04 disco 2 4.6

A few thousand miles ago I pulled the motor and did a full rebuild. Bearings, rings, all gaskets, had the heads redone with new valve seals etc, new injectors, coils, plugs, wires, you name it. Basically everything except cam bearings.

Upon first start it had codes for 02 sensors, upstream and downstream I believe, and what sounded like a minor exhaust manifold leak. It ran well so I didn't address it. Fast forward 3000ish miles my CEL starts flashing yesterday, Cylinder 3 misfire, noticed a little tick in the engine as well. Pulled the oil cap & it appears to have coolant droplets, not sludge. But it was definitely yellow. Coolant temp stayed below 180° while I limped it home 20 more miles. In that time it developed random misfire code as well. It seemed to run smooth however.

So at this point I'm pretty certain either the HG or timing cover gasket has failed, hence coolant in the oil. I have read that the upstream 02s can cause misfires, but I'm guessing that's not the cause in my case. The engine tick leads me to believe the coolant immediately toasted the main bearings.

Once I get it towed back to my garage this week I'll pull plugs, inspect plug wires etc. Part of me wants to replace all the 02 sensors and see if that clears any codes, but the engine tick and exhaust leak sound (which I'm now thinking might be external HG failure) makes me hesitant to throw any parts at it. Obviously pulling the intake and heads off is the next step.

Any recommendations would be greatly appreciated.

 

As you suspect, I’m pretty sure new O2 sensors won’t clear your codes. I would fix the know problems first.

 

Could just be a cracked head gasket, and ticks in pushrod V8's are pretty common for everywhere. As @Harvlr says start with what you know. In my limited experience on mains if there is enough coolant to damage a main the end to fail pretty epicly.

 

Start with a compression test before you pull everything apart. That will tell you where your problem is if it's a head gasket.

Under the cap being a bit yellow isn't too strange, especially if you drive short distances a lot. Happens from condensation. What does the oil itself look like?

 

Agreed.

Yes would be great if internals were ok!

Haven't drained it yet but the dipstick oil looked fine, didn't see any particulates either.

Today I drove it onto the towing trailer and it sounded worse and the coolant reservoir was bubbling, which far as I know is never normal. It sounded like both HGs were blowing out the side.

 

Here are the codes. All the 02 and powertrain codes were present before the misfire and engine noise

 

What are your fuel trims? That reads vacuum leak to me the evap and random misfires. I'd smoke it first or check your lines.

I agree with above to also compression test or leak down before pulling heads off if you don't find a vacuum leak.

But following KISS, I would start with what my trims tell me and see if I mis routed or cracked a vacuum line when reinstalling first. The o2 sensors could just be doing their job and telling you way too much O2.

 

I would go after the Coolant Temperature code first. Maybe a bad sensor or wiring open circuit. The ECU uses coolant temperature to help determine fueling, so could impact misfires and driveability.

Basically knock out the codes one by one, although folks sometimes ignore Bank 2 Sensor 2 HO2S codes if they can't afford a new sensor.

 

Only for the first 39 seconds or so,, then it goes in to closed loop and uses the 02s and the maf.

 

Appreciate all the responses.

I agree that it would be nice to knock out the codes one by one, however it's inevitable that it will need to be torn down, and at the very least need head gaskets.

Another thing to note, is the previous owner stripped out quite a few already repaired with heli coil head stud threads in the block.

I was able to drill them out and install time-sert inserts, but they didn't all sit flush and I had to grind them down with a Dremel. I'm thinking that my HG failure may be due to that, or at least a contributor.

Not sure if the block can be decked at this point, but hope to start tearing into it this week.