another burnt valve

[thebestdj07]

anyone have any idea what would cause me to keep burning exhaust valves? its a stock msp6 with 140k. about 4000 miles ago on cyl 3 it burnt one getting onto the highway. had it replaced and ran good. same thing happed today. 0 compression on cyl 3 and ~150 on the rest with the engine warm. it always has left a black smoke cloud when going wot.

[Agent_Orange]

Obviously your cylinder temps/EGTs are above normal levels if your repeatedly cooking valves.

Any CELs?

Any way to monitor your AFRs?

What is the state of your EGR system?

[sidekick]

Has the timing chain ever been replaced? Have you adjusted the valves?

[thebestdj07]

no cel prior to it happening. i have a wideband but no place on the factory pipe to put it. egr was cleaned this past winter when the head was off. timing chain and vvt were done also. valves clearance was checked last time head was off all were in spec.

it does use alot of oil say quart ever 150 miles.

[sidekick]

If you're using a quart of oil every 150 miles, I'd say you have much bigger issues... But bad injector? Or injector stuck open? Major detonation in cylinder 3? Did they re-machine the valve seat when replacing the bad valve last time? If the valve is not making good contact with the seat, you can get major hot spots, which could then lead to a burnt valve.

[thebestdj07]

yea the shop re machined the seat into the head. as far as the oil what would you think? the turbo just got a new chra installed.

[Gr8Speed]

Who tuned it?

[thebestdj07]

Originally Posted by Gr8Speed Who tuned it?

mazda lol. its bone stock

[Enki]

Let it burn another one and lemon law (if applicable) that car.

[thebestdj07]

Originally Posted by Enki Let it burn another one and lemon law (if applicable) that car.

i wish in ohio its 12mo or 18,000 miles.

[Turbo_Steve]

If you are going to fix it I would replace the injector on that cylinder for sure. Also replace your primary o2 sensor if it's never been changed. Clean or replace the maf sensor too. 140k is probably a good idea to change all 4 injectors. But 1 quart every 150 miles tells me you need a complete rebuild.

[sheston]

That's your problem, being stock - JK. You just need some E85 or Meth to cool down the combustion