no spark, injectors firing:cps good.

So 95 xj Sport, OBD1, 4.0 auto.
No spark
What I have tried:
checked codes: no codes
I have +12v to the coil.
I am not getting a pulsed -ve ground when cranking.
I believe the 2x cps are good and working, the node light on the #1 injector flashes continuously when cranking.
previous experience has shown when either cps is not working I only get an initial pulse on the injector node light then nothing. Also getting a strong smell on petrol when cranking.
I have continuity ( .2 ohm ) from the -ve coil loom plug to pin 19 on the pcm.
re checked the pcm ground connection-its good.
swapped in a known working PCM, same symptoms.

History: was driving fine no concerns, pulled it in to shed for oil and filter change and cooling system flush. no crank no spark.

just for shits and giggles I plugged in another coil- no spark.

Any ideas?

sorry that should read:
History: was driving fine no concerns, pulled it in to shed for oil and filter change and cooling system flush. crank & no spark.

i checked for resistance between the different pins at the cpm connector quite a few had a restiance around the 17 ohm mark.
.....my understanding was the wire that earthed the coil was single use IE that it was not joined to any other circuits.

Have you tried unplugging the CPS and then cleaning the connecter and plugging it back in. I have had this trick work on several jeeps that have had no spark issue. Also one time I was able to spray some degreaser down on the CPS and then hosed it off and had that fix it, my guess that time there was oil from the back of the valve cover or mud that had gotten on it and was causing it to not get the correct signal from the flywheel.

Have you tried a new coil or a known good working coil?

Yes on the coil.
Yer I am getting injectors so believed the cps was fine, cheap and quick to clean though

The coil shares in power (usually orange or orange with stripe depending on the year) with the injectors (the injectors trigger on the ground side in OBD 1-2. The power in is controlled by the ASD relay and is fused (20 amp if I remember correctly).

The out power from the coil is grounded in the PCM to trigger the coil. Maybe a grey wire in your year (it sometimes changes colors year to year). If you have power to the coil, you should have power all the way to the PCM. The PCM will pulse the voltage to ground to trigger the coil (most all coils trigger to ground, all the way back to non electronic points type ignition).

Best guess is the ground side wire between the coil and the PCM is open.

An off the wall possibility is a sensor is shutting down the PCM coil to ground trigger circuit. Never seen it before, but the programming for the PCM does change periodically and it may be something I just never had to deal with before. On some of the early models, when the MAP was way faulty and/or getting no power, the program would shut down the injectors. Sometimes the engineers change stuff just to justify the paycheck.

Just had another thought, maybe the high voltage is shorting to ground before (or in) the distributor before it gets to the spark plug cables. You mentioned you did a flush, you really have to be careful of coolant (like salt water), it conducts electricity way better than plain water and plain water can stop you in your tracks if it gets into the wrong spot. Plain water won't usually cause issues if you have less than 6 volts (like sensor circuits) you usually don't lose much amperage or have significant line loss until it gets above 9 volts. Coolant or salt water has significantly less resistance than plain water does.

no spark and the coil and PCM have been replaced with known good and still the same problem focuses the problem to wiring.

You have checked continuity from the coil to the PCM but have you checked for a short to ground on that same wire? (grey at the PCM, grey/black at the coil.)
There is also a connector near the battery that can corrode. Sometimes terminals in connectors can corrode to the point that even though they show good or "ok" continuity, they cannot carry a load. The demands of electron flow at low current such as a DVOM puts out is quite different that the load requirements of the coil itself.

You also state you have power to the coil...but you don't clarify if this is continuous or while cranking. It should only receive power while cranking. If it has continuous 12v with only key-on, that is a problem.

there's a ground on that side of the motor. make sure you didn't bone it during the filter change.

87manche said:

there's a ground on that side of the motor. make sure you didn't bone it during the filter change.

Click to expand...

Excellent point!
The ones 87manche is referring to reside on the stud that secures the dipstick tube to the block.

Digger87xj said:

Excellent point!
The ones 87manche is referring to reside on the stud that secures the dipstick tube to the block.

Click to expand...

it's always the last thing you touched

thanks for all of the input.
I got the FSM out and followed that.
I had to make up this tricky jumper with a .33 Mf capacitor.
first time i touched it to pin 19 on the loom side of the 60 way connector got this basterd nasty yellow spark.
pooped myself, Stopped re-read everything did it again got a sexy little blue spark.
same sexy little blue spark when i did it direct to the coil pins.
nothing definitive at that stage .
so i put it together and gave it a go, started up first time.
got me fvkd, but it works now.

got to love a jeep.