No spark
#1
No spark
1994 Jeep Cherokee Country. Last week it cut out while driving. Tested Alternator, all good. Then it started running rough like i had gotten bad gas. Added Heet, no help. Rough starting then would cut off, and not restart and act like it was flooded. Changed plugs, wires, ignition coil, distributor cap, rotor, distributor pick up, crankshaft sensor. STILL NO SPARK!!! What Should I check now??
#6
CF Veteran
Joined: Nov 2010
Posts: 5,817
Likes: 105
From: In the middle of Minnesota!
Year: 1999
Model: Cherokee
Engine: 4.0
The ASD circuit is in play as well if memory serves me.
A longshot, but try swapping the ASD relay inside of the PDC (black box under the hood) with a non-critical relay. These relays are all the same part number so swapping is not an issue. And after verifying ASD circuit and freshening electrical grounds, then I'd say either the ignition switch or as a diagnosis of exclusion and after ruling everything else out, possibly the computer.
------------------------------------------------------------------
Spark: 12 volts from ignition switch to the ASD relay; when the key is first turned on the PCM provides a ground to the ASD relay to energize it, then the ASD relay passes 12 volts to the coil primary side. If no crank sensor signal is generated after a couple of seconds the PCM cuts the ground to the ASD relay (and fuel pump relay too) and that cuts power to the coil (and fuel pump). Key to START and once again the PCM energizes the ASD relay. Now, a critical element is the crank sensor--no signal from the crank sensor and the PCM won't trigger the coil to provide spark.
A longshot, but try swapping the ASD relay inside of the PDC (black box under the hood) with a non-critical relay. These relays are all the same part number so swapping is not an issue. And after verifying ASD circuit and freshening electrical grounds, then I'd say either the ignition switch or as a diagnosis of exclusion and after ruling everything else out, possibly the computer.
------------------------------------------------------------------
Spark: 12 volts from ignition switch to the ASD relay; when the key is first turned on the PCM provides a ground to the ASD relay to energize it, then the ASD relay passes 12 volts to the coil primary side. If no crank sensor signal is generated after a couple of seconds the PCM cuts the ground to the ASD relay (and fuel pump relay too) and that cuts power to the coil (and fuel pump). Key to START and once again the PCM energizes the ASD relay. Now, a critical element is the crank sensor--no signal from the crank sensor and the PCM won't trigger the coil to provide spark.
Last edited by tjwalker; 05-16-2016 at 06:59 PM.
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