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Colorado Chapter Discussion of Chapter issues. Please keep Tech Topics on the Tech Forums.

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  #1  
Old October 21st, 2021, 04:31
1-tonxj 1-tonxj is offline
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4.0 issues .

I have a random miss at idle and at higher RPM. I have new plugs that were gapped . The distributor is new as is the cam sensor in it . The plugs weren't very old but i plan to replace them since I ripped one apart when it wouldn't pop off the plug while I was playing with things on my day off . The ignition coil is basically new . The fuel pump is new . All my grounds are new and all cables are oo- Guage aftermarket kit . All the sensors on the throttle body are new as is the cps. It starts right up runs ok then progresses to run poorly as it continues to run . Fuel in tank was drained out and fresh fuel put in . Vaccine lines seem good . Engine has 98k on it . I bought a borescope , compression tester and despite some ignition parts being new I bought a complete tune up kit with performance ignition coil these all should be delivered before I get home on my next day off ...lol... Any suggestions . My 4.0 is a 99 pre coil pack which should be obvious since it has a dizzy . I'm also noticing all 6 plugs look to have rather immediate carbon fouling it doesn't look like oil but I can clean them run the jeep and they are immediately dirty ...lol...I'm really not looking forward to pulling a head ;-)
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Old October 21st, 2021, 12:28
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Kittrell Kittrell is offline
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Re: 4.0 issues .

Seafoam it? See where that gets you.
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  #3  
Old October 21st, 2021, 18:10
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Re: 4.0 issues .

Heat soaked fuel line?
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  #4  
Old October 22nd, 2021, 04:15
1-tonxj 1-tonxj is offline
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Re: 4.0 issues .

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Originally Posted by Fred View Post
Heat soaked fuel line?

No this starts just a few seconds. After starting everything is cool the fuel line isn't heat soaking. One thing I think the fouled plugs started after the eBay injectors so I going to swap them out and see if they are part of my issue .
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Old October 25th, 2021, 19:58
1-tonxj 1-tonxj is offline
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Re: 4.0 issues .

Had Two hours when I got home so I ran it to temp ran a can of seafoam through it then tested cyclinders 1-5 before running out of light 6 will have to wait until tomorrow before I head back out for another 7 days . Comp on 1-5 was 130 130 135 140 145 ...that's all in the spec of 120-150 psi . I don't expect cylinder 6 to be out of spec but you never know and besides it's all 6 sooting up not just one so I'm leaning towards ignition and fuel system issue as it would effect all 6 cyclinders . So I still need to eliminate the eBay injectors as a problem and I need to make sure my ignition coil has a good block ground as I don't think I sanded the brown dog mounts before installing them where the coil grounds mount ... lol...that 4.0 don't realize it's real close to getting pulled since a V8 is always on my mind .
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Old October 26th, 2021, 08:32
SlowXj SlowXj is offline
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4.0 issues .

Plugs turning dirty that quick is normally unburnt fuel.... normally this is weak spark (you say you've got a new coil so doubtful) or a rich condition. This could be quite a few things from o2 sensor, tps, and my best guess.... your injectors..... start there and report back.

Also may wanna check your fuel pressure for something weird

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  #7  
Old October 26th, 2021, 12:35
1-tonxj 1-tonxj is offline
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Re: 4.0 issues .

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Originally Posted by SlowXj View Post
Plugs turning dirty that quick is normally unburnt fuel.... normally this is weak spark (you say you've got a new coil so doubtful) or a rich condition. This could be quite a few things from o2 sensor, tps, and my best guess.... your injectors..... start there and report back.

Also may wanna check your fuel pressure for something weird

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The coil was new but it was from oriellys I've had parts go bad or DOA right out of the box .I also need to check the connection to block for the coil my brown dog mounts were installed and I never ground off the paint so there might be an issue . I also put in those eBay 4 hole injectors and the eBay fuel pump ... As you said it looks like over fuel . It's even shooting up my up stream O2 sensor . Next home time I'm to along a full weekend I should have time to go through a few things ...lol...going to start by swapping back the stock fuel injectors and replacing the pump.
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Old October 26th, 2021, 13:11
SlowXj SlowXj is offline
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4.0 issues .

I wouldn't replace the pump before checking pressure....

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  #9  
Old October 27th, 2021, 15:04
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Re: 4.0 issues .

Clogged CAT???
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  #10  
Old November 1st, 2021, 17:16
md21722 md21722 is offline
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Re: 4.0 issues .

Lazy upstream O2 sensor?
Leakdown test?
I've had some funny problems with ignition coil...
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  #11  
Old November 1st, 2021, 17:18
md21722 md21722 is offline
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Re: 4.0 issues .

Valve seals?
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  #12  
Old November 1st, 2021, 18:42
1-tonxj 1-tonxj is offline
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Re: 4.0 issues .

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Originally Posted by old_man View Post
Clogged CAT???

No such animal on my XJ .
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  #13  
Old November 1st, 2021, 18:50
1-tonxj 1-tonxj is offline
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Re: 4.0 issues .

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Originally Posted by md21722 View Post
Valve seals?

I just put in the new 6 hole Bosch injectors replacing the 4 hole no name brand I got off eBay . This immediately cleaned up most of my issue . All that's left is to clean up the mess they left behind with the dirty plugs and dirty upstream O2 sensor . I bought new up and down stream 02 sensors since I still need to weld in a mini catalytic converter into the pipe to install the down stream sensor . I canceled my eBay order for ignition kit and went with a DUI from performance ignition ...lol...I don't need anymore hit and miss parts wasting my time like those shit injectors .
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