940 DTC -RPM sensor signal absent intermittently help

I'm not sure if this should be in this section or the performance one, so feel free to move if needed. The car is equipped with a wasted spark conversion and Stage1 chips. I'm running a MSD coil #8239 and an AEM 3-channel igniter. Also for about a month prior to the no-start condition the car was only cranked up and idled for a few minutes two to three times a week. '95 944t

OK so I've been hunting down what was cranking no-start and now that the car is running again I'm getting a flashing CEL under load and DTC 2-1-4(no other codes in fuel or ignition). Prior to this I diag'd the car out to a bad CPS and replaced it with a new Beck/Arnley unit. There were no codes during the no-start phase of things. The new CPS got the car back to a starting and running state, but you can only just crack the throttle before it starts acting up. The car idles reasonably smooth. Primary and secondary sides of the coil test good. The spark plugs are clean and less than 1k miles. I Ohm'd out all the wiring, connections and solder joints and they seem fine. The injectors are working. The tach seems to be giving accurate readings, but that's just a guess. I haven't been able to find a test procedure for the CPS, is there one? The tone ring seems OK looking through the CPS hole, but I guess it could be damaged in some way that doesn't cause a noise while spinning. And if my memory is holding out the CPS mounting bracket is in a fixed position, so nothing needs to be adjusted. I'm guessing I got a DOA sensor, but I wanted to see if I should be checking something or somewhere else first. Thanks

I have gotten a bad brand new sensor. It gave me a no start problem when that happened on my wagon. It was a bougicord one which is the OEM brand of sensor. So, it happens. A Beck Arnley one is usually reboxed OEM. If all the wiring is good then the only things left are the EZK box itself or something like the sensor. That is if there isn't anything wrong with the tone ring. If you have to check out the tone ring. You can remove the starter and get a good look at the condition of it.

OK well I guess ordering another sensor isn't too much trouble, finding a good EZK might be a bit more fun Anything I should double check before I head that direction?

If the wiring is good and the crank sensor can be relied on. Then it's the ezk box that is left in the chain of operation. You can start your trouble shooting at the ignition amp. Check that it has an input signal. If it doesn't work back to the sensor and computer. If there is an input but no output then the amp itself is faulty or if it's switching then move to the secondary ignition system like the coil, cap, rotor, and wires. Check the coil switching with a test light.

OK that's where I was on this too. I've got another sensor on order, so while I wait I'll double check all the wiring I previously tested. I know the coil tests fine. Plugs and wires are good. I swapped in a new spare AEM ignition driver for testing pre-CPS replacement, so I'll give that a shot again. Something I was thinking about today was the factory ignition module. As per the wasted spark installation guide I left it hooked up. I'll need to double check, but I don't think it's necessary anymore. If that's acting up could it be part of the issue? Some times when you get systems on top of systems components that shouldn't matter start to matter when they fail.

The ignition amp if the input failed could drag down the switching signal coming from the EZK box. I've never had that happen with an EZK but old electronics can do weird stuff.

Hooray it was just a DOA crank sensor. Thanks for the help!

Glad you got that sorted out.