Johnson 90hp skip,miss genius needed

[pick401]

Background-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)

Findings --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 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.

 

[wilde1j]

Re: Johnson 90hp skip,miss genius needed

Well, you should started by diagnosing, rather than replacing parts. Way less expensive. I would suggest diagnosing ignition system. Try downloading CDI's Troubleshooting Guide here:
http://cdielectronics.com/Support.aspx
If you don't have a DVA adapter, you'll need that also. Available here: http://www.usatoolwarehouse.com/usatoolwarehouse/ESI-640.html

Check power pack, stator and all ignition wiring for starters.

 

[kenmyfam]

Re: Johnson 90hp skip,miss genius needed

Did you check the fuel pump ??????
Could be starting to fail.

 

[pick401]

Re: Johnson 90hp skip,miss genius needed

Checked the ignition components as best I could Coils were cracked so not a bad idea to replace, Stator was putting out decent cranking voltage but the popwer coil on stator was begining to melt/leak so not a bad idea to replace. The power pack was the last thing I replaced since a dealer put a new one in only a couple of years ago. At this point it's pretty irrelevent since the whole ignition system has been changed.

As far as the fuel pump goes I checked that when I checked the fuel delivery system. Had an old vro from a previous repair swapped them same problem no difference what so ever. Even took both vro's apart, checked the fuel flow while cranking and tried pumping the ball while running no difference.

This problem appears to be more global whole engine than an individual system. i was wondering if there could be enough internal corrosion that water is getting into the crank then cylinders or if thers could be a crack where air is getting into the intake/crank area??

 

[kenmyfam]

Re: Johnson 90hp skip,miss genius needed

checked the fuel flow while cranking

How did you perform this and what did you see ???

 

[ondarvr]

Re: Johnson 90hp skip,miss genius needed

Primer not working correctly and letting fuel flow into the intake?

 

[pick401]

Re: Johnson 90hp skip,miss genius needed

Primer not working correctly and letting fuel flow into the intake?

ondarvr this sounds like a possibility could you elaborate and give me a process to test. I'll try it out.

 

[ondarvr]

Re: Johnson 90hp skip,miss genius needed

Pull off the fuel line leading to it and plug both sides, then take it for a spin.

 

[pick401]

Re: Johnson 90hp skip,miss genius needed

How did you perform this and what did you see ???

Kenmyfam I took apart both vro's and compared internal components. The extra vro had a problem with the oil end I believe it was the mechanical internal sensor. It's a little mechanical pin/lever that responds to the ocillations of the diaphram. So the rest of the vro was working fine. All internal diaphrams were intact seals looked good put air pressure (pulsing) on inlet tube to see if diaphram was working. Everything looked fine no air leaks and vro appeared to be working. Put vro on motor disconnected ful line to carbs disconnected powercoil to powerpack cranked engine fuel was flowing.
Also took a clear hose connected it to vro oil inlet filled with some oil and watched it flow into engine. Also connected a clear hose to the fuel inlet on vro to see if there were any air bubbles none present.

I even started the engine and pumped the primerball to increase fuel flow no real difference.

 

[pick401]

Re: Johnson 90hp skip,miss genius needed

Pull off the fuel line leading to it and plug both sides, then take it for a spin.

Well ondarvr great idea tried it no luck still behaving poorly. The skip/miss is usually accompanied by a pretty loud knock in the crank area. When I took things apart they didn't look to bad but the piston rods were discoloring on the crank side (brownish). Changed the bearings but could they be so worn out that they are causing this skip knock problem. I also didn't change the sealing metal rings around the crank they didn't look to bad should I look here? I'm really frustrated with this engine.

 

[TLL]

Re: Johnson 90hp skip,miss genius needed

Remove the flywheel and check to make sure the magnets are not loose/cracked. Sometimes the glue will fail and the magnets will come just a little loose, causing a miss and the noise you may be hearing. They can be epoxied back into place if not damaged.

 

[noelm]

Re: Johnson 90hp skip,miss genius needed

OK, lets go way back to the start, you have replaced a bag of parts and it is not fixed (indeed you may have stuffed something else in doing so) you have pulled it to bits (also may have introduced another new probelm) you found a bearing surface that has discoloured, that means that surface is TOAST! it will fail, trust me, a mechanical fault will rarely give you an intermittant miss (skip) you have what was probably a minor problem, thrown a bucketful of cash at it, and you are no closer to fixing it, you need to ask yourself, how far do you go with a motor that has a dodgey crank bearing without seeking proper help or doing some proper fault finding?

 

[pick401]

Re: Johnson 90hp skip,miss genius needed

Remove the flywheel and check to make sure the magnets are not loose/cracked. Sometimes the glue will fail and the magnets will come just a little loose, causing a miss and the noise you may be hearing. They can be epoxied back into place if not damaged.

Funny you should say that TLL I did just that yesterday. I put a large screw driver against the crank cover and to my ear (it does work ). listened for the noise moved it around and it sounded like it was coming from the top of the crank/flywheel. Took the flywheel off checked the magnets none loose. There also was no visable evidence of anything contacting the stator or cover area under flywheel. Thanks for the idea we are on the same page.

 

[pick401]

Re: Johnson 90hp skip,miss genius needed

OK, lets go way back to the start, you have replaced a bag of parts and it is not fixed (indeed you may have stuffed something else in doing so) you have pulled it to bits (also may have introduced another new probelm) you found a bearing surface that has discoloured, that means that surface is TOAST! it will fail, trust me, a mechanical fault will rarely give you an intermittant miss (skip) you have what was probably a minor problem, thrown a bucketful of cash at it, and you are no closer to fixing it, you need to ask yourself, how far do you go with a motor that has a dodgey crank bearing without seeking proper help or doing some proper fault finding?

noelm the bearings have been changed. The problem is exactly what it was before I started so I didn't complicate any problem just haven't solved current one. The way I looked at was the things I changed were worn or old so they were probably likely to go at some point anyway and in the end I'd get an almost new engine I could depend on. However this problem has got me perplexed. By the way I did take it to a dealer at one point and he told me he thought the crank bearings were shot, but he didn't want to take apart a 10yr old engine. Also took it to a suposeidly good marine mechanic who wanted me to bring it to him the next day, he proceeded to have the boat parked in his lot for the next 14 days without so much as strating it. I think the problem is here in RI the season is short and it's hard to sustain a business/living being a outboard marine mechanic.What I really need is a good outboard mechanic that is willing to work with me. On that note I've got a couple of names and after one more test I'm going to give them a try. By the way I can probably recoup a good percentage of the money I spent on the parts on ebay if I need to. and finally there's always a rebuilt powerhead w/12 month warranty shiped directly to my door and all those new parts would go great on that. All of my options are open. I'm just a real curious guy always have been. I like mechanical things and repairing/rebuilding them. This is just my experimental endeavor into the world of outboard engines and boy what a learning experience it's been.

 

[trendsetter240]

Re: Johnson 90hp skip,miss genius needed

You say you replaced the rod bearings on the crank side; what about the needle bearings on the wrist pin side of the rod?

 

[trendsetter240]

Re: Johnson 90hp skip,miss genius needed

You say you replaced the rod bearings on the crank side; what about the needle bearings on the wrist pin side of the rod?

Guess I should be more specific, the above would be to identify what is making the ping noise. If you can hear it with a screw driver to your ear as you said.


As for the missing above 2000RPM, have you checked timing?

 

[TLL]

Re: Johnson 90hp skip,miss genius needed

Have you checked the gearcase? Sometimes a broken gear tooth can fool a person and resemble a miss. Also the sound will transmit through the drivetrain up to the flywheel. A quick gearlube check will verify. My guess is you already did this, but I had to ask.

 

[noelm]

Re: Johnson 90hp skip,miss genius needed

I am not suggesting you are not a competent mechanic, or that you should just throw your motor away, but just swapping part after part, and pulling things to bits rarely fixes anything other than a spare parts guys wallet, you need to get a genuine manual, and actually trouble shoot, step by step, swapping parts does not find out what it is, it finds out what it isn't!

 

[pick401]

Re: Johnson 90hp skip,miss genius needed

Have you checked the gearcase? Sometimes a broken gear tooth can fool a person and resemble a miss. Also the sound will transmit through the drivetrain up to the flywheel. A quick gearlube check will verify. My guess is you already did this, but I had to ask.

TLL you must be psychic I talked to a guy that does the machine work on powerheads today he told me the same thing. And no i didn't check the lower unit the thought never crossed my mind, but I can see how the sound could transmit right up the drive shaft. My next step tomarrow will be to check the lower unit. I'll get back to you guys on what I find.

 

[pick401]

Re: Johnson 90hp skip,miss genius needed

You say you replaced the rod bearings on the crank side; what about the needle bearings on the wrist pin side of the rod?

No I didn't change the wrist pins. I know I probably should have while I had the engine apart but didn't. I really didn't see alot of wear on the rod to shaft bearings but I figured while I had it apart they should be changed. The compression was so good I didn't want to mess with taking the pistons out and changing the rings and rehoning/boring the cylinders. Which i would have felt obligated to do if I would have removed the pistons. But you have a good point and the wrist pins have crossed my mind. Upon visual inspection they looked ok and there didn't seem to be alot of play in them when I pushed pulled on the rods. Could some wear on the wrist pins only be responsible??