Coil test result - JeepForum.com
 
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post #1 of 3 Old 06-13-2017, 10:22 AM Thread Starter
Karlinwa
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1989 FSJ Cherokee 
 
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Xj Coil test result

1989 XJ 4.0 new crank position sensor Sudden new crank no run , tested coil 5.4m across secondary been told reference is 12 is this low enough to cause no run?
Thanks in advance.

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post #2 of 3 Old 06-14-2017, 07:40 AM
cruiser54
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First off, don't assume your new CPS is good. Test it:

http://cruiser54.com/?p=50

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post #3 of 3 Old 06-14-2017, 09:55 PM
BagusJeep
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A low reading may not mean anything, the coils are so fine it may just be a temperature variation.

It may also indicate that there is an internal short between those coils. This will lower the amount of voltage available at the plug. Again this may not stop the engine, the 20kV your coil may be capable of is only rarely used, the voltage to ionise the gap between the plug points can be as low as 3kV. Hence sometimes a shorted secondary will still run, depends on where it is shorted. I woudl start off with the basics before changing the coil and the CPS and control unit are the place to start.

Have you checked for spark at the plugs, first thing to check?

Next thing to check is whether you are getting a grounding signal on the negative side of the coil, I think it is a grey wire. take this off and see if it beats in time with turning the engine over. You can use a meter for this or a test light.

If it is beating, the CPS is fine.

Then check the coil positive side for 13V in Start and Run. Sometimes the ASD relay gives trouble, without voltage to the coil, injectors and fuel pump it is not going to start.

Check for voltage at injectors and pump.

If all working fine but no spark you can see, I would suspect the coil was not man enough to ionize the air in the gap. As long as your plugs are correctly gapped, it would pinpoint the coil as the issue.

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