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29-08-2009, 11:23 PM
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#1
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Registered User
Boat make: Donzi 22ZX
Engines: 454 mag mpi
Cruising area: Solent
Join Date: Jul 2009
Posts: 29
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454 mag mpi problem?
Hi guys, any help appreciated.
My temp gauge is swinging up and down like a loon and causing my boat the run bad, i presume the ecu is thinking its in cold start and chucking loads of fuel in? any ideas on whats causing this to happen?
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30-08-2009, 09:45 AM
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#2
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Registered User
Country: Guernsey
Occupation: Engineering
Boat make: None, boo!
Engines: Turbines mainly!
Cruising area: The inside of my workshop!
Join Date: Mar 2008
Posts: 2,646
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Bad sender, the gauge won't make the engine run rough, but the ecu may take a feed from it's sender which is causing the issue you describe?
Best to take it out and test it in a pot of water with a voltmeter
James
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30-08-2009, 10:11 AM
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#3
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Registered User
Boat make: Donzi 22ZX
Engines: 454 mag mpi
Cruising area: Solent
Join Date: Jul 2009
Posts: 29
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My mechanic told me the ecu and the gauge have seperate senders so unlikely both are wrong?
he changed the thermostat and its still the same.
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30-08-2009, 11:24 AM
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#4
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Registered User
Country: Uk
Location: London
Occupation: Mercury main dealer
Boat make: Baba
Engines: 200xs
Join Date: Feb 2008
Location: London
Posts: 361
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There is a seperate sender for the guage and a seperate sender for the ecm. Both senders are located in the thermost housing.. If the guage is flickering and the engine is running rough, then the only thing the have in common is the thermostat so thats where i would be looking first.
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30-08-2009, 12:30 PM
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#5
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Registered User
Boat make: Donzi 22ZX
Engines: 454 mag mpi
Cruising area: Solent
Join Date: Jul 2009
Posts: 29
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Thats what my mechanic said, its had two new thermostats in it now and its still the same. bit lost with it tbh.
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30-08-2009, 01:12 PM
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#6
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Registered User
Country: Guernsey
Occupation: Engineering
Boat make: None, boo!
Engines: Turbines mainly!
Cruising area: The inside of my workshop!
Join Date: Mar 2008
Posts: 2,646
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Is it possible the problem isn't related to the temp gauge giving dodgy readings then? You could just have a dodgy gauge sender and some other totally unrelated problem.
Whilst i know nowt about this specific engine, i'm figuring that the only reason the gauge is reading off is that either a, the gauge is dodgy... b, the sender is dodgy... c, somehow your water temp is fluctuating wildly... d, there's something in the water causing the gauge(s) to give false readings e, there's not enough water.
Is the engine raw water cooled or closed loop? If closed loop, have you checked the coolant level? If raw, have you checked your water pump(s)? One of the most logical options seems to be to me that there's not enough water in the system, thus water is only occasionally hitting the senders, making the gauge fly around, and giving false readings to the ecu? If that were the issue, no amount of changing senders or stats would help. I know it sounds stupid but it's often things like that which catch me out!
I can't see options a,b or c causing the engine to run rough.
Then again, i could be talking complete cr*p here, i'm no marine engineer, just thinking out loud, hope its of help!
Cheers, James
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30-08-2009, 02:09 PM
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#7
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Registered User
Boat make: Donzi 22ZX
Engines: 454 mag mpi
Cruising area: Solent
Join Date: Jul 2009
Posts: 29
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Thanks for the advice James, the engine is raw water cooled, i will mention for my mechanic to check the water pumps and change the senders and report back.
Any other ideas welcome, really want this sorted asap.
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30-08-2009, 03:35 PM
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#8
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Registered User
Country: Guernsey
Occupation: Engineering
Boat make: None, boo!
Engines: Turbines mainly!
Cruising area: The inside of my workshop!
Join Date: Mar 2008
Posts: 2,646
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No worries mate, I'd be glad to help! Can you give us any more info on how the engine is running rough?
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30-08-2009, 04:07 PM
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#9
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Registered User
Boat make: Donzi 22ZX
Engines: 454 mag mpi
Cruising area: Solent
Join Date: Jul 2009
Posts: 29
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The gauge swings about a lot, the engine runs perfect when the gauge is reading correctly but soon as it drops down it struggles to rev and splutters a tad then when the gauge comes back up it runs perfectly again, i presume this is because the ecu thinks its in cold start and chucks loads of fuel in.
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30-08-2009, 04:32 PM
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#10
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Registered User
Country: Guernsey
Occupation: Engineering
Boat make: None, boo!
Engines: Turbines mainly!
Cruising area: The inside of my workshop!
Join Date: Mar 2008
Posts: 2,646
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How often does the gauge go wild, and how long for at a time? Does it do it whilst idling about or just when you're under way? Any running issues when cold?
Sounds like you're right about the cold start thing, it's like a choke being engaged eh. Question is, why is it doing it? My money's on no water.
James
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30-08-2009, 04:41 PM
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#11
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Registered User
Boat make: Donzi 22ZX
Engines: 454 mag mpi
Cruising area: Solent
Join Date: Jul 2009
Posts: 29
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Quote:
Originally Posted by larby
How often does the gauge go wild, and how long for at a time? Does it do it whilst idling about or just when you're under way? Any running issues when cold?
Sounds like you're right about the cold start thing, it's like a choke being engaged eh. Question is, why is it doing it? My money's on no water.
James
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Does it all the time from first start up, takes a few seconds to go from cold to hot then back down again, Matt told me his computer reads it the same as the gauge does.
It ticks over just fine when cold or hot, it just dont like reving while the gauge reads low, splutters and struggles to get on the plane.
Soon as it goes up it pops out the water like normal, it will still run at top speed even with the gauge going up and down but you can hear the odd splutter so ive not used it since.
First started doing it mid last week so Matt put another new thermostat in it and i tried it out yesterday and it was still the same.
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30-08-2009, 04:43 PM
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#12
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Registered User
Boat make: Donzi 22ZX
Engines: 454 mag mpi
Cruising area: Solent
Join Date: Jul 2009
Posts: 29
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What you say about no water does seem to make sense, what would be causing that though?
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30-08-2009, 05:12 PM
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#13
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Registered User
Country: Guernsey
Occupation: Engineering
Boat make: None, boo!
Engines: Turbines mainly!
Cruising area: The inside of my workshop!
Join Date: Mar 2008
Posts: 2,646
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Cool, no water would be down to the water pump, or possibly a blockage. Assuming it's got a raw water pump like my 502, i'd check that first, they can burn out pretty easily especially if run dry for a mo for any reason, or if it hasn't been replaced for a bit it may have perished, resulting in not a lot of water making it through the system. There's also the pump on the front of the block but i believe they're pretty indestructable so unlikely to be that. As the senders require being immersed to get a good reading, they'll flick down to cold when they're dry.
James
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30-08-2009, 05:15 PM
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#14
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Registered User
Boat make: Donzi 22ZX
Engines: 454 mag mpi
Cruising area: Solent
Join Date: Jul 2009
Posts: 29
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Thats great, ill get on checking that out next week and report back, thanks for the help.
Jamie
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30-08-2009, 05:21 PM
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#15
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Registered User
Country: Guernsey
Occupation: Engineering
Boat make: None, boo!
Engines: Turbines mainly!
Cruising area: The inside of my workshop!
Join Date: Mar 2008
Posts: 2,646
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No worries, best of luck
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30-08-2009, 06:47 PM
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#16
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Registered User
Country: Uk
Location: London
Occupation: Mercury main dealer
Boat make: Baba
Engines: 200xs
Join Date: Feb 2008
Location: London
Posts: 361
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pull the plugs out, that will tell you if its stuck on cold start or not. Black sooty plugs means to much fuel not enough air
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30-08-2009, 08:47 PM
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#17
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Registered User
Join Date: Jun 2009
Posts: 670
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Quote:
Originally Posted by larby
Cool, no water would be down to the water pump, or possibly a blockage. Assuming it's got a raw water pump like my 502, i'd check that first, they can burn out pretty easily especially if run dry for a mo for any reason, or if it hasn't been replaced for a bit it may have perished, resulting in not a lot of water making it through the system. There's also the pump on the front of the block but i believe they're pretty indestructable so unlikely to be that. As the senders require being immersed to get a good reading, they'll flick down to cold when they're dry.
James
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my thoughts too...having software to read fault codes from ecu is allways a great help aswell
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30-08-2009, 09:18 PM
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#18
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Registered User
Boat make: Donzi 22ZX
Engines: 454 mag mpi
Cruising area: Solent
Join Date: Jul 2009
Posts: 29
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Its not showing any fault codes.
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2000 Donzi 22zx (454 mag mpi)
My Supra
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31-08-2009, 08:00 AM
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#19
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Registered User
Country: Guernsey
Occupation: Engineering
Boat make: None, boo!
Engines: Turbines mainly!
Cruising area: The inside of my workshop!
Join Date: Mar 2008
Posts: 2,646
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Quote:
Originally Posted by pro-rig
pull the plugs out, that will tell you if its stuck on cold start or not. Black sooty plugs means to much fuel not enough air
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Now why didn't i think of that!! Good plan!
Quote:
Originally Posted by baj666
my thoughts too...having software to read fault codes from ecu is allways a great help aswell
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Quote:
Originally Posted by JamieP
Its not showing any fault codes.
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Would it necessarily show a fault code if the above is an issue though? There's no 'fault' for it to recognise, it just keeps thinking it's cold?
James
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31-08-2009, 09:35 AM
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#20
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numbskull
Country: United Kingdom
Location: South
Occupation: none
Interests: none
Boat name: Leviathan
Boat make: Phantom 28
Cruising area: South Coast
Join Date: Mar 2004
Location: South
Posts: 15,959
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On the 454 / 502 MAG MPI there is a very thin earth (ground) wire from the ECU loom that is connected to the bell housing (flywheel cover in merc speak) piggy backed along with a load of larger cables. We had that wire break off it's ring end on the race boat which caused erratic, spluttery running. it would also stop whilst flying (when airborn-throttle shut) and the motor would need restarting after landing, it would restart easily, though still farty. Seemed to cut out with every long flight. Most annoying.
Was a very thin and not at all robust 'black' wire, but it was clearly quite important.
Might be worth a look.
Can't remember if it affected the guage. they definitely have a dedicated sender for the guage, independant of the ECU feedback.
Are you sure the main battery connections to motor are good/secure and the engine loom to dash is all good? We also had a bad engine ground cable once that gave a similar fault, though ours turned out to be the side of the block ripped out, where the engine mount bolts to it, and our battery ground cable was bolted to one of the mount bolts!
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