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502 MPIs

Old 02-23-2017, 05:27 PM
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This should be good.......
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Old 02-23-2017, 06:30 PM
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Problem solved!!!

Someone messed with the timing.... bad!

I put her into service mode to check timing and codes. The only code was for the manifold air temp (23) and that's because I disconnected it. So, checked timing... 35 degrees btdc in service mode. No wonder she wouldn't run right!! Set the timing at 8 degrees.... running like she's supposed to!

Thanks for the suggestion about the timing!!
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Old 02-24-2017, 06:46 AM
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Originally Posted by articfriends
I haven't tested, flowed and cleaned a set of mpi 502 injectors YET that didnt have at least one low one and one high one, fwiw. Definately get injectors flowed and cleaned before trying to drive boat in case they ARE screwed up so you dont melt a piston!
Yeah what he said! I flow tested my two years ago, well last year one got clogged...melted a piston. Flow testing and cleaning of injectors will now be part of yearly maintenance.
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Old 02-24-2017, 07:40 AM
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Are injected engines that much more prone to failure? Is this just a 502/454 MPI issues, or does this affect the blue engines and 496?

How many hours is one looking at in terms service interval? And, is it possible to treat the fuel so that the interval can be extended or prevented, or is there some type of design flaw with the injectors themselves that causes flow issues?

Kind of scary folks!
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Old 02-24-2017, 08:00 AM
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Good story, usually the opposite.. Run techtron thru it to clean injectors.
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Old 02-24-2017, 08:08 AM
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Yes, usually the story is quite the opposite.

I think there was some funny stuff going on with the deal; perhaps they were really looking to keep the boat from being sold. After going over everything, I cannot believe that this mechanic could have gotten the engine this far out of whack without it being on purpose.
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Old 02-24-2017, 08:13 AM
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Its possible the distributor slipped being that its on a reverse rotation engine
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Old 02-24-2017, 08:21 AM
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Old 02-24-2017, 11:37 PM
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Originally Posted by TomZ
Are injected engines that much more prone to failure? Is this just a 502/454 MPI issues, or does this affect the blue engines and 496?

How many hours is one looking at in terms service interval? And, is it possible to treat the fuel so that the interval can be extended or prevented, or is there some type of design flaw with the injectors themselves that causes flow issues?

Kind of scary folks!
Maggetti marelli fiat injectors on the 98 to 2001 454/502 mags arent the greatest for matching, even new from mercruiser, a east coast guy sent me 8 new injectors he paid the big dollar for from mercruiser, 1 flowed 8 to 10% lower than 6 that were close, 1 outflowed the rest by 16 to 20%, he ended up getting two more from a place in fla or georgia that flowed really close to the 6 good ones for about 90$ a piece instead of the 150 or 160 each he paid for from mercruiser. Brian orlandi had same problem, he was flowing, testing and installing 16 new ones on a boat that had some kind of insurance claim, he ended up using 5 or 6 old ones to get 16 that matched fwiw. I always thought mercruiser tuned stock 502s pig rich out of laziness and retuned them much cleaner but now im convinced they do it because they were avoiding warranty claims from injectors flowing low, especially over time as they get older and fouled up. I have done about 15 sets of 454/502 mag gen 6/mefi3 injectors now since buying my machine last year and have seen mismstched flow in almost every set. About half of them came to.me after guys melted a cylinder, i would never run a 15 or 20 year old efi motor in something i owned without pulling injectors and checking/cleaning themnon a machine, cost so little compared to a meltdown, Smitty
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Old 02-25-2017, 07:15 AM
  #30  
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Hey TomZ - anyway you can find out what other boats these people worked on, or what they work on in the future ? A lot of us may be interested in them when they go up for sale right after said work is done.

Edit in; though if run under load one would think headgaskets and/or piston damage may occur.

Last edited by SB; 02-25-2017 at 07:20 AM.
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