1993 Jeep Cherokee No spark

Tiny
TDGAST
  • MEMBER
  • 1993 JEEP CHEROKEE
1993 Jeep Cherokee 6 cyl Four Wheel Drive Automatic

I am getting no spark when I try to start my Jeep. I have replaced plugs, wires, etc and still no spark. I have also went on to replace the coil, crankshaft position sensor, and camshaft position sensor. I still have no spark. All fuses are good. I am at a loss as to what I can check next. Any help as to what direction I can go now would be great. Thanks. Also has a new battery.
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Monday, September 6th, 2010 AT 6:12 PM

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Tiny
CARADIODOC
  • EXPERT
Hi tdgast. Welcome to the forum. I don't have a service manual so I'll try to do this from memory. You should have an automatic shutdown (ASD) relay. The first step is to determine if that is turning on. By '93, this was a Chrysler product and I think they were using the standard, fairly reliable circuit. You can measure the voltage feeding the ignition coil, (typically dark green with an orange stripe), the injectors, or one of the small terminals on the back of the alternator. Both small terminals on the alternator will have voltage at the same time, one will just be a little lower).

You should find full battery voltage on those places two times. The first is for just one second after turning on the ignition switch, then it will go back to 0 volts. The voltage will turn on again during engine rotation, (cranking or running). That voltage comes from the ASD relay which is turned on by the Engine Computer when it gets pulses from the two sensors you replaced.

As an alternative to measuring the voltage, you can pop the cover off the ASD relay and watch to see if it clicks when a helper cranks the engine.

When you replaced the crankshaft position sensor, was it new, and did it have a paper spacer or plastic rib on the end? One of them must be present to properly set the air gap. If there was no spacer, the sensor can be broken from hitting the ring on the flex plate or it won't generate a sufficient signal if it is too far away.

Caradiodoc
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Monday, September 6th, 2010 AT 6:55 PM
Tiny
TDGAST
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All parts were new when installed and I believe that there was a spacer. My uncle actually installed the sensors. I will check the things you mentioned, thanks for the insight.
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Monday, September 6th, 2010 AT 7:04 PM
Tiny
CARADIODOC
  • EXPERT
If the crank sensor came from the dealer, they should have provided the paper spacer. It will slide off when the engine is started. Many aftermarket sensors have a plastic rib molded in that wears away as the engine runs. When those are removed and reinstalled, you are supposed to cut off the remaining rib and use a new paper spacer.

Just thought I'd mention that in case you plan on removing the sensor to inspect it.

Caradiodoc
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Monday, September 6th, 2010 AT 7:49 PM

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