1993 Jeep Grand Cherokee No power to coil and no spark

Tiny
PLOCO
  • MEMBER
  • 1993 JEEP GRAND CHEROKEE
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 223,000 MILES
I have a 1993 Jeep Grand cherokee laredo 6cyl 4x4 auto trans. Before I tuned up this vehicle it would start fine sometimes and wont start other times and get no spark off of the coil. I replaced the cap, rotor, plug wires, plugs, coil and the crank position sensor. It started up the 3rd try and test drove it and the next morning it didnt start. I checked for spark off of the coil and no spark. Did not replace the modulator in the distributor. Also the fuel pump did not work but I tested the fuel pump and it works and replaced the relay switch and has power on the fuse box in the engine compartment. I tested the relay by removing the cap and turned the key to on pos. No spray off fuel hose. But when I moved the relay switch to make contact the pump worked but only when I did that. What could be the problem? Its like the power got cut off to the coil. And the fuel pump has power on the relay pluged into the fuse box but wont activate when the key turned on. Thanks for your help.
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Saturday, October 30th, 2010 AT 10:36 AM

6 Replies

Tiny
JDL
  • EXPERT
Any applicable mil codes? The cam sensor is in the distributor. The computer has to see both cam and crank signals or it won't ground the relays, asd and fuel pump.

To check for mil codes, you turn the key just till the dash lites come on, no further, then cycle the key, on--off, on--off, on. Then the mil starts flashing, you count the flashes to get the codes. Your looking for two digit codes.
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Saturday, October 30th, 2010 AT 12:55 PM
Tiny
PLOCO
  • MEMBER
Thanks guys. I havnt checked the codes yet. And the cam sensor is under the plate in the distributor with the set of wires that comes out of it? Thats probably it. Thanks again guys. This site is the best for the do it urselfer. Ill check the codes and It will be till the 17th of this month till payday to replace the cam sensor then I can reply back and let you know if that worked.
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Saturday, October 30th, 2010 AT 8:47 PM
Tiny
MAVERICK777
  • MEMBER
I purchased a new jeep May of 1993, one month and it would not start, dealer changed coil, six more during warranty time, then august 2005 it happened again, I pulled on the wire loom in the area of the coil, it stared, I went and pushed down on the wire loom and it died and would not start, I checked the two wires going to the coil and found a plug connector, between the wire loom and coil was bad. I cut the two wires and connected the wires direct. From 2005 to present day 2016, it has not had any more problems, it started every me and has never died. MILAGE 197,445.
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Thursday, August 25th, 2016 AT 12:50 PM
Tiny
LOUIEG1979
  • MEMBER
@maverick777

any way that you can send me some more info on how you did this? What is the wire loom?
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Monday, January 15th, 2018 AT 2:04 PM
Tiny
LOUIEG1979
  • MEMBER
I am having the dreaded no spark issue on my daughters 1995 with the 4.0.
Parts Replaced:
coil
Crankshaft position sensor
Cap and rotor
wires and plugs are all good
checked fuses
fuel pump is working.

Seems like there is no power going to the coil.

Help!
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Monday, January 15th, 2018 AT 2:06 PM
Tiny
CARADIODOC
  • EXPERT
You have to understand how this system works to know how to diagnose it. It's identical to most other brands, but the part names are different.

The Engine Computer grounds the coil in the automatic shutdown, (ASD) relay for one second when you turn on the ignition switch. That sends 12 volts to the ignition coil(s), injectors, alternator field, oxygen sensor heaters, and fuel pump, or it grounds a separate fuel pump relay when one is used. The fastest test is to listen for the hum of the fuel pump for that one second.

Once the engine is rotating, (cranking or running), the computer needs to see signal pulses from the crankshaft position sensor and the camshaft position sensor to know it's time to turn the ASD relay back on. That is done so if a fuel line is ruptured in a crash, the pump won't dump raw fuel onto the ground where it would be a major fire hazard. With a ruptured line, there can't be any fuel pressure. With no fuel pressure, no fuel will spray from the injectors, the engine will stall, there won't be any sensor signal pulses, and the computer turns off the ASD and fuel pump relays. The fuel pump stops pumping fuel.

It's common for a failed cam or crank sensor to not set a diagnostic fault code just from cranking the engine. They usually only set while a stalled engine is coasting to a stop. Also, if the battery was disconnected or run dead, that will erase any fault codes and that valuable information will be lost. When there is no fault code related to a crank / no-start, you need to connect a scanner to view live data, and see what the Engine Computer is seeing. I have a Chrysler DRB3 for all of my vehicles. That lists both sensors with a "No" or "Present" during cranking to show if those signals are showing up.

Another fast way to determine if the ASD relay is turning on is to measure the voltage at the ignition coil or any injector. Look for the wire that is the same color at every injector and the ignition coil, or you can use either small terminal on the back of the alternator. A test light works best for this test because digital voltmeters don't respond fast enough. Back-probe that wire, then watch when 12 volts shows up. That is a dark green / orange wire on cars and minivans. Not sure about Jeeps. You should see the test light turn on for one second, then turn off, when the ignition switch is turned on. That proves the ASD relay is okay and the computer has control of it. What is important is if that voltage comes back during cranking. If it does not, the problem is with one of those sensors.
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Monday, January 15th, 2018 AT 6:09 PM

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