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donzi182003
02-14-2005, 12:49 PM
Hello everyone,
Unfortunately I have a small problem with my Donzi. When i open it up to full throttle it has a small miss. No one else notices it but me. After examining my tach i see that I am not crazy and it is in fact there. I changed my water separator yesterday thinking it was water in the tank and it still did it. I run 87 octane. My next guess is to switch to 93 octane see what happens. If that doesnt work I dont really know where to go from there. I would really appreciate it if someone could shed some light as to what may be causing the miss. Keep in mind the motor has just over 50 hours.

Thanks,
Ed

onesubdrvr
02-14-2005, 01:25 PM
You may want to check all your plug wires and plugs. Also, have you seen any difference in temperature? Which engine do you have, some do not require the higher octane fuels, some do

Wayne

Donzigo
02-14-2005, 02:01 PM
I've run 93 for a year or so...........IMHO, it makes a big difference.

donzi182003
02-14-2005, 02:19 PM
I am also going to change the plugs and check the wires. I have a 2003 350 mpi. The manual says it should run on 87. Also I have not seen any difference in temp.

Madpoodle, where in the Keys are you all going to run to? Alabama Jacks? I may have to be in Jupiter on Saturday so I may be S.O.Luck but i might be able to get out of it.

McGary911
02-14-2005, 03:52 PM
If you're doing the plugs and wires, might as well do the coil too. Even if it isn't the problem, it never hurts to have an extra coil in the box.

Cuda
02-14-2005, 03:55 PM
I doubt the 93 will make any difference. If the engine doesn't ping on 87, it doesn't need any more than that, as a matter of fact there are some schools of thought that say 93 will make less power. The numbers indicate how hard it is to ignite basically.

I'd check the plug wires and the distributor cap. If you have access to a machine that indicates firing voltage, you should be able to track it down fairly easily.

Cuda
02-14-2005, 03:57 PM
Try running it after dark. You might find spark jumping somewhere to ground.

donzi182003
02-14-2005, 04:04 PM
I actually do have access to such a machine.My wires are 50 hours old so i dont think its the wires but plugs might do the trick. The boat runs perfect all through the rpm range so it has to be something very simple . Also my engine is electronic ignition.. no distributor. Has anyone ever had water in the gas and noticed this? because my initial thought was that it was just simply water in the fuel.

vette53
02-14-2005, 09:15 PM
Has the engine been running fine on the 87 octane? Did it run fine earlier and you just noticed this? I agree that plugs and wires are the easiest to check. What plugs are you using? Too hot a plug could lead to the detonation. Has your spark advance changed? I have seen it when the advance had changed and over advanced ignition timing causing a premature detonation. But the temp will usually go up as the cylinder pressure goes up.

donzi182003
02-15-2005, 08:39 AM
I am running the factory plugs the motor is a 2003 with 50 some odd hours so i have seen no need to change em yet. When i first bought the boat i ran 93 for 2 gas tanks then i read the manual and it says 87 so 87 it was. It ran fine and it still runs perfect. The miss is very minimal and it is ONLY at wide open throttle. I can run 4400 rpm all day long (not that I ever would) without a problem. But when i take it to 4500 it misses back to 4400-4450.

BUIZILLA
02-15-2005, 09:05 AM
I think your tach is off and your hitting the rev limiter...

JH

donzi182003
02-15-2005, 09:45 AM
I also thought the rev limiter was the problem but if it was that, why would it still continue to do it with passengers on board and why didn't it ever do it before? I also run a 25p mirage prop. It would be very difficult to over rev a 350 mpi with a 1.62 drive ratio with a 25p. Im goin nuts here.

Frustrated,
Ed


P.S. Does anyone know how where I could find a conversion sheet for the Mercury plugs to NGK plugs?

donzi182003
02-15-2005, 09:59 AM
Allright... I spoke to a mechanic and he tells me my boat has an in line fuel filter that is probably clogged. I am still in shock that I did not realize that i had an in-line:splat: I also found out from him that I have platinum spark plugs and they last over 100 hours. He makes a good point. He says if the plugs were bad it would miss through the rpm range. I really hope this works.

Blewbyu
02-16-2005, 03:22 PM
Put your plugs on a plug tester.Pressure increases as rpm builds-and plugs DO tend to miss more at high RPM.If your plugs are Champion-waste 'em. Use single elecktrode plugs-NGK is consistently good. Platinum is not necessary. Overrated. Clip a timing light near each plug to see if you have a wire that intermits.Make sure all wires securely plugged into cap. If your plugs are easy to reach-replace them at the beginning of each season.Cheap insurance.
Regards-Blewbyu

donzi182003
02-16-2005, 03:45 PM
Thanks alot guys for all your advice. I am going to start the process of elimination today. I actually called MC marine which is a certified merc dealer and they told me that i need to give em the serial # on the motor and they are going to check if the thing is still under warranty. They say Merc had a few promo offers in 2003 in which they gave 3 yr warranty. If thats the case ill fix my problem and take it to them to run a diagnostics on it just in case. Ill be sure to post when I get the boat runnin 100%.

Thanks,
Ed

Ranman
02-16-2005, 04:11 PM
I also thought the rev limiter was the problem but if it was that, why would it still continue to do it with passengers on board and why didn't it ever do it before? I also run a 25p mirage prop. It would be very difficult to over rev a 350 mpi with a 1.62 drive ratio with a 25p. Im goin nuts here.

Is that 1.62 drive a Bravo or Alpha? Shouldn't matter but something sounds off to me. I have a 97 350 MPI+ and 1.65 bravo one and can turn a 25P Mirage every bit of 5000RPM. In fact, I put a nice K&N arrestor on the intake and now pull it to 5200 on the tach at 70.5MPH. Granted I have an unusually strong motor, but 4500 doesn't sound right to me? Are you trimming the drive up at WOT? What is your top speed?

MOP
02-16-2005, 04:45 PM
I am with Blewbyu on the pressure issue, the plugs do get harder to fire under load at high RPM and will often arc at the to the plug base or coil body. Revving an engine under no load many times will not produce the arcing. Even with best plugs and wires it is important to use grease both on the plug boots and coil towers. I have never seen a service manual that does not have it as a step during cleaning and reassembly even the lowly Sealoc says to use extreme pressure grease. I like the silicone supplied by the manufacturers of high perf ignition systems.

Phil

donzi182003
02-16-2005, 07:24 PM
RANMAN

I Turn 4500 Rpm With A 1.62 Alpha. Top Speed Is About 66 Gps As Far As I Have Seen. I Have Never Held It Wot For More Than 30 Seconds In Order To Acheive Top Speed. The Engine Says That The Wot Rpm Should Be 4600-5000. I Got The Serial # To The Engine Today And I Am Going To Call The Dealer Tomorrow To See If The Warranty Is Still In Effect. P.s. I Am Not Totally Ignorant.. I Just Bought The Boat From Someone Else And He Was Not Very Knowledgeable On The Warranty Info.


Ed

Ranman
02-16-2005, 10:28 PM
RANMAN

I Turn 4500 Rpm With A 1.62 Alpha. Top Speed Is About 66 Gps As Far As I Have Seen. I Have Never Held It Wot For More Than 30 Seconds In Order To Acheive Top Speed. The Engine Says That The Wot Rpm Should Be 4600-5000. I Got The Serial # To The Engine Today And I Am Going To Call The Dealer Tomorrow To See If The Warranty Is Still In Effect. P.s. I Am Not Totally Ignorant.. I Just Bought The Boat From Someone Else And He Was Not Very Knowledgeable On The Warranty Info.


Ed

Are you trimming the drive up to get max speed and RPM'S?

donzi182003
02-17-2005, 08:38 AM
You bet I am. trimmed down ill only get 4100-4200

Morgan's Cloud
02-17-2005, 10:21 AM
You say that you don't have a distributor ?

My friend with the 28ZXO had a high speed miss just like yours a few months ago ... 350 Mags late 2003 I believe.. After a thorough going through the mechanic discovered that the contacts in the distributor caps were all bunged up from the environmental conditions in the engine room ... vents appeared to be allowing in large amounts of very salty air ... even though engines look absolutely new.
He felt that there must have been a defective batch of caps that Merc used as he's never seen that on an engine with such low hours .

Changed them out and all is well again !

Hope it's that simple for you ...

donzi182003
02-17-2005, 10:29 AM
Morgans Cloud,

My Engine Does Have A Distributor What I Meant To Say Was That It Doesnt Have Points.had A Brain Fart.. Sorry. That Scenario Actually Makes A Heck Of Alot Of Sense. I Havent Taken The Cap Off To Check. Like I Have Said Before It Has To Be Something Minor Such As That. Ive Been So Busy Lately That I Havent Had Time To Try To Correct The Problem. I Appreciate The Input Because I Dont Want To Have To Spend Too Much Money Replacing New Parts In All The Wrong Places. Thanks To This Thread I Have Been Able To Hear Quite A Few Angles To Approach The Problem. Ill Let You Know How The Cap Looks.

Thanks Alot,

Ed

Rootsy
02-17-2005, 10:48 AM
get in the habit of replacing the cap, rotor and plugs every spring... and make sure you put a dab of never-sieze on the threads for the screws holding the cap down... and a smear of grease on the distributor shaft where the rotor slides over...

JR

donzi182003
02-18-2005, 08:34 AM
Morgans Cloud,

I took the distributor cap off this morning at 6 am and as you predicted it had salt on it despite it looking brand new. The amount of salt was pretty significant so I am crossing my fingers that the problem lies there. If i can get out of work early enough today I am going to take it out and check it out. I cleaned the cap for now and it ran fine at home but I am most definitely going to change cap and rotor right away. Ill keep ya posted on what happens.

Thanks,
Ed

Morgan's Cloud
02-18-2005, 09:09 AM
Ed ,

It is'nt too often that I know about a cure and it's simple also :biggrin:

What confused my friend when he had this problem was that it coincided with him almost running the fuel tank dry and he thought it was fuel related (dirt in tank got sucked up). Did'nt sound like that to me but strange things happen to boat engines huh ?

Let us know how it goes .

Steve

Actually, while I'm at it ... this reminds me of how valuable it is to know where we do our boating ... as in we say where we are located under our board name !

If I did'nt know you were in a salty environment and assumed you were in fresh water , your question would'nt have been as significant to me ...
(just something else to ponder ... ;) )

donzi182003
02-21-2005, 12:26 PM
Hey everyone I have some bad news about the boat. I took out cap and rotor, cleaned it and changed spark plugs. On Friday afternoon i took it out and it still missed. However there was some good news. After running for about 5 minutes an intermittent alarm went off. This alarm means that the engine is receiving a fault code from the smartcraft system. After a bit of research i found out that the smartcraft has a guardian mode that if a certain fault code is sensed the engine will go into guardian mode, therefore only allowing me to use 90% of its power (explaining low wot rpm Ranman). My mech is comin tomorrow to plug it into the computer. Ill let you know how it turns out.

Ed

Dax McDavid
02-21-2005, 12:59 PM
I agree with morgans cloud it sounds like an electrical corrosion problem. Have an 2001 22zx did the exact same thing. Mechanics looked all over that sob and found nothing. I looked over it myself and found that the main ground wire for the engine was hooked up to a corroded connection in back of the boat. Took the connection apart cleaned it sanded the rust off with sandpaper has ran great ever since. Donzi placed this main ground connection right below the air vent that water constantly washes in while standing in waves. I am telling you check this out first before you spend alot of money doing diagnostics our symtoms sound exactly alike!!!!!!!!!!!!!!!

:smile: daxmc

donzi182003
02-24-2005, 09:46 AM
Hey Guys I Had My Mechanic Come Over. The Bad News Is That The Damn Thing Is Out Of Commission For A Week. The Good News Is That Mercruiser Is Payin For The Part. Afetr Hooking The Boat Up To The Computer I Had My Mechanic Give Me A Scolding For Revving The Boat Up In Neutral To 4250 Rpm... I Told Him There Was No Way In Hell That I Could Be Stupid Enough To Do That And I Held My Ground. After 5 Minutes More Of Fidgeting With It He Told Me That He Was Wrong And Apologized For Making The Accusation That I Was A Complete Neanderthal And I Had No Idea How To Use A Boat. It Turns Out That The Sensor That Tells The Smartcraft Whether The Motor Is In Gear Or Not Is Fried. The 4200 Rpm Was Me Runnin Across The Bay At 60 Mph And The Sensor Thought The Boat Was In Neutral. All My Shift Brackets And The Sensor Need Replacing. The Miss Is Because The Motor Thought It Was At 4200 In Neutral, Guardian Mode Was Turned On. Guardian Mode Lets You Use Only 90% Of Your Power. Looking At The Smartcraft I Could See That In The Neutral Position The Computer Said "in Gear" And In The Forward Position It Said "neutral". Last Thing I Was Expecting It To Be Ill Tell Ya That Much. Just Letting Everyone Know That The Intermittent Beep Heard Every Minute Is Not Always Low Drive Oil. It Could Mean That Theres An Active Fault Code, As I Have Now Learned.

Releived,
Ed

Morgan's Cloud
02-24-2005, 09:54 AM
And just imagine how much better it's going to run with a nice clean distributor cap too :biggrin:

I feel your relief .

Steve