2001 TJ 4.0 has rough idle and cylinder misfires

tictactno

tictactno

New Member
Joined
May 18, 2023
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19
Location
MI
Picked up my first Jeep a couple weeks ago.
2001 TJ Sport 4.0 Manual 6 Inline

It ran great for the first 2 weeks, then started to feel a little rough. Occasionally slippy after a gear shift or brake to gas, but the most prevalent issue was that when I would brake, it would lope real low on the rpms, then often just sputter out completely. If I kept the brake hard to the floor it was a bit better, but when I let my foot off the break altogether? It was fine.

The below had been done just prior:
  • New Evap hoses
  • Coil pack injectors (platinum autolite plugs, I took those out though as you'll see later)
  • Injector wire connectors
  • Rocker arms
  • Push rods
  • Valve cover gasket
  • Evap system pump

The rpm issue started getting worse, then the engine started misfiring in multiple cylinders, a variety of evap codes, and a catalytic converter code. Occasionally it does throw white smoke for about 2 to 3 minutes, once or twice a week...

So last weekend, I did the following:
  • New Battery Terminals
  • Campion Copper plugs
  • Checked and topped of all fluids.(did not do the oil as the previous owner JUST did, but used synthetic)
  • Coolant appears to be green, so I didn't put the 50/50 HOAT I had picked up. It was mother's day and wasn't really in a position to keep messing around in the driveway.
  • There are a few hoses that have some pretty shifty connections. I think they are vacuum hoses (please be kind, this gal here is brand new to Jeeps).
  • In fact, I found one that was zip tied this past weekend, put a clamp on that. Then another with a ton of black electric tape on it, took that off and put another clamp on that. I'd like to replace some of those connectors/elbows, but they look like they might be a pain to find.

Took it for a nice long ride afterward and it was running great. Much better then when I scooped it up, and the *whispers* 🤫 engine light turned off for the first time since I've owned it. 🤫

I was excited! Perhaps, I'd successfully made it a happy enough Jeep to then keep me happily cruising for the summer!
Thought I was in great shape, then on my way home from the lake, I couldn't drive more than 60 mph on the highway without it feeling like it hopping down the highway. Not side to side, not losing control, I'm not sure how better to explain it. I ended up pulling to the side of the highway for a few minutes, then just kept my spread the rest of the way home. However, it never threw any new codes and the engine light is still off.

I have noticed that the front differential is leaking a bit, so I picked up a new seal for that and plan to replace that tomorrow.

Thoughts or suggestions on what else I should try?
I'm thinking O2 sensors. After that I might have to take it in if I want to enjoy it this summer. 😭
 
This is where I pay a reputable mechanic with high end diagnostic tools to hook them up to the TJ and pinpoint the exact issue before firing shots in the dark and just replacing things.

Not to be obtuse, but is it throwing any codes?
 
If you have white smoke, that indicates coolant in the combustion chambers. The 01s are known for cracking heads.

Remove the oil fill cap and look straight down.

If you see coolant, bubbles, sludge etc, in the oil on top of the head, it's cracked. Was there any sludge in there when you did the rockers?

maxresdefault.jpg
 
When you say the front differential is leaking a bit; can you determine whether it's leaking at the yoke for the driveshaft or at the front cover ?
The leak at the front cover can easily be fixed, but the leak at the yoke should be repaired by a knowledgeable mechanic otherwise you can change the preload on other the ring and pinion which will wear the gears prematurely.
 
Chris said:
This is where I pay a reputable mechanic with high end diagnostic tools to hook them up to the TJ and pinpoint the exact issue before firing shots in the dark and just replacing things.

Not to be obtuse, but is it throwing any codes?
Click to expand...

After what I did last weekend? No. Not even after the engine was feeling frumpy on the highway when I pulled off. Drove about 60 the rest of the way home. Which was about 30 minutes. No codes still, haven't driven it since.
 
CharlesHS said:
When you say the front differential is leaking a bit; can you determine whether it's leaking at the yoke for the driveshaft or at the front cover ?
The leak at the front cover can easily be fixed, but the leak at the yoke should be repaired by a knowledgeable mechanic otherwise you can change the preload on other the ring and pinion which will wear the gears prematurely.
Click to expand...

CharlesHS said:
When you say the front differential is leaking a bit; can you determine whether it's leaking at the yoke for the driveshaft or at the front cover ?
The leak at the front cover can easily be fixed, but the leak at the yoke should be repaired by a knowledgeable mechanic otherwise you can change the preload on other the ring and pinion which will wear the gears prematurely.
Click to expand...

O thought it was at the front cover, but I'll take another look today. Maybe it's running that way and appear it's at the front cover. 🤔
 
JKP said:
If you have white smoke, that indicates coolant in the combustion chambers. The 01s are known for cracking heads.

Remove the oil fill cap and look straight down.

If you see coolant, bubbles, sludge etc, in the oil on top of the head, it's cracked. Was there any sludge in there when you did the rockers?
Click to expand...

I checked all fluids last week and the oil appeared a nice consistency, I'll double check this afternoon
 
Chris said:
This is where I pay a reputable mechanic with high end diagnostic tools to hook them up to the TJ and pinpoint the exact issue before firing shots in the dark and just replacing things.

Not to be obtuse, but is it throwing any codes?
Click to expand...

These are the specific codes that fired prior to the last weeks changes:

Prior to that, I was getting specific 3 and 6 cyclinder misfires.

Screenshot_20230520-104308_FIXD.jpg
 
tictactno said:
Picked up my first Jeep a couple weeks ago.
2001 TJ Sport 4.0 Automatic 6 Inline

It ran great for the first 2 weeks, then started to feel a little rough. Occasionally slippy after a gear shift or brake to gas, but the most prevalent issue was that when I would brake, it would lope real low on the rpms, then often just sputter out completely. If I kept the brake hard to the floor it was a bit better, but when I let my foot off the break altogether? It was fine.

The below had been done just prior:
  • New Evap hoses
  • Coil pack injectors (platinum autolite plugs, I took those out though as you'll see later)
  • Injector wire connectors
  • Rocker arms
  • Push rods
  • Valve cover gasket
  • Evap system pump

The rpm issue started getting worse, then the engine started misfiring in multiple cylinders, a variety of evap codes, and a catalytic converter code. Occasionally it does throw white smoke for about 2 to 3 minutes, once or twice a week...

So last weekend, I did the following:
  • New Battery Terminals
  • Campion Copper plugs
  • Checked and topped of all fluids.(did not do the oil as the previous owner JUST did, but used synthetic)
  • Coolant appears to be green, so I didn't put the 50/50 HOAT I had picked up. It was mother's day and wasn't really in a position to keep messing around in the driveway.
  • There are a few hoses that have some pretty shifty connections. I think they are vacuum hoses (please be kind, this gal here is brand new to Jeeps).
  • In fact, I found one that was zip tied this past weekend, put a clamp on that. Then another with a ton of black electric tape on it, took that off and put another clamp on that. I'd like to replace some of those connectors/elbows, but they look like they might be a pain to find.

Took it for a nice long ride afterward and it was running great. Much better then when I scooped it up, and the *whispers* 🤫 engine light turned off for the first time since I've owned it. 🤫

I was excited! Perhaps, I'd successfully made it a happy enough Jeep to then keep me happily cruising for the summer!
Thought I was in great shape, then on my way home from the lake, I couldn't drive more than 60 mph on the highway without it feeling like it hopping down the highway. Not side to side, not losing control, I'm not sure how better to explain it. I ended up pulling to the side of the highway for a few minutes, then just kept my spread the rest of the way home. However, it never threw any new codes and the engine light is still off.

I have noticed that the front differential is leaking a bit, so I picked up a new seal for that and plan to replace that tomorrow.

Thoughts or suggestions on what else I should try?
I'm thinking O2 sensors. After that I might have to take it in if I want to enjoy it this summer. 😭
Click to expand...
 
tictactno said:
Picked up my first Jeep a couple weeks ago.
2001 TJ Sport 4.0 Manual 6 Inline

It ran great for the first 2 weeks, then started to feel a little rough. Occasionally slippy after a gear shift or brake to gas, but the most prevalent issue was that when I would brake, it would lope real low on the rpms, then often just sputter out completely. If I kept the brake hard to the floor it was a bit better, but when I let my foot off the break altogether? It was fine.

The below had been done just prior:
  • New Evap hoses
  • Coil pack injectors (platinum autolite plugs, I took those out though as you'll see later)
  • Injector wire connectors
  • Rocker arms
  • Push rods
  • Valve cover gasket
  • Evap system pump

The rpm issue started getting worse, then the engine started misfiring in multiple cylinders, a variety of evap codes, and a catalytic converter code. Occasionally it does throw white smoke for about 2 to 3 minutes, once or twice a week...

So last weekend, I did the following:
  • New Battery Terminals
  • Campion Copper plugs
  • Checked and topped of all fluids.(did not do the oil as the previous owner JUST did, but used synthetic)
  • Coolant appears to be green, so I didn't put the 50/50 HOAT I had picked up. It was mother's day and wasn't really in a position to keep messing around in the driveway.
  • There are a few hoses that have some pretty shifty connections. I think they are vacuum hoses (please be kind, this gal here is brand new to Jeeps).
  • In fact, I found one that was zip tied this past weekend, put a clamp on that. Then another with a ton of black electric tape on it, took that off and put another clamp on that. I'd like to replace some of those connectors/elbows, but they look like they might be a pain to find.

Took it for a nice long ride afterward and it was running great. Much better then when I scooped it up, and the *whispers* 🤫 engine light turned off for the first time since I've owned it. 🤫

I was excited! Perhaps, I'd successfully made it a happy enough Jeep to then keep me happily cruising for the summer!
Thought I was in great shape, then on my way home from the lake, I couldn't drive more than 60 mph on the highway without it feeling like it hopping down the highway. Not side to side, not losing control, I'm not sure how better to explain it. I ended up pulling to the side of the highway for a few minutes, then just kept my spread the rest of the way home. However, it never threw any new codes and the engine light is still off.

I have noticed that the front differential is leaking a bit, so I picked up a new seal for that and plan to replace that tomorrow.

Thoughts or suggestions on what else I should try?
I'm thinking O2 sensors. After that I might have to take it in if I want to enjoy it this summer. 😭
Click to expand...

I updated this to indicate Automatic. I have no clue how I ended up putting Manual in there. Probably wishful thinking from my initial search for a Jeep.
 
I don't think it's been mentioned yet, but you can download the Factory Service Manual (FSM) for you Jeep under the Resources section on this forum. As CharlesHS stated, the pinion seal requires a very specific procedure to ensure the preload is correct. You can remove the diff cover and replace the fluid and diff cover seal without any issues though.
 
JKP said:
I don't think it's been mentioned yet, but you can download the Factory Service Manual (FSM) for you Jeep under the Resources section on this forum. As CharlesHS stated, the pinion seal requires a very specific procedure to ensure the preload is correct. You can remove the diff cover and replace the fluid and diff cover seal without any issues though.
Click to expand...

I currently have the Haynes Repair Manual, but it's like a dang "choose your own adventure" book. 😆 Constant redirect to a different chapter or section after like 4 sentences. I'm always getting lost in it.

I'll check out that download. Hopefully it's searchable, that'd be stellar.
 
This is a much bigger issue than I had thought. Yesterday, I got under there a bit more and see that it was actually leaking transmission fluid. Check the fluid, running, in neutral, and here it came, drip drip drip. Tranmussion fluid was beyond low, I'd say empty! Remember, I just topped off fluids before my drive home Sunday.
Went and picked up 4 quarts (really wishing I would have got something cheaper than what I did 🙃). Start it, put it in neutral, and the fluid is just POURING out. 3 minutes in neutral and at least a quart or more had made its way out.

I researched for aboit 5 hours last night and together combined. Looked at quite a few diagrams, and cant tell exactly what I'm looking at. Its definitely not great.

Took a video and watched it in slow motion to figure where it's coming from and it appears to be back here.

Screenshot_20230521-122350_Gallery.jpg


VideoCapture_20230521-135159.jpg


Screenshot_20230521-024144_Gallery.jpg


20230521_124419.jpg
 
There are extra hose clamps on both the transmission lines and the lower radiator hose that can be seen in pictures 1,3 & 4; this may indicate someone was trying to resolve leaks where the hose slips onto the barb fitting.
In the pictures you cannot determine whether the leak is caused by a loose fitting, hose to fitting leak, cut in a hose or what.
You will need to get under the Jeep and examine the area where the leak is occurring. There is so much transmission fluid covering the underneath of the transmission and engine areas that I suggest you clean the suspected areas to determine the exact location of the leak.
 
Thanks! That's the plan tomorrow.
I'll be cleaning all, then checking hoses and connections.

After that, if I'm still experiencing issues, I found a reputable mechanic that has a focus on older Jeeps. Being in Michigan and all of our sand dunes, it sounds like there a quite a few, but picked one from a suggestion of some folks I know that off road heavily. While my Jeep I just got as a cruiser and camping, I'm sure they've seen some challenging problems. 😳

Really appreciate everyone's fast responses! This was my first post here. I'm sure I'll be an active member at this point!
 
I got under there today and just replaced the connections and transmission lines myself. Was actually super easy. I've never done work under a vehicle before, that was new for me. But it went great!

I don't even know what kind of hosing they used previously but it was definitely exhausted. It looked like some sort of vaccum hosing. No structure to it and was mushy.

Couldn't find a catalytic converter under there though. 🤔

Problem for another day I guess. 😆

Running good at the moment!
 
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