Engine and helm warning horn

[Pescadora]

I own a 1995 Carolina Classic that I bought early in 2013. I have now put two seasons of charter-boat fishing on her since then without any engine-related problems other than this topic. She was re-powered in 2006 by the previous owner with an 8.1L Volvo MPI engine. The issue I would like to solve is the warning horns, both on the engine and on the helm, which continually sound. They were disconnected when I bought the boat for that reason. I have good oil pressure and optimum temps at the gauges at all times, so those problems are not the cause.

My research has led me to the fact that there are senders and switches for both oil pressure and coolant temps (fresh water cooled engine). I believe the senders are connected to the gauges and the switches are suppose to provide warning in the even of fault.

Both the horn mounted on the engine and the buzzer on the helm use the same color coded wire Tan/Blue stripe.

All that said, my main question is: what sends the signal to the horn/buzzer? One of the switches? Or is the ECM reading the switches and sending the signal?

 

[Fun Times]

Hi there!

Typically you'd only need one of the warning horns. Chances are the older engine that came in the boat utilized the horn at the helm and the engine that's new to the boat utilized the horn mounted to the engine. Just out of curiosity, Any idea what used to be in the boat?

Bear in mind that even though you see all the gauges working normal doesn't necessarily mean the ECM doesn't see something else happening.

The gauges utilize their own set of analog sensors/sending units while the ECM uses a different set of digital sensors which could also sound the warning horn....Plus you have a set of exhaust riser temperature switchs which will sound the horn.

You'll want to get yourself an infrared temperature gun and check the actual engine and exhaust temps. You may also want to investigate the two exhaust switches, riser temps, and inside riser/manifold condition for excessive corrosion blockage, etc. as that seems to be a usual cause of problems especially if you run in salt water.

If you can't find any obvious problems, you may have to either get your MPI engine scanned by someone such as a dealer or buy yourself a marine scan tool from a place like Rinda Technologies.

http://www.rinda.com/marine/marine.htm#merctool
http://mefiburn.com/compareversions.asp

Hope you find something easy, keep us up to date and good luck.

 

[gm280]

I like "Fun Times" post that cover it pretty well. On the outside change you could also have defective sensor that needs replaced if everything he suggest doesn't solve the problem. IDK JMHO!

 

[Pescadora]

Howdy, thanks for the detailed reply. The original engine was a carbureted 7.4L Volvo, circa 1994, and all it did have was the helm buzzer. The replacement engine is a 8.1 Gi-A, zero hours at factory installation, but still about five years old when it was installed in 2006 - 117 hours on it when I purchased in 2013. Serial number and production number dates to end of 2000 or earlier 2001. There are no riser sensors and there were no ports for said sensors on the risers, which I've just replaced along with manifolds, hoses, elbows, etc as they were all end of life. The ECM hardware is version 4 - software release 8. I can't find any ECM category that looks like exhaust temp either, so maybe not on this version?

Riser and manifold castings were dated June and August of 2000. I'm kind of PM addict, going after most anything that might fail when I'm 50 miles out there. New exhaust is by Stainless Marine as it has *much* better provisions to prevent water ingestion. This is a jack-shaft boat, where the engine is located amidships under the helm deck. Outdrive is a Volvo DP-D1, with which I'm well familiar. Take it (and transom shield) off and apart every winter like changing tires.

Had her scanned (DIACOM) soon after purchase. Three pages of data some of which is not exactly intuitive. (Troll Mode?) But starts without malfunctions = 255. Same with starts without warning. Not running and cold when scanned, so much of the sensor output (low oil pressure input- on, oil pressure sensor voltage = 0.00VDC, ECT Temp = 49.1F) would be expected. What gives me hope that it's not the ECM is "Total Trouble Codes = 0". Since the Manifold air temp was 51.8F and the engine cold, this gives me a clue that the engine coolant temp sensor is probably okay. Bet that's what runs the engine temp gauge also(?)

After all that, and your reply, I'm kind of trending to either a defective oil pressure switch or a defective engine coolant overtemp switch. Maybe unplug them one at a time with the engine running and see what stops the horn? I notice that the tan/blue stripe wire to the horns (both of them) is (-), meaning ground. So a wiring problem is possible also. (insulation tear).

Given all my previous experience was with distributors and carburetors, going to an "electronic" engine was kind of scary.

Thanks for the scan tool link. It led me to a Diacom Marine PC software kit. I could really use one of those.

 

[Fun Times]

Thanks it helps knowing what engine model you have to know the layout of the engine a little bit better. I was thinking you must of had an engine model that was made somewhere around early 2000's since you had an engine mounted warning horn. I believe on theses engine models Volvo went to the helm mounted horn somewhere around 2004/05ish.

You are correct, looking up your engine model parts, it doesn't show any temp sensors on the exhaust system so that's one thing that could go wrong checked off the list of many others that could still sound the warning horn. http://www.volvopentastore.com/Exhau...view_id.773215

Here is a list of sensors for your engine model, http://www.volvopentastore.com/Elect...view_id.773227

In the sensor list above, you will notice item number 17 is the flame arrestor for the throttle body. It appears your engine model also has the Manifold air temp sensor mounted to the backside of flame arrestor which I recall Volvo doing back then on the 8.1's. The "Manifold Air Temp" is different than the "Engine Coolant Temp".

The Manifold air temp reads atmospheric temperature to slightly help adjust the ECM's fuel table programmed into the ECM.
The Engine Coolant Temp sensor (sometimes called switch by Volvo while Merc calls them sensors or senders) also helps adjusts the fuel table and should be found somewhere on or next to the thermostat housing. Item number 18 is the digital unit for engine coolant for the ECM to read and would sound the alarm.
Item number 20 is for the analog temp gauge at the helm that reads engine coolant temp.

Here's your full engine parts catalog for you if ever needed. http://www.volvopentastore.com/Marin...view_id.765235

Well the nice thing is you have old data of how your engine was running while normal, so now when you scan the engine, it may help tell you what seems to far out of operating range sounding the horn.

PS, a weak 12 volts system while running could also sound the horn. Be sure all electrical connectors are clean from corrosion and tightened down.

 

[Pescadora]

Thank for spending the time to post on this. You've validated much of my thinking thus far and pointed out a new element: ECT and fuel mapping.

One key point is: nothing has changed from when I bought the boat and scanned the ECM. The horns rang continuously then (when I hooked them back up), and they still do today. (when I hook them up)

My thinking now is this: ECM says "all is well"...and yet horns still sound continuously. But ECM is reading that #18 temp sensor to adjust the fuel map, so if it was bad, then a scan should show an ECT fault.

All leading me toward oil pressure switch (#4), which should be ground with engine off, or oil pressure below 6lb - 0.00VDC, which it is with engine off. Sensor #5 says 35-50psi (at gauge) depending on temp and RPM. Same galley (tee connection). Think I'll unplug #4, engine off and see if the horns quit. They should. The rest will have to wait until Spring when I can hook her up on the hose and start the engine.

Too bad I can't sign up for a Volvo Tech course somewhere. Engine and Outdrive. I'm looking at that upper gearcase on the bench and would like to get into it. Have the shop manuals, but lack the tools and training.