350 magnum mpi mysterious failures

ljc cox · Apr 14, 2006

Re: 350 magnum mpi mysterious failures

We currently have a Merc technician looking at the engines. We have worked with him before on an unrelated problem and he seems knowledgable. However, so far he is mystified. The serial numbers are:OL67588 and OL676592. We buy our fuel at several places. They all sell either 87 or 89 octane. Have not checked knock sensors, but will do so. Thanks for the tips everybody. Lots of stuff to ask Mercruiser about. Laura Houston Tx

Don S · Apr 14, 2006

Re: 350 magnum mpi mysterious failures

Your OL67588 number is one digit short, and was trying to compare the engines. Would really like to see the info on that engine as well. Seems back in Nov. 2001 there were some problems getting the proper rpms on the OL676592 engine, along with some ignition problems later on. How was that all resolved???? Have you had any Merc reps visit since 2001 when the long block was installed in the '92 engine? When I say Merc reps, I mean directly from Mercruiser that fly in as Billy Powel did in 01, not just the techs and owners of the local buisness.

ljc cox · Apr 15, 2006

Re: 350 magnum mpi mysterious failures

Hi Don, Thanks for checking all this. The full number os OL675888. On the other engine(starboard), after replacement of the long block, we had numerous complaints, primarily that it would not make rated power. At first it would only develop a maximum rpm of 4500-4600.They changed the props and tuned them several times.They changed the fuel sensor. At one point "strange" timing marks were noticed. The Marine Max mechanic advanced the timing 2 degrees with a slight improvement in rpm. Mercruiser told MM to set base timing again, adjust tachs and throttles. Proprs were retuned again to 4850 rpm and sync pod changed. Both engines in acceptable range. Except, now throttles sloppy and have as much as six inches spread. Tuned props again. New MM mech notices prop shafts need alignment. After props tuned and prop shaft align, both engines at 4800 rpm. Later, synced rpm drops to 4600. Port engine develops problem and fails. Found broken spark plug, good compression check. Port 4800/starboard 4600 rpm max. Husband notices mismatched flame arrestor covers. Port says "ski" model with max WOT 5000rpm. Starboard has different placard with max WOT 4800rpm. Mercruiser (Billy Powell) says engines are the same and sends new cover for port. Props retuned again. No help. Port fails again. Found no spark on #5cylinder. Bad ignition coil and ignition sensor. Both replaced. Were told that 4600 rpm was best starboard will do in hot weather. Port makes 4800 rpm in same weather. Installed flowscan. Discovered starboard consumed 2 gph more than port. Dan Pride and MM says normal. Basically told everything normal (i.e. go away). At that time, the only difference was the rpm and fuel flow and evryone involded swore it was normal. If you have any insight, please let me know.... Thanks !! Laura

ljc cox · Apr 15, 2006

Re: 350 magnum mpi mysterious failures

Don, Billy Powell was at the boat last year after the port replacement because we kept smelling gas but Mm couldn't find leak. We finally discovered oil leak. Fixed, cleaned up, and smell went away. Thanks Laura

ljc cox · Apr 17, 2006

Re: 350 magnum mpi mysterious failures

Hi Don S. Hope you had a good weekend. Any insights to offer us on cause of failure. I've been doing some more research and am coming across a lot of opinion that the boat is probably underpowered. This combined with an auto engine that really wasn't designed for the work it is doing, is dramatically shortening the engine life. Thanks for your time !! Laura

muc · Apr 17, 2006

Re: 350 magnum mpi mysterious failures

Hi Laura, Sorry to hear about your problems. When you have had the props retuned was this done at a prop repair shop that uses prop scan or MRI? If not I think that would be a good starting point. When you talk about total failure two times on the port motor, do you mean the long block was replaced twice or was it when the ignition coil and spark plug went bad? A better time line of what happened when and what parts were replaced will help with diagnosis. Why were the V-drives replaced? When you talk about the 2 gal. per hour difference, do you mean at all R.P.M.s on the flowscan? What does the mechanics laptop computer/DDT (scan tool) say about fuel flow? Why did correcting an oil leak cure a gas smell problem? I would be happy to help you but as you can see I have many questions. Muc

ljc cox · Apr 18, 2006

Re: 350 magnum mpi mysterious failures

Dear Nuc, Thanks for the sympathy. The props were sent out to a shop by Marine Max. I am not sure how they did it. Will check! Which method is better?? The port has failed once. January 05. Long block replaced. Blown headgasket and destroyed piston. MM couldn't tell me why it failed. The starboard longblock was replaced by Mercruiser when the boat had 30rs due to excessive oil consumption during breakin. After replacement, the engine never made more than 4650 RPM. Props tuned, ingnition coil changed, new plugs, etc. It ran for a short time at 4800 then fell back to a maximum of 4650. Mercruiser said that is just that engine's max. After we installed flowmaster guages, discovered starboard burned 2 gph more than port all rpm. MM said that was normal. V drives never replaced. I don't know what the mechanics laptop/DDT said. Am not sure they checked?? Oil leak - supposedly the smell was the solvent in the oil being hot. Whatever the reason, after the oil was fixed, there was no more odor. According to our current mechanic, the ECM's show no fault codes or record of overtemp or RPM.There is also no evidence of water ingestion we are told. The SB engine does show evidence of excessive fuel burn - all black and sooty according to mech. What's your take???? Thanks!!! Laura

Don S · Apr 18, 2006

Re: 350 magnum mpi mysterious failures

Since you are doing this all on your dime, why not swap the ECM's from one engine to the other. Quick and easy way of eliminating the question of the ECM somehow limiting the rpm. You can also do that with other suspected parts.

ljc cox · Apr 19, 2006

Re: 350 magnum mpi mysterious failures

They tried swapping ECM's not long after the first starboard longblock was changed in order to see if that would improve RPM. No difference. Besides, the starboard engine is in pieces on the shop floor. My main thing is to figure out what could cause BOTH engines to fail at about 400hrs. It seems like too much of a coincidence to me. Thanks Laura

muc · Apr 19, 2006

Re: 350 magnum mpi mysterious failures

Hi Laura, Prop scan or MRI are both good and is the only way I know to be sure the props are matched. After the props are matched it would be a good idea to test fuel pressure and gallons per hour at all R.P.M.s, check to see if the DDT agrees with your flow scan. Your mechanic should be Certified or Master Mercruiser, ask to see his diploma. What R.P.M. do you usually run at? Muc

ljc cox · Apr 19, 2006

Re: 350 magnum mpi mysterious failures

Hi Muc, The mechanic is mercruiser certified. Spoke to Billy Powell ( Mercruiser Rep) and the only answer they can come up with is the combustion chamber is getting too hot because the engine is working too hard. Why is the engine working too hard, is the next question. They are looking into the drives and propeller and gearing. Hoping to get some answers and solutions soon. Will let all you guys know what the end result is. I do appreciate the inputs. They really helped us talk to Mercruiser and Sea Ray. Thanks Laura

muc · Apr 19, 2006

Re: 350 magnum mpi mysterious failures

Hi Laura, The reason I ask about The R.P.M.s that you spend most of your time running at is because I have had a few customers that have experienced the same types of failures. The only reason that I was able to come up with was that they all would spend a lot of time at 2500 to 3500 R.P.M. and that seems to be a speed that a cruiser style boat motor is working very hard. I feel that this can lead to excessive combustion chamber temperatures. I either instructed them to change their operating habits or did a prop change to better suit how they ran their boat and havent had any repeat failures. I hope that you are able to find what is causing your failures and correct it. Good Luck Muc

lilmandavis · Apr 19, 2006

Re: 350 magnum mpi mysterious failures

i know that on the sea ray im working on right now that there are no exaust flappers. and when i lowered the boat off the lift it almost sunk itself without the exaust rubbers on. the water line is only like 5 inches from the bottom of the riser. no evidence of water consumption except a broken rod!! low compression gives soot. its got the 5.7 liter mag in it. well it did. its a 2000

bandit86 · Apr 19, 2006

Re: 350 magnum mpi mysterious failures

I wonder if you got a bad series of O2 sensors, the ecm will compensate for a lean or rich signal and not give trouble codes untill an open or short circuit is detected. if you O2 sensors are wrong 10-20% you could be running extremely lean without your computer knowing anything is wrong because by leaning your engines out it achieved the air/fuel ratio it is looking for.

lilmandavis · Apr 19, 2006

Re: 350 magnum mpi mysterious failures

maybe they are sucking a little amount of water and the rings are grinding away with the silt in the water? maybe thats why the oil smelled like gas? is there excessive blowby? is the oil thin or does it still have its viscosity? black oil? or clear brown? does it steam at the docks? (exaust?)

Reel Poor · Apr 19, 2006

Re: 350 magnum mpi mysterious failures

I agree with muc, and he has reinforced what rodbolt posted earlier. That boat needs to be proped so the wot rpm is right at 5200 rpms to get any life expectancy out of engines at all. I would still recommend a set of big blocks, they would cure your boats ailments but would probably make your check book sick.

uaw9fan · Apr 19, 2006

Re: 350 magnum mpi mysterious failures

Sorry bandit.Boats don't have O2 sensors Yet!!!!. Good thought though.

ljc cox · Apr 20, 2006

Re: 350 magnum mpi mysterious failures

Hi Everybody, Great comments. Muc, I think you hit the nail on the head. Merc has all but admitted that running this set of engines at the boat manufacturer reccommended best/fuel efficient speed/RPM results in excessive combustion chamber temperatures and premature failure of the engine. Merc and Sea Ray are talking. Haven't heard back yet. Laura

Reel Poor · Apr 20, 2006

Re: 350 magnum mpi mysterious failures

Thats cool they're talking to themselves. Sea Ray, Mercruiser and many others are all owned by the Brunswick Boat Group. At least they're doing something. Go here and look. brunswick.com

ljc cox · Apr 21, 2006

Re: 350 magnum mpi mysterious failures

Yeah, I've known that for a long time. They also used to have a stake in Marine Max, but sold that a while back. Nobody called me today. Will have to give them whatfor again about not returning calls on Monday. Squeaky Wheel Laura

350 magnum mpi mysterious failures

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