This was posted on the other forum, what do you guys think?

[Haltech]

Originally Posted by cld12pk2go But if we are starving #4 of air, that means it will be running rich... Does not compute...

Not true... by starving it of air, the computer is going to sense this and lower the fuel output to that cylinder, causing you to go lean.

[cld12pk2go]

Originally Posted by Haltech Not true... by starving it of air, the computer is going to sense this and lower the fuel output to that cylinder, causing you to go lean.

And how exactly is the ECU going to know that one cylinder is getting less air?

It doesn't measure the mass airflow in or the AFR out of each cylinder so it can't.

The other cylinders will run leaner to compensate to achieve the desired average AFR from the WBO2.

[Haltech]

Well if you have a better theory to cyilnder #4 being the blown cylinder on all of these engines, take a stab at it.

Im just stating the obvious. I bet if you did testing with 4 thermocouplers and monitored the cylinders EGT, #4 is going to be the hottest.

[cld12pk2go]

Originally Posted by Haltech Well if you have a better theory to cyilnder #4 being the blown cylinder on all of these engines, take a stab at it. Im just stating the obvious. I bet if you did testing with 4 thermocouplers and monitored the cylinders EGT, #4 is going to be the hottest.

I am not stating that there is not some reason that #4 might be failing more than the others. What I am stating is that the reason you originally put forward can obviously be eliminated (less airflow due to intake manifold being more restrictive on that cylinder does not seem to be a credible mechanism for producing detonation since this would result in a richer/cooler cylinder).

I have no data on the EGT, but that could be a factor. Another that could be interesting is if the cooling passages are such that that cylinder could been more likely to have hot spots or higher average temps. Or if that cylinder is getting more crud built up in its intake runner that is getting sucked in...

[Haltech]

True, it good be several things. Im just going with my gut here and thinking its a airflow problem. Sometimes, logic supersedes form in this case. Ive experienced this on Fords as well.

[4thStroke]

I know with the Ford 4.0 SOHC V6, its the same cylinder that blows, when the motor fails, its usually always this cylinder (cant remember which one, its been a while). Same for their 4.6 V8. It was described to me as the greedy cylinder. It makes the most power, because it runs lean, cant get the fuel it needs, then goes boom.

Cylinder 4 probably does run the hottest, beacuse its running lean compared to the other cylinders. As far as how this lean condition is created, i have no idea.

[cld12pk2go]

Originally Posted by 4thStroke I know with the Ford 4.0 SOHC V6, its the same cylinder that blows, when the motor fails, its usually always this cylinder (cant remember which one, its been a while). Same for their 4.6 V8. It was described to me as the greedy cylinder. It makes the most power, because it runs lean, cant get the fuel it needs, then goes boom. Cylinder 4 probably does run the hottest, beacuse its running lean compared to the other cylinders. As far as how this lean condition is created, i have no idea.

Well, there are only two possibilities for creating a lean case: More air or less fuel.

The mechanism by which either would occur is what we are trying to determine.

[enganear]

Originally Posted by cld12pk2go Well, there are only two possibilities for creating a lean case: More air or less fuel. The mechanism by which either would occur is what we are trying to determine.

The intake manifold is pretty symmetrical. The exhaust manifold is another story. #4 cylinder may see more or less scavenging due to the unsymmetrical dynamics of the exhaust plumbing. Have any of these blown engines had an aftermarket manifold?
-enganear

[winniep]

That is an EXCELLENT observation AND question. Hopefully we can get an answer to it. Especially due to the fact that I am considering an exhaust manifold.................

[bombdotcom]

so an aftermarket exhaust manifold couldve prevented this? from what youre sayin of course

[enganear]

Originally Posted by bombdotcom so an aftermarket exhaust manifold couldve prevented this? from what youre sayin of course

Just a hypothesis based on observation. It is the only obvious factor that is different. I would like to know if any of the blown engines had aftermarket exhaust manifolds to support or dispute the hypothesis. I am not saying this is the cause, just that it COULD be the cause....

If we are always seeing the #4 rod through the block, there must be a reason.

Keep seeking the truth.
-enganear

[jonscapri]

Originally Posted by enganear Just a hypothesis based on observation. It is the only obvious factor that is different. I would like to know if any of the blown engines had aftermarket exhaust manifolds to support or dispute the hypothesis. I am not saying this is the cause, just that it COULD be the cause.... If we are always seeing the #4 rod through the block, there must be a reason. Keep seeking the truth. -enganear

It might be something to do with the bottom end as well. I've seen a few of the Ford Zetec engines do this with the pots mod. One way you can tell with cylinder is running lean or rich is to take the spark plug out. It won't tell how much exactly but you can always tell by this tried and trued method.

Now if you can get an old school engine scope to check things out you might be able to tell more about what is happening.

Also do a compression test on the engine hopefully before too much damage is done. Of course there is a ton of variable to check, and see what is the culprit. I think that having the EGR port right there by #4 may be one of the issues going on here.