1999 V4 Looper Phantom SLOW mode activation

[72lightning]

Seeking some guidance on this issue I'm having with my Johnson 1999 130hp - J130PLEED.

I have added analogue head temperature sensors into the 1/8 threaded holes near the factory thermostat housings, with dashboard digital displays.
These read slightly than laser pointer hand held temp reading device pointed onto the heads - perhaps due to internal temps being higher than the external surface temps.

Motor starts and runs fine.
At Idle:
Temperature display increases and stabilizes at around head temp = 70C / 160F.
Cross checks:
Thermocouple contact on engine block immediately behind thermostat housing reads 55C/130F and 59C/140F. Stable.
Laser Hand held device reads approx 60degC and 62degC. Stable.

At above approx 1500rpm:
Head Temperature display decreases and stabilizes at approx head temp = 50degC / 120F.
I'm therefore assuming the Pressure relief mechanism in the thermostat is working.

Yesterday a Mechanic also checked water pump, tell tale, and thermostat operation - all got the okay.
The motor and the cooling system appears to be working as it should - perhaps a little hot at idle.

At various times after the motor has been running at low rpm (<1500) the over temp alarm activates, and activates SLOW mode.
Sometimes SLOW mode activates without any O/T Alarm or light.

The above head temp readings are still true at this time.

When tested on the dry, the factory O/T sensors are still open circuit. IE; volts are measured across the Tan wire to Ground.

I have tested the Blocking Diode following genuine manual instruction - Diode is blocking in one direction - conducting in the other.
So issue appears to be on Motor side of the blocking diode.

My question:
What could be causing this Bogus Over Temp alarm and SLOW mode?
Any / all suggestions and input will be gratefully received.

I'm in New Zealand and our southern hemisphere summer is in full swing - boat comes with us on holiday starting next week.

To to chuck the kitchen sink at this I have a new EMP (engineered marine products) after market power pack (300-30010) on order - to arrive early next week.
Also a set of factory Port / StBD OverTemp sensors. Not New.
If these sensors don't work out i can use the head temp digital display auxilary relay output to do the job of activation of O/T into the power pack.


I have also been reading CDI electronics trouble shooting guide. I know - not EMP, but there are a couple of wee gems of info in this doc.
- Tan overtemp wiring should be located as far away as possible from the park plug wires.
- spark plug wires have to be "Gray inductive resistive wires"

From these points i take it (and i have read elsewhere - perhaps on scream and fly) that interference from HT spark plug firing can be induced into the Tan overtemp wire(s) and cause false O/T triggers and SLOW mode.

Does anyone have any experience with this phenomenon that can comment?

 

[Crosbyman]

have to tried a good desalting to clear all passages of deposits
" Mechanic also "checked" water pump" but when was the impeller replaced ?

I doubt tan wire is being induced but anyting is possible ..If you think it is you could always sleeve it with a metallic braid mesh and ground one end to stop ignition HF noise

 

[72lightning]

Thanks for the input.
The water pump wad replaced completely not 50hrs ago.
Tell tale is good. Not quite as good as was when first done though.

 

[Faztbullet]

Your motor is a 90° not a 60° so information is incorrect.

 

[72lightning]

Hi Faztbullet,
Thank for your post.
I take it you are the same faztbullet as on marine engine forum?
Pasting my response on there...


I double checked the doc I read that info on.
Its actually the installation instructions, which has a troubleshooting section.
Seems there are two of these instruction docs.
One specific for the CDI part number 113-4041. This doc doesn't have the specific content I quoted, but still mentions the possibility of RF interference.
The other doc, the one I quoted from is a generic one that covers multiple power packs, and under the section for "Carburated 1995-2006 Model Years" it has the content I quoted.
Comment from other contributor seahorse says this is a possibility along with some checks to do around spark plugs and temp sensors. I did these checks yesterday, and lo and behold, found a couple of loose and slightly corroded connections.
I'm yet to run it again following. Noise is an issue at our house.
The thermostats have been almost completely replaced. Vernatherm, diaphragm, and vernatherm spring. The stbd diaphragm had a small split in it. And I've read that the newer vernathern springs have lower tension, to help provide a cooler idle temperature.
After running with the above changes done, no bogus over temperature alarm. And better temp control on the port side (more in line with expectations). Although it seems with the change to thermostat on stbd side, this has effected the over pressure relief opening on the port side. Both used to open quickly above 1500 and cooler both sides down quickly. Now only stbd is quick, port is much slower.
I'm thinking this could be due to the stbd opening and that making the water pressure pressure drop with that meaning port side has lower pressure than before and therefore it's pressure relief opening is later.
This means port is about 10degc higher than stbd at 1500rpm plus.

I feel im getting close. New power pack arrives Monday although I'm not sure I'll fit it since finding those spark plug connection concerns.

Many thanks