Maybe find the CPS signal input wire at the ECM, then check for voltage pulses (5V) during cranking. If no pulses, then could be open circuit (bad wire or connector), or bad sensor. If there are pulses, could be bad ECM or other problem with injector power (fuses and relays) or ground circuits. Pulses will be very short time duration, so need to look carefully.

Maybe before checking CPS signal, check if the injectors are pulsing (very short duration). There is a test light (noid light) for checking injector pulses, or use a multimeter with a mechanical needle, or a digital meter should dance around a bit (but might be hard to see). Injectors should receive 12V supply when the key is ON, then the ECM provides pulsed ground signals to activate the injectors. Connecting to the signal wire (injector still connected) should pulse between 12V and zero (when ECM pulse is on). This will help determine if problem is with fuel (if there are no injector pulses) or spark (if there are injector pulses).

 

Have you verified spark? You say coil packs are new-ish and wires...but have you actually checked for spark at spark plug?

You have two fuses for the coil packs, in Drivers Compartment Fuse Box, and a Ignition Relay (yellow, lefthand bottom corner of fuse box).

Bought a Dll, after previous owner had changed fuel pump, after having intermittent rough running issues, then quit completely, crank but not start. Dragged it home thinking CPS, swapped it without really verifying anything, still wouldn't start, swapped it again with another one l had lying around, still wouldn't start. Hmmm? Okay, time to verify some stuff. Fuel pump - good pressure and running while cranking. Pulled a plug, could smell gas, good, means injectors are working. Then cranked it over...no spark. Went to drivers compartment fuse box, both fuses good (believe it was #13 & #14...but its in the owners manual)...but as l was moving my hand around in there with test-light...the Ignition Relay fell out into my hand. Pushed it firmly back into its spot...cranked it over...fired right up.

 

I have a tool coming Wednesday to verify spark. I haven’t done that yet but just so far assumed that new parts wouldn’t be the issue.

So far everything points to some kind of electrical issue since all the hard components have been addressed.

I checked those relays you mentioned @ArmyRover , thanks for the heads up.

What’s so puzzling to me is just how sudden and out of nowhere this problem arose. This is a very well sorted Disco. Meticulously clean. Lives a posh life (for a 4x4) in a climate that’s extremely mild. Basically my point being, typically things break when operated at thermal or mechanical limits and this Disco doesn’t even come close to experiencing those.

The most recent repairs were when I replaced the O2 sensors a week before all this to fix a code related to B1S1. Code cleared and on we went.

I guess after verifying spark, my next step is just going to be finding a ECU/BCU and swapping those out.

 

Where would I put the MM probes in this situation? Sorry for the newb question. Still learning troubleshooting with a multimeter.

 

There might be something indirectly affecting the fueling, maybe the electrics powering the fuel pump or something wrong with the fuel lines. I think it is still a good idea to check the fuel pressure.

 

Pulled a plug after attempting to crank again to see if there was fuel in the combustion chamber, and indeed, smells like gas and there's gas on the threads of the plugs. So injectors indeed seem to be firing.

Just another data point: I was reading through the Nanocom manual and noticed an output variable they call Tooth Count. I cranked the engine over with the NC plugged in and the value didn't budge from zero. Assuming I conducted this properly, it should've I think? Here's the excerpt:

 

Alrighty, just tested cylinder 6 and 8 for spark and neither made any glowy action happen while cranking over. I didn't bother testing the rest.



OK just to recap everything in this megathread:

Air: MAF swapped out with a spare, no change (NC); IACV cleaned and appears functional, NC.
Fuel: Fuel pump replaced, NC; verified fuel getting sent to cylinders by removing spark plugs. Fuel pump is working, verified by activating the fuel pump relay using the Nanocom.
Spark: Despite having new coil packs, wires, and plugs, we have no spark.

CPS replaced twice.

 

Okay, we've verified...No Spark.

1) Now, did you check coil pack fuses in drivers compartment fuse panel? If no power at fuse, there are mega-fuses in Engine Compartment Fuse Box that supply interior panel). If fuse is blown, short in supply circuit to coils.

2) Did you make sure Ignition Relay (yellow one, left lower corner of fuse panel) is firmly in place? Relay could also be bad.

3) The relay will have supply voltage, ignition volt (when key is turned to second position) and a ground supplied by ECM (when key is turned to second position).

 

1. I visually inspected the fuses and didn't see anything out of sorts other than a bit of copper oxidation. Should I be using a multimeter to test these?

2. Yes! Thanks so much for mentioning that. It was all good. I swapped it out with some spares I had on hand and no change.

3. OK so this I need to read up on how to test properly, not sure and still learning how to use a MM.

 

Also just to bring back to the forefront - this was a days long degradation with worsening and worsening idle/starting issues, not just a hard on/off symptom.