[Kirby N.]

Hello-

My LJ is having issues. It has about 150K on it. It has been throwing a bad catalytic converter code for a long time- maybe 3 years. So it has had a constant check engine light on. About 6 months ago, it starting going into limp mode and idling rough at times- as well as throwing a P0300 code and other specific cylinders. So I decided it was time to do some overdo maintenance. Here is what I did:

New Catalytic Converters.
New o2 sensors (4)- NGK
New clutch kit- the old throwout was making a little racket- heavy duty LUK
New oil pan and valve cover gasket, new rear main- I had a little oil seep that I wanted to fix.

New Spark Plugs- Champion Copper
New TPS- Mopar
New Crankshaft Position Sensor- Mopar
Camshaft position sensor- I had replaced the OPDG with a new crown unit at probably 90k miles- I used a new Mopar Camshaft Position Sensor at the time (someone had replaced the opdg with a doorman unit before me- so I upgraded but didn't have the original sensor- but saved the crown sensor)- so I have tried with both mopar and crown camshaft sensor.

Still getting the P0300. Sometimes it will also throw a P0301, sometimes a P0305. It stopped doing the limp mode, but will idle rough and start flashing the Check Engine light. It has gotten significantly colder here- so I wondered if it would go into limp mode if it was hotter.

Next I tried:

New Mopar Coil Rail
Autolight XP985 plugs
I also discovered it was still leaking oil out of the front main seal, so I replaced that along with the harmonic balancer. I also discovered the radiator had a leak, so I replaced that with a new unit.

Now, pretty consistently, it will throw a P0300 code and a P0304. It idles rough sometimes. Sometimes it will do the flashing Check Engine Light. It seems to have good power and drive fine, but the light and the idle is the concern.

Each time, multiple times, when I swap parts I will pull the positive cable and let it sit for 15 minutes and ground it out.


I am a little out of ideas and thought maybe someone would have some insight for me. Considering pulling the heads and having them gone through and a valve job- but that is 800$, so I am hoping you would have some other ideas before getting there.

Any thoughts?

I also put a blue driver on it- but I dont know what to look for, so it didn't help much.

Thanks in advance.

Kirby

 

[johncanfield]

Throttle position sensor maybe?

 

[rlenglish]

If you disco the battery it resets the ecu. Then in order to run the missfire monitor the adaptive numerator needs to relearn. This is done during deceleration. That is why the problem goes away for a while.

Looks like you have done the basics so my next step would be a hot engine compression and a leak down test. You can buy cheap testers at most parts stores. Up here we have Princess Auto, I think Harbor Freight is about the same.

Next would be the fuel rail. You have now what is a ageing vehicle and could have debris in the rail. Usually you can remove the rail and injectors and tap them out on a clean white cloth or paper. Any sediment will show up then.
If you pull the rail make sure you have new o-rings for the injectors as they will need replacing.

Is your throttle body clean. Do you have any vacuum leaks?

 

[Kirby N.]

Throttle position sensor maybe?

I changed the throttle position sensor already. Not beyond trying again.

 

[Kirby N.]

If you disco the battery it resets the ecu. Then in order to run the missfire monitor the adaptive numerator needs to relearn. This is done during deceleration. That is why the problem goes away for a while.

Looks like you have done the basics so my next step would be a hot engine compression and a leak down test. You can buy cheap testers at most parts stores. Up here we have Princess Auto, I think Harbor Freight is about the same.

Next would be the fuel rail. You have now what is a ageing vehicle and could have debris in the rail. Usually you can remove the rail and injectors and tap them out on a clean white cloth or paper. Any sediment will show up then.
If you pull the rail make sure you have new o-rings for the injectors as they will need replacing.

Is your throttle body clean. Do you have any vacuum leaks?

Thank you. This is helpful.

I dont know of any vacuum leaks- but I did notice a hanging idle- so perhaps that is a symptom of a vacuum leak. It will hang for just a minute when I stop, if I stab the throttle it goes back to normal idle.

I haven't cleaned the tb, but I could do that.

Its my wife's daily, she drives it and doesn't worry about a thing- up and down the highway.

I will start with inspecting the wiring and looking for a vac leak. Then buy a Harbor freight compression tester and do that test then move on to the fuel injection.

 

[Mouse]

Definitely clean the TB. The hanging idle is something my TJ does when it is dirty.

 

[DAA]

Given everything else you've tried, it's definitely way past time for a compression and leak down test. Given the symptoms, I'd go straight to the leak down test first. What you are seeing is pretty consistent with a burnt exhaust valve. Which, can and will kill your new cats if run long enough like that. From what I've seen, a burnt exhaust valve (usually #6) is not uncommon on the last couple years of the 4.0. Mine went that way with fewer miles on it.

- DAA

 

[rlenglish]

You need shop air for a leak down though.

 

[DAA]

True.

Unless you just want to be medieval about it.

- DAA

 

[rlenglish]

Just did this last week. Always do it that way when the heads are off. Windsheid washer works good.
I have done running compression tests when I don't have shop air but I don't know how you could do it with the solid coil assembly.

 

[wolfstar]

Hello-

My LJ is having issues. It has about 150K on it. It has been throwing a bad catalytic converter code for a long time- maybe 3 years. So it has had a constant check engine light on. About 6 months ago, it starting going into limp mode and idling rough at times- as well as throwing a P0300 code and other specific cylinders. So I decided it was time to do some overdo maintenance. Here is what I did:

New Catalytic Converters.
New o2 sensors (4)- NGK
New clutch kit- the old throwout was making a little racket- heavy duty LUK
New oil pan and valve cover gasket, new rear main- I had a little oil seep that I wanted to fix.

New Spark Plugs- Champion Copper
New TPS- Mopar
New Crankshaft Position Sensor- Mopar
Camshaft position sensor- I had replaced the OPDG with a new crown unit at probably 90k miles- I used a new Mopar Camshaft Position Sensor at the time (someone had replaced the opdg with a doorman unit before me- so I upgraded but didn't have the original sensor- but saved the crown sensor)- so I have tried with both mopar and crown camshaft sensor.

Still getting the P0300. Sometimes it will also throw a P0301, sometimes a P0305. It stopped doing the limp mode, but will idle rough and start flashing the Check Engine light. It has gotten significantly colder here- so I wondered if it would go into limp mode if it was hotter.

Next I tried:

New Mopar Coil Rail
Autolight XP985 plugs
I also discovered it was still leaking oil out of the front main seal, so I replaced that along with the harmonic balancer. I also discovered the radiator had a leak, so I replaced that with a new unit.

Now, pretty consistently, it will throw a P0300 code and a P0304. It idles rough sometimes. Sometimes it will do the flashing Check Engine Light. It seems to have good power and drive fine, but the light and the idle is the concern.

Each time, multiple times, when I swap parts I will pull the positive cable and let it sit for 15 minutes and ground it out.


I am a little out of ideas and thought maybe someone would have some insight for me. Considering pulling the heads and having them gone through and a valve job- but that is 800$, so I am hoping you would have some other ideas before getting there.

Any thoughts?

I also put a blue driver on it- but I dont know what to look for, so it didn't help much.

Thanks in advance.

Kirby

Hello-

My LJ is having issues. It has about 150K on it. It has been throwing a bad catalytic converter code for a long time- maybe 3 years. So it has had a constant check engine light on. About 6 months ago, it starting going into limp mode and idling rough at times- as well as throwing a P0300 code and other specific cylinders. So I decided it was time to do some overdo maintenance. Here is what I did:

New Catalytic Converters.
New o2 sensors (4)- NGK
New clutch kit- the old throwout was making a little racket- heavy duty LUK
New oil pan and valve cover gasket, new rear main- I had a little oil seep that I wanted to fix.

New Spark Plugs- Champion Copper
New TPS- Mopar
New Crankshaft Position Sensor- Mopar
Camshaft position sensor- I had replaced the OPDG with a new crown unit at probably 90k miles- I used a new Mopar Camshaft Position Sensor at the time (someone had replaced the opdg with a doorman unit before me- so I upgraded but didn't have the original sensor- but saved the crown sensor)- so I have tried with both mopar and crown camshaft sensor.

Still getting the P0300. Sometimes it will also throw a P0301, sometimes a P0305. It stopped doing the limp mode, but will idle rough and start flashing the Check Engine light. It has gotten significantly colder here- so I wondered if it would go into limp mode if it was hotter.

Next I tried:

New Mopar Coil Rail
Autolight XP985 plugs
I also discovered it was still leaking oil out of the front main seal, so I replaced that along with the harmonic balancer. I also discovered the radiator had a leak, so I replaced that with a new unit.

Now, pretty consistently, it will throw a P0300 code and a P0304. It idles rough sometimes. Sometimes it will do the flashing Check Engine Light. It seems to have good power and drive fine, but the light and the idle is the concern.

Each time, multiple times, when I swap parts I will pull the positive cable and let it sit for 15 minutes and ground it out.


I am a little out of ideas and thought maybe someone would have some insight for me. Considering pulling the heads and having them gone through and a valve job- but that is 800$, so I am hoping you would have some other ideas before getting there.

Any thoughts?

I also put a blue driver on it- but I dont know what to look for, so it didn't help much.

Thanks in advance.

Kirby

Hi. Thought I would jump in. It has been posted many many times on all the boards. But in case you havent seen it TJ Rubis and probly other models running the 4.0 engine have a lot of issues with spark plugs other than the exact model they came with from Mopar. I have seen this first hand. Get rid of the Champion wizbang plugs and put in a new set of the NGK plugs. The standard plugs it came with. And do that every 10k miles too. Its something to do with the PCM only liking what it came with. They are cheap and work great. I change them every oil change at 5000 miles. Its a jeep thing.

 

[Kirby N.]

You need shop air for a leak down though.

I have shop air and a nice shop to work in, but I am at the busiest time of year at work and have had 0 time to work on it. With the recommendations, that will be one of the first things I do, I just have not the time yet.

True.

Unless you just want to be medieval about it.

- DAA

I dont understand how you would test compression with the heads off or with washer fluid. All for learning though if an explanation isn't too much to ask.

Hi. Thought I would jump in. It has been posted many many times on all the boards. But in case you havent seen it TJ Rubis and probly other models running the 4.0 engine have a lot of issues with spark plugs other than the exact model they came with from Mopar. I have seen this first hand. Get rid of the Champion wizbang plugs and put in a new set of the NGK plugs. The standard plugs it came with. And do that every 10k miles too. Its something to do with the PCM only liking what it came with. They are cheap and work great. I change them every oil change at 5000 miles. Its a jeep thing.

Thanks! I have always run champion coppers in Chrysler products, but I did read that the later model 4.0s really like that particular auto light plug with the double platinum. I also saw on my fender tag sticker deal that these later 4.0s came with ngk so I considered trying that- but with the same results with both the champ coppers and the auto lights, I dont think it is going to do it- and the auto lights costs me a good $50, so I would be hesitant to pull them out and chuck them now (even though I just did that with the low mile Champions).

 

[Dminvegas]

I have an '03 Tomb Raider that had a misfire issue cylinder 1 then 3 then random ones. I chased it for a out 2 years. Here is a list of what I changed:

Air filter
Plugs (autolite xp985) x3
NGK zfr5n - 3559(oem)
Coil packs
Plug boots and springs
Crank sensor
IAC valve
TPS sensor
Fuel injectors
Injector o-rings
MAP sensor
Clean throttle body
Fuel rail is wrapped with header wrap
Intake heat shield
Injector insulation
Fuel pump assembly
Fuel pump relay and fuse
Cam shaft position sensor
Louvered hood w/ rad fan
Fuel Injector cleaner
O2 sensors
Mini Catalytic converters
Main Catalytic converter
Replaced vacuum lines
Replaced all battery cables
Cleaned and reseated pcm connectors

I did find the pcm connector locks were not holding the plugs in tight and they were full of dust so I made a bracket to hold them in tight. When that did not fix it I bought a smoke machine to look for vacuum leaks. I found there were two 90° vacuum boots under the intake that were shot and the throttle body was leaking around the butterfly shaft. After I replaced the throttle body and sealed the TPS with a little rtv, the misfire has not come back. In fact it is running very smooth and the valve train is quite now.

 

[rlenglish]

Compression test gives the indication of rings sealing. Leak down is for valves sealing. It is a little more complicated but that is the basics. A running compression test can give indication of air flow restriction, like excess carbon on valves or a valve not opening enough.
Whenever I have a cylinder head off, like if I was doing a head gasket. I flip it over and inspect the combustion chamber and valves. Then you fill the combustion chamber with fluid, I use washer solvent because it is blue but Varsol or water works fine. Then after a half hour or so if the valves are not sealing properly you will see fluid coming out of the intake or exhaust ports.

 

[DAA]

I have shop air and a nice shop to work in, but I am at the busiest time of year at work and have had 0 time to work on it. With the recommendations, that will be one of the first things I do, I just have not the time yet.

I dont understand how you would test compression with the heads off or with washer fluid. All for learning though if an explanation isn't too much to ask.

As @rlenglish explained, I meant the leak down test, not the compression test. The leak down test had shown #6 exhaust to be leaking. After the head was off, I double checked them all again with the method described by @rlenglish .

- DAA

 

[Kirby N.]

Thank you! That helps immensely and makes sense now!

like I said, I have a really busy few weeks at work, but I plan to dig into it in a week or so with all the advice you have given me here I know where to start and where to go from there- thank you.

Someone mentioned sludge in the oil from never getting up to temp- it does get up to temp. It’s the car we drive on road trips and around town. When I drive it I also run up the rpm’s. It’s just not my wife’s driving style and she drives most day- might need to adjust that though.

I did get a chance to do an “Italian tune up” the other day when we went out for dinner. Ran it up high in the rpm’s through the gears a few times. After that it threw 306 code on top of the 300 and 304 and started making a little clatter in the valves- tick tick tick.

So I am expecting for the compression check and leak down- to be revealing. I will try the washer fluid trick Also- but I think it will all indicate it needs the valves gone through. It’s actually not a terrible job on the 4.0 and I am happy to do it if it would fix it.

 

[Kirby N.]

well, I think I found the smoking gun.

I drove it pretty hard getting out to my shop to tear into it. Before I tore into it, I ran the codes and it had a p0300, p0304, p0305, p0306.

Then I took off the throttle body and cleaned it. It was a little dirty- not filthy. The elbow below the intake is really loose and someone zip tied it on- so probably doesn’

Next I inspected all the wires. Didn’t see anything concerning there. I’ll order some wrap for them.

Then I did the compression test. Here is what I got:


1-130
2-132
3-130
4-40
5- 120
6-135

So now we will start tearing down the engine and get the valves checked. I hope it isn’t rings, but it seems like there is a ton of blow by- so I wonder. The pcvs have a ton of oil
Around them and so does the crank vent where it goes in the air cleaner and I cleaned it all up when I did the valve cover.

 

[johncanfield]

Good time to repower!

 

[Kirby N.]

Nah. I have had 2 5.7 hemi converted LJs. One was done with teraflex parts at desert rat and the other was an aev Montana build. While they were fun, they weren’t super reliable and the details that just weren’t correct drove me nuts. This is my wife’s daily and I need high reliability. So even if it needs a complete overhaul, it will be going back to stock.

I researched up that you can tell when f it is rings by adding some oil on top of the piston then checking compression again. If it goes up significantly then it is rings. Something to do with the oil causing the rings to seal. I will be doing that today before I go any further.

 

[rlenglish]

Only a few drops of oil and turn the engine over a few times before installing the compression gauge or you will hydraulic your tester.