2006 4.0 TJ hesitating / running rough when under load

[Alan J]

A couple of weeks ago I took a wrong turn at deer camp, high centered in a mud hole that was about 14 inches deep and had to get winched out. I hit the rest of the water holes pretty hard after getting freed then noticed the engine running rough under load at around 1.8k to 2k RPM’s in 3rd or holding at 2k in 4th and 5th gear on the way home. Since then I replaced the plugs and coil pack which were due to be changed anyway, coil pack had 133k miles on them, but didn’t solve the problem. It’s not throwing any error codes and is idling smoothly and accelerates okay in 1st and 2nd. Any suggestions on what to check next would be greatly appreciated.

P.S. Chris, thanks for all the posts on Bosch O2 sensors. I didn’t know any better and purchased Bosch a couple of years ago then continued to get error codes during warm weather. Will soon replace with NGK/NTK.

 

[Chris]

A couple of weeks ago I took a wrong turn at deer camp, high centered in a mud hole that was about 14 inches deep and had to get winched out. I hit the rest of the water holes pretty hard after getting freed then noticed the engine running rough under load at around 1.8k to 2k RPM’s in 3rd or holding at 2k in 4th and 5th gear on the way home. Since then I replaced the plugs and coil pack which were due to be changed anyway, coil pack had 133k miles on them, but didn’t solve the problem. It’s not throwing any error codes and is idling smoothly and accelerates okay in 1st and 2nd. Any suggestions on what to check next would be greatly appreciated.

P.S. Chris, thanks for all the posts on Bosch O2 sensors. I didn’t know any better and purchased Bosch a couple of years ago then continued to get error codes during warm weather. Will soon replace with NGK/NTK.

It could be possible the issue is related to that Bosch O2 sensor in all honesty. I say that because they are known to have issues.

I might replace that first to see what happens. Whatever is going on, it sounds like something electrical / sensor related.

My best suggestion is keep driving it and trying to make it act up until it throws a code.

 

[Alan J]

Thanks for the quick reply. Will give it a couple of weeks to throw a code then will replace O2 sensors regardless.

 

[John Wolf]

Mine was sluggish at higher rpms too a couple months back. Put NGK O2 sensors in and cleared it right up, runs great since. You may have fouled yours in the slosh, or maybe something backed up in the cats? Codes should re-appear after a couple weeks if you don't disconnect the battery, if there is still a problem with sensors or emissions.

 

[Jerry Bransford]

Exactly what spark plugs are you using? Single-tipped platinum plugs, the type with the platinum coating on just one side of the spark plug gap, like the Autolite AP-985 or Champion 3034 will cause misfires and stumbling with the distributorless waste-spark ignition system used in newer 4.0L engines. For newer engines, if you want platinum tipped, they need to be double-tipped so the platinum coating is on both sides of the gap. Autolite's APP-985 and Champion's 7412 being two good models to use. For iridium tipped, Autolite's XP-985 will significantly outlast the platinums by at least 100k miles, they're good for no less than 200k miles.

 

[Alan J]

Not sure I'll by another part for the TJ without reading the forum first.

Previous plugs where Platinum +4 plugs that were rate for 100k miles. They had over that when I changed them and were still running good prior to the big splash.

Local parts store was out so I went with Bosch single fine wire Iridium plugs part # 9656

New coil pack is NGK part number 48662

 

[Jerry Bransford]

Generally speaking, Bosch plugs don't work well in our Wranglers, Bosch is too limited on their heat ranges according to a Bosch engineer who opined that on a Jeep forum years ago when asked why Bosch plugs don't work well for us. Not saying those particular fine wire (a good thing) iridium plugs are causing the problem but not many of us trust Bosch for spark plugs or O2 sensors... as much as we push Bosch for their unsurpassed quality fuel pumps.

 

[Alan J]

Chris, you nailed it. Gave up on getting an error code and replaced the 2yr old Bosch units this weekend with NTK's. Both downstream sensors were pretty black. Also followed Jerry's advice and switched to Autolite XP985 plugs. Thanks for the help!

Have a Happy New Year!

 

[Chris]

Chris, you nailed it. Gave up on getting an error code and replaced the 2yr old Bosch units this weekend with NTK's. Both downstream sensors were pretty black. Also followed Jerry's advice and switched to Autolite XP985 plugs. Thanks for the help!

Have a Happy New Year!

Glad that solved the issue! Thanks for the update as well. I always like when threads have happy endings.

 

[Nimbley]

I wouldn’t even put Bosch spark plugs in my lawn mower. I used to keep a coffee can full of brand new Bosch plugs that I pulled for misfire problems. I’d show them to the customer when they insisted it wasn’t their new Bosch plugs causing the problems. Definitely stick with Autolite spark plugs.

 

[AndyG]

That is very symptomatic of a plugged catalytic converter.

 

[Alan J]

Not to say that the cats aren't crapping out on me, but the it ran fine until the engine began warming up then it would run rough only under load or during acceleration. No problems with either since replacing with NTK O2s.

Pictures of the old O2 sensors below. Let me know if it looks like typical wear or if I should start a go fund me account for new cats.

 

[AndyG]

If she's running good she's good.