Rough idle following spark plug change - Jeep Patriot Forums
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post #1 of 14 (permalink) Old 02-09-2017, 10:47 PM Thread Starter
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Unhappy Rough idle following spark plug change

My 2008 Patriot WAS running great, but due to a drop in gas mileage from 19+ to 17mpg City driving, then discovering the plugs were suppose to be changed at 30k (I have 40k)..........I decided to change the spark plugs.

Replaced with original OEM NGK (ZFR5F-11)plugs, used antiseize and Dielectric on plugs. My gas mileage is no better and now my engine idles rough, it idles like the AC is on but it is not.

I made sure the gap was per owners manual .44.

Advise welcome!:

Last edited by 08Patriot=; 02-09-2017 at 10:55 PM.
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post #2 of 14 (permalink) Old 02-10-2017, 12:02 AM
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Mine never idled rough on the very rare occasion I used dash controls instead of a window crank for AC. It ran rough when I switched out for Champion double-platinum plugs, but once they were properly gapped(which I thought I remembered was .41, not .44), it ran fine.

Also, engine would sound different if an O2 sensor was bad, but then your check engine light would be on. Maybe air filter is getting dirty?

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post #3 of 14 (permalink) Old 02-10-2017, 07:51 AM
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Your fuel economy sounds rather low to start with. Regardless, if the problem started after changing the plugs, I'd bet on a bad plug or loose connection.
Be sure all the connections are secure.
If so, try disconnecting one at a time so see if you can isolate the problem to a particular cylinder.
Presuming you can, maybe you have a bad plug or a bad coil. At 9 years old, it could be a bad coil, though mine are still OK. (Don't jinx me!)

FYI, OEM plugs should come pre-gapped and if you messed with them that could be the problem.
From what I've read on other posts, .44 seems to be right, but there is conflicting info out there. DO you have a decal under the hood? Have you checked the owners manual?
Here's a thread I just checked: Spark Plug Gap question

Oh, I just realized this is your first post. Welcome to the forum!
Use the search window at the top right of this page and see what else you can find.
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post #4 of 14 (permalink) Old 02-10-2017, 03:52 PM
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Gap .43
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post #5 of 14 (permalink) Old 02-10-2017, 06:27 PM
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one of the leads/packs will be bad

your moving the leads has done something

...pull one lead only at a time and if there is no change in idling with one lead, then you have found problem. if each time you pull a lead, the engine gets worse then the problem is elsewhere
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post #6 of 14 (permalink) Old 02-10-2017, 06:54 PM
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Hi.
Welcome.
Is there a chance that you got some anti-seize compound on the porcelain insulators?
If so, that can cause a mis-fire. Anti-seize compound in an EXCELLENT conductor of high-voltage electricity....
As already mentioned, check your connections.
Did you have your battery disconnected while changing plugs?

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post #7 of 14 (permalink) Old 02-11-2017, 11:57 AM Thread Starter
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?

Quote:
Originally Posted by That phucker View Post
Hi.
Welcome.
Is there a chance that you got some anti-seize compound on the porcelain insulators?
If so, that can cause a mis-fire. Anti-seize compound in an EXCELLENT conductor of high-voltage electricity....
As already mentioned, check your connections.
Did you have your battery disconnected while changing plugs?
I put a very small amount of Anti-seize on the threads I don't know if it got on the Porcelain.
NO, I did not disconnet the battery, was I suppose to?
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post #8 of 14 (permalink) Old 02-11-2017, 11:59 AM Thread Starter
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Quote:
Originally Posted by RossoRacer View Post
Mine never idled rough on the very rare occasion I used dash controls instead of a window crank for AC. It ran rough when I switched out for Champion double-platinum plugs, but once they were properly gapped(which I thought I remembered was .41, not .44), it ran fine.

Also, engine would sound different if an O2 sensor was bad, but then your check engine light would be on. Maybe air filter is getting dirty?

The check engine lights has not come on and I changed the air filter with no change in rough idle.
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post #9 of 14 (permalink) Old 02-11-2017, 12:02 PM Thread Starter
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Clarify please.

Quote:
Originally Posted by harold View Post
one of the leads/packs will be bad

your moving the leads has done something

...pull one lead only at a time and if there is no change in idling with one lead, then you have found problem. if each time you pull a lead, the engine gets worse then the problem is elsewhere
Are you referring to the wires that connect to the ignition coil "Leads"?
Am I suppose to disconnect one lead with the Jeep engine running?
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post #10 of 14 (permalink) Old 02-11-2017, 12:12 PM
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As long as you didn't have anti seize all over your fingers while handling the plugs, you should be okay that way.

I generally disconnect the battery while doing the plugs and air filter. This allows the ECM to re-learn it's fuel trim mapping based on the new plugs. It gives me an opportunity to clean the battery terminals, too.
Your idle might be even worse after doing that but it should correct itself in short order.
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post #11 of 14 (permalink) Old 02-13-2017, 01:20 AM
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Quote:
Originally Posted by 08Patriot= View Post
Are you referring to the wires that connect to the ignition coil "Leads"?
Am I suppose to disconnect one lead with the Jeep engine running?
yes and no

if you are confident, then yes

if not, no

what i am trying to get you to establish is if you disable one cylinder, does that change how the engine runs?

theory - if you disable cylinder 2 for example, and it idles the same as when it is connected, then you have established there is a problem there and you can investigate (be it broken plug or coil pack or lead)

if that makes sense
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post #12 of 14 (permalink) Old 02-13-2017, 11:42 AM Thread Starter
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Quote:
Originally Posted by harold View Post
yes and no

if you are confident, then yes

if not, no

what i am trying to get you to establish is if you disable one cylinder, does that change how the engine runs?

theory - if you disable cylinder 2 for example, and it idles the same as when it is connected, then you have established there is a problem there and you can investigate (be it broken plug or coil pack or lead)

if that makes sense
I will try that, Thanks!
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post #13 of 14 (permalink) Old 02-13-2017, 11:44 AM Thread Starter
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Question

Quote:
Originally Posted by harold View Post
yes and no

if you are confident, then yes

if not, no

what i am trying to get you to establish is if you disable one cylinder, does that change how the engine runs?

theory - if you disable cylinder 2 for example, and it idles the same as when it is connected, then you have established there is a problem there and you can investigate (be it broken plug or coil pack or lead)

if that makes sense
Yes, now that you clarified. Do I disconned the lead
while engine is running?
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post #14 of 14 (permalink) Old 02-13-2017, 06:58 PM
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Yup.
Doing this while it's running will give you a check engine light though.

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