1990 Johnson 90hp failure 2 stroke

[yogiselle]

Motor still giving me problems in the water. Before heading out put motor on fresh water hook up "out of water" and everything ran and sounded great. At boat launch motor started and idle fine and worked great out of no wake zone and then ran at full throttle around 3800 rpms for about 3 minutes then motor slowley lost its rpms to then completley shut off. motor started again very easy ran for around a minute then slowley died off. ( All fuel lines and filter and pump are brand new and working properly. ) motor was getting fuel. On the third restart motor was not cranking over properly and large pressure was coming from the exhaust. I thought maby battery was bad so i switched to back up and same problem persisted. after around 15 cranks motor seemed to free up and cranked properly and ran for another 2 minutes then slowley died off leaving me 100 yards from returning to docks. Tried cranking it for another 45 minutes and motor still would not crank very similar to low voltage. I then removed both wires from the two heads "my guess is temp. wires" and motor started and ran all the way back to docks with no issues. Any ideas or help would greatly help. Runnin boat in salt water and running a mix of 50:1 oil pre mixed in tank.

 

[jtexas]

Re: 1990 Johnson 90hp failure 2 stroke

What kind of boat is this motor on, that it only makes 3800 RPM at WOT? You're lugging the motor at all throttle settings (not enough RPM for the given throttle position) -- that will eventually result in catastrophic failure. You're going to need a prop with about 11 inches less pitch. For more information, read the second post in this thread: http://forums.iboats.com/showthread.php?t=158076

Anyway, no need to guess...just do some basic troubleshooting.
1. Compression test -- all cylinders should be within 5 or 7% or so of the average PSI.
2. Spark test (not a "spark plug" test): get an inline spark tester (couple bucks at autozone), set the gap for 7/16", clip it to the engine block, attach the plug leads (one at a time) and look for a strong blue spark while cranking. If it can't jump a half-inch gap in the open air without a spark plug, it's not firing in the hole under heat & compression.

If it's not in slow mode with the temp switches disconnected, the powerpack is functioning normally; if it's in slow mode and the motor's not overheating, either the switch is faulty or a wire is accidently shorted to ground.

If the temp switch is throwing the motor into SLOW mode, the alarm should be sounding...when you disconnect a wire and ground it to the cylinder head with the key "on", you should hear a steady tone.

Otherwise troubleshoot the tan wires to the warning horn, and test the horn to make sure it sounds when connected to 12V.

Report your results.

 

[yogiselle]

Re: 1990 Johnson 90hp failure 2 stroke

Tex,

I completed the compression check and spark test and all elements are great. Compression is within 5 psi all around and spark is jumping more than 1/2" inch. I grounding brown wires from head and no sound was heard. I followed wires and found that the two coming from heads go to a group of wires. 5 total wires are connected together, two from the heads, 1 going to a weather connector joined by two other wires "connector not connected to anything", and the other two remaining wires going back to engine main wire plug. 1 wire going into plug and 1 wire cut and taped off. When i recieved boat both tan wires to engine heads where not hooked up. Again when last on the water and motor started having problems both wires where hooked up and motor would not turn over at all. turn key and motor would only turn a quarter turn before stoping. Unplugged both wires going to the heads and motor would then turn over perfect and start up on second crank.

 

[Haffiman]

Re: 1990 Johnson 90hp failure 2 stroke

Looks almost like something is seizing up.
Have you checked the gearbox oil?

 

[yogiselle]

Re: 1990 Johnson 90hp failure 2 stroke

Gear box oil was replaced along with all lower unit lubricants. Motor only seems to act like locking up when over heating wires are connected.

 

[yogiselle]

Re: 1990 Johnson 90hp failure 2 stroke

still need help

 

[oxbeast1210]

Re: 1990 Johnson 90hp failure 2 stroke

to me it almost sounds as if the switch for overheat and slow is faulty and causing you to go into slow cause it thinks its overheating but then again that would just limit your rpm i don't think it would completely shut it down

 

[ezeke]

Re: 1990 Johnson 90hp failure 2 stroke

You don't have S.L.O.W. on that engine but it will bind up and stop if it overheats.

The tan wires from the cylinder heads should have no connection to the ignition system on that engine; trace the wires and find the short.