Diacom Test Need Help

[Richard Seccombe]

I recently replaced the sea water pump impellers on both 496 Horizons. A Diacom recording on both engines showed normal sea pump pressure. I then pulled both raw water sea strainers and cleaned them out. Nothing to speak of was caught in the strainers. As soon as I replaced the strainers and ran more tests, the sea pump pressure was all over the place.

One week passed and I ran the tests again. Now both engines are reading 43.46 PSI and I'm getting error codes thrown for excessive sea pump pressure. There is never any deviation from 43.46...it just stays there...even if the engines aren't running.

I have disconnected both cables to the sea pump sensors and made sure there is a good connection. When I unplug them, I get the 2 beeps every minute and the Diacom readout says I'm down to 90% of full power available.

Could I have dislodged some junk that stopped up both sensors, are the sensors in any way slaved together, or is there something else that is making the readings inaccurate? I find it strange that BOTH engines are behaving the same exact way.

Both engines are exhausting plenty of water, both the manifold exhaust temps are around 110 F, and the overall coolant temp is at 158 F.

I guess my next step is to replace both sensors but I hoped that possibly someone else has run into a similiar problem.

Thanks,
Richard

 

[muc]

Re: Diacom Test Need Help

Might want to run a ground wire to the sensors. Static electricity can cause this problem.
Good Luck Muc

 

[Richard Seccombe]

Re: Diacom Test Need Help

Hi MUC,

Thanks for the response. When you say run a ground wire to the sensor, do you mean just grab a wire, temporarily touch one end to a known ground and the other to the sensor body, or permanently ground the sensor body to a known ground? Forgive me...I'm a bit new at this.

The actual code was "Sea Pump CRT HI" and the PCM Manual says faulty wiring to the sensor or the sensor itself is bad. I checked the wiring for any obvious shorts or breaks and couldn't find any.

Thanks,
Richard

 

[muc]

Re: Diacom Test Need Help

Hi Richard,
You didn?t post serial numbers so I can only assume that you have inboards (because of the strainers) and an early model (because of the nature of the problem).
Mercruiser had some problems with these sensors.
1. The paint job on the cooler that the sensor screws into was too good and the water hoses that connect to the cooler had too high electric resistance, this caused static electricity to build up in the sensor and damage the sensor.
2. The first generation of sensors had some problems and MCM redesigned them.
When you buy the new sensors try to get some that are less than 2 years old (the package will have a date on it and the sensor should be a different color).
When you install the new sensors, no sealant on the threads and run a permanent 12 ga. ground wire from the engine block to an area on the cooler that you have cleaned the paint off of.
This information comes to me from MCM tech support based on the serial number of the engine that I was working on with a similar problem. Don?t know if it will help you.
You asked if the sensors are slaved together, no they are not but some boat manufactures will install a master/slave cable between the two engines that will among other things, pull the other engine down into power reduction when one engine drops to 90% of full power or lower.
Good Luck Muc

 

[Richard Seccombe]

Re: Diacom Test Need Help

Hi MUC,

Yikes!!! You really know your stuff!!! Thanks so much for all of this valuable information. For reference the engines are inboard and the serial numbers are 0M027519 and 0M027533.

It sounds like I probably trashed both sensors by playing around with them.

When the impellers were replaced, there were several circular groves in the pump body at each end of the housing where the ends of the impeller contact them which I've read is a bad deal and decreases the pump's efficiency. At this point I probably ought to replace both pumps and sensors.

When I looked up the pumps I noticed that the original part number has been superceeded by a newer one. Do you know if the newer pump does a better job of grounding the pump/sensor assembly or should I still install a dedicated ground wire?

Thanks again for taking the time to research this for me. I was coming up empty with hours of searching. I'm really happy with the Diacom software. God only knows how long it would have taken me to find out why I was getting 2 beeps every minute and without your help, I could have ended up replacing everything only to get the same results.

If your ever in the Ventura CA neighborhood, name your poison and I'll pick some up

 

[muc]

Re: Diacom Test Need Help

I don?t know if the new pumps will change anything. I would still run a ground wire.
Good Luck Muc

 

[Richard Seccombe]

Re: Diacom Test Need Help

Hi MUC,

I replaced both sensors and ran a dedicated ground strap from each sensor to the block. I fired up the Diacom software and the pump pressures are on the money and respond perfectly to the engine RPM.

Thanks again for all of your help,
Richard