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Old 07-18-2013, 06:52 PM   #29
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It's a 1990 fuel injected 460. That means that it has oxygen sensors, electronic ignition, and the fuel air mixture is controlled by the computer. With that information an intake manifold leak (IML) will introduce extra air into the system that is not accounted for by the MAF (mass air flow) sensor. You would probably set the check engine light on with a lean code. I doubt you have an intake manifold leak without setting some codes.

I'm also somewhat against adding any means to increase your coil output. There is sufficient voltage available on these electronic ignition systems to jump any spark plug gap you have. That's why today you can go for 100,000 miles without changing plugs. Save your $$$$ for some good plug wires.

Bad plug wires are one of the reasons the auto industry went to coil over plugs or COP. It eliminates one area where the older systems failed and that is plug wire breakdown causing misfires.

TeJay
Great information but this engine uses a MAP (manifold absolute pressure) sensor. If these engines have an intake leak, usually the idle rpms would be higher than expected and not controllable. Everything else is spot on though.
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Old 07-18-2013, 07:00 PM   #30
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If by chance you do have a damaged valve, the dealer I work at has used ProMaxx Performance for saving customers money on reman heads. They are pretty cheap and seem to back their work very well. We had a few issues over the years with their heads and they were prompt on correcting the issue. The good thing about a 460 in a class A, is they are easy to work on.
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Old 07-18-2013, 07:04 PM   #31
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After re-reading the first post and seeing wet plugs being mentioned, I can't but wonder how old the gas is? Old gas will not fire under load and could cause the wet plugs.
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Old 07-18-2013, 08:58 PM   #32
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Actually that is not accurate at all. They valve can stick at a given RPM. The early Focus 2.0L engines had an issue with valves sticking causing the same exact symptoms. The test was to warm up the engine to full operating temps and then hold the RPMs at 2500 for a few minutes. After that time return it to idle. If there was a misfire at that time, the valve was sticking.
But we are not talking about a ford focus!!!! Lol
He has a 460 and have never seen a sticking valve in one. Just my .02
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Old 07-18-2013, 09:16 PM   #33
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But we are not talking about a ford focus!!!! Lol
He has a 460 and have never seen a sticking valve in one. Just my .02
It really doesn't matter what engine is being talked about, the statement was incorrect. But I agree, I have never seen a sticking valve in a 460 but that does not mean there has never been one. A lot of 460's out there. It just means you and I have never seen one.
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Old 07-18-2013, 09:45 PM   #34
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It really doesn't matter what engine is being talked about, the statement was incorrect. But I agree, I have never seen a sticking valve in a 460 but that does not mean there has never been one. A lot of 460's out there. It just means you and I have never seen one.
Gotta love Internet cowboys. Have a nice day!!!
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Old 07-18-2013, 10:20 PM   #35
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Hey you guys are awesome!! After driving it more an removing the cat which has made it louder I am realizing the miss is constant and it can be described as a " dead miss " my mechanic did a compression test and during a regular compression test they were all at 85 across the board but when the compression test was done on the cylinder that we have determined is giving us the problems, we did it while the motor was running and it would not build compression......final diagnosis valve failure of some degree. Now I am going to try the combustion chamber cleaner as a hail marry but if that doesn't work I will be pulling the heads. Something I am not looking forward to in a van but I don't have the 2k to have it done and I do have 3 weeks off in August so hopefully I can get it done in a week so I can travel for 2 weeks. It is still drivable but as a bit of a perfectionist I just can't stand it. Sorry now that I'm in combustion cleaner mode I am hoping people will chime in again and tell me their results if the have done it. Thanks again for the help everyone I had a melt down today and was ready to quit camping but determination will get my pride and joy back on the road again in good health
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Old 07-18-2013, 10:37 PM   #36
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After re-reading the first post and seeing wet plugs being mentioned, I can't but wonder how old the gas is? Old gas will not fire under load and could cause the wet plugs.
I have run a few tanks through it now as well as Lucas treatment, no luck
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Old 07-19-2013, 06:58 AM   #37
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Hey you guys are awesome!! After driving it more an removing the cat which has made it louder I am realizing the miss is constant and it can be described as a " dead miss " my mechanic did a compression test and during a regular compression test they were all at 85 across the board but when the compression test was done on the cylinder that we have determined is giving us the problems, we did it while the motor was running and it would not build compression......final diagnosis valve failure of some degree. Now I am going to try the combustion chamber cleaner as a hail marry but if that doesn't work I will be pulling the heads. Something I am not looking forward to in a van but I don't have the 2k to have it done and I do have 3 weeks off in August so hopefully I can get it done in a week so I can travel for 2 weeks. It is still drivable but as a bit of a perfectionist I just can't stand it. Sorry now that I'm in combustion cleaner mode I am hoping people will chime in again and tell me their results if the have done it. Thanks again for the help everyone I had a melt down today and was ready to quit camping but determination will get my pride and joy back on the road again in good health
Well glad you found the problem but you still led everyone astray with chasing a (quote) intermittent misfire under load. I know some don't know but it just makes me upset when so many people rack their brains and take the time to post help and then to find out we weren't given the right info. Okay rant over sorry if some take this wrong.
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Old 07-19-2013, 09:11 AM   #38
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Well glad you found the problem but you still led everyone astray with chasing a (quote) intermittent misfire under load. I know some don't know but it just makes me upset when so many people rack their brains and take the time to post help and then to find out we weren't given the right info. Okay rant over sorry if some take this wrong.
Well my friend I respect your opinion greatly but as most of us here we all have made mistakes and I think anyone who has followed this thread as well as the other "problematic 460 " thread have learned alot by reading, after we are on this forum to learn and share our knowledge and experience, not complain about other people's mistakes. At the end of the day we are in the RV lifestyle because we are passionate about it don't mind talking about it when were not actually out there with our feet up in a lawn chair
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Old 07-19-2013, 09:23 AM   #39
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But we are not talking about a ford focus!!!! Lol
He has a 460 and have never seen a sticking valve in one. Just my .02
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Gotta love Internet cowboys. Have a nice day!!!
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Originally Posted by lx22 View Post
Well glad you found the problem but you still led everyone astray with chasing a (quote) intermittent misfire under load. I know some don't know but it just makes me upset when so many people rack their brains and take the time to post help and then to find out we weren't given the right info. Okay rant over sorry if some take this wrong.
Awfully critical for someone from FRIENDSwood. If Mitchyb had known it was a full time miss in the beginning, I'm sure he would have described it that way. Kudos for keeping us up to speed on what he was discovering as he went along. I hope he cures the problem with additives, but I'll be watching to see what happens next.

In the beginning I was thinking he was one of those DIY guys who just throw parts at a problem, but he's developing into a much more 'investigative' mechanic. A lesson for many of us.
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Old 07-19-2013, 12:30 PM   #40
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Hey guys need some help as now that I am going to be tearing the engine down I'm going to pull the other head off as well which has me thinking this would be the right time to either ceramic coat the stock manifolds or add headers. Does anyone have any recommendations of what header to use or the other route may have some manifolds that they have removed? The clearance is very tight and so is my timeline so I don't have alot of time to do trial fits. Thanks guys!!
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Old 07-20-2013, 12:33 AM   #41
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Back to the compression was 85 all across the board. What makes you so sure it is only the heads that are the problems? If it is the heads it is certainly both but 85 is low enough to bring rings and a host of things into question. You take the heads off for sure check the cylinders for wear.
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Old 07-20-2013, 05:50 PM   #42
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Back to the compression was 85 all across the board. What makes you so sure it is only the heads that are the problems? If it is the heads it is certainly both but 85 is low enough to bring rings and a host of things into question. You take the heads off for sure check the cylinders for wear.
A cylinder leakage test would help with this a lot. The rocker arms would need to be removed first. However since all of them were equal except for one, I suspect the gauge is not reading correctly.
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