Mk II oil pressure alarm

[John Langford]

I see that you survived your move Ken. If you have any thoughts on the results I posted for the tests you suggested I would love to hear them.

[KWKloeber]

John, Life intervened, hope this helps:

Reattached the alarm switch and ran the engine
No alarm at start up but strangely when I shut down got an anemic oil alarm. Opened the panel and checked the voltage at the alarm and it was 3.78 volts which might explain the anemia. With the engine switch still on and the buzzer still bleating, I checked the voltage at the fuel pump. It was 13.75v. And when I did that test the alarm buzzer stopped sounding and then started up again when I removed the test leads.

With (only) the key on, there should be no V to the fuel pump.  The schematic tells me that V is supplied thru the preheat solenoid while preheating.
I wonder if there was residual psi that was closing, or partially closing, the oil switch?

I went back to the panel and turned off the engine switch. I then bypassed the ignition switch and applied power from the positive feed at the buss bar to the P terminal on the alarm switch. Still anemic and under 4v despite being fed from a source measuring 14 volts. Does this suggest some kind of ground issue in the alarm circuit?

The P terminal connects to the switch, so it seems that there's something robbing voltage.  I wonder if the oil switch is possibly "partially?" shorted to ground and bleeding off current enough that it robs the alarm?  I've never seen that happen but I guess anything is possible. 
The switch doesn't operate through ground (as the single terminal switch does.)  There isn't a good ground from the switch to the engine (thru a painted bracket bolted to the block) but I suppose it's possible that a poor ground exists there.

[KWKloeber]

John

Correction.  With other than 0.0 V at the P terminal, that means that some V is being backfed to (not being bled off from) the alarm, which prevents it from sounding (or is anemic).  I don't know at what V level it is anemic vs totally shut off. 

That back feed might be because there's residual psi (V back fed thru a closed oil switch) or maybe the switch is "leaking" V back to the alarm even in the zero psi (switch open) position?  I suppose you could do a continuity (ohm) test thru the switch terminals, but it's probably just as easy to spin a new one in to see what happens.  If it is a partially "leaking" switch this is the 1st I've run across that (but as you know anything goes in the marine world) they typically just fail in the open position and never get any alarm.  Maybe partially open/closed is the signature just before final failure???

[KWKloeber]

John, earlier tests:

I measured voltage across plus and minus alarm terminals. Zero reading on P terminal. 0.368v on C just out of interest.

Took the alarm switch out of circuit. Check tabs and they seemed solid.

Grounded the P terminal and got solid alarm signal. Much stronger than usual.

Ok, that seems normal. A-0k on the alarm.

Checked continuity between P wire and panel ground at panel buss bar, 960 ohms.
Voltage on P wire with power on is 0.06 and with preheat added is12.26v.

Ok, that seems normal.  The ohms seem a little low, I would expect 1000+ , but not a problem.  Preheat solenoid is OK, as it is backfeeding V to the alarm as at the same time is powering the fuel pump.

Finally, can't tell if fuel pump is operating during pre heat. No ticking as noted earlier.
Thanks again for your willingness to pursue this with me. I am learning a lot even if an answer hasn't emerged yet.

At least we know it is getting powered correctly, which is the key.  So. I'd conclude that your solenoid and the 10a fuse, and the resistor to ground (buried inside a heat shrunk wire) is okay.

With your more recent test, this points to the oil switch, but it failing in a fashion that I've never seen before.  Always surprises on a boat I suppose.

If the switch is bad, then that means we're correctly interpreting the troubleshooting results.  As I said before you could test the switch, but not worth the effort.  Just for yucks when you remove it I'd check the resistance across terminals and to the case to see if there is leakage.  if anything but 0.0 ohms (no psi, switch open) then that means that, at zero psi, it's indeed leaking JUST enough voltage back to the alarm P terminal to make it anemic, but not robbing enough V going to the fuel pump to shut it down.  From your panel tests, it appears that about 0.5 V or so back fed is the shutdown level of the alarm?

[John Langford]

Thanks Ken. I appreciate you taking up this file again. I will, in due course, try a new switch and report back.

If the switch is the problem then it's behaviour is erratic, either silent, anemic or full throated. My sense is that it never changes behaviour once it starts up. It's either anemic, loud or completely silent for that cycle. I have never had it change from one mode to another once it starts.

[KWKloeber]

John

Yep it's a strange one but you know how that goes on a boat.
I thought the only full howling you got out of it was forcing the alarm at the panel, not relying on the oil switch.

[John Langford]

Yes that was the maximum noise. But I occasionally get a healthy beeping that is easily differentiated from the wheezy anemic mode.

Bloody hell, we have now developed a spectrum of literary descriptors for the performance of this silly switch. Maybe I need a life🙁

[John Langford]

Just received a new oil pressure alarm switch. I understand that polarity of the switch is not an issue,  but before trying to replace the switch I wondered if the old one can be spun off by hand and the new one spun on the same way. Or is a wrench required for both removal and installation?

[Breakin Away]

Just received a new oil pressure alarm switch. I understand that polarity of the switch is not an issue,  but before trying to replace the switch I wondered if the old one can be spun off by hand and the new one spun on the same way. Or is a wrench required for both removal and installation?

I had a similar problem 2 years ago, and had quite a bit of difficulty getting the old switch off. It was way too tight to get off by hand, and very tough to get a wrench in due to tight confines. You'll find discussion on the topic here:

http://c34.org/bbs/index.php/topic,9214.msg67504.html#msg67504

I ended up using a 1-1/16" crows foot tool:

https://www.amazon.com/gp/product/B002YK7MEG/

I do have a related question regarding an anemic oil pressure alarm. When I first turn my key to the "on" detente position (motor stopped), I get no alarm. If I turn it past to the glow plug position, then immediately let it come back to the detente position, the alarm puts out a healthy beep. This is consistent and repeatable. Is this normal, or is there corrosion or other faulty connection that gets "knocked off" by moving the key to the glow plug position? If it's not normal, what is the suggested fix? Do I need to disassembel the key swtich and clean up the contacts? Could I just squirt some WD40 into the key hole and move it around a bit? (I haven't tried this because I don't want to make a mess that's even tougher to clean up.)

[KWKloeber]

John

There's a factory bulletin re: the switch and a wrench that you might want to read on the TechWiki (Manuals).

The switch should be installed hand snug plus a turn.

Was yours? Who knows!

[KWKloeber]

Breakin

WD40 isn't the best treatment for an electrical switch. Possibly electronic cleaner/lube if it's sticky or dirty.  If the contacts are burned it's toast, and for the cost of a good Cole-Hersee switch it's not worth the time to mess with it much.  Its guts are not user serviceable.

[Breakin Away]

 I guess my main question is whether it is normal for the low pressure alarm to not be active until after you have turned past the detente. Does that mean replacement is needed, or would the replacement just do the same thing?

[John Langford]

I've noticed the same phenomenon on occasion. I go through periods when I get silence when I turn on the key, then an anemic beeping after engaging then disengaging the glow plugs. It is not "normal" as the alarm should sound whenever there is no oil pressure.  BTW, I regularly dose the internals of my key switch with a contact cleaner to no ill effect. A new switch cost about $35.

I have not tried to take off the old alarm switch yet. Thanks for the reference to the tech wiki.

A final note. This alarm switch problem is quite common. Over the last few weeks I've talked to a number of 34MkII owners whose alarm has not worked properly for a long time. Maybe only obsessive compulsives worry about it😬😬😬

[KWKloeber]

I guess my main question is whether it is normal for the low pressure alarm to not be active until after you have turned past the detente. Does that mean replacement is needed, or would the replacement just do the same thing?

The alarm should sound with the key in the first (ignition) position. The oil switch/alarm is interconnected in a way to the glow plug solenoid, so there could be something going on there when you go to the "S" position. Unfortunately this is just another remnant of the really stupid wiring on the B engines. Ron did the best thing and rewired his XPB to eliminate the faux pas.

Does your fuel pump run in the first position? Or when you return to that position?

[Breakin Away]

I guess my main question is whether it is normal for the low pressure alarm to not be active until after you have turned past the detente. Does that mean replacement is needed, or would the replacement just do the same thing?

Does your fuel pump run in the first position? Or when you return to that position?

I am 95% certain that the fuel pump only runs when the key is turned and held in the solenoid position. It does not run when initially turning the key to first position, or when returning to first position after heating the glow plugs. However, the buzzer does continue when returning to first position, so I guess it's possible the pump continues to run but I can't hear it.

By the way, once the buzzer comes on, it is not anemic at all (hence the "can't hear it" comment about the little ticking pump).

It sounds like I should just replace the key switch, and that should fix the problem. (I know you don't like the wiring scheme, but changing that is above my pay grade.) I'll try shooting some contact cleaner in there first just to try. Is there a good substitute part, or should I just order the genuine Westerbeke key switch?