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Discussion Starter #1
I bought a 98 zj with the 4.0 in it. Replaced the crank sensor and still no spark, gauge cluster voltage and fuel doesn’t work and the check engine light doesn’t light up ever. Tried pulling codes but it was failing to read it. Any suggestions on what to check next?
 

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On my 96 XJ with the 4.0 I had the same problem Turned out to be the cam sensor. Try unplugging yours and see if your gauges work and you can pull codes.
 

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If your symptoms are accurate, I think you might have a bad ECM. There is a known problem with the screws in the module being too long and causing it to short out. But check to see if you have voltage to the crank position sensor in the distributor and then to the CPS and throttle position sensor. If no voltage, this is the problem
 

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If your symptoms are accurate, I think you might have a bad ECM. There is a known problem with the screws in the module being too long and causing it to short out. But check to see if you have voltage to the crank position sensor in the distributor and then to the CPS and throttle position sensor. If no voltage, this is the problem
I do have voltage
On my 96 XJ with the 4.0 I had the same problem Turned out to be the cam sensor. Try unplugging yours and see if your gauges work and you can pull codes.
The cam sensor which is right on the distributor?
 

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id have to take a look to see if there’s power at the crank sensor but I’m 99 percent sure there is
 

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If your cam and crank sensors are working, the output side of them will make the volt meter cycle from 5V to 0 when you crank. The real readings will be in between, but it will show fluctuation
 

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If your cam and crank sensors are working, the output side of them will make the volt meter cycle from 5V to 0 when you crank. The real readings will be in between, but it will show fluctuation
How can you check the output side of them? Do you have wiring diagrams for each?
 

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I don't have wiring diagrams, but the way the pros do it is to stick a pin in the back of the plug and read off it. One wire should be hot all the time, the other will have fluctuating voltage
 

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But check to see if you have voltage to the crank position sensor in the distributor and then to the CPS and throttle position sensor. If no voltage, this is the problem
^^This is also important^^

You could have a fault in the security system as well. The security system can cut the voltage at the ignition coil. Usually, it will start but will die after a second or two.

I would also recommend a light layer of Dielectric grease on the ECU connectors. The pins can get corroded and just plain dirty.. The 93-96's ECU did have that bad connector on the ECU side of the connection, but I believe they had most issues worked out by 98.
 

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If it does wind up being the ECU, it is not the end of the world. I bought a used ECM about 7-8 years ago. There are many forums out there that said you had to get the ECU flashed. You don't. I didn't need to. It was plug and play. Just make sure you get one with the exact last 5 or 6 digits (enlarged letters in the part number on the upper right side) of the P/N on the face of the ECU sticker.

Welcome to the forums. It's always great to see another running ZJ out there on the road.
 

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Discussion Starter #14
Is
^^This is also important^^

You could have a fault in the security system as well. The security system can cut the voltage at the ignition coil. Usually, it will start but will die after a second or two.

I would also recommend a light layer of Dielectric grease on the ECU connectors. The pins can get corroded and just plain dirty.. The 93-06's ECU did have that bad connector on the ECU side of the connection, but I believe they had most issues worked out by 98.
Is there a way to tell or to bypass the security system?
 

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Discussion Starter #15
Well I have good power at the crank, cam, and throttle position sensor. Tried backing the screws out with no luck. Any other tips? I’d hate to have to buy a ecm since they’re $180 when I only paid $80 for the jeep lol
 

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Do you have fuel pressure?
 

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If no spark is the issue, have you checked your coil and have you determined the cam position sensor is working yet?
 

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But did the cam sensor out side fluctuate when cranking? If not, it is not working
 
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