Exhaust manifold replacement on 2005 4.0

[Ascho7]

Hey All,

I've been having oxygen sensor issues for a bit now since I got my TJ a little over a year ago. I've replaced the two sensors (NGK) that the codes called for, but am still getting one of that same code after a few hundred miles of driving (I don't have codes or NGK Sensor bank up/down #'s it is on hand), but right now my assumption it is with my exhaust manifold from a little research. My jeep is still currently winterized, so I haven't taken it apart yet. I'm not sure if I have a cracked exhaust manifold or not, but right now if any of you have any input it would be appreciated. My next step for passing emissions is checking and replacing all four sensors to be safe, and checking my exhaust manifold at the same time. I have heard that non-OEM manifolds are subject to cracking easier, and if any of you had any input on what exhaust manifold or any other parts to replace while I'm at it I would really appreciate it. I have a 2005 with the 4.0 6 speed, and any other tips/advice would be helpful. Thanks again!

 

[AjRagno]

It would be exceptionally rare for the exhaust manifolds on a 2005 4.0L to crack. Further, if they were cracked, you would be able to find evidence fairly easily, either with a visual inspection or with a soapy water test. Possible, though also uncommon, would be that the exhaust manifold bolts have backed out and the gasket is leaking.

What is the history of the codes you've had?

 

[Ascho7]

It would be exceptionally rare for the exhaust manifolds on a 2005 4.0L to crack. Further, if they were cracked, you would be able to find evidence fairly easily, either with a visual inspection or with a soapy water test. Possible, though also uncommon, would be that the exhaust manifold bolts have backed out and the gasket is leaking.

What is the history of the codes you've had?

Thank you for the input, as I said I don’t have my sensor receipts and info at hand with me, but I believe the two codes that have been thrown are p0133 and p0171 both for bank 1 (if I remember correctly), and then one other sensor that I replaced but can’t remember which bank or upstream/downstream or the code that it was. I’ll be taking a look so I can see for myself what it actually looks like on the inside in a weekend or so, and figured this would be a good day to get any input

 

[JKP]

You can get the codes by turning the ignition on off on off on and reading them on the odo. Post them when you get them.

Unlikely the manifolds are cracked or manifold to head bolts are loose.

More likely is the manifolds to cats bolts are loose.

 

[AjRagno]

P0133 is for bank 1/sensor 1. With an inline 6, bank 1 is cylinders are 1, 2, 3. Cylinder 1 is at the front of the engine and 02 sensor 1 is before the catalytic converter.

P0133 sets if the 02 sensor does not respond quickly to changes in the air/fuel ratio. If you have not replaced this sensor, you should now. This code can also set if there are issues with the wiring or the connector.

P0171 is lean bank 1. The 02 sensor after the front catalytic converter is indicating that there is too much air and too little fuel detected in the exhaust. This is most often due to a poor connection from the exhaust manifold to the downpipes with the catalytic converters.

Get a 15mm socket and see if you can tighten the flange bolts. The specs are only 23 lb/ft so don't go too tight. These bolts can back out over time. If the previous owner already replaced the cats, they may not have re-torqued the bolts after a few drive cycles. It would also be an issue if the downpipe to exhaust manifold is not perfectly aligned.

View attachment 244831

 

[Ascho7]

P0133 is for bank 1/sensor 1. With an inline 6, bank 1 is cylinders are 1, 2, 3. Cylinder 1 is at the front of the engine and 02 sensor 1 is before the catalytic converter.

P0133 sets if the 02 sensor does not respond quickly to changes in the air/fuel ratio. If you have not replaced this sensor, you should now. This code can also set if there are issues with the wiring or the connector.

P0171 is lean bank 1. The 02 sensor after the front catalytic converter is indicating that there is too much air and too little fuel detected in the exhaust. This is most often due to a poor connection from the exhaust manifold to the downpipes with the catalytic converters.

Get a 15mm socket and see if you can tighten the flange bolts. The specs are only 23 lb/ft so don't go too tight. These bolts can back out over time. If the previous owner already replaced the cats, they may not have re-torqued the bolts after a few drive cycles. It would also be an issue if the downpipe to exhaust manifold is not perfectly aligned.

View attachment 244831

Great write-up, I'll be looking at doing this over the weekend, and appreciate the attention to detail and helpful knowledge. I'll update on results!

 

[FarFire70]

While it's rarer on the two piece exhaust manifold, my 05 cracked both the front and rear. Front wasn't too bad/loud but when the rear cracked it sounded like a tractor.

Agree with advice to crank down where the manifold meet up with the downpipes. Mine loosen there all the time. Impact gun is your friend there.

May be worth seeing how your cats look. They go bad and break apart. I'm on my fourth set going in now...

 

[Gilly11277]

My TJ is an 05 - I have noticed some slight ticking when I accelerate. Going to check for loose bolts. If the flange bolts are loose, would it be advisable to use a more heat resistant loctite on them?