMH sensor if okay-check all the ground circuits on the computer-if okay have the computer further checked-

Any applicable trouble codes? You should be able to get some codes with the mil lite.

Did you check primary voltage at the ignition coil, engine cranking, dark green wire with orange tracer should be hot use a voltage tester. If no voltage, I'd have to check for proper cam and crank sensor signals.

Inspect and test the camshaft and crankshaft position sensor-

Check and test fuse no.21 20amp and the ASD relay

Otherwise you mean it will crank but not start? Has the Check Engine light been coming on? If so, have you read the diagnostic fault codes?

I don't know if this applies, but it's worth mentioning. It was somewhat common for the dowel pin between the camshaft and sprocket to shear off, and the sprocket would spin slightly on the camshaft. This would mimic a timing belt that jumped a tooth. The Engine Computer would know that from seeing the change in the relationship between the signals from the camshaft and crankshaft position sensors.

When it looks as though the timing belt jumped one tooth, the computer turns on the Check Engine light and sets a fault code related to "cam and crank sync". At two teeth off, the computer shuts the engine down to prevent internal damage. At three teeth off, open valves will hit the pistons as the engine coasts to a stop and would be bent.

There is a procedure to relearn the relationship between the two sensors when one is replaced. It requires the DRB3 scanner, but I've never actually had to do that. The computer always learned the relationship as soon as the ignition switch was turned on, and the engine started right away.

Is it possible the fuel pump isn't starting up? 80,000 miles is a little soon for worn brushes in the motor, but you might have a helper try banging on the bottom of the fuel tank while you're cranking the engine.

Woops, I see you listed no spark or fuel. That would sure lead to the sensors you replaced. To prevent overlooking something simple but unlikely, try switching the Automatic Shutdown (ASD) relay with one of the other ones, but next I think I would send you to the dealer to ask if it's necessary to perform the cam / crank sync relearn procedure. I suspect the sitting with the ignition switch turned on for 15 minutes will be an important clue.

Caradiodoc

Interesting observation. Remember, it can't spin very much or the valves will hit the pistons. I hope the dowel pin is the problem, but I've never heard of it causing an intermittent no-start.

Caradiodoc