Burnt valve symptoms?

Discussion in 'Fox 5.0 Mustang Tech' started by MarSaleenMustan, Jul 20, 2005.

  1. The car out of nowhere started idling/shaking rough, then as i'm going it sounds like an exhaust leak... its defenetly not as fast as it was before. the reason why i think it may be a burn valve is because it got pretty hot a couple times within the last two weeks because i forgot to turn on the electric fan and it was somewhat low on oil. anyone know if this is the case? either way i have a freshly rebuilt motor going into it but this just means i'm going to have to get it done faster.
  2. Burnt valves are usually caused by something that holds the valve open when the power stroke is in progress. The resultant flow of hot gases past the valve damages the sealing faces.

    Do a compression test to locate burnt valves. A blowdown compression test is best.
    See http://jrichker.stangnet.com/Mustan...ession_tester/Blow_down_comprssion_tester.htm for more info on how it works & how to build your own blowdown tester.
  3. A burnt valve will not just pop up all of the sudden, it takes time and many, many miles. In fact, it's almost a thing of the past on our cars. I would suspect that you have a loose spark plug or something in your valve train is acting up. If the engine got really hot you might have warped a head or blown a head gasket, but if that were the case you would have other symptoms. Try to determine where the exhaust sound is coming from, you might have a combination of several problems
  4. I was thinking possible headgasket too, since like i sad i ran it hot just last Saturday(the problem started Tuesday afternoon). and also when i say idling bad, the idle it self is pretty stable, doesnt fluctuate, but the motor shakes quite a bit, almost like its missfiring... the only thing though is it sounds like an exhaust leak... which blackGT suggested could be a loose spark plug.. i'm going to check that out. I mean the car has been running since no problem its just that its down on power and makes that exhaust leak sound once i get going.
  5. I had another thought on this, do you have your original cats on the car ? If so and you are getting a rushing sound (like spewing) in your exhaust system, your cats could be clogged, and that will make them run like dog meat.
  6. I'm thinking head or intake gasket. I had a similar issue myself and it turned out to be the intake gasket. When the gasket finally went, I had coolant going into the engine. Not a good thing. Also, why are you gambling with an electric fan that can be switched on and off? One real happy accident and you're out a motor. Maybe a fan controller? Maybe? :rolleyes:
  7. well i'm somewhat stumped... i checked to see if any of the spark plugs might be loose enough to where they could be removed by hand but no, i moved the cables around(some were touching the stock header) and wala, its like it was before... it might have been arcing or something because the boots had some burn spots on them, sort of like a tack weld. i'm thinking this was the issue. who knows.... as far as the DC controller... I dont have that money for now, not to mention at the track i can turn the fan on in between runs to cool things down a bit. it works perfectly when i remember :D