04-03-2011, 11:22 PM | #31 |
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At the risk of sounding stupid and acting like captain obvious, from what I'm getting out of your theory is that pretty much the problem lies within the ECU not knowing when the manifold passage is blocked, since it only looks at the EGR sensor for comformation.
So if you could "switch" off the EGR maps (not saying that you should, just throwing a "what if" situation out in the open). Wouldn't there be less of a chance the HG's to blow since the "Compensating Maps" are not there to kick in, meaning that the timing will not advance and fuel mixture will not lean? Just thinking outloud here.. |
04-03-2011, 11:30 PM | #32 | |
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04-04-2011, 10:07 AM | #33 | |
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04-04-2011, 02:54 PM | #34 | |
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(there are a couple v6s that use a different firing order in that they label the cylinders differently, but the overall firing order is the same) Anyway, fantastic job by you (and Q if he helped with this part) of finally proving via EGR modifier what many of us (including you obviously) have been suspecting for years. |
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04-04-2011, 03:47 PM | #35 |
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A trick I picked up from my engine class is you take the numbers 123456 and split them in half 123/456. Put the last three numbers underneath the first three and count them one from the top and one from the bottom.
Ex. 123 456 1,4,2,5,3,6. Hope this helps. |
04-04-2011, 05:43 PM | #36 |
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OK > I printed off Vic's cylinder numbers from post #19.
I remember when I asked the guy who rebuilt my engine which cylinder / head gasket blew out, he pointed to #6. I'm assuming drivers side are cylinders 4-5-6 and passenger side is 1-2-3. This would make sense to me for I had pools of coolant on the garage floor at driver's side rear cylinder. Not a surprise that Tyson is staying out of this thread.
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04-04-2011, 06:20 PM | #37 |
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Not trying to be a jerk and prove you wrong, considering I know nothing about engines or how they break, but:
BHG #1: ~130,000 miles. Engine repaired. BHG #2: ~195,000 miles. Engine swapped. ALL scheduled maintenance was done (doesn't say EGR was cleaned, but says 30K, 60k, 75K, etc. services were performed), so unless the dealership was incompetent/ ripping me off, the EGR was inspected/cleaned as it should have been. Or maybe I just had a bad engine? Any other ideas as to why my HG's kept blowing? Edit: Also, let's say someone has a 250,000 mile Legend that hasn't had BHG before, but the EGR had never been cleaned or inspected. If they were to clean their EGR and nothing else was about to cause BHG, would that prevent a BHG, or would the damage already be done?
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04-04-2011, 06:40 PM | #38 | |
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As to your imaginary scenario, it goes back to what Matt said about the HG seeping very slightly at first and showing almost no effects at first. There could be no damage done or there could be a process that is happening. HG's will deteriorate eventually and if some part of the gasket has already started to fail then eventually it will completely. |
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04-04-2011, 06:41 PM | #39 |
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^ Intake manifold removal just to clean out the EGR is VERY unlikely for a dealer to do as part of regular maintenance. My 98 Accord (J series motor) had issues with the EGR system getting clogged on the earlier intake manifold designs (much like the C32 v. C35 bottom section of the manifold). It's recommended to clean it out but the dealer won't touch it unless an engine code is tripped, you ask for it specifically, or, there is a recall in effect.
Thankfully the J series motor (OBDII) has a code for insufficient EGR flow which senses that there is actually exhaust gasses entering the intake manifold. Not that I can give any additional credit to Matt's hypothesis as he knows for more than I, but I do know quite a bit about how engines work and it seems extremely likely that he is correct. The main thing that has me convinced is the fire ring "herniation", I mean, you would have to have some high cylinder head temps and huge spikes in pressure to cause that, suggesting long-term detonation damage. That and the EGR compensation maps, which I saw in his earlier thread, it just looks like a recipe for detonation and extreme pressures and temps at the cylinder head; and since the latent heat is going to be the worst on the rear most cylinders, it really makes a lot of sense. I know one thing is for sure, the next 3.5 I do, or have done (lol...yeah, I'd have to win the lottery for that ), I am going to use the bottom of the 3.5 manifold that I have lying around with my Type II manifold. I actually remember Reboticon's thread a long time ago, when he compared all of the intake manifolds and noticed the baffle for the EGR system in the 3.5...I remember thinking that that looked like a somewhat significant change, though, at that time I wasn't sure how. Of course I have learned a lot since then and completely understand it. Also, the PCV oil catch can seems like a GREAT idea. It's funny, why do I think about such things with my older Cherokee's and older, how should I say, more simple engine designs but never thought about adding one for the Legend. Anyway, Matt, we seriously owe you SO much for your persistence, time, effort and, well intelligence, to try and figure out why BHG/SHG's happen so frequently. Also, and I know that this is very insignificant, BUT, it may also be why there are so many repeat failures as most people aren't thinking EGR has anything to do with a head gasket job, most jobs would probably just go through the top end, do the HG and seals up top and button it back up, only for the gasket to repeat failure relatively shortly after the job. Thanks again for all of the information that continues to help us in the Legend community Important Question below: Ok, going out on a limb here but, other than maintenance of the EGR system and a PCV oil catch can, just wondering if an auxiliary EGR flow detection system could be integrated into the the Legend ECU, something that could trip Code 12 by using a sensor that uses the same range of voltage as the EGR valve lift sensor. Perhaps that could be tied in together or used instead of that particular sensor. That way at least the EGR compensation maps would be bypassed appropriately, to PREVENT damage. Last edited by soloist; 04-04-2011 at 06:59 PM. |
04-04-2011, 07:44 PM | #40 | ||
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I think Wes and Soloist answered your question adequately, if you'd like I can go into further detail. -Matt
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