Reply
 
Thread Tools Search this Thread Display Modes
 
Old 06-01-2020, 06:56 PM   #21
Veteran Member
 
City: Alpharetta, GA
Vessel Name: About Time
Vessel Model: Meridian 368
Join Date: Mar 2020
Posts: 30
So, a quick update and the saga continues. MarineMax came out a couple of days ago and used the diagnostic tool on the engine. They said that I was having a multiple cylinder misfire and that the IAC was running at almost 100% duty cycle...or something like that. They were going to replace the IAC, but the mechanic thinks that may not be the issue. He thinks it's my plugs.

About 6 months ago, I replaced my plugs using the plugs and gap specified in the Service Manual (AC Platinum 41-983, gap 0.060). This particular mechanic has taken issue with me using the AC Delco plugs ever since I installed them even though that's what the manual specifies. He says they're crap and that I should have used NGK plugs. As near as I can tell, the engines have been running fine for the last 5 months.

More importantly, he's telling me that the 0.060 gap in the manual is a 'well known' misprint, and that the correct gap is 0.045. Before I incur the expense of the IAC replacement, he is suggesting that I replace all of the plugs with NGK and a 0.045 gap. I can't find anything online to substantiate that there's a misprint in the manual. Every reference that I find says the same thing, AC Delco Platinum 41-983 with a 0.060 gap.

I was wondering if anyone was familiar with the MerCruiser 8.1L (496) engine and has heard about this 'misprint'.

I sure don't want to go through the trouble of changing 16 plugs unnecessarily and possibly gapping them wrong on top of that. He's not trying to get me to pay him to do the job. He even loaned me a couple of tools to do it myself. He seemed very sure of himself on the 0.045 gap.
__________________
Advertisement

__________________
Frank
Frank60 is offline   Reply With Quote
Old 06-02-2020, 08:59 AM   #22
Senior Member
 
Newtrawlerowner's Avatar
 
City: Delray Beach, FL and Denver, CO
Vessel Name: PartnerShip II
Vessel Model: 2003 Mainship 400
Join Date: Nov 2019
Posts: 176
The IAC is at 100% because the engine runs so rough due to the misfire. I seriously doubt replacing the IAC (Idle Air Control) will have any effect.
As far as spark plug gap a narrow plug gaps burn excessive fuel better leading to less plug fouling while a wider plug gap can foul easier and requires a higher ignition coil voltage. The trade off is in higher RPM engine performance. The engine manufacturer tests the engine and its systems for maximum performance at all RPM ranges. Run a narrow gap and you may find you have other performance issues.


If the manual has "A well know misprint" ask the mechanic to show you some reprinted page or bulletin that shows the correct gap.



Several other forums about Mercrusier mention the plug type to use. Some of these engines came with Denso plugs and while others used NGK or AC Delco.

AC Platinum 41-983, gap 0.060 is the preferred plug for this engine as per several other forums. I really think its user preference. Maybe this mechanic had a bad experience with AC plugs and decided to use NGK.

I would question the 0.045 gap though. I don't think the engine will perform properly.

When I've gotten information that I either don't trust or is contradictory to what I believe to be true, I ask several others with knowledge on the subject for their professional opinion. Call several other boat repair shops. Avoid talking to the "front counter". Call some smaller shops where you are talking to the guy that actually maintains boats. But call 2 or 3. You will get a consensus on what spark plug to use and what gap should be.
As a business consultant I tell my clients I will never tell them anything I can't prove using other sources.


The bigger issue is why are the plugs fouling. A leaking fuel injector(s), faulty fuel pressure regulator, a weak ignition coil or even a couple of bad spark plug wires can cause source of the problem. Once you correct the misfire, run the engine(s) to see if the problem comes back. If so you fixed the symptom but not the cause.
__________________

Newtrawlerowner is offline   Reply With Quote
Old 06-03-2020, 05:27 PM   #23
Senior Member
 
Mischief Managed's Avatar
 
City: Hampton Beach, NH
Vessel Name: Mischief Managed II
Vessel Model: 1992 Tollycraft 44 CPMY
Join Date: Oct 2018
Posts: 378
.045" gap is normal on older Mercruiser engines. I would use the recommended .060" on the 8.1 unless you changed to MSD ignition instead of the stock stuff. Swap coils from one engine to the other and see if the problem follows the coil. I cannot recall all the details, but have you ruled out water in the fuel?
Mischief Managed is offline   Reply With Quote
Old 06-03-2020, 06:29 PM   #24
TF Site Team
 
Comodave's Avatar
 
City: Au Gres, MI
Vessel Name: Never Say Never
Vessel Model: President 41 DC
Join Date: Jul 2015
Posts: 11,856
Have you contacted Mercury corporate support? I don’t have Mercury engines but they must have some kind of phone support for issues like this. Ask them about the well known misprint and see if they know about it. Also if MarineMax replaces the part and it doesn’t fix the problem are they willing to reinstall the original part and not charge you for the unneeded part?
__________________
Boat Nut:
If you are one there is no explanation necessary.
If you aren’t one, there is no explanation possible.
Comodave is online now   Reply With Quote
Old 06-03-2020, 06:57 PM   #25
Guru
 
KnotYet's Avatar
 
City: Los Angeles
Join Date: Feb 2020
Posts: 637
I would pull a plug or two from the misbehaving engine just to have a look.
If they are clean and grayish to light brown that means those cylinders are firing ok.

Do your engines have HEI distributers? The ones with the coil built into the cap?
KnotYet is online now   Reply With Quote
Old 06-04-2020, 03:36 PM   #26
Veteran Member
 
City: Alpharetta, GA
Vessel Name: About Time
Vessel Model: Meridian 368
Join Date: Mar 2020
Posts: 30
Confirmed Plug Gap

I spoke with Mercury Marine and a couple of other mechanics and confirmed that I have the right plugs and properly gapped. Not that that's settled, we can go back to looking for the cause. Waiting for MarineMax to come back to continue diagnostics and/or replace the IAC. On the lake here it seems that everyone is backed up two or three weeks for service. That's painful when the weather is so nice, and I'm stuck at the dock. Thank you for everyone's input.
__________________
Frank
Frank60 is offline   Reply With Quote
Old 06-04-2020, 03:43 PM   #27
Veteran Member
 
City: Alpharetta, GA
Vessel Name: About Time
Vessel Model: Meridian 368
Join Date: Mar 2020
Posts: 30
Quote:
Originally Posted by KnotYet View Post
I would pull a plug or two from the misbehaving engine just to have a look.
If they are clean and grayish to light brown that means those cylinders are firing ok.

Do your engines have HEI distributers? The ones with the coil built into the cap?
My engines are fuel injected. There is an individual ignition coil at each cylinder.
__________________

__________________
Frank
Frank60 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



» Trawler Port Captains
Port Captains are TF volunteers who can serve as local guides or assist with local arrangements and information. Search below to locate Port Captains near your destination. To learn more about this program read here: TF Port Captain Program





All times are GMT -5. The time now is 01:52 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012
×