94 9.9hp oil pressure question

[4scoleo]

I'm working ona 9.9 Yamaha that I acquired froma friend who had been plagued by an intermittent problem with engine stalling and not coming up to full rpms. After three trips to the authorized dealers, who repeatedly cleaned his carb and check book, he rebuilt the carb then the fuel pump and then gave up and bought a new one. After following a couple threads on this forum I'm starting to think it's the oil pressure switch so I'll ask a couple questions. First, the oil pressure switch is a normally closed switch wich grounds out the indicator light. The Clymer manual says that it should be closed from 0-1.4psi and open from 7.1-9.9psi. What happened to the 5.7psi in between? If we're talking about variations of less than 2 psi a lot can happen in almost 6 psi. Second, assuming this is the problem, what happens in the CDI when the link to the light, through the switch, is grounded? And is that a cause for the engine to refuse to come up to speed?
FYI The engine will run at it's lower speed for an unpredictable time and just die. It will immediately start again and run smoothly at it's reduced speed until it does it again.
PS The Clymer manual is pain in the exhaust manifold!
Scotty

 

[4scoleo]

Re: 94 9.9hp oil pressure question

I'm working ona 9.9 Yamaha that I acquired froma friend who had been plagued by an intermittent problem with engine stalling and not coming up to full rpms. After three trips to the authorized dealers, who repeatedly cleaned his carb and check book, he rebuilt the carb then the fuel pump and then gave up and bought a new one. After following a couple threads on this forum I'm starting to think it's the oil pressure switch so I'll ask a couple questions. First, the oil pressure switch is a normally closed switch wich grounds out the indicator light. The Clymer manual says that it should be closed from 0-1.4psi and open from 7.1-9.9psi. What happened to the 5.7psi in between? If we're talking about variations of less than 2 psi a lot can happen in almost 6 psi. Second, assuming this is the problem, what happens in the CDI when the link to the light, through the switch, is grounded? And is that a cause for the engine to refuse to come up to speed?
FYI The engine will run at it's lower speed for an unpredictable time and just die. It will immediately start again and run smoothly at it's reduced speed until it does it again.
PS The Clymer manual is pain in the exhaust manifold!
Scotty

Hey Guys! Please!
Somebody out there knows the answer to what happens in the CDI. I turned wrenches for thirty years, but without a schematic for the CDI all my mechanical experience isn't worth spit for this diagnosis.

 

[rodbolt]

Re: 94 9.9hp oil pressure question

if the CDI detects low oil presure or overheat it will misfire the cylinders and limit RPM to about 2000 RPM max but wont shut down.
what your manual is trying to tell you is the CDI detects low oil pressure at about 1.4 psi and the switch should open at about 7 psi but there are tolerances to everything. all you need to be concerned with is does the switch close and does it open. can be tested with a multimeter.
the pink wire going into the CDI is the alarm wire.

 

[4scoleo]

Re: 94 9.9hp oil pressure question

if the CDI detects low oil presure or overheat it will misfire the cylinders and limit RPM to about 2000 RPM max but wont shut down.
what your manual is trying to tell you is the CDI detects low oil pressure at about 1.4 psi and the switch should open at about 7 psi but there are tolerances to everything. all you need to be concerned with is does the switch close and does it open. can be tested with a multimeter.
the pink wire going into the CDI is the alarm wire.

Thank you sir. That gives me something to work with.

 

[sdsaw]

Re: 94 9.9hp oil pressure question

Well, since dealers have been working on the problem, they must have checked for a clogged oil filter, right?