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496 beep and rpm fluctuation

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496 beep and rpm fluctuation

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Old 09-18-2017, 10:19 AM
  #21
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to be clear you posted -- a 496 MAG Not the HO MAG ?

you have to get the correct PCM - there is different PCM's - you have to watch out what you buy and these sellers on the net are clueless with no idea how the operations of one apps truly works. . They have no idea that an inboard ECM / PCM is different that an I/O ECM / PCM and that HO is different than a MAG no HO --- just a few examples of the many.
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Old 09-18-2017, 10:23 AM
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Originally Posted by BUP View Post
Have you replace the TACH and or checked all of its harness adaptions here ? Connections at cannon plug ? transom harness connections ?

I know I replied to this guys post. Maybe its interference from the empty beer bottle and beer koozy ? haha

Where is this guys post ?

New TACH, no. The engine physically turns off and back on. You can feel it the boat, it lists to port side when it happens. I like the Alt wiring theory. I know the shop has no put that down on any of it's inspections, nor have I checked it.

All tho I just had to replace the IAC on that engine......... Since replacing it he has not reported the engine off/on problem.

The engine harness, connections, and 12 or 15 pin connector were "supposedly " Unplugged and inspected for damage by the shop.
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Old 09-18-2017, 10:26 AM
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depending on serial number 10 pin or 14 pin
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Old 09-18-2017, 11:11 AM
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Originally Posted by BUP View Post
for the 555 controller most likely an alternator wire issue would should in the scan as a Voltage fault. Wanted to mention this from the post that were brought up about that issue. Also voltmeter testing would have found that problem as well. always start at the battery and work way thru all the other power systems, ie starter cables, power relays and or breakers, alternator and so on.

If you want to send me your PCM I can see if I can fix it . If I can not for a fix - a very min charge like 50 bucks with shipping back to you would be included.

If I can fix it of course the changes will apply depending on what is the issue(s). Not all PCM 's are repairable.

I will not be available until next Monday. So far I have fixed about 60 percent of the 555 PCM's / ECM's With that said I have not done that many but gaining more ground for that part of the business.
Thanks, I may take you up on that. Looking for another one to get my by for now, and will more than likely send this one out for repair and keep as a spare.
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Old 09-18-2017, 11:15 AM
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Originally Posted by BUP View Post
to be clear you posted -- a 496 MAG Not the HO MAG ?

you have to get the correct PCM - there is different PCM's - you have to watch out what you buy and these sellers on the net are clueless with no idea how the operations of one apps truly works. . They have no idea that an inboard ECM / PCM is different that an I/O ECM / PCM and that HO is different than a MAG no HO --- just a few examples of the many.
Correct, mine are not HO's.

The ebay ad listed above shows Part number 866090T05 is in the description, but shows 8M2002205 on the unit itself. Seller told me "dont worry about the number difference as that number is used by mercury only". I don't trust it.
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Old 09-28-2017, 08:42 AM
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[QUOTE=BUP;4583002]

If you want to send me your PCM I can see if I can fix it . If I can not for a fix - a very min charge like 50 bucks with shipping back to you would be included.

If I can fix it of course the changes will apply depending on what is the issue(s). Not all PCM 's are repairable.
QUOTE]

The new PCM solved my issue. I'd like to send you the old one to see if it can be fixed, so I can have a spare. Let me know if you want to look at it. I tried to PM you, but you are full. PM me with how to contact you.
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Old 09-28-2017, 05:15 PM
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Sorry about the full OSO Pms. I sent a visitor message and a PM to you. You can send me your PCM 555 as I PM all the info. THANKS.
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Old 08-09-2018, 12:14 AM
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I am having the same problem!!! Were you able to get your pcm repaired? Would love some HELP
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Old 08-09-2018, 02:07 AM
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this PCM in the thread had multiple issues, Clock chip, IAC circuit and capacitors. Let me know if I can help and testing of the PCM 555
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Old 10-23-2019, 12:20 AM
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Hi, newbie here. I am having a very similar issue on my 2006 Mercruiser 496 mag 0W632320

I get a single short beep, drop in revs and then immediately returns and carries on ok. Usually happens shortly after starting (about first 5 minutes) and usually only once per trip although have had a couple more occasionally.

last time I went out I did a bunch of runs to try and figure out what is happening.
I noticed that when the beep occurred the revs dropped to about 600 - you can feel the boat slow momentarily- but it doesnít sound like it is running rough or misfiring- the alarm is a single beep for about a second. Boat then carries on running as normal. This was happening shortly after starting up - within a few minutes. I did about 7 or 8 starts and it happened every time.

The revs showing on the Smartcraft tachometer drop and the digital voltage display on the Smartcraft gauge goes down to 0 volts for a few seconds but the display stays live. The analog voltage gauge doesnít move.

I have VesselView mobile and it doesnít give me any fault codes.

I started checking all of the connections to see if it could be a ground short but havenít found any loose or damaged connections.
Have checked all fluids and all ok.
I checked the harness connection at the engine and that seems ok.

Strangely enough - I disconnected all of the Smartcraft gauges and just left the VesselView Mobile hooked up and the problem became a lot less frequent. I did about 5 starts and it didnít happen but then on the last run out it happened after about 25 minutes. Iím guessing that is just coincidence that it improved when the gauges were disconnected. Iím not sure if a fault in the Smartcraft gauges or CAN cable could cause a problem.

So I think it is fair to assume that I am losing voltage somewhere in the system....the fact that the gauges stay live and show 0volts....does that mean that my ignition switch and harness are ok or is that too much of an assumption? Is the interruption so quick that the gauges donít respond?

Noting that the previous issue on this thread was resolved by a new PCM (and the similarity in serial #) - is there an easy way to test if my issue is Ďupstreamí or downstream of the PCM?

I am based in Australia and donít have a scanner but do have multimeter.

Thanks for any guidance, tips or ideas!
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