What are my plugs telling me?
#1
Newbie
Thread Starter
Join Date: Mar 2018
Posts: 3
Likes: 0
Received 0 Likes
on
0 Posts
Year: 1996
Model: Cherokee(XJ)
Engine: 4.0
What are my plugs telling me?
New XJ owner...1996 with 150k. After a couple weeks of driving it, it started running VERY rough at idle when cold for a couple of minutes and then would get better. Still was never what I'd call smooth. This coincided with a coolant and thermostat change, which was done because of overheating shortly after startup. I don't think it's relevant but didn't want to leave out the detail.
Pulled plugs this morning and I think what I'm seeing is oil fouling in #4 and possibly coolant burning in #5. See attached pic...
Thoughts?
Pulled plugs this morning and I think what I'm seeing is oil fouling in #4 and possibly coolant burning in #5. See attached pic...
Thoughts?
#2
::CF Moderator::
Join Date: Aug 2011
Location: Prescott, Az
Posts: 43,864
Received 1,524 Likes
on
1,236 Posts
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
Looks to me like #4 isn't firing.
#4
::CF Moderator::
Join Date: Aug 2011
Location: Prescott, Az
Posts: 43,864
Received 1,524 Likes
on
1,236 Posts
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
#5
CF Veteran
Join Date: Nov 2010
Location: In the middle of Minnesota!
Posts: 5,804
Received 99 Likes
on
88 Posts
Year: 1999
Model: Cherokee
Engine: 4.0
I'd try a new plug in #4, gapped to .035
As long as you're at it, would be a good time to get a compression test done. It's a great "snapshot in time" of the condition of the engine. A compression test can be very helpful in diagnosing anything internal that might be going on. Great data point for determining direction. Do all 6 cylinders, not just #4.
The compression spec for the 4.0 is 120-150 psi, with no more than a 30 psi variation between cylinders.
As long as you're at it, would be a good time to get a compression test done. It's a great "snapshot in time" of the condition of the engine. A compression test can be very helpful in diagnosing anything internal that might be going on. Great data point for determining direction. Do all 6 cylinders, not just #4.
The compression spec for the 4.0 is 120-150 psi, with no more than a 30 psi variation between cylinders.
#6
Junior Member
Join Date: Sep 2017
Location: Central NJ
Posts: 58
Likes: 0
Received 0 Likes
on
0 Posts
Year: 1999
Model: Cherokee(XJ)
Engine: 4.0
How many miles on these plugs?
#4 looks like it's oil fouled.
#3 looks like has splash deposits
#5 looks leaner than all the others.
If it were mine, I would install six new, properly gapped plugs, drive it about 50 miles and pull them out. Take the same picture and compare them to each other and this photo.
KenR
#4 looks like it's oil fouled.
#3 looks like has splash deposits
#5 looks leaner than all the others.
If it were mine, I would install six new, properly gapped plugs, drive it about 50 miles and pull them out. Take the same picture and compare them to each other and this photo.
KenR
Last edited by KenR; 03-14-2018 at 08:33 AM. Reason: Add info.
#7
Senior Member
Join Date: Sep 2008
Location: Sioux Falls, SD
Posts: 897
Likes: 0
Received 12 Likes
on
9 Posts
Year: 1999
Model: Cherokee(XJ)
Engine: 4.0L
Check the cap and rotor too. They may be worn. My 99s cap/rotor were completly shot when I purchased the Jeep. Quick replacement of everything but the wires and my MPG increased. Smooth as buttah too now.
Trending Topics
#8
CF Veteran
Join Date: May 2015
Location: Arizona
Posts: 4,481
Likes: 0
Received 16 Likes
on
12 Posts
Year: 97
Model: Cherokee
Engine: 4.0
Judging by how clean the bottom of the threads are on #5, It looks like it could be a replaced plug newer than the rest and correctly burning lean as these do, or it could "possibly" be burning coolant in that cylinder if it is the same age as the rest.
#9
Newbie
Thread Starter
Join Date: Mar 2018
Posts: 3
Likes: 0
Received 0 Likes
on
0 Posts
Year: 1996
Model: Cherokee(XJ)
Engine: 4.0
I installed new plugs after taking these out. I like the suggestions though...I'll drive a bit, pull and compare, and do a compression test while they're out.
I pressure tested the cooling system yesterday and it held for the most part, but had dropped to 15 psi after 15 minutes. If it is leaking coolant into a cylinder it's just starting.
I'm sure I'll know more after the compression test - thanks all for the suggestions.
I pressure tested the cooling system yesterday and it held for the most part, but had dropped to 15 psi after 15 minutes. If it is leaking coolant into a cylinder it's just starting.
I'm sure I'll know more after the compression test - thanks all for the suggestions.
#10
::CF Moderator::
Join Date: Aug 2011
Location: Prescott, Az
Posts: 43,864
Received 1,524 Likes
on
1,236 Posts
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
I installed new plugs after taking these out. I like the suggestions though...I'll drive a bit, pull and compare, and do a compression test while they're out.
I pressure tested the cooling system yesterday and it held for the most part, but had dropped to 15 psi after 15 minutes. If it is leaking coolant into a cylinder it's just starting.
I'm sure I'll know more after the compression test - thanks all for the suggestions.
I pressure tested the cooling system yesterday and it held for the most part, but had dropped to 15 psi after 15 minutes. If it is leaking coolant into a cylinder it's just starting.
I'm sure I'll know more after the compression test - thanks all for the suggestions.
#11
Newbie
Thread Starter
Join Date: Mar 2018
Posts: 3
Likes: 0
Received 0 Likes
on
0 Posts
Year: 1996
Model: Cherokee(XJ)
Engine: 4.0
About the same. A little less rough at cold start (not lumpy like it was, but not smooth), smooths out when driving, gets a little bumpy when stopped.
The thing I'm going to need to figure out is whether the oil in #4 is coming from a valve seal or if I've got bad rings. Compression test should reveal a lot when I get to it.
The thing I'm going to need to figure out is whether the oil in #4 is coming from a valve seal or if I've got bad rings. Compression test should reveal a lot when I get to it.
#12
CF Veteran
Join Date: May 2015
Location: Arizona
Posts: 4,481
Likes: 0
Received 16 Likes
on
12 Posts
Year: 97
Model: Cherokee
Engine: 4.0
About the same. A little less rough at cold start (not lumpy like it was, but not smooth), smooths out when driving, gets a little bumpy when stopped.
The thing I'm going to need to figure out is whether the oil in #4 is coming from a valve seal or if I've got bad rings. Compression test should reveal a lot when I get to it.
The thing I'm going to need to figure out is whether the oil in #4 is coming from a valve seal or if I've got bad rings. Compression test should reveal a lot when I get to it.
Thread
Thread Starter
Forum
Replies
Last Post
pdowty68
Cherokee Chat
14
04-11-2014 03:07 PM
EvstaG
Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go here
9
03-16-2014 08:57 PM
Surfaccing
Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go here
8
05-17-2009 01:39 PM
jherrin215
Stock Grand Cherokee Tech. All ZJ/WJ/WK Non-modified/stock questions go here!
6
07-25-2007 11:37 AM
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)