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Unread 08-04-2015, 03:15 PM   #1
neuman
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2008 Jeep Grand Cherokee 4.7 v8 running rough after..

I have a 2008 Jeep Grand Cherokee 4.7L Flex Fuel V8. I recently changed the spark plugs (all 16) purchased mopar plugs from a dealer on eBay.

Broke one ignition coil (first one pulled off), replaced it with a ignition coil from o'reilly auto parts.

Now my jeep is running like garbage. I was overdue on spark plugs (didn't change bottom plugs at 102k miles, it had 135k miles) jeep drove worse after I changed the plugs then it did before. Feels like a misfire when you take off and just driving normal, no codes coming up. Took it to the dealer and they can't find anything. I get about 16 MPG highway vs 19/20 before the spark plug change. Has an odd sound (howling like) when throttling. Again, this all started right after I changed the spark plugs.

Any ideas?

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Unread 08-04-2015, 03:17 PM   #2
paroxysym
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are they gapped properly?
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Unread 08-04-2015, 03:39 PM   #3
RCS1300
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Did you use the right plugs?

Yours may be FR8TE2 Bosch Nickel Yttrium plugs for the intake and FR8T1332 Bosch Iridium plugs for the exhaust.

The problem may have been "Mopar" plugs from a Dealer on Ebay....
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Unread 08-04-2015, 03:40 PM   #4
paroxysym
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Quote:
Originally Posted by RCS1300 View Post
I do not have the HO 4.7 but I believe my 4.7 has the same electrical connectors.

Did you put back the electrical connector to the IAT sensor? Although that connector unplugged should have thrown a code.

Did you use the right plugs? For my Jeep Champion RC12MCC4 Copper Plus plugs were the correct ones.
yea I was going to say that maybe he unplugged something, and didn't plug it back in- as I did the same thing when I did my plugs this weekend. but it would have thrown a code.... plus id like to believe the dealer caught it too.

did you put ****ty gas in it?
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Unread 08-04-2015, 03:48 PM   #5
RCS1300
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Quote:
Originally Posted by paroxysym View Post
yea I was going to say that maybe he unplugged something, and didn't plug it back in- as I did the same thing when I did my plugs this weekend. but it would have thrown a code.... plus id like to believe the dealer caught it too.

did you put ****ty gas in it?
I looked up the spark plugs for that vehicle and they are special. One set for intake and one set for exhaust. Since revised my initial post #3.
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Unread 08-04-2015, 05:33 PM   #6
modernblueWK
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Neuman, verify that you installed the correct plugs. I installed a set of incorrect plugs awhile back after being sold the wrong ones. The jeep did not run as poorly as you describe but the mpg and power went down.

Check all your connections. You might unplug that new o'reilly coil and see how it runs. It could be a dwell issue with that coil. Pull that plug also and see what it looks like.
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Unread 08-05-2015, 08:45 AM   #7
neuman
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Yes, I installed the proper plugs. I verified the plugs on http://www.wkjeeps.com/wk_sparkplugs.htm but the eBay auction also confirmed it was the right plugs for my jeep. Ordered from stevewhitemotors, http://goo.gl/XDNduY similar to this auction. During the install I replaced them with the exact same spark plug I pulled out (newer plugs obviously ) I believe one plug had blue writing on it and the other had green. I did not gap them
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Unread 08-05-2015, 09:32 AM   #8
modernblueWK
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When I did my plugs 3-4 of them had gaps of .020 or so. The boxes were in good shape but the gaps were off. That may be your issue.
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Unread 08-05-2015, 09:43 AM   #9
RCS1300
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Try disconnecting the electrical connection to the new coil while idling to see if it runs smoother. If so, he new coil may not be a good replacement.

The reason I suggest this is that it is the only other item you changed during the last service.
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Unread 08-05-2015, 09:53 AM   #10
paroxysym
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you could always pull the coil pack and test it with a multimeter... did the same with mine when I did my plugs, just to see if after 153k any of them were dead. hell go through all of them and see if any of the other coil packs took a dump..


I think if one of the coil packs were acting up, even if it is brand new- it would through a misfire code/CEL
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Unread 08-05-2015, 10:05 AM   #11
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Quote:
Originally Posted by paroxysym View Post
you could always pull the coil pack and test it with a multimeter... did the same with mine when I did my plugs, just to see if after 153k any of them were dead. hell go through all of them and see if any of the other coil packs took a dump..


I think if one of the coil packs were acting up, even if it is brand new- it would through a misfire code/CEL
Most likely it would throw a code with a completely dead coil. A failing or lazy coil may not throw a code. Improper gaps could cause incomplete or improperly timed combustion which could cause the knock sensors to pull timing. It may not register a full misfire to throw a code.
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Unread 08-10-2015, 05:04 AM   #12
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Just getting ready to change my plugs...both top and bottom.
I got a complete set of 16 off ebay. I confirmed that they were the correct part numbers for both the top and bottom bank.
Each plug in a separate OEM box and labeled correctly.
I WILL confirm the proper gap before installing AND be sure to reconnect all items that are removed during the installation.
Probably have to remove the coolant container as well as the electrical stuff on the drivers side to get at the front two lower plugs.
I like as much room to work as I can get.

Keep us posted on your solution.
Thanks.
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Unread 08-26-2015, 11:56 AM   #13
neuman
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hdsport, how did your install go? Were the plugs gapped properly?

I have yet to check my plugs. I have been too busy with kids starting school. I plan to pull them out and check each plug within the next few weeks. Will report back once I resolve.
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Unread 08-26-2015, 06:32 PM   #14
hdsport
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Quote:
Originally Posted by neuman View Post
hdsport, how did your install go? Were the plugs gapped properly?

I have yet to check my plugs. I have been too busy with kids starting school. I plan to pull them out and check each plug within the next few weeks. Will report back once I resolve.
Intake plugs were a slight bit over so I tweaked them to spec.
The exhaust were OK and went in as is.

The install went slow because it was my first time.
First, I removed the engine covers.
Next I removed the coolant reservoir and just set it on the radiator.
I ordered in a 5/8 spark plug socket from NAPA with an integrated swivel but the OD was too big and the socket would not fit in the plug hole.
So, I knew my old Craftsman 5/8 spark plug socket fit in the hole so I tried the rear plug, exhaust. I had a little trouble wriggling the socket to engage the hex of the plug so I ground down the OD on my bench grinder to give me a little more play room. This worked great and I proceeded to change all 8 plugs on the Pass side. Top (intake) were easy. Used a lot of dielectric on the coil and jumper wire. Be sure to insert the jumper and listen for a 'snap' when it is seated in the hole.

Next, the Drive side was the bigger problem....I had to get my jeep mechanic buddy to remove the fuse boxes and tie the lower harness away from the exhaust plug area. This allowed easy access to the lower bank, front two plugs as well as easier access to the rear ones.. (I'm not confident with the electrical stuff so I had someone who is experienced do the removal and re-installation. Battery was also removed.)

Suggestion....I cut about a 6 inch piece of rubber hose that went over the plug (snug fit) and used this to start each plug into the threads. Also, a very little Silver anti-seize on each plug to aid in the installation. Once seated as far as I could go with the rubber, I just pulled it off and proceeded to use my 3/8 ratchet to tighten and finally a torque wrench to spec.

I would have no problem doing this job again.....with the experience that I have.
First time is always a little more of a learning curve.

Checked the engine on the computer when finished. No misfires, no codes and Jeep is happy.

Let me know if I can be of anymore assistance.
Take your time, the task is not that difficult, just takes some time.
Regards.
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Unread 08-28-2015, 07:43 AM   #15
neuman
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Thanks for the feedback. So yesterday I pulled the intake plugs off (only the front 6 as they were still hot and the back 2 were hard to reach) Figured I'd check the gap. Out of the 6, 2 were good 4 needed a slight fix and I mean slight, I don't see why it would be a problem. It was one line past or before the .040 (.038). It appears that the misfire I was feeling when driving is now gone (or better anyways).

Noticed I'm leaking a bit of coolant so I have to take it in the shop now (lifetime warranty).
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