1996 Jeep Cherokee Coil Intermintent power

Tiny
RAMFAM
  • MEMBER
  • 1996 JEEP CHEROKEE
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 13,500 MILES
Just purchased a Jeep and it stopped running on the 3rd day. Opened distributor Cap and found wire to be crimped up against the housing and cap (noticed an exposed wire. The Rotor tip was melted off. Replaced the rotor and Cap although it didn't start. No spark at Plugs, so tested power to the Coil. When I initially turn the key to on. I get 12V for about 1 second and then it goes out. When I crank it over. No power 12V power is read. Need some help. Thanks.
Saturday, December 13th, 2008 AT 1:28 PM

6 Replies

Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
Check for trouble codes, I believe you can cycle the ignition switch on and off, third time leave it on, watch the mil to flash, count flashes to get the codes. You just turn the key on til the dash lites come on, you don't crank it.

The ASD relay supplies voltage to the coil--injectors and whatever. During cranking if the computer doesn't see the proper cam and crank signal, it may not ground the asd relay.

You need to do some testing.
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Saturday, December 13th, 2008 AT 2:02 PM
Tiny
BMRFIXIT
  • MECHANIC
  • 19,053 POSTS
JD is correct
check ASD relay
what we found very common is the crank sensor

when cranking does check engine light goes out !
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Saturday, December 13th, 2008 AT 4:07 PM
Tiny
RAMFAM
  • MEMBER
  • 4 POSTS
I've switched the Relay with one of the other ones. I also did the check with the codes. It flashed Code 12. Basically telling me I disconnected the battery.

My main question is am I supposed to get a constant 12V or is it supposed to be just for about a second or two when I check the input to the Coil.

When I engage the ignition key, the Check engine light comes on, it also stays on while cranking, but it goes out when I stop cranking while the key is still forward.
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Saturday, December 13th, 2008 AT 4:38 PM
Tiny
BMRFIXIT
  • MECHANIC
  • 19,053 POSTS
No signal from the crank sensor or cam sensor
ASD relay will not allow the power to the coil
most common is a bad crank sensor
if you had broken wire in the cam sensor
need to have that fixed too
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Saturday, December 13th, 2008 AT 7:07 PM
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
I agree with the moderator. Something else, you might check for voltage at the injector/s with the engine cranking.

The asd relay supplies voltage to the coil--injector/s and the heater circuit of the o2 sensor, I'm not sure what else. If there is no voltage with engine cranking, that will lead you to the asd relay, that doesn't mean the relay is faulty. You'll have to check the relay circuits.

A lot of systems have an initial prime koeo, key on engine off, for a second or two. The computer may ground the asd relay for a second or so, then computer has to see the proper signals with the engine cranking, or it won't ground the asd relay. I have also heard of the o2 heater circuit causing problems on some systems. Sometimes I unplug all the o2 sensors, see if the voltage comes back on the other circuits.
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Sunday, December 14th, 2008 AT 11:10 AM
Tiny
RAMFAM
  • MEMBER
  • 4 POSTS
Well, it turns out it was the Crank position sensor. Problems a lot worse then expected. The Sensor was cracked, it happened when my wife floored the accelorator. Meaning I've got some issues with the Torque Converter.

I installed a new one, I first rotated the torque converter until the metal pad that causes the sensor to function was positioned right under the Sensor. The tolerance on the holes allow for a little slop so I didn't want it to low.

I cranked it a few times and removed it to see if there was any scrapes on it. Did not look like it hit, so I did the same procedure and re-installed it. Cranked it over and it fired right up.

The answer to my question: Yes there is only an intermintent Volt reading when the Key is positioned forward. It only last for about 1 second.

Next project See why sensor was broken. Could be the crank or the torque converter.

Thanks.
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Sunday, December 14th, 2008 AT 12:18 PM

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