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Old 04-03-2011, 04:13 PM   #11
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Not really wanting to take off my I.M. is this something I can ask the stealership to do?
You could, but you're going to pay for it. Typically any person can remove the intake manifold and replace it in a matter of 90 minutes to 2 hours with basic hand tools. If its your first time it will likely take a little longer. Just take care and mark all your vacuum and coolant hoses. It's really quite simple.
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Old 04-03-2011, 04:42 PM   #12
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Excellent write up, Matt! I think your theories are spot on and well thought out, but I am a little confused by your scenario you presented. You say this...

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The EGR system does not operate at all times, it only operates at light throttle and at cruising RPMs. EGR operation at idle will cause a very rough idle and engine stalling and EGR on rapid acceleration will reduce the engines power output without any help to emissions.
The EGR maps only work at light throttle, cruising RPM's and never under idle or WOT or high throttle positions? But then you say this....

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To further elaborate on why the knock and oxygen sensors aren’t capable of adjusting I will give you an example. First, you need to understand that the knock sensors are completely ignored by the ECU after 4000 RPM (the knock sensors are basically microphones and the engine is making too much noise for them to work correctly at high RPM) and the oxygen sensors are ignored at high throttle positions. So imagine that you are traveling on the highway with the EGR clogged, the ECU doesn’t know its clogged and is happily operating the EGR valve, seeing the valve lifting, and using the EGR compensation maps. The lack of EGR *AND* the increased timing from the compensation maps are causing super high cylinder temperatures (as would be evidenced by excessive NOX emissions if you had a gas analyzer). You come up to a slow moving car and decide to floor the gas to pass it, the cylinder temperatures are already extremely high and now you are putting a high load on the engine, can you see what’s going to happen here? The high cylinder temperatures combined with the instant load on the engine cause an almost instant blow out of the gasket. I believe this is precisely the scenario of how Legend head gaskets are blown.
I realize that cruising on the highway will most likely be at around 3000 rpms, or lower, but never higher than 4000 unless you're really hauling ass. (your timing map has EGR activation at 900 to 3000 rpms) So, the EGR maps would be working (with it clogged) having lean, advanced timing conditions at lower highway speeds or city streets. I'd agree that this cruising scenario would cause the BHG, but then you say you stab the throttle to pass a car and that's when you're at the most danger??? Wouldn't the maps switch out of the "EGR area" at that point of WOT and reduce timing, slightly, and increase fuel (which is very rich from what I've observed); reducing detonation? I could see the most dangerous scenario for someone with a clogged EGR would be just cruising around on city streets at the RPM's (900 to 3000) that I am understanding create these lean conditions, but not when at WOT therefor cooling the cylinders and entering into a more safe, rich condition.

Do you think this is more plausible?

Also, I've had a theory that also might contribute to BHG, maybe you could touch on this? #6 (and #3) cylinders are the most common to blow being at the rear we know. If we know anything about ITB's, the point of them is to equalize air flow to each cylinder (maximizing power) because a standard intake manifold will have air enter and each cylinder ends up getting an unequal amount of air, but hopefully close. Fuel is sprayed evenly at each cylinder and is adjusted (I'm simplifying here) by the oxygen sensor at each 3 cylinder bank but all 6 injectors fire evenly.

Maybe, with our intake manifold designs, the air entering is going in and heading straight to the back of the IM and the cylinders getting the most amount of air are 6 and 3 and the rest of the cylinders are just getting what's left in a sense. This would cause the O2 sensors to see that the cylinders are all burning stoich but in reality the 6 and 3 are getting the most air and burning much leaner that the other 4. Maybe this is part of it too?
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Old 04-03-2011, 05:37 PM   #13
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Very Very insightful! That was very well explained. Is there a set mileage for actually replacing the head gasket on the recommended dealer maintenance schedule??
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Old 04-03-2011, 06:37 PM   #14
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Excellent write up, Matt! I think your theories are spot on and well thought out, but I am a little confused by your scenario you presented. You say this...


Do you think this is more plausible?
The key to this theory is heat and ignition timing. Thats why I didn't go into too much detail on the fuel. The combustion temperatures are increased from the long period of cruising with the EGR clogged and increased timing. This heat is most definitely latent, most of it accumulating on the exhaust valve. Detonation takes place instantly under the right conditions, much sooner than the ECU can compensate for with reduced timing or increased fuel (which will also act to quench the heat). I'm obviously simplifying some of the operation of things here so that it is understandable to all (I hope ). The base point that I'm trying to make is that with the EGR clogged, detonation is more likely than not to happen.



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Originally Posted by Vic Cardenas View Post
Also, I've had a theory that also might contribute to BHG, maybe you could touch on this? #6 (and #3) cylinders are the most common to blow being at the rear we know. If we know anything about ITB's, the point of them is to equalize air flow to each cylinder (maximizing power) because a standard intake manifold will have air enter and each cylinder ends up getting an unequal amount of air, but hopefully close. Fuel is sprayed evenly at each cylinder and is adjusted (I'm simplifying here) by the oxygen sensor at each 3 cylinder bank but all 6 injectors fire evenly.

Maybe, with our intake manifold designs, the air entering is going in and heading straight to the back of the IM and the cylinders getting the most amount of air are 6 and 3 and the rest of the cylinders are just getting what's left in a sense. This would cause the O2 sensors to see that the cylinders are all burning stoich but in reality the 6 and 3 are getting the most air and burning much leaner that the other 4. Maybe this is part of it too?
You have a real valid question here, even a casual glance at the intake manifold shows what appears to be unequal distribution, but I am certain it is done intentionally. It is my belief that Honda engineers spent quite some time engineering the manifold for proper harmonics. It appears that the cylinders closest to the throttle body are smaller which would lend credence to the opposite scenario of what you presented - the ports grow in size from front to back so that each cylinder has *equal* flow. I believe the C32's best feature is its dead flat torque curve. This efficiency in both flat torque curve and horsepower output per litre doesn't lend credence to cylinders having unequal flow. In the interest of staying on topic, once again my theory is based more on ignition timing and heat than either fuel mixture or air intake.

-Matt
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Old 04-03-2011, 07:01 PM   #15
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Pattern Failure
Just about every Legend I have seen in my shop with a seeping head gasket has failed on the number 6 cylinder – the passenger’s side rear most cylinder. The fire ring in the gasket blows out of the cylinder into the coolant passage on the exhaust side of the head. We will discuss later in this document why the gasket blows like this all the time – pattern failure.
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My reasoning for wondering this is because while I have done far less HG jobs than you, I see cyl 3 blow as often as 6. Completely possible that this is just weird coincidence for me, but I would like to hear from other southern members who have had BHGs, so that we can either rule it down to #6 or if it is 6 and 3.
OK, is that a typo in the first part? You are calling Passenger rear cylinder cylinder 6? THAT is the one I always see blow, but I'm pretty sure it is #3. Everything I have seen has called it 3, and when Cam and Crank marks are lined up so that #1 piston is at TDC, #1 piston is passenger side. Now that I know we are talking about the same cylinder, that makes me even more sure, but is it #6 or #3?
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Old 04-03-2011, 07:17 PM   #16
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OK, is that a typo in the first part? You are calling Passenger rear cylinder cylinder 6? THAT is the one I always see blow, but I'm pretty sure it is #3. Everything I have seen has called it 3, and when Cam and Crank marks are lined up so that #1 piston is at TDC, #1 piston is passenger side. Now that I know we are talking about the same cylinder, that makes me even more sure, but is it #6 or #3?
I was wondering the same thing honestly. I thought 1-3 ran along the pass side and 4-6 on the driver side, so if the pass rear cylinder is blown that would be the #3 cylinder.
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Old 04-03-2011, 07:41 PM   #17
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OK, is that a typo in the first part? You are calling Passenger rear cylinder cylinder 6? THAT is the one I always see blow, but I'm pretty sure it is #3. Everything I have seen has called it 3, and when Cam and Crank marks are lined up so that #1 piston is at TDC, #1 piston is passenger side. Now that I know we are talking about the same cylinder, that makes me even more sure, but is it #6 or #3?
Oh yeah.. heres your challenge, find the firing order and diagram within the service manual. I distantly remember a TSB - the bulletin was about the manuals exclusion of the firing order and if I recall the firing order was included in the TSB. I'll edit out the cylinder number until someone finds it.

-Matt
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Old 04-03-2011, 07:58 PM   #18
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Not that it's a big deal or anything...
http://service.arnach.net/index.php?x=1&z=2690&y=110
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Old 04-03-2011, 08:08 PM   #19
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Not that it's a big deal or anything...
http://service.arnach.net/index.php?x=1&z=2690&y=110
In a place you might not expect to find it... Ok now find the firing order . Also, I fixed the original post with cylinder #3.

-Matt
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Old 04-03-2011, 08:15 PM   #20
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Are there legends in other markets without the EGR system like the g1's?
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