Reply
 
Thread Tools Search this Thread Display Modes
 
Old 08-17-2010, 10:50 PM   #1
Lt. JG
 
Join Date: Nov 2009
Location: Ladner, BC
Posts: 21
Default 5.0 MPI Mercruiser over revving

Just returned from a short cruise on the river. 1900 SR3 with 5.0 MPI
All gauges reading normally except tach.
Normally idles at just under 1000rpm. Today idled at 1200rpm. Normal cruise is 30mph at 3200rpm. Today same speed and 4500rpm.

To be honest, my ear tells me the engine is actually idling at the normal rev level.

Could the tach have suddenly lost its calibration or is something else wrong?

I'll have it checked by my mechanic but I'm wondering if anyone else has experience with this.

Thanks!
__________________

__________________
<><><><><><><><><><>>
2006 Maxum 1900 SR3 5.0 MPI
2007 Ford Expedition Limited Max
Captain's Cove Maxum is offline   Reply With Quote
Old 08-18-2010, 01:56 PM   #2
Admiral

 
ss3964spd's Avatar
 
Join Date: Jul 2009
Location: Fairfax Va
Posts: 1,512
Send a message via Yahoo to ss3964spd
Default

Yup. Actually, your 5.0 should idle closer to 6, maybe 7, hundred RPM - which is where my 5.7 MPI always idles.

Although my indicated idle has remained the same, I have started seeing strange readings, small fluctuations, on the tach at cruise speeds in the last month or so. Sometimes it will read many hundred RPM's higher than the engine is actually running. Everything else is dead normal and there is no change in engine note to correspond with the tach changes. I don't think it's a tach calibration issue, more likely a wiring/connection or feed from the ignition system that is wonky.

Since the engine is running completely normal I've not worried about it thus far, but will eventually get around to figuring out what it is.

Dan
__________________

ss3964spd is offline   Reply With Quote
Old 08-18-2010, 02:03 PM   #3
Lt. JG
 
Join Date: Nov 2009
Location: Ladner, BC
Posts: 21
Default

Thanks Dan

Is there anyway to trouble shoot this w/o special diagnostic equipment?
__________________
<><><><><><><><><><>>
2006 Maxum 1900 SR3 5.0 MPI
2007 Ford Expedition Limited Max
Captain's Cove Maxum is offline   Reply With Quote
Old 08-18-2010, 02:07 PM   #4
Admiral

 
seapuppy's Avatar
 
Join Date: Nov 2005
Location: Everett Wa
Posts: 4,681
Default

CCM
sometimes the tach connections at the dash get a bit of corrosion on them...the tach will all of a sudden gain a few hundred rpms while the engine is running great....just tap on the tach and see if it comes back down...if it does..then it's a loose or corrroded connection...
mine has done this several times over the yrs...just tap it a few times and it should return to normal...


SP
__________________
Don't compare your life to others. You have no idea what their journey is all about.
------------------------
SSN683 Association member
Par Excellence
------------------------------
2008 Bayliner 340 - "Wild Whim"
--------------------------------------
I live in my own little world....but it's okay-they know me here!!!

Avid practitioner of the martial art: KLIK-PAO.
Tap-Rack-Bang

Anyone that sez "Size doesn't matter" has never owned a boat!
seapuppy is offline   Reply With Quote
Old 08-18-2010, 03:32 PM   #5
Lt. JG
 
Join Date: Nov 2009
Location: Ladner, BC
Posts: 21
Default

Thanks SP
Giving it a tap is quite a bit less expensive than calling a mechanic!
I'll give it a try this a.m. Gives me an excuse to visit the marina!
__________________
<><><><><><><><><><>>
2006 Maxum 1900 SR3 5.0 MPI
2007 Ford Expedition Limited Max
Captain's Cove Maxum is offline   Reply With Quote
Old 08-18-2010, 07:04 PM   #6
Lt. Commander
 
Nimh's Avatar
 
Join Date: Jun 2009
Location: Puget Sound, WA
Posts: 180
Default

My tach has recently started doing this too, especially in rougher seas. Bounce hard and it's off by 3-500 rpm's, take another good jolt and everything is back in check.

I've read it's not unusual, and it may be as simple as disconnecting the leads, clean them up and re-install. I've also heard there may be a small dial on the back of the tach for calibrating to different power plants that just needs to be cycled and set to the original increment. Again, corrosion making it behave poorly. I just haven't yet opened mine up and done it yet.
__________________
Jim and Angie
2005 Maxum 2400 SE
5.0L MPI with Bravo 3

Nimh is offline   Reply With Quote
Old 08-19-2010, 02:38 AM   #7
Lt. JG
 
Join Date: Nov 2009
Location: Ladner, BC
Posts: 21
Default

Thanks again SP!

Just gave the tach a rap with my knuckles and we're back to normal.

Saved me a whack of money .... I donated to the site as a result!
__________________
<><><><><><><><><><>>
2006 Maxum 1900 SR3 5.0 MPI
2007 Ford Expedition Limited Max
Captain's Cove Maxum is offline   Reply With Quote
Old 08-19-2010, 03:14 AM   #8
Admiral

 
seapuppy's Avatar
 
Join Date: Nov 2005
Location: Everett Wa
Posts: 4,681
Default

haha....greatly appreciate the donation....although I don't see it...but hey!!...keeps us in beer and women...hahaha..glad to help..



SP
__________________

__________________
Don't compare your life to others. You have no idea what their journey is all about.
------------------------
SSN683 Association member
Par Excellence
------------------------------
2008 Bayliner 340 - "Wild Whim"
--------------------------------------
I live in my own little world....but it's okay-they know me here!!!

Avid practitioner of the martial art: KLIK-PAO.
Tap-Rack-Bang

Anyone that sez "Size doesn't matter" has never owned a boat!
seapuppy is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Powered by vBadvanced CMPS v3.2.3

All times are GMT. The time now is 10:26 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2020, vBulletin Solutions, Inc.