1997 Evinrude 90 misfire

[liltuffy]

Hey guys, the past couple of trips the old V4 90 'rude has been having a misfire issue coming on about 3200rpm, darn thing runs perfect with great spark right up till the trouble point.
Pushing the throttle down revs start to come up and vibration comes on and stays on by I guess one cylinder not firing, pushing the throttle further doesn't fix the problem. Sometimes you put the throttle down and it goes just fineas if nothing is wrong, intermittent problems drive me nuts.
I have the genuine manual and followed the troubleshooting flowchart to isolate the problem to either a charge coil issue or a power pack. Trouble is I don't have the special service tool meter to fully diagnose the cause and it needs to be done under load (don't have a test prop either) and don't just want to cough up $300 on boats.net for something I may not need.
I know The Lump had a similar problem with his 115 but was wondering if anyone has some thoughts on the matter.

Cheers, Craig

[Chimo]

Why dont you get an OMC tech to diagnose your issue? When there's no-one still working and able to fix our stuff who really is to blame?

Just spend your money once and get the job done right IMHO

Cheers
Chimo.

Do you want a number?

[liltuffy]

Hi Chimo, costs associated with fixing boats is not a discussion I want to get in to here. I'm pretty handy around engines and was just looking for some advice and relevant experience or knowledge.

Thanks a number for a reputable mechanic would be appreciated.

Craig

[cormorant]

Narrow down fuel blockage and crap in your carby first. Clean em and check that ethanol has not broken down inside of fuel hose or ethanol has not dissolved chunks or wax/ varnish gelled fuel in carby bowls. A sticking carb float can do this. Litle bits of crap in a fuel jet. Check fuel pump screen filter. Next time it happens see if pumping the fuel bulb will bring revs straight back up. Stuffed fuel bulb can cause temporary fuel blokage / restriction or a hole in either that or a fuel line, clamp can airate fuel causing loss of power.

Coolling system - when things get very hot they break down. Check you don't have a blockage , any temp alarms , faulty thermostat, faulty temp probe.

Obviously fresh plugs. Do both plugs look the same colour / pitting? Are you using the right plugs. Confirm silly things like butterflys in carby are all solid, choke is not intermittently turning on, linkages are all OK, spark advance is not sticking.

Plug leads break down. Check routing of leads. Check no spark is being lost ( I wouldn't be using my finger) but in the dark under load you may see the lead shorting on something.

Electrics- check there is no wires rubbing or melted on the powerhed or bared wire in the loom that can cause a intermittant fault. As always check electric outputs and ensure it is putting out correct voltages.

Oh well that is all the homework that I know isn't in the manual for you to start with. Tell us if it narrows it down.

[Chimo]

PM sent..........

[liltuffy]

Narrow down fuel blockage and crap in your carby first. Clean em and check that ethanol has not broken down inside of fuel hose or ethanol has not dissolved chunks or wax/ varnish gelled fuel in carby bowls. A sticking carb float can do this. Litle bits of crap in a fuel jet. Check fuel pump screen filter. Next time it happens see if pumping the fuel bulb will bring revs straight back up. Stuffed fuel bulb can cause temporary fuel blokage / restriction or a hole in either that or a fuel line, clamp can airate fuel causing loss of power.

Coolling system - when things get very hot they break down. Check you don't have a blockage , any temp alarms , faulty thermostat, faulty temp probe.

Obviously fresh plugs. Do both plugs look the same colour / pitting? Are you using the right plugs. Confirm silly things like butterflys in carby are all solid, choke is not intermittently turning on, linkages are all OK, spark advance is not sticking.

Plug leads break down. Check routing of leads. Check no spark is being lost ( I wouldn't be using my finger) but in the dark under load you may see the lead shorting on something.

Electrics- check there is no wires rubbing or melted on the powerhed or bared wire in the loom that can cause a intermittant fault. As always check electric outputs and ensure it is putting out correct voltages.

Oh well that is all the homework that I know isn't in the manual for you to start with. Tell us if it narrows it down.

Fuel I don't believe will be the issue, got a Racor big arse filter with integral water trap - changed the filter and trap about 2 months ago but hey I'll check. Crap in carby - I'll run some cleaner through it. Primer bulb - just put a brand new one in. Cooling system - problem occured last time about 1 minute after start up. Plugs have done about 34 hours and are the same brand and model of plug I have always used since new (manufacturer recommended). Everything esle you mention doesn't seem to be a problem but boy you have given me a number of things to cross off the list of possibles.

Thanks a bunch

[FishHunter]

Easy way to see if its ignition and which cyl is to hook a timing light up and watch the light, moving it from plug lead to lead while its missfiring. If the light stops flashing you have found the guilty cyl and you can concentrate your attention there.
My V6 150 had similar issues and it was the power pack.

Sent from my X10i using Tapatalk 2

[cormorant]

Is it as simple as a new plug out of the box is stuffed? Guess you are already onto this. Think of all the things that have changed just before it started.

Like you said - who knows what it is and it is a case of narrowing it down and checking all symptoms to actually diagnose intermittant ones. I have caused and solves some really "obvious" ones in the years. Torn a bit of hair out as well.

[Triple]

Just had a similiar issue on the old mans 98 johnson 90hp.. Intermittent misfire underload once warm, check carbs etc and was told 99% more than likely the optical sensor or powerpack, Best price of just powerpack in Aus $428 :o.. Seeing as though motor is now 14yrs young and preventative maintanence is better than post maintanence on the water so we lashed out and bought new genuine optical sensor, powerpack, coils, leads, thermostats + orings and a complete water pump rebuild kit for $547 delivered from boats.net. 8-) Could of got them a hundred bucks cheaper but others required to use a parcel forwarding service and didn't want the hassle of that. Fitted ourselves and problem solved. Probably was just the $62us optical sensor ($122au at local dealer) but worth doing as all user reports online state powepack lasts around 10yrs (depending on engine hours of course) and sensor not far behind.

[liltuffy]

Just had a similiar issue on the old mans 98 johnson 90hp.. Intermittent misfire underload once warm, check carbs etc and was told 99% more than likely the optical sensor or powerpack, Best price of just powerpack in Aus $428 :o.. Seeing as though motor is now 14yrs young and preventative maintanence is better than post maintanence on the water so we lashed out and bought new genuine optical sensor, powerpack, coils, leads, thermostats + orings and a complete water pump rebuild kit for $547 delivered from boats.net. 8-) Could of got them a hundred bucks cheaper but others required to use a parcel forwarding service and didn't want the hassle of that. Fitted ourselves and problem solved. Probably was just the $62us optical sensor ($122au at local dealer) but worth doing as all user reports online state powepack lasts around 10yrs (depending on engine hours of course) and sensor not far behind.

Makes a lot of sense cause I'm pretty fussy with fuel and thoroughly clean carby's etc at each 100 hrs. Motors got about 830 hours on board and I've always maintained it well. Few other blokes I've spoken to seem to be striking the same issue over the last 12 months so I reckon it might just be the electricals have had enough.

Cheers guys.

Craig