| Author |
Message |
    
Steve Pickering
New member
Username: pick401
Post Number: 1
Registered: 11-2009
| | Posted on Sunday, November 01, 2009 - 03:20 pm: | 
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[B]Background[/B]-On my way back from a fishing spot I was running wot when the engine began to miss, skip. Limped back in (30 minutes) took the boat home and started to work on the problem. The skip was not preceed by any mechanical noise. Boat was running fine all summer. I have a water seperating fuel filter and a battery kill switch an internal tank and the boat is primarily used in salt water.
I have a 2000 90hp Johnson that has a miss, skip. At high speeds above 2000 rpm it's more significant. When it skips there's a ping,knock coming from crankshaft area. Been playing around with this engine for a month now let me give you a list of things I've tried. Compression about 125# all 4 cylinders.
Isolated fuel system with seperate tank and fresh gas---no change
Changed coils, plug wires, stator, powerpack---no change
broke engine down changed crank shaft bearings---no change
changed piston rod to crankshaft bearings also--No change
Rebuilt carbs changed all fuel gaskets checked reed valves----No change
Removed and resealed heads----No change
Cleaned out the exhaust while engine was apart
Move battery from under center console to back of boat---No change
Isolated kill circuit--No change
Disconnected voltage regulator-- no change
Removed each plug wire one at a time to see which cyclinder was the culprit no change in performance still skiped and missed cannot isolate 1 particular cyclinder as the problem.( I used a grounded old plug so I wouldn't damage the electrical system)
[B]Findings[/B] --some wear on crankshaft especially upper bearings but didn't mic them. I couldn't feel a ridge with fingers/fingernail just discoloration. Piston rods had some flaking taking place near the crankshaft end but didn't seem to bad. Some evidence of water leaking from top of head down to cylinders. Thermostat inner seal was deteriorated. When I had the engine apart I checked the reed valves none broken or bent open all seemed to open and close easily.
So far I've got about $1600 into it with no results does anyone have any idea what could cause this. I was pertty thorough and careful but I'm totally stumped there's nothing left to change and the engine still runs like crap. |
Dcramer
Advanced Member
Username: dcramer
Post Number: 187
Registered: 05-2008
| | Posted on Sunday, November 01, 2009 - 09:03 pm: |
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Optical sensor? |
Steve Pickering
New member
Username: pick401
Post Number: 2
Registered: 11-2009
| | Posted on Tuesday, November 03, 2009 - 05:19 pm: |
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Changed it sorry forgot to mention on list. |
Tim Lyden
Member
Username: tal55lyd
Post Number: 21
Registered: 11-2007
| | Posted on Tuesday, November 03, 2009 - 05:56 pm: |
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After you clean carbs did you use same gas supply if so clean carbs and fresh gas supply make sure float are set right, spark is to avance will cause spark knock check timeing |
Dcramer
Advanced Member
Username: dcramer
Post Number: 190
Registered: 05-2008
| | Posted on Tuesday, November 03, 2009 - 11:27 pm: |
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I still think you have an ignition issue. If you have a timing light, I would check the ignition timing the old fashioned way. Could the optical encoder be cracked or dislocated? You could try disconnecting the wire for the Quickstart. I know you said the powerpack was replaced, but the quickstart adds around 8 degrees of timing at low rpm for warmup. If that doesn't disengage above 1200 rpm like it's supposed to, you will certainly have issues. Are the plug wires mixed up by chance? are they close enough together to be cross-firing? What spark plugs are you using..I believe that engine calls for Champion QL78YC. Non suppression plugs will cause issues with the OIS/2000 ignition. I wouldn't use anything but what is recommended even if you have a brand preference.
It looks like you've checked all the difficult stuff. My gut is that something simple is causing the problem. Often it's better to troubleshoot until you are reasonably certain you're on to the problem before changing parts.
By the way, does activating the fuel primer change the skip in any way other than bogging down the engine? That would be the sure way to rule out fuel issues. |
Steve Pickering
New member
Username: pick401
Post Number: 3
Registered: 11-2009
| | Posted on Thursday, November 05, 2009 - 04:14 pm: |
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Thanks for the intrest guys. Plug wires new not close. Also new encoder cracked the old one removing it. Tried disconnecting wires for kill switch/quickstart no change.I believe the wire for quickstart is on the same side of the powerpack harness as the kill switch.I even checked the circuit that supplies power from the starter selenoid until the power coil kicks in. It was working fine supplied around 10 volts to powerpack then shut once starter released. I read this circuit was supose to supply 11.5 volts but the engine starts until the powercoil takes over so I assumed everything was ok. Also not sure how a circuit supplies 11.5 of a 12 volt system while a starter is turning over an engine. I'm Using ql78yc plugs. Also checked the timing with timing light. I've really been through this engine I think it's haunted. It's pretty bizarre I really tested alot of stuff and the final step was to look at a mechanical issue (bearings) and that didn't even work. I've got a pretty good grasp of the workings of a 4 stroke engine and I'm really stumped? These 2 strokes can be really finicky. The only ignition thing I didn't check was the voltage output at the plugs.
Pumping the fuel primer doesn't have any effect on the problem.Also tried using a remote tank of fresh gas. |
jwbmarine
Senior Member
Username: jwbmarine
Post Number: 5096
Registered: 11-2005
| | Posted on Thursday, November 05, 2009 - 08:24 pm: |
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When it skips there's a ping,knock coming from crankshaft area---for u to hear this,..u have a serious prob going on...i am thinking,..after re-reading,.all u have replaced...is wtr related..wtr injestion,possibly...that,DOES cause a pinging sound. |
jwbmarine
Senior Member
Username: jwbmarine
Post Number: 5097
Registered: 11-2005
| | Posted on Thursday, November 05, 2009 - 08:30 pm: |
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what did the pistons look like?....did u inst a NEW vro pump,on this eng during ur overhaul?...what is the actual,eng temp,..via temp gun,....temp of each bank and engine,during this episode?..r ur warning systems active,and VERIFIED,functional,..low oil,no oil,overheat,..any lites?,horns?...if still on the vro,WHICH,is now an OMS pump,...after rebuild,was that system verified,..not just connected back..???what about the wrist pin,to piston clearence,ck'ed?.. |
Phil Kicksee
Member
Username: red_goat
Post Number: 66
Registered: 05-2009
| | Posted on Thursday, November 05, 2009 - 09:44 pm: |
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Have you checked the temperature sensing curcuit?
Maybe the engine thinks its hot and going into a stumble mode. |
jwbmarine
Senior Member
Username: jwbmarine
Post Number: 5104
Registered: 11-2005
| | Posted on Thursday, November 05, 2009 - 09:50 pm: |
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very good point,..coould be going into slow,...sounds like the only thing has'nt been repl,..is temp senders......when it does this BS..disc temp senders and rock on,.....and see whaty it does,... |
Steve Pickering
Member
Username: pick401
Post Number: 4
Registered: 11-2009
| | Posted on Friday, November 06, 2009 - 07:47 pm: |
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Checked the slow system disconnected heat sensors one of first checks.Pistons brownish carbon very thin coating. No holes visable cracks etc...Didn't use a temp gun to verify engine temp. No warning horns lights etc.... Oil flowing. Checked vro flow at cranking squeezed primer bulb while running. Didn't change wrist pins compression was so good didn't want to mess with removing pistons and replacing/reboring/rehoning. But they have been on my mind. Just didn't think there was much wear pushed pulled on rod didn;t seem to be much slop. I know it's not the best measurement. On another board someone suggested thye lower unit could be mussing a tooth/bearings probs/etc.. and drive shaft hanging and sound transmitting through crank. This is next thing I'm going to check. Thanks for all the ideas eventually one way or another I'm going to figure it out. bottom line the same problem that existed before I started still exists.
The water injestion thing did cross my mind. I removed the heads there was evidence of water leaking from inner thermostat gasket on both sides. Omc used a lame o ring gasket system on these engines and I believe they were prone to leaking. Any how i resealed the heads and there was no evidence of steam cleaning of plugs heads. I also didn't detect significant warpage of heads used a straight edge. Has anyone heard of water leakage internally on these engines. |
Phil Kicksee
Member
Username: red_goat
Post Number: 70
Registered: 05-2009
| | Posted on Friday, November 06, 2009 - 08:04 pm: |
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Try another prop!
that one may be slipping and grabing at the rubber bushing |
