Learn Me: 2006 Mazda Tribute 2.3, no power, sounds like E36 M3...

My in-laws just rolled into my driveway with their 2006 Mazda Tribute. They had just left five minutes earlier. He said that they lost power and it would barely make it up the hill. It was LOUD. I popped the hood, expecting to find a cracked exhaust manifold, but the engine was clearly pressurizing the valve cover as it had blown the little rubber boot off of some kind of sensor and oily mist was coming out. It was 8:30 pm and 35 degrees out. I closed the hood and gave them a ride home. I won't get another chance to look at the engine until Monday.

The engine is a 2.3 four cylinder with 120k miles. He said that it didn't overheat, though it barely would have had time to make it up to normal operating temperature anyway. I didn't smell coolant and nothing seems to be dumping out from underneath, but I didn't spend much time looking at it either.

On Monday, I'll pull the valve cover, take a peek and do a compression test. What should I expect to find?

A blown head gasket?

Broken valve spring?

Bad valve?

Something else?

I've never even ridden in this thing before and know nothing about these engines. Do they use a timing belt or timing chain? Are they interference engines?

What other issues do they have?

Is it worth fixing?

I know I'm not offering up a lot of info here because I haven't really gotten my hands on it yet. Please enlighten me. Thank you.

If its the 2.3 duratrc/mzr and I'm fairly sure it is, they have an insidiously weak pcv/vac system. I'd start there. They're parked in between the runners of the intake mani and are a bitch to get to without the ford tool. Thankfully, that should be a timing chain motor. The other possibility, and if this is the case you might be effed, the timing tensiomers go bad on this motor, fast. If the chain gets sloppy.. You.can figure out the rest.

He was able to drive the car about two miles once things went bad.

Check the oil level too. Bad PVC valves in these engines suck them dry fast. :(

Clogged cat? Can you test vacuum to tell?

They are timing chain engines. They are also interference engines. There are no timing marks or keyways on the cams or the crank. You put in the crank lock tool, put on the cam lock tool, then torque the bolts down. Don't mess with the crank damper bolt unless you want to pull everything apart to retime it.

All that said.

The first assumption I would make is that the PCV system froze, crankcase pressure blew it apart, and the engine is now trying to run with massive false air issues.

Waitaminute. That boot goes over the hole for the cylinder head temp sensor. The cylinder head temp sensor threads into a blind hole in the casting, and the boot is just there to keep stuff from falling into the spark plug wells.

What the heck.

Bad exhaust valve?

I guess its possible it dropped a valve, though these things are pretty damned.sturdy, so it would have to had suffered some serious neglect, or a freak accident. I'm intrigued.

UPDATE:

Number 3 spark plug blew out of the cylinder head. Took the threads with it. Helicoil time.

Well, that's a relatively painless fix!

And it makes sense. The coils can't really come out, so cylinder pressure would blow that little dust boot off, and if the valve cover leaked at all then the oil in the valley would get blown out with it.

This was the new exhaust system.

Wow, that's a new one. Thanks for the update.

It's been Helicoiled, a new plug and valve cover gaskets were installed and it's on its way back home.

All things considered, not a horrible job.