Help! Genuinely considering selling my 04 Disco over this misfire/rough idle. I rebuilt the engine ~800 miles ago and it’s been like this ever since.

Misfires, rough idle, and codes for all 4 O2 sensors, and all 4 O2 sensor heaters. O2 sensor values around 0.45V at idle.

Lots of condensation/water coming out of exhaust. Occasionally will get Cyl 8 misfire and stiff brake pedal.

Have tried:

- smoke test
- new Walker upstream O2 sensors
- removing/cleaning upstream O2 sensors
- swapping plugs, wires, injector (cyl 8 )

- plugging the brake booster line
- replaced intake manifold gasket
- resetting adaptions
- checked O2 sensors related fuses

Funny enough, it ran/idled perfectly for 1 day about 2 weeks ago. So I doubt it’s something mechanical

.

 

Replied in your Facebook group also but recommended starting here. https://landroverforums.com/forum/di...sfires-126863/

 

I went through a similarly bleak misfire situation, feel free to check out this tome on the whole debacle: https://landroverforums.com/forum/di...pisode-125864/

 

Can you do a compression test for the cyls. And also I know you may not want to hear this either as you said you already rebuilt it. Just rule out engine coolant leaking into the air system. Because even 1 burp of coolant into the exhaust can foul all the O2 sensors. I rebuilt mine but mine the water pump failed but not after going through the codes you shared and intermittent rough idle and misfires. I had a small leak that let air get into the system and intermittent caused an overheat without knowing and coolant wasn't dropping a lot to notice. Once my pump failed then yeah I noticed big-time in the freezing cold. Fun doing that without a garage or indoors. after replacing I I flushed and tested for exhaust gases in the system Incase the head gasket or block got damaged again. Replaced all the O2s again been good for 1yr now misfires stopped and plugs were changed again. I got the p0420 p0430 p1173 so I think my manifold bolts broke. So I'll probably be doing manifold like you already did. I have the cold start yapping that quiets after warming up low power til warm then fine smooth ride. 04 D2 HSE V8. Oh also check your alternator voltage and battery for bad cell even if seem to have juice. I recall a time I had batteries killing a cell very often ended up being my alternator was on its way out it worked but intermittently was not full output and caused electric anomolies with misfires and O2 triggers.

 

Where in the PNW are you located?

 

This sounds exactly to me like a bad ground issue. If the fuel injection harness does not have a good ground (in 2 places) it will misfire and run like garbage.

Saw this SAME thing on my friends D2 the day prior to a Moab trip last year. It was pressing because we would be off grid for 10 days so we had to fix it. What we found: The little ground strap that goes from the back of the engine to the firewall was broken in half. It would intermittently contact itself and be ok, but the engine moving around caused it to get an intermittent ground.

Also, check your main ground strap.
It would be a very easy fix. Check or replace that little ground strap on the back of the motor first. Then your main one. Heck, I’d just replace the ground cable (avail new from A-B they remade the cable their own house brand for pretty cheap).

If either is dodgy, you will get these exact symptoms. Weird codes, weird nonsensical intermittent misfires. O2 codes.

In my experience, you start to see fuel injection symptoms like this well before you see charging/alternator issues from the bad ground.

 

I had similar issues years ago. The problem turned out to be a damaged O2 wiring harness clip.