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sprinkles08
sprinkles08, ASE Certified Technician
Category: Jeep
Satisfied Customers: 21601
Experience:  Chrysler/Dodge/Jeep Master Certified, ASE Master and Advanced Certified, Trans and Hybrid Specialist
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Installed a new ignition coil rail and it does not start,

Customer Question

installed a new ignition coil rail and it does not start, almost sounds like it is not timed right, when I place the old rail on it starts, but in testing #2 does not spark on the old rail. any idea? Thanks
JA: What is the voltage at the battery?
Customer: Brand new battery
JA: What is the model/year of your Jeep?
Customer: 1999 jeep grand Cherokee lorado 4.0 6 cylinder
JA: Are you fixing your Grand Cherokee yourself? What have you tried so far?
Customer: new PCM, new CPS, new spark plugs, new fuel filter, new throttle
JA: Anything else you want the mechanic to know before I connect you?
Customer: maybe the grand Cherokee has two different coil rails for that year?
Submitted: 1 month ago.
Category: Jeep
Expert:  sprinkles08 replied 1 month ago.

Hello and welcome to JustAnswer!

There are quite a few things that could cause a no start condition and it's very possible that there is now a combination of problems with all the parts that have been replaced.

The first step in diagnosing the problem is to use a scan tool or code reader to see what fault codes are currently setting. Do you know what codes are setting?

Customer: replied 1 month ago.
Tested the old coil rail which is special to this engine, the # 2 cylinder was not firing when grounded. Had the car codes pulled up previously and showed 2,4,6, cylinder not firing. This is the second rail ordered and they both do not allow the car to start where the old ignition rail starts but misses on #2. Trying to figure if the firing of the new rails throws the timing off.
Expert:  sprinkles08 replied 1 month ago.

The first step in diagnosing the problem is to use a scan tool or code reader to see what fault codes are currently setting. Do you know what codes are setting?

Customer: replied 1 month ago.
Engine code PO304, PO302, PO306
Expert:  sprinkles08 replied 1 month ago.
Is number two the only cylinder missing spark?
Customer: replied 1 month ago.
tested the ignition rail by using a steel rod grounded to the frame and holding it 1/2 inch from the rail to generate a spark, the old rail showed number 2 cylinder with no spark. The curious thing is the new rail when starting turns over but will not start, like it is retarded timing wise. I have been all over the Internet searching and this is a real issue with many similar 4.0 jeeps. So what could change the timing with a new rail, there must be different capacitors that delay the spark in the new ignition rails is the only thing I can think of and trying to see how and if any adjustment can be made. If it was not for the old rail to test back....thanks
Expert:  sprinkles08 replied 1 month ago.
With the replacement coil plugged in have you checked for spark on every cylinder?
Customer: replied 1 month ago.
Will test the new rail in the same way as old rail, impossible to test when Installed. Also will check Ohms in both to compare.
Expert:  sprinkles08 replied 1 month ago.

Let me know what you find!

Customer: replied 1 month ago.
Very much appreciated
Expert:  sprinkles08 replied 1 month ago.
You're welcome!