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Ignition coil

2K views 19 replies 4 participants last post by  Digger84 
#1 ·
I have a 97 wrangler tj 2.5. Just did engine swap 95 into my 97. I have power to my ignition coil but not getting a spark. Brand new coil. Is there supposed to be a ground wire running to the coil anywhere?
 
#4 ·
Could is too vague to be useful you need to determine if the other wire the non hot one is getting a pulsed ground signal because no coil will make a spark without that pulsing ground

If it is and coil not making spark on primary wire then suspect the coil

If it is not then damaged wires or bad PCM or bad wiring to PCM or bad crank angle sensor

I would also verify pulsed ground to injectors and proper 5 volt output from PCM on the 2 wires that are supposed to have a 5 volt output
 
#5 ·
Could is too vague to be useful you need to determine if the other wire the non hot one is getting a pulsed ground signal because no coil will make a spark without that pulsing ground If it is and coil not making spark on primary wire then suspect the coil If it is not then damaged wires or bad PCM or bad wiring to PCM or bad crank angle sensor I would also verify pulsed ground to injectors and proper 5 volt output from PCM on the 2 wires that are supposed to have a 5 volt output
How do I check for the pulsing ground
 
#7 ·
Never did a 95 97 swap


If it was me I would pull the 2 wire plug off the coil and put a meter set to DC volts across the two leads on the harness and observe while cranking could use a 12 volt light instead of meter

Could also do same with any one of the injector harness plugs

Then make PCM is feeding plus 5 volts to cam and crank angle sensors speed sensor and MAP sensor as 97 PCM seem to fail that way often
 
#8 ·
Never did a 95 97 swap If it was me I would pull the 2 wire plug off the coil and put a meter set to DC volts across the two leads on the harness and observe while cranking could use a 12 volt light instead of meter Could also do same with any one of the injector harness plugs Then make PCM is feeding plus 5 volts to cam and crank angle sensors speed sensor and MAP sensor as 97 PCM seem to fail that way often
While checking volts on injector plugs, wasn't getting a reading when using both leads on the plugs. Only when I grounded it somewhere else I was getting a light. But when I checked my actual battery it showed it needed to be charged. And I was getting 5 volts on my cam sensor and 12 on my coil. And I also noticed it didn't pulse as I was trying to start it.

I know it's a lot thrown at you. I'm just trying to figure this all out with your help so I'm not shoving anymore money out than I need to
 
#15 ·
Cranking is about 85 to 150 rpm
So if a revolution is a cycle that is 1.5 to 2.5 Hz
But each injector only fires every other rotation so that is .75 to 1.25 Hz
Now with a single coil we get 3 per revolution on a six so that would be 4.5 to 7.5 Hz
Think even the cheapest harbor freight digital meter would report at the injector pulse frequency but granted the coil frequency would be more of a prob
however with the coil pack each only fires once pre revolution (as each pair fires twice every 720 degrees rotation) so pulse frequency on cranking 1.5 to 2.5 Hz but duration I am unsure of so for multiple reasons easier to use test light or meter on injector harness
 
#16 ·
Even at .75 Hz the sampling frequency needs to be at least 1.25 Hz (dictated by nyquist rate). I'd guess the cheapo mulitmeters are sampling at 1 Hz or less. Even most high dollar ones I don't think they sample much more than 4 Hz.

Like I said, wrong tool for the job. If you don't have a mulitmeter that can read frequency a test light is a good alternative. If you want more than that you'd need an oscilloscope.
 
#17 ·
Well took 12 volt car battery held red to pos and tapped black to neg at about 4Hz and did not go 12.6 to zero but steady change in numbers at about same freq as my tapping and never settled on any number with one of my free harbor freight digital meters

So not a good way to measure 4Hz voltage amplitude but appears to be a fine free tool to detect it

So looks to me like it would work fine for looking for injector pulse while cranking but not starting still not so sure about coil both because of higher freq and unsure of pulse duration

But I'll defer to the double Es if you say it is a bad tool for the job
 
#18 ·
Well took 12 volt car battery held red to pos and tapped black to neg at about 4Hz and did not go 12.6 to zero but steady change in numbers at about same freq as my tapping and never settled on any number with one of my free harbor freight digital meters So not a good way to measure 4Hz voltage amplitude but appears to be a fine free tool to detect it So looks to me like it would work fine for looking for injector pulse while cranking but not starting still not so sure about coil both because of higher freq and unsure of pulse duration But I'll defer to the double Es if you say it is a bad tool for the job
So with me not getting a pulse on the injectors, it could be a bad wire somewhere or bad pcm
 
#20 ·
The PCM has three plugs a black plastic one a gray plastic one and a white plastic one and each has three rows of wires

On the middle row of wires on the black plug near the middle of the row is an orange wire with key on it should have 5 volts that it supplies to the 4 sensors
 
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