Do the gen IV 24dohc motors tend to burn up valves? Ford made diagnosis - Page 2 - Taurus Car Club of America : Ford Taurus Forum
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post #11 of 20 (permalink) Old 03-22-2012, 10:55 AM
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Outside all other factors, if the burnt valves are exhaust valves, check for cracks in the exhaust manifold nearest the valves. You can usually hear a click click click click when the manifold cracks, but not always. That can lead to burned exhaust valves. Also leads to premature failure of the o2 sensor causing it to run rich, washing out the cylinders, ruining spark plugs, ruining the catalytic converter. Easy to overlook a cracked manifold but they can cause trouble.

If you do hear a clicking under the hood take a piece of hose and put one end to your ear, move the other end around the engine compartment. You should be able to locate the source fairly quickly.

Also, only use regular unleaded gas in low compression engines. Using "premium" high octane fuel in a low compression engine will lead to quicker carbon deposit buildup, which can heat up and cause detonation and also carbonize your valves pretty good, leading to a burn. It's because the high octane fuel will burn slower than normal in a low compression engine, leaving a lot of unburned fuel behind to carbonize (also provide a slightly false reading to the o2 sensor and destroy the catalyst), not to mention decreased performance compared to regular octane. It's not "premium" in any way, shape or form. It's for high compression and forced induction engines only.

Last edited by meal4zombies; 03-22-2012 at 11:15 AM.
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post #12 of 20 (permalink) Old 03-22-2012, 11:39 AM
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Yes, I was looking his problem up on TCCA 'Topic Finder' Then scrolled down to 'Engine' then clicked on 'Oxygen Sensor Terminology'. There is a wealth of info there and the sensors come up frequently on here as trouble makers. My concern was for the upstream and downstream sensors and how this may be related to this problem.
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post #13 of 20 (permalink) Old 03-22-2012, 11:43 AM
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And yes, O2 sensors are maintenance items, and should be replaced every 80-100k miles. If they fail, they tend to cause other problems long before a sensor related code will ever be set.


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post #14 of 20 (permalink) Old 03-22-2012, 11:51 AM
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Thats what I was looking for. What gave me a scare was codes can come after the sensors start giving a problem. I thought this could possibly be related to his problem.
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post #15 of 20 (permalink) Old 03-22-2012, 12:28 PM
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^^^^ Yup, exactly what I am thinking.

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post #16 of 20 (permalink) Old 03-22-2012, 09:25 PM
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Quote:
Originally Posted by KhanTyranitar View Post
And yes, O2 sensors are maintenance items, and should be replaced every 80-100k miles. If they fail, they tend to cause other problems long before a sensor related code will ever be set.
I would go for 120K miles. That's when I replaced mine.

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post #17 of 20 (permalink) Old 03-22-2012, 09:44 PM
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I would go for 120K miles. That's when I replaced mine.

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Meh, just done at 159k, all is well.


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post #18 of 20 (permalink) Old 03-22-2012, 11:10 PM
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The main problems with putting it off till that kind of mileage is severalfold. Firstly, as the sensors deteriorate, the voltage they generate decreases, which causes the computer to interpret the signal as a lean condition. The computer will add more fuel, which will cause it to see the signal it wants, but you are now running rich. Running rich doesn't just waste fuel, it causes carbon build up, which can cause all sorts of other problems. It plugs up the EGR system (I think that most EGR faults actually begin life as carbon deposits in the sensor and lines from rich operation). The second problem is the longer the sensors are left in, the greater the risk that they will seize in place, making removal and replacement much more difficult. This makes the removal more labor intensive, and there is always the chance that the may not be removable.

Putting it off may be tempting, but remember, todays cars are actually much cheaper to maintain in consideration of how long parts last and how infrequent major failures are. So having to replace a part every 100,000 miles should not be considered a big deal. We should gladly replace maintenance items such as spark plugs and O2 sensors.

I would find it unlikely that a bad O2 sensor could cause burnt valves though, the lean reading causes a richer mixture, which actually cools and slows the combustion down, which would make burnt valves less likely. However, enough carbon deposits might cause knocking or pinging, which in theory could cause valve damage, so I wouldn't rule it out, though I think you'd have to have an awful lot of pinging going on to cause that.

The Duratec is a lot less likely to have burnt valves than the older OHV 3.0L engine. That engine had lousy valve seats, and when they wore out, the head would crack and that would cause a leak past the valves, which would chew up the valve and cause it to warp. The Vulcan is a pretty good engine all around, but the heads are lousy. Few high mileage Vulcans can be found with good exhaust valves. They will still seem to run fine, but the performance will be down, and the economy suffers a little. The Duratec is however, more likely to have a valve seat issue than some other DOHC engines. I think this problems is far more common on the Escape than on a Taurus, the Escape is heavier, and is under more load more of the time, so that means it burns hotter too, and it doesn't get the best cooling due to the extra crowded engine compartment of the Escape (its more crowded than a Taurus).


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Last edited by KhanTyranitar; 03-22-2012 at 11:55 PM.
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post #19 of 20 (permalink) Old 03-23-2012, 10:51 AM
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Quote:
Originally Posted by KhanTyranitar View Post
The main problems with putting it off till that kind of mileage is severalfold. Firstly, as the sensors deteriorate, the voltage they generate decreases, which causes the computer to interpret the signal as a lean condition. The computer will add more fuel, which will cause it to see the signal it wants, but you are now running rich. Running rich doesn't just waste fuel, it causes carbon build up, which can cause all sorts of other problems. It plugs up the EGR system (I think that most EGR faults actually begin life as carbon deposits in the sensor and lines from rich operation). The second problem is the longer the sensors are left in, the greater the risk that they will seize in place, making removal and replacement much more difficult. This makes the removal more labor intensive, and there is always the chance that the may not be removable.

Putting it off may be tempting, but remember, todays cars are actually much cheaper to maintain in consideration of how long parts last and how infrequent major failures are. So having to replace a part every 100,000 miles should not be considered a big deal. We should gladly replace maintenance items such as spark plugs and O2 sensors.

I would find it unlikely that a bad O2 sensor could cause burnt valves though, the lean reading causes a richer mixture, which actually cools and slows the combustion down, which would make burnt valves less likely. However, enough carbon deposits might cause knocking or pinging, which in theory could cause valve damage, so I wouldn't rule it out, though I think you'd have to have an awful lot of pinging going on to cause that.

The Duratec is a lot less likely to have burnt valves than the older OHV 3.0L engine. That engine had lousy valve seats, and when they wore out, the head would crack and that would cause a leak past the valves, which would chew up the valve and cause it to warp. The Vulcan is a pretty good engine all around, but the heads are lousy. Few high mileage Vulcans can be found with good exhaust valves. They will still seem to run fine, but the performance will be down, and the economy suffers a little. The Duratec is however, more likely to have a valve seat issue than some other DOHC engines. I think this problems is far more common on the Escape than on a Taurus, the Escape is heavier, and is under more load more of the time, so that means it burns hotter too, and it doesn't get the best cooling due to the extra crowded engine compartment of the Escape (its more crowded than a Taurus).
The Duratec is more likely to have vacuum leaks from PCV and clean air inlet ells to the valve covers resulting in lean conditions. IMHO.

Run hard lean it makes exhaust get hot, valves and manifolds. Lean flame propogation rate is slower causing the flame to go out arouond the valve and into the exhaust manifold. A piston airplane pilot can explain what happens if they select a lean mix to try to stretch fuel. I have only read about it.

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post #20 of 20 (permalink) Old 03-23-2012, 03:14 PM
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A lean mixture might propagate slower, but it is more prone to spontaneous detonation. A lean mixture also burns hotter (this is why vehicles enrich the mixture under acceleration and by turbo cars enrich the mixture under boost). Vacuum leaks are just as likely on Vulcans, so this is not more likely on a Duratec. Hot exhaust is flowing around the valve whether the mixture is lean or not, if you believe the mature burns entirely inside the engine, you are mislead. The exhaust valve opens towards the end of the power stroke, and the fuel is very much still burning and expanding as it exits through the valve. Its the temperature of the gas, that determines whether a valve warps. A lean mix burns hotter, and if it detonates, it strips away the boundary layers, which makes the metal parts get much hotter. This in turn will make the metal softer, and under the severe stresses it has to undergo anyway, can cause failure.

The older 3.0L Vulcan is much more prone to this type of problem, a flame hardened cast iron seat is nowhere near as durable or long lasting as the hardened steel alloy seats used in the Duratec. That cast iron seat is only a couple hundredths of an inch thick, and once it wears through, the valve will quickly wear in to the head. A hardened steel seat is not only much harder, but much thicker.


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