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93 Jeep Cherokee has very weak spark from the coil and will not start

Have tried everything but a (crank position sensor) but I think this is doubtful because weak fire means that it is triggering the ign. system. Injectors fire perfect with a noid lite. How ever I dont think the signal from the distributor (cam position sensor) has anything to do with Ignition fire. I would like to know what makes the ignition fire weak or strong. I thought that if the crank position sensor sent the magnetic pulse to the PCM its job was over with even if it were a weak or strong signal. The PCM tells the coil to fire but what determines how hot the spark gets. Could it be dwell time or something like that? I know I will probably figure this out sooner or later but if someone has had this same problem it would save me a lot of diognosing. Im getting lazy at 64yrs old. HELP !!!!!!!!!!

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  • Cars & Trucks Master
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You are correct in your understanding. If the coil has at least 12 volts and gets a ground signal from the computer, the coil should fire. The coil actually sparks when the ground is removed.
The cam and crank sensors tell the computer when the cylinders are at top dead center which also opens the injectors.
Have you checked to see if you have battery voltage at the coil, and tried another coil ?

Posted on Dec 12, 2012

  • Steve Sears Dec 12, 2012

    Yes I do have battery voltage at the plugin on the coil and it is a new coil

  •  Stephen
    Stephen Dec 12, 2012

    Do you know if you can power the coil and make it spark correctly by grounding it ? Any chance the coil wire is bad ?

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SOURCE: 96 jeep grand cherokee 4.0

change the computer .... PCM get a used one it fixed mine had same problem

Posted on Feb 19, 2009

  • 14036 Answers

SOURCE: hello im a mechanic at

SOUND LIKE PROBLEM IN THE PCM IT CONTROLS FUEL INJECTORS. THE PCM DRIVING CIRCUIT BOARD NOT CONTROLLING FUEL INJECTORS. YOU NEED A GM TECH 2 SCANNER TO RUN DIAGNOSTIC CHECK ON PCM CONTROL CIRCUITS TO SEE IF PCM IS IN FAULT.

Posted on Jun 24, 2011

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SOURCE: 1996 Jeep Grand Cherokee No Start

i have a 1996 jeep grand cherokee and im not getting spark to the plugs.i replaced the crankshaft sensor and ignition coil already and still having problem.if i replace the camshaft sensor would that fix the problem ??? Or what should i do ???

Posted on Jul 23, 2012

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