2004 D2 with 117k miles. I have misfires on Cyl 2 & 6 that I can't figure out. It's bad enough that it makes a popping sound under load.

The previous owner cross threaded half the spark plugs (around SAI pipes) so it ran rough with several misfires, which is how I bought it.

I replaced the heads with a used pair that I had from a different project when a back tap thread tool couldn't fix the plug holes.

The compression on the 2 cylinders are both 175psi.

I have replaced the plugs, wires, coil packs, fuel injectors, catalytic converters, and the front O2 sensor (on that bank).

The only other thing I can think of is worn cam lobes.

Has anyone experienced a similar issue?

Do these persistent misfires seem symptomatic of a bad/worn camshaft?

Thanks in advance

 

How long had the heads been sitting, that you installed? Could be a valve hanging up, if they've been sitting for awhile and you did not have them reconditioned. Usually, a popping noise through exhaust or intake is valve hanging open or not sealing properly. If the cam lobes were worn, you'd just have a miss...since valves won't be opening correct amount or at all. But, typically...you'd also have valvetrain noise...if this were the case.

l'd pull the valve covers and look for unusual movement on those two cylinders.

 

I’ve had a worn cam lobe before. That was the exact symptom.

misfire plus backfire under load.

 

Odd that you would have a misfire "popping" back through either manifold, exhaust or intake, since the valves are the only component that connect the two, cylinder and both manifolds. If cam lobes are worn down or off, the valves would not be opening sufficiently, starving the cylinder of air during intake stroke, and camshaft being worn would not change the timing of their opening, and this is how you would acquire a popping, valve hanging open during compression stroke (or if you had a bad valve or seat, but compression test would show this fault).

Anyhow, just weird...

 

The heads I used apparently only had 1500 miles on them after they were machined. They looked like they were in good shape, but I'm not sure how much you can really tell from just looking at them.

I always thought that if a valve wasn't seating, the cylinder wouldn't have good compression, but I might be wrong.

I did pull the valve cover off to see if I left anything undone, but didn't appear as though there was an issue. Everything was tight & the bolts were torqued down, with no cracking or breaks in the shaft or arms.

I hat throwing parts at a problem, but I'm tempted to just replace the cam and hope that fixes it.

 

Yes, a bad seating/cracked/worn valve will show low compression (like l mentioned in second post). But a valve that sticks open after being opened is a whole different issue. During a simple compression test the valve does not normally rotate, but while running...it rotates...so...if valve stem is bent, warpped or just sticking in certain position...it will hang open.
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Did you have misfire prior to changing plugs, coils and wires?

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I changed the fuel injector o-rings, plugs, wires, & coils at the same time when I reassembled everything, and it's been misfiring since
I swapped out different plugs, wires, injectors, and coil pack one at a time with no change.

I know the heads were not in use for at least a year, maybe 2 before I installed them.

I bought another gasket kit because I was considering pulling the head and taking it to a machine shop to have checked out, but wanted to get advice here on the cam before I did that.

 

In your first post, you mention it had several misfires when you bought it.

And after replacing heads, doing tune up and injectors...you have two, #2 and #6.

What cylinders were misfiring prior to removal of head and tune up? And, were the misfires before as noticable as the misfires you have now? Trying to get an idea if and what has changed along the way here, has it gotten somewhat better or worse after your attempt at repairing issue; fewer misses, or did it always have just two misses, #2 and #6, and now they are now more pronounced?

To me, it sounds like you may have crossed a couple plug wires. This is about the only other scenario l can imagine, since it could be firing on intake stroke (while intake valve is open). Since you say it sounds like it's popping under hood. If it were firing during exhaust stroke, igniting unburned fuel, it would pop out the exhaust system and most likely throw 02 sensor codes. I'd double, triple check the wires first, before doing anything else, especially if you've noticed the engine runs worse after tune up.

If everything checks out and you still want to check cam, buy or rent a dial-indicator and measure lift on all cylinders at pushrods/rocker arms.