Mk II oil pressure alarm

[John Langford]

Hi Ken
Not a boot, it turns out, but a some tight wraps of electrical tape over the two alarm switch spade fittings. Sorry for the misleading information but, as you are aware, I am working from feel alone.

I have now uncovered the two terminals on the switch and determined that the single wire terminal connection to the fuel pump positive terminal is good. No break in the wire. The schematic says that one of the two leads from other terminal goes via the "excitation" terminal on the alternator to the alarm buzzer and the second goes to the key switch. The integrity of these two connections is proving more difficult to sort out. I will work on it and report back. The alternator connection will be hard to test because with an external regulator the alternator wiring is harder to sort out. For me at least. With long leads on the multi tester I might be able to sort it out.

The key switch connection raised a question. Since the failure of the alarm to sound regularly every time I turn the key or stop the engine I have had it come on momentarily on a few occasions when I turn the key switch to the on position but before I engage the glow plugs. Is there any chance that the intermittent sounding of the alarm could be the fault of the key switch rather than the wiring at the alarm switch? I should add that since the failure of the alarm circuit, the alarm has never sounded, even intermittently when I stop the engine.

Final thought. As I work on this with your help I can't help but reflect on what this kind of detective work would cost and how unsatisfactory the outcomes might be if I had to hire a mechanic not particularly familiar with Universal engines to solve this problem.

[KWKloeber]

J

Ok
Whoever wrapped it may have been aware of the broken tab issue and did that to help protect the oil switch.

Pull the terminals off the oil switch and tape them so they don't ground out, it's the same as zero oil pressure and you've temp taken the oil switch totally out of the equation. Of course make sure the tabs are ok.  If no change (still weak/no alarm) then presume that there's a different cause than the oil switch (it doesn't turn ON the alarm, it turns the alarm OFF; see below.)

I feel your pain about access.

The key switch delivers 12v to the oil switch first, then (via the dual wire terminal) to the alt field excite terminal. Then (via a dual wire terminal there) 12v is fed back to the alarm + terminal. It's the stupidest wiring I've ever seen. Why not 12v right from the key switch to the alarm? The engineer who designed that should automatically have his license revoked. i.e. the alarm should have 12v to it whenever the key is on, there's NO POINT in routing it to the oil sw and alt and back to the panel.

SO- I would temp bypass that circuit to take it out of the equation (in fact there's no reason NOT to make it permanent.  i.e., run 12v to the alarm + terminal from one of your gauge +v posts.)
If all is well (strong alarm) again, it points to that circuit being the issue. If no change (weak/no alarm) then presume that there's a different cause.

I still feel your pain about access.

How the alarm works (or doesn't in your case) is completely back asswards from how you would think and how it does on the M-35. On the B, the alarm is "always on".  Like the M35, it sounds when the alarm P (pressure) terminal is grounded. So on the 35, no oil pressure, the switch closes and then alarm sounds. Easy peazy.

But your 35B ALWAYS HAS 12v to the alarm and it is ALWAYS grounded, so it ALWAYS alarms. When the oil Sw closes (with +5 psi pressure) the switch closes and BACKFEEDS voltage to the alarm ground (P terminal) via the preheat solenoid. The backfeed acts against (cancels out) the 12 v- ground, and the alarm "looses" its ground and shuts off. Yeah, HUH?? 

SO, since the alarm is supposed to be always grounded, that's the other weak point in the system. It might be a bad ground connection (via the 10a auto reset (not allowed by ABYC) fuse and resistor to ground at the preheat solenoid terminal.) fed from the fuel pump via the red wires in the below:



BTW when you have oil pressure (oil sw closed) the harness is constantly bleeding off current thru that  resistor to ground. HUH, What???  Revoke his license then tar and feather the designer.

Lemme kno what develops?

K

[KWKloeber]

John

PS - yes it's possible that a burned contact in the key switch could cause a weak/intermittent alarm (as could a poor ground at the preheat solenoid as I describe below.) BUT it doesn't compute unless you have power issues with everything else on the panel, as they are all fed thru the same contact. So if your tach, gauges, lights, blower have no issues I'd not suspect the key switch. But that's easy to check; just bypass the switch with a jumper to the alarm + terminal.

K

[John Langford]

Hi Ken
I did the two tests you suggested. I took the alarm switch out of the circuit and got no sound out of the alarm when the key switch was turned on. I then put the switch back in the circuit, turned the key and provided the alarm with 12 volts from the big red positive wire in the harness terminal in the engine instrument panel. Same thing. The alarm did not sound.

I gave some thought to the rationale for including the alarm switch, alt field and fuel pump in the same circuit. These are all functions that you want to start up before preheating and pushing the start button. Does that make sense?

Does the failure of these tests suggest where else we might look for a problem? One other observation. Having manipulated the two connections to the alarm switch I didn't get the sense that there is a break between the wires and the female connectors to which they are attached.

[KWKloeber]

John

To your first question, actually the alt excite and the alarm need to have power just AFTER start they don't need to be powered before start.  But even if they did there's no earthly reason to run the key switch power to the oil switch, to the alt, and then back to the panel to power the alarm. Power to the alarm COULD come  from anywhere on the panel that gets power with the key on (eg, direct from the key switch I terminal (not recommended), from any gauge light feed (also not recommended) or from any gauge v+ terminal (that's what I recommend) from the + side of the preheat or start button (both not recommended.). Doing what Wb did, would be similar to powering the gauges by running a circuit from the key Sw, to oil Sw, to the alt, and back to the panel gauges. I appreciate your trying to save the designer's integrity BUT that circuit doesn't even power the fuel pump before start, the pump is initially powered (until there's oil pressure) by the preheat solenoid. Nope, license revoked, tar AND feather that engineer.

Even tho you powered the alarm right from the panel feed (with no luck,) let's verify that there's voltage returning to the alarm + terminal (from the alt.). If there is 12v, we can eliminate the (idiotic) roundabout   alarm power circuit (but I would still make the change and power it from right at the panel.)

Keep the oil Sw out of the equation. There's no reason to have it plugged in until we find the culpret (remember the Sw doesn't turn ON the alarm, it turns it OFF) so let's just leave it isolated for now.

Also, just to be precise, the break occurs on the switch male tab(s,) not on the harness wire/female terminal(s.) Taping them together probably prevented that from happening ( flexing/snapping off of a male tab.)

Just to ck the alarm, ground the P terminal, it should sound off. If not there's a different problem.

With good 12v to the alarm, if it sounds when you ground the P term, your symptom then points to the ground circuit being bad. The ground is established thru the 10a auto-reset circuit breaker (bolted to the preheat solenoid I terminal) and thru the resistor to engine ground. (I'm not referring to the 20a manual reset breaker.)  If either the 10a breaker or resistor have failed you have no alarm.  Does the fuel pump run while preheating?  If so the breaker is good, if not the breaker has probably failed. If the breaker is good it may be the resistor has failed. In other words, the breaker only is needed to power the fuel pump (before there's oil pressure,) but both the breaker and resistor are needed for the alarm to sound.  You can check this by removing the alarm P wire, and check continuity to panel ground with the key off. It shouldn't be an open circuit, nor be zero ohms. Resistance should be a little over 1K ohms. Honestly I don't know where that resistor resides or how it's connected to the preheat solenoid I terminal because I don't have a B engine.

One other test - with the wire to the alarm P terminal removed chk for voltage on that wire with the key Sw on, and then while preheating.

Apologies this is taking the long route to the cause. Yours is the daffynition of "conundrum."

Come to clearing my senses (CRS,) a customer with an XPB had a physically broken off 10a breaker. That would manifest your alarm symptoms BUT your fuel pump won't operate while preheating. Maybe you don't even notice if that happens?

Report back!

-k

[KWKloeber]

John

I found a pic of the resistor, it's also on pg 43 of the parts manual, #17.

See the black heat shrink bulge below on the vertical wire left of the solenoid?

The short jumper comes off the same solenoid "I" terminal that the circuit breaker is bolted to (lower right-hand terminal) and goes to a ground bolt (probably the solenoid mount bolt.)

I wouldn't go looking for it unless the test below shows the alarm ground path is bad.  This is really getting off into the weeds as to the cause.

-k

[John Langford]

Hi Ken
I am on it today and will report back this evening.

Some potentially useful evidence re the 10amp breaker and resistor. This alarm issue emerged gradually. First it was weak, then intermittent and finally silent except for the very occasional weak sounding and, even then, only prior to startup. During he course of all this (and including the completely silent phase) I was on a cruise and the glow plugs and fuel pump continued to run without problem. But I can't be sure if the pump ran during preheat because I replaced the original mechanical Facet pump last year with the newer electronic version that apparently doesn't tick like its predecessor. I did have a fuel starvation problem earlier this summer but that disappeared when I changed the 2 micron primary Racor filter element. The old one was very dirty suggesting that I might have a sediment problem in my tank. Previous filter elements have lasted considerably more hours. Excuse the possibly extraneous context.

[KWKloeber]

PS

That should be ".... a two micron...".   Damn Seri and the phone she rode in on.

******

I wonder if the guts of the breaker can get corroded? The one in that picture we had to replace, it was in very bad shape.

No problem on the content, will get to the bottom of it. Always good to have more rather than less info.

We can get into it later, but eight to micron is not recommended for the primary filter

[John Langford]

Ken,
Re the third test, checking the continuity of Alarm P wire to panel ground. Is it the continuity of the disconnected Alarm P wire or the P terminal when the P wire is disconnected
?

[John Langford]

Answered my earlier question. I just finished the four 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.

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.

Finally, can't tell if fuel pump is operating during pre heat. No ticking as noted earlier.

Will send picture of preheat solenoid.

Thanks again for your willingness to pursue this with me. I am learning a lot even if an answer hasn't emerged yet.

[John Langford]

As promised

[John Langford]

Hi Ken
Reattached the alarm switch and ran the engine just to make sure I hadn't crossed any wires while testing yesterday. 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. 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?

Hope those might be a useful observations.

[KWKloeber]

John

I'm right smack in the middle of a move, I'll review the test results and get back ASAP.

-k

[John Langford]

No problem Ken. I'm in no rush. The boat works even if the alarm doesn't at this point. This engine hasn't lost a drop of oil in its 20 years of service and I monitor the oil daily when cruising.

I hope you don't hate moving as much as I do.

[KWKloeber]

As James Clapper described going before Congress, it's a step below trying to fold a fitted sheet.