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Old 03-18-2010, 11:24 AM
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RicardoJM RicardoJM is offline
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Default UZJ100 Ignition Coil and Plugs

Saturday morning my UZJ100 started idleing rough and would not accelerate smoothly. It was very apperant that something was not right and within a couple of miles the MIL (malfunction indicator light or check engine light) was flashing.

When I got home, I plugged in my code reader. My code reader is a very low end model with two aspects that I came to dislike; the cord is too short and it automatically clears codes after displaying them three times. I did not see the code with my reader because in the time it takes me to get down under the dash, it had cleared. Many thanks to Jeff Z. who let me borrow his Scanguage II. Using his code reader, I was able to see that the computer was reporting P0305. Some quick research on MUD and I found that my issue was related to cylinder 5; spark plug, ignition coil or fuel injector. The most common issue is ignition coil failure.

I picked up new spark plugs and an ignition coil at Groove. I found the ignition coil in cylinder 5 was not good and after swapping it out and putting in the new ignition coil the idle and power issues from the morning were resolved. The spark plugs for this truck are rated for 100k miles and my truck has 137k miles. I really don't know if my plugs have ever been swapped out; so I did this yesterday afternoon. This truck is very different than my FJ40; each cylinder has its own ignition coil and it must be removed to get access to the spark plugs. In this write up, I will cover what is involved with replacing spark plugs and ignition coil.

There are very few tools required to do this job. The tool kit in the truck has everything you would need if you had to do this job on the road; spark plug tool and 10mm wrench. I was at home, so I used a torque wrench. I also used extensions as they were handy for the plugs at the back of the engine. Here is everything that I used for replacing the spark plugs.



My truck has a pretty cover plate with a nice V8 logo. To remove this cover, you need to remove two nuts and two bolts. The cover will then lift straight up to reveal the engine.



There is an air intake tube assembly that must be removed to get access to the spark plugs on the passenger side of the block. To remove this assembly, you need to remove two bolts, two clamps and disconnect 4 hoses. You can then remove this assembly and have easy access to all four plugs.




Next you disconnect the clip that provides power to the ignition coil. Push on the tab to release the clip and pull up. The shadows make it a bit hard to see, but here is the clip removed.



Next you remove the bolt that holds the ignition coil in place and remove the ignition coil. I didn't snap a photo of the bolt, but you will know which one it is. If you are replacing the ignition coil, here is where you would swap in the new one.





The next step is to remove the spark plug. It is about 5" down the tube and here is where the extensions come in handy.



After checking gap is set at the factory, but it is good to check) the gap on your new plug to make sure it is at spec. Install the new plug by hand and use the torque wrench (13 ft lbs) for the final tightening of the plug. Put the ignition coil in, insert the bolt by hand and use the torque wrench (66 in lbs) for final tightening of the bolt. When putting plugs, bolts and nuts back; doing so by hand makes sure you don't cross thread. I found the FSM (two volumes) on e-bay a while back and am really glad to have all the detailed information in them.




The last step is to connect the clip that provides power to the ignition coil. You are done with the plug swap. Repeat the process for all plugs on the passenger side of the block. Before going to the driver's side re-install the air intake tube assembly.

Then go over to the drivers side and do the same. Access to the two cylinders at the rear can be made much easier if you remove the wiring harness wire and the bracket it hangs on. Access to rear most cylinder is the tightest. Most people that have posted up indicated that two 3" extensions worked best. I found that approach worked for me as well. When you are all done, replace the engine cover.




After replacing my plugs I notice an improvement in power and smoothness. It is not dramatic, but it is noticeable. My old plugs were very clean but also very worn; the gap was right at the edge of acceptable. I took my time as I did this work, checking and double checking as I went along. It took 2.5 hours.
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Old 03-18-2010, 11:51 AM
Phrog Phrog is offline
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Great write-up! Thanks for posting.

-Phrog

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Old 03-18-2010, 12:09 PM
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Great writeup Ricardo

Top notch work as always
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Old 03-18-2010, 02:08 PM
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Nice work, Ricardo. Only think I'd add that I do differently is I always duct tape the plug socket to the extension- helps to insure I don't leave anything behind when I pull out... also, did you put any anti-seize on the plug threads?
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Old 03-18-2010, 04:51 PM
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Quote:
Originally Posted by nakman View Post
Nice work, Ricardo. Only think I'd add that I do differently is I always duct tape the plug socket to the extension- helps to insure I don't leave anything behind when I pull out... also, did you put any anti-seize on the plug threads?
That is some good advice. On every plug, it took a bit of wiggle to get the socket to release from the plug. By the 8th one, I got the routine down. Duct tape would have made it much easier.

No anti-seize on the threads. I had read both sides of this debate. The plugs I pulled did not have it and all of them took some muscle to break free. Once the initial bond was broken, they came out with finger pressure.
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Old 03-18-2010, 05:07 PM
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DaveInDenver DaveInDenver is offline
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Nice write up Ricardo. As always.

I always anti-seize my plugs using the copper stuff. Actually I slather anti-seize on everything for that matter. But on the 22R it's not uncommon for the 'breaking loose and finger tight' part to be because you are bring threads from the head with you. I have this fancy NAPA spark plug hole Helicoil kit just for this...
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Old 03-18-2010, 05:30 PM
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nakman nakman is offline
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I always anti sieze mine too.. but didn't realize there was a debate? I'm just paranoid that the "extra muscle" required to break them free will just bust the thing.. then an hour job turned into a weekend job just like that. but hey I'm no mechanic, we all know that!
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Old 03-18-2010, 05:48 PM
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farnhamstj farnhamstj is offline
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Nice work, good write up.
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Old 03-18-2010, 06:02 PM
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What'd the old plugs look like? just curious...

I always anti seize mine too, didn't realize there was a debate either... Had too many "almost" not come out, or come out with half the threads.
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Old 03-18-2010, 08:25 PM
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Three Wheel Ben Three Wheel Ben is offline
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Ricardo,

You can tell if the plugs are original by a little painted/stamped mark on the very top. Sometimes it is a letter and sometimes it is a shape. Only has it from the factory, replacement plugs don't have them.

Antiseize = good, unless it is a Land Rover, then the plugs won't ground.
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