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engine alarm question for HP500 EFI experts

Old 07-16-2006, 08:25 PM
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Default engine alarm question for HP500 EFI experts

Port engine alarm comes on whenever the boat gets up on plane and I go about 1/2 mile. Doesn't do it all of the time - of the last 5 trips we made with the boat, it did it 2 of those trips, today being the second time it did it. Checked the drive bottle and it is within the full/add marks and no foaming. This past trip, the alarm came on so I disconnected the alarm wire for the drive bottle, and no change. Oil pressure and water temperature are fine ... oil pressure is 60 - 80 psi and water temp is 150 - 160 when the alarm starts. Port motor gauges are reading almost identical to starboard motor and both are what they should be for a stock 500 EFI. Interesting part is that if I shut the port engine off and restart, the alarm stops. I can immediately then run it at idle for as long as I want and alarm does start again. Push throttle to 2000 rpm (both engines,running but not enough to get on plane) and I can run still run with no alarms - I have repeated this several times for up to about a mile or more each time. Push throttles to 3000 rpms, boat gets on plane, and I go about 1/2 - 1 mile and the port engine alarm starts. Drive bottle alarm wire is disconnected, water temp is 150 - 160 (same as starboard engine), oil pressure is steady at 60 psi (same as starboard engine) and volts on both voltmeters is reading 14 volts. Each engine is running off its own battery so there is no "crosstalk" between the two engines, as far a charging circuits are concerned. Shut off engines and check battery voltage and both are right at 13 volts (just after shutting off engines). Merc manual says that the only things that will set off alarms are 1) low oil pressure, 2) high water temp, 3) low drive oil level, or 4) low voltage. I don't have any of those and it only does it when I get on plane and go about a mile. I can "plow" at 2000 rpm for 1-2 miles and no alarms. And, the kicker is, that some days it does it, other days is doesn't - no real pattern to which day it will do it. Any Ideas?? Don't know what to look at or look for next.
Thanks,
Bob T.

Last edited by bob_t; 07-16-2006 at 08:29 PM.
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Old 07-16-2006, 08:38 PM
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Default Re: engine alarm question for HP500 EFI experts

Mine was doing same thing a for last 2 yrs, right up to couple weeks ago. Sounding with no reason, but mostly right after startup. Same as you, all items and voltage checked fine. Tracked it down to a poor connection at the t-stat housing temp alarm sender. connected/disconnected the plug a few times and the warning stopped.
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Old 07-16-2006, 09:07 PM
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Default Re: engine alarm question for HP500 EFI experts

Been trying to track down the alarm sensors - supposed to be a tan wire with purple stripe for all alarm sensors. On front of intake in water passage there are two sensors - one is a two pin sensor that has a yellow wire and a black wire - that connector is a "plug in with lock" type, other sensor that looks alot like the one on my old HP 500 carb motor, has a single "push on/friction fit" tan wire - no purple stripe. I pulled the single wire one off and the temp gauge went to "0". Didn't try to start the motor - didn't want to chance really messing something up! We just bought the boat about a month ago and are finding out the guy wasn't as "honest" about things as he said he was ... go figure! Did have scan done on engines and no codes and only 115 hrs on each engine. Its a 35 Lightning Twin Step. The first 4-5 times out we didn't get any alarms. Then one day, out of the blue, no pun intended, the port engine alarm goes off! Next 3 times out, no alarms, then today, alarm starts again, over and over, every time we get up on plane, . Gauges all read good, just really annoying (maybe the previous owner just forgot to tell me about this, on his "perfect/everything works boat". Yeah, even the alarms work!
We did test drive the boat, for about an hour and no alarms during that ride. Didn't get it surveyed because last time, I found more than the surveyor found. After 10 years of Fountains, and about 20 years of working on boats, you kinda know what to look at/look for. I guess I missed something ???
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Old 07-16-2006, 09:22 PM
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Default Re: engine alarm question for HP500 EFI experts

This is what I can see from the wiring diagram in the service manual for the 500efi:
Tan wire is for the water temp. sender.

There are two switches in the Audio Warning System, this two wires are connected to: Oil pressure switch and Drive unit oil level bottle switch. This wires are blue/tan.

The blue tan wire goes from the starting and charging wiring to the efi wiring/ECM, then the tan/blue wires goes back from the ECM to the starting and charging wiring and from there to your dash and buzzer.

Have you looked at the switch in the drive unit oil level bottle?

PS: This switches break the ground circuit when activated and are only off/on

Last edited by Hydrolift; 07-16-2006 at 09:34 PM.
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Old 07-16-2006, 09:58 PM
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Default Re: engine alarm question for HP500 EFI experts

Thanks for looking, I do appreciate it ... talked to local Merc Mechanic and he didn't have any real good advice, but he doesn't work on many 500 EFI's, though. He told me that the alarm switches "complete" the ground circuit when there is a "problem", ie, they are normally open switches, so now I am confused. Drive bottle wires were connected when alarm first went off. Shut off engine and disconnected drive bottle wires at the recommendation of another friend, effectively making that sensor "always open", so it should not be tripping the alarm, per what he told me. Merc owners manual says that water temp can trip alarm also - is that (and all the other sensors) thru the ECM or is this whole alarm system a stand-alone system, not tied to the ECM? I will have the engine scanned again sometime this week to see if it has any codes in it. The engine runs fine - if it were a" real" problem, I would think the gauges would be showing it and/or engine would be having some noticable "issues" or be dead!

Last edited by bob_t; 07-16-2006 at 10:02 PM.
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Old 07-16-2006, 10:00 PM
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Default Re: engine alarm question for HP500 EFI experts

here you go I make it easy for you, here is the alarm wiring diagram,


all the alarm senders are hooked to beige wire with blue tracer and by diconecting them they are disabled as your mec said
Attached Thumbnails engine alarm question for HP500 EFI experts-l101.jpg   engine alarm question for HP500 EFI experts-l102.jpg  

Last edited by GOODT; 07-16-2006 at 10:03 PM.
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Old 07-16-2006, 10:10 PM
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Default Re: engine alarm question for HP500 EFI experts

The alarm system is not a standalone system on the 500efi I would think. The wires from the alarm switches connect through the starting and charging wiring and the EFI wiring to the ECM and back. I would think that the ECM could trigger the alarm if water temp to high.

I am not a expert this is just may thoughts and facts from the manual.
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Old 07-16-2006, 10:15 PM
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Default Re: engine alarm question for HP500 EFI experts

Originally Posted by Hydrolift
The alarm system is not a standalone system on the 500efi I would think. The wires from the alarm switches connect through the starting and charging wiring and the EFI wiring to the ECM and back. I would think that the ECM could trigger the alarm if water temp to high.

I am not a expert this is just may thoughts and facts from the manual.

That's how I understand my MPI to be. Thru the ECM. Not like my previous carbed motor that was just like the above picture.

Last edited by US1 Fountain; 07-16-2006 at 10:21 PM. Reason: clarification
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Old 07-16-2006, 10:27 PM
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Default Re: engine alarm question for HP500 EFI experts

this is true that is the only alarm sender that is controled by the ecmoil press and lube bottle have sep senders
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Old 07-17-2006, 06:48 AM
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Default Re: engine alarm question for HP500 EFI experts

So, if I understand what has been said so far, my ECM thinks something is wrong and must be water temp or oil pressure that it thinks is bad? I'll try to wiggle myself back along the motor (maybe would be better get Houdini to help get into a position to actually see the oil pressure switch) and disconnect that one. That would only leave the ECM or water temp sensor? Water temp shows solid 150 -160 on gauge, though, and no eratic jumps so would doubt it is water temp?
Would the ECM hold a code if the alarm goes off? Thanks for the help so far!
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