2001 Grand Cherokee ignition coil failure
I would know, how can I test the ignition coil pack? and the voltages of the connector to be sure if I need buy another one, or know if the fail is in the wiring or other device. 2001 Grand Cherokee 6 Cyl. 4.0L Thank you. Does it trigger the check engine light? What is it doing? Is it misfiring? At what speed range(s)? Worse when damp out? Can you see any sparks jumping along plastic cover out under the hood at night? Is the cover clean of any greasy dirt? For actual testing - I am not sure there is a surefire test with the vehicle say turned off(unless of course if the coil were completely dead). Testing with an oscilloscope hooked up with engine running and possibly put under a load would maybe show something. Also, if that is where the suspicion lies, you could weigh out cost from junk yard to that of pro-analysis, and likely pro-replacement (as one might be too embarrassed to have it tested, say confirmed, then say you will DIY it at home?). Coil packs on Jeeps VERY RARELY fail entirely.....The most common problem is the plug boots rott and the spark leaks out to the head. That would cause a misfire in a cylinder or two, but not an entire pack. Chrysler uses a Main power relay....(A.S.D.- Auto Shutdown) to supply fuel pump , Ignition coil, Fuel Injectors, and possibly O2 sensor heaters with power. Does the truck Run????----What lead you to suspect the Coil??? Is there adequate fuel pressure????( The test port is on the center of the fuel rail, on the drivers side). While Junkyard parts do make great test pieces....Without a definite direction to follow, even used parts can get expensive . Throwing parts at it may turn out to be more of a burden than just breaking out and having it fixed. On spark testing tools... it appears that these tools, which look similar to spark plugs have a large gap of .25 inch. So I guess they have a much larger gap than a spark plug and that is the test. That if there is enough voltage to make a good spark with this testing tool, then your coil is working ok. A properly working electronic ignition system will be able to jump a spark across a spark tester's spark gap (preset at .25). You should see a crisp blue spark. Here is the tool... Kent-Moore J-26792 HEI Test A/C Plug Here are more spark testers... Spark Plug Testers Spark Plug Ignition Testers | Toolfetch Another thing to check for is cracks in the spark plug wires. If you see cracks, replace the wires. Or look at the engine running at night. See if there are any sparks on the wires. An interesting fact: Higher cylinder pressures and/or more fuel (more rich) will need a higher voltage for there to be a spark. Originally Posted by Bill190 An interesting fact: Higher cylinder pressures and/or more fuel (more rich) will need a higher voltage for there to be a spark. I remember when I was young in the business, Watching guys standing at an oscilloscope, talking about Low compression and firing voltages. I know now that it makes a difference, but after all of these years, I still have no clue as to why.... A 4.0 L jeep has no plug wires....It has one long Pack which spans the length of the engine, With 6 little Booties that fit over each of the plugs. I suppose you could unbolt it , flip it over and test under Cranking conditions, .......... Mother Mopar strikes again...the Harness is too short to lift the pack up, and there certainly isnt enough slack to flip it. If you remove it completely, you could probably OHM-Test it......The green/black wire in the connector is common power....So you would read from common to each of the triggers. reasonable guess at best. An open coil will indeed set a check engine light....but the truck would need to be running before the PCM self tests would occur. This is basically a simple No-Start diagnosis, which with basic preliminary knowledge and basic electrical tools (A 12v Circuit tester , I consider basic..) Should prove Do-able without Guesswork or PArts Tossing Originally Posted by Unclediezel I remember when I was young in the business, Watching guys standing at an oscilloscope, talking about Low compression and firing voltages. I know now that it makes a difference, but after all of these years, I still have no clue as to why.... I guess then we can consider ourselves lucky that high compression diesels then found another way to fire.
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