Things to do to this Jeep? - Page 5 - JeepForum.com
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post #61 of 76 Old 12-02-2020, 12:38 PM Thread Starter
Rapidrob
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Today the engine has a miss. One cylinder is not firing and missing. The plugs are new and still very clean. The cold start/ idle control valve is clean and working properly.
If I gun the engine, I see a puff of white smoke which is NOT oil, it is gas. So, that leads me to the front upstream O2 sensor as many here have said the 1998 4.0 engines are prone to have fail.
I ordered one from Rock auto ( NTK/NGK) which is OEM for my Jeep, or at least that is what is in it now and it looks to be very old.
I hoping this solves the miss problem as it is not always there, which is another symptom of a dying O2 sensor so I've read.


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post #62 of 76 Old 12-02-2020, 01:27 PM
LordHobbit
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white smoke is coolant. Black smoke is gas. Blue is oil

93 red ZJ 196k 4.0. Spent more money than I should have ...
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post #63 of 76 Old 12-02-2020, 03:36 PM Thread Starter
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There is no coolant in the oil, no oil in the coolant. No sign of the head gasket leaking,nor does the coolant level drop.

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post #64 of 76 Old 12-02-2020, 03:43 PM
zjosh93
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How have you determined that the white smoke is not oil? Burning oil is "blue" but it can be hard to distinguish between oil and water because the blue tinge to oil smoke is often very light. When you gun it is the puff of smoke at the end when the engine is decelerating? On decel oil can get pulled in past worn valve guides or up around the rings.

Fuel smoke is black as LordHobbit mentioned.
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post #65 of 76 Old 12-06-2020, 03:26 PM Thread Starter
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I replaced the O2 sensor as it was original to the engine. It did not look bad at all. The new one went in with out too much of a fight. The engine is running a lot leaner now which is good, but there is still an intermittent miss every now and then.
I pulled all the new plugs and the only plug that showed any signs of a problem is number one. While all the other plugs insulators are nice and bright white, number one is orange. So I did another compression test with my 60 year old tester and I got at 195 degrees F warmed up:

CY1:115 PSI
CY2:125 PSI
CY3:115 PSI
CY4:125PSI
CY5:125PSI
CY6:125PSI
I'm thinking that cylinder number 1 has a bad head gasket area. I'm still get SOMETIMES gas/air bubbles in the overflow tank after a long run at highway speeds.
I swapped the plug with number 3 cylinder to see if the plug was bad and there is still an intermittent miss on number one cylinder.
The plug wires test out just fine. No grounding ( arcing) to the engine can be seen or heard. The new ignition coli is throwing out one heck of a spark when I tested it.
I'm not sure it this is a fuel injection problem?

I'm only going to use the Jeep when it snows here.
I found a new 13 PSI radiator cap I'll put on to reduce the pressure in the cooling system just in case cylinder one is leaking into the coolant. There are no signs in either the oil or coolant of any leaks.

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post #66 of 76 Old 12-06-2020, 03:52 PM
TonyStadnichuk
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I don't ever remember those 4.0's as being a smooth engine at idle. But durable all the same. Power on the road is good?
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post #67 of 76 Old 12-06-2020, 03:58 PM Thread Starter
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Yes, up to 75 MPH it is running great. I'm getting 17 MPG and hoping with the new O2 sensor I may gain a little more.

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post #68 of 76 Old 12-06-2020, 04:25 PM
TonyStadnichuk
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Don't ask me why I thought of this. I think that 4.0 has solid lifters. Do you need to do a valve set?
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post #69 of 76 Old 12-06-2020, 04:52 PM Thread Starter
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The engine has no sound of clacking of the lifters, it is very quiet.

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post #70 of 76 Old 12-06-2020, 05:10 PM
1996maroonzjf
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The 4.0 has hydraulic lifters. There are no adjustments needed to the valvetrain.

-Tim
(2) '96 4.0s
#1-'10-'18
#2- HP30/Ford 8.8 - 4.56, OME HDs, 5100's, IRO Adj Arms/Track Bars
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post #71 of 76 Old 12-08-2020, 03:55 PM Thread Starter
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No change in the mileage. Still 17 MPG.
I added a 13 PSI radiator cap today as well.

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post #72 of 76 Old 12-09-2020, 03:24 PM Thread Starter
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Waiting on the CB radio and antenna to show up after building the antenna mount.
I remember that in 2016 I was given a Rear View Mirror Dash Cam for my VW, but it turned out to be too heave the the little VW's mirror.
I does how ever fit the Jeep with no problems and it still works after sitting almost 5 years.
I ran the power cord up to the windshield with very little effort and it is well hidden.
A nice accessory to have with today's drivers.

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post #73 of 76 Old 12-09-2020, 08:19 PM
TonyStadnichuk
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Did you figure out your miss and white smoke issue?
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post #74 of 76 Old 12-09-2020, 09:19 PM Thread Starter
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I ran the Jeep for 25 miles at 75 MPH yesterday after replacing the front O2 sensor and the miss has gone away.
I have not seen the white smoke / steam since then as well. I have not ruled out I may have a pin hole leak in the head gasket around cylinder number 1.
The spark plug has an light orange color to it and the others do not,still bright white after 100 miles.
Not sure what that might mean as the engine is running very smooth now.
Perhaps the computer has adjusted for the new O2 sensor. Time will tell.

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post #75 of 76 Old 12-18-2020, 03:54 PM Thread Starter
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Its been more than a week since I put in the new O2 front sensor. The computer is now "used" to the sensor and the engine no longer has a miss and a very smooth idle.
No smoke of any sort is showing now.
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