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no spark at coil

B

bigdaddyround

NAXJA Forum User
Location
Killeen, Tx
I just replaced the Ignition control module and the coil because Oreily said they were bad. Bad tho they may be, I still have no spark coming from the coil. So I guess that means that there is no power to the ICM? I checked the Crank position sensor and it has the proper resistance. Looking at the Haynes manual, it gets its power from the ECU and thru the fuel pump. The fuel pump is running while it is cranking, so thats not it right? So it must be the ECU? Is there anything else that could cause this? I am so fed up with this Jeep. Please help me fall in love with it again.
 
bigdaddyround said:
I just replaced the Ignition control module and the coil because Oreily said they were bad. Bad tho they may be, I still have no spark coming from the coil. So I guess that means that there is no power to the ICM? I checked the Crank position sensor and it has the proper resistance. Looking at the Haynes manual, it gets its power from the ECU and thru the fuel pump. The fuel pump is running while it is cranking, so thats not it right? So it must be the ECU? Is there anything else that could cause this? I am so fed up with this Jeep. Please help me fall in love with it again.
Click to expand...
Do you have voltage to the ICM? Don't guess
It's one of the wires in the 3 wire plug.
 
Last edited:
On the three-wire connector to the ICM, it is "A", should have 12 volts from the B Latch relay. "B" wire in that connector is the ICM ground--it runs to the dipstick tube. There on the dipstick tube are also the grounds for the ECU and the o2 sensor. Make sure the dipstick tube grounds are stripped down to bare metal, treated with an anti-corrosive agent, and make the connections TIGHT.

Check the above and post up what you find.
 
they hooked up the ICM to a diagnostic machine and checked the coil with a Ohm meter. It should have 12v DC while the engine is cranking/running? If it doesnt, it is the relay or the ground? If it was the ground wouldnt there be some symptoms before it just quit all together?
 
bigdaddyround said:
they hooked up the ICM to a diagnostic machine and checked the coil with a Ohm meter. It should have 12v DC while the engine is cranking/running? If it doesnt, it is the relay or the ground? If it was the ground wouldnt there be some symptoms before it just quit all together?
Click to expand...
I had power to the ICM thru the wire joe mentioned. But there was no spark from the coil.
Try juggling your relays to see if it could be a bad relay or if you get 12 volts to the "A" side of the plug as joe mentioned.
Mine turned up good....you should get voltage with the key in the on position. If not you will need to work your way back from there.
 
Renix systems are PARTICULARLY susceptible to ground issues, and this accounts for a large proportion of the problems Renix owners experience. How is the unibody ground strap at the back of the head to the firewall?
 
bigdaddyround said:
dont know. gonna have to check it tomorrow. Another day, another jeep problem.
Click to expand...

Yeah, today my 265 air conditioning failed--driver's side window crank handle broke, so I rolled down the passenger's side window and opened all four vent wings, climbed in the driver's seat and pulled out onto the street, then I TRIED to turn on the blower--nothing.
 
Lets see, since I bought this thing in april, ive replaced all for brakes, had to swap in a 96 master cylinder and booster, replaced the fuel pump, the fuel pump filter, the fuel pump lockring, 2 output shaft seals, 1 rear diff pinion seal, diff cover gasket, fan clutch, pressure bottle and cap, thermostat, and i think that is it. And I always seem to find this stuff the day or two before I have a trip planned. Gotta love old trucks.
 
Ok, I checked the voltage coming from and going to the relay. Its only 1.5 volts on both sides. So it must be the ECU right? Im going to hit up the Pick and Pull and see what I can find.
 
Have you cleaned your C-101 connector at the firewall on the drivers side?
I cleaned mine.....but I don't think it was ever my problem...but it has been for others.
 
Yeah, the ECU is triggering the relays with grounds, not power. I would follow B.RAIDER's suggestion--hit the C101 connector but also check under the relays themselves for corrosion.
 
ITS ALIVE!!!!!! Went to the junkyard, found a ECU for 20 bucks, plugged it in and lo and behold, IT WORKED!!. I went ahead and got a new relay, cleaned all the connections, and cleaned the grounds. Fired right up on the first crank. Thank you so much to everyone who pitched in. Now the trip for tomorrow is back on! Long live the JEE!
 
Glad you got it!

Have a good time on your trip.

BTW, if you have the old ECU 5-90 would like to get it for testing. I will PM him to contact you.
 
Recommend you remove the c101, cut each wire one at a time and solder them together. Put some heat shrink on before you solder. I ruined my ecu in a short circuit in the c101.
 
Ron Hyslop said:
Recommend you remove the c101, cut each wire one at a time and solder them together. Put some heat shrink on before you solder. I ruined my ecu in a short circuit in the c101.
Click to expand...

Good point, those C101 connectors are bad news.
 
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