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Old 16 June 2010, 14:10   #1
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Engine used too little?

This is a possible given reason for my engine misfiring & cutting out at low revs - sounds a bit iffy to me...
Engine Merc 40 4-stroke ELPD, 3 years old, serviced / winterised annually, suddenly - halfway through the day starts misfiring & cutting out at idle. Only 3rd time out this season. We had bene running for 2 hours at @ 15kts c.3000rpm , then sotpped for 2 hours for lunch & some beach time. Trouble started after this. full tank of fresh fuel when we set off.

Get home OK, can't find anything obvious (to my unmechanical eye) so over to the local chappies to fix. They've checked, diagnostics say all is well but problem's still there when the engine runs.

Mercury have suggested that a "lack of use" may have caused old fuel to gum up one or more of the injectors. Is this likely or possible? If so what's the solution?? What else could be the trouble? I'm confused!

LT
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Old 16 June 2010, 14:48   #2
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Old fuel can be problematic, but not after a winter's storage.

I have a few cars that are rarely driven, several that wouldn't come out of the garage from October to April. Never had a problem.

I'm no expert on outboard engines, but they're not that dissimilar. Having said that, it's highly likely to be the injectors, but quite why they're playing up, I wouldn't know.
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Old 16 June 2010, 15:35   #3
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I'd be very suprised if that was the cause. Surely the ecu wouldl compensate for bad combustion by trying to inject more fuel and possibly throw a code on the diagnostics. Dodgy plug perhaps or sensor/wiring?
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Old 16 June 2010, 18:01   #4
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Quote:
Originally Posted by Erin View Post
I'd be very suprised if that was the cause. Surely the ecu wouldl compensate for bad combustion by trying to inject more fuel and possibly throw a code on the diagnostics. Dodgy plug perhaps or sensor/wiring?
Over compensation from the ECU (depending on its simplicity) could lead to misfiring and, should, as you say, put a code up.

I'm not sure how complex the ECU's are on outboards, would a partially blocked injector be picked up by the ECU?

I assume the plugs would have been checked as a matter of course - their condition could tell you something.
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Old 17 June 2010, 04:58   #5
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I would say that lack of use is possible but not really a valid excuse by Mercury. I think that a blocked injector is most likely. One at a time disconnect them and see if it makes a difference to the running of the engine. If you disconnect one and the engine makes no difference in vibration or tone. That injector is the problem. This is how we identified the blocked injector on a 1 year old 4 stroke honda. This honda also showed no faults when hooked up to the engineers computer.
Good luck, four strokes are really fussy.
Dan
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Old 17 June 2010, 05:17   #6
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Originally Posted by lakelandterrier View Post
This is a possible given reason for my engine misfiring & cutting out at low revs - sounds a bit iffy to me...
Engine Merc 40 4-stroke ELPD, 3 years old, serviced / winterised annually, suddenly - halfway through the day starts misfiring & cutting out at idle. Only 3rd time out this season. We had bene running for 2 hours at @ 15kts c.3000rpm , then sotpped for 2 hours for lunch & some beach time. Trouble started after this. full tank of fresh fuel when we set off.

Get home OK, can't find anything obvious (to my unmechanical eye) so over to the local chappies to fix. They've checked, diagnostics say all is well but problem's still there when the engine runs.

Mercury have suggested that a "lack of use" may have caused old fuel to gum up one or more of the injectors. Is this likely or possible? If so what's the solution?? What else could be the trouble? I'm confused!

LT
PLEASE NOTE THE DIAGNOSTIC system will only pick up electrical faults if this is the one i heard about the other day the injecters were working electricaly ok but one didnt sound correct i suggested to the person i spoke to remove the injecters and operate using a small 9v battery to operate and put power tune into the injecter it would be a reverse flow and that would hopefully clear out any debris
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Old 17 June 2010, 08:00   #7
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Hi everyone,

Thanks for the replies and suggestions.

We've run the engine for a couple of hours with fuel stabilser/cleaner in the mix, which seems to have more or less cleared the problem up (still the odd misfire).

I'm wondering a bit of old / contaminated fuel had gummed up the injector (although I'm not sure why that wouldn't affect all of them).

I'm a bit reluctant to strip out the suspect injector unless I have to.

I'll run her this weekend with brand new fuel, clean tank and stabiliser & see how she goes.

The problem is only at idle, so if she starts playing up again I will be able to get back as long as I keep some revs on. If the problem's still there then I'll have to take out, check & refit the injector.

LT
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Old 17 June 2010, 08:13   #8
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Assuming your problem is a blocked injector, that would make sense - injectors work on a constant (or monitored so the open time can be adjusted to suit) pressure, so if one is blocked, unless you have suoper eficient emmissions monitoring, then the brain won't pick it up, especially if there's nothing wrong wioth the electrical side of the injector.

Also at idle you are on ridiculously short "injector open" times, so a small blockage will have a bigger effect proportionally, and hence show up more easily.

On the dodgy connection front, be an idea to unplug & re pluig a couple of times to clean the pins in the connector. Having said that, a dodgy connection would likely pull a fault cosde i nthe ECU, as it il lbe lookingfor electrical problems (assuming it looks for anything at all!)
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Old 17 June 2010, 10:26   #9
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Quote:
Originally Posted by lakelandterrier View Post
This is a possible given reason for my engine misfiring & cutting out at low revs - sounds a bit iffy to me...
Engine Merc 40 4-stroke ELPD, 3 years old, serviced / winterised annually, suddenly - halfway through the day starts misfiring & cutting out at idle. Only 3rd time out this season. We had bene running for 2 hours at @ 15kts c.3000rpm , then sotpped for 2 hours for lunch & some beach time. Trouble started after this. full tank of fresh fuel when we set off.

Get home OK, can't find anything obvious (to my unmechanical eye) so over to the local chappies to fix. They've checked, diagnostics say all is well but problem's still there when the engine runs.

Mercury have suggested that a "lack of use" may have caused old fuel to gum up one or more of the injectors. Is this likely or possible? If so what's the solution?? What else could be the trouble? I'm confused!

LT
if you want to ring me on monday and either let me know how you get on over the w/end and/or i will go into my reply in more detail if you want 01869 326411
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Old 18 June 2010, 05:23   #10
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Uncle Al -
Thanks for the explanation & offer of further advice. I'll drop you a PM or call you on Monday & let you know how she run over the w/e

Regards
Bob
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