Well, I don’t know if you need to put a vacuum gage on the pick up hose. I would simply pump the oil tank primer bulb and look for external leaks caused by building pressure with the oil line primer bulb.
Sure, there is a possibility that there is an air leak from before the primer bulb into the tank pick up, but this is not very likely. In order to perform this vacuum test, you would have to pull the pick up out of the tank, drain the oil out of the line, then remove the filter and somehow plug the inlet hose. A messy job indeed. You mentioned replacing the oil tank filter, did your clean out the tank and fill with fresh TCW 3 lube? Like I said, sometimes the oil sits in the tank and gets gelled with age, or when mixed with different brands of lube. It is also a good idea to change the lube to ensure there is no moisture/water in the bottom of the oil tank. This is a very common problem, especially when the oil tank sits low in the bilge. Keep in mind the no oil alarm does not know the difference between oil and water. As for the oil pump crankcase hoses, a visual inspection should do. There will be signs of wetness on the hoses and surrounding area if there is some sort of leak.
There is no specific code that indicates a bad system check gage/tach unit. Again, are you only getting the no oil alarm? Or, are you getting a check engine warning also? Again, ECU codes are only stored when you see the “check engine” warning. There are four warnings you can get: “low oil”, meaning the oil level in the tank is 1/4 full or less/ “no oil”, meaning the pressure switch on the oil pick up pump has sensed a low pressure condition/ “overheat”, meaning the engine has overheated, or “check engine” meaning the ECU has senses one of many possible faults which will be stored and can be retrieved with a laptop and the prober cable/software. It is tough to evaluate the system check gage. Does it do its self check when you turn the key on? In other words, the alarm should sound briefly, all the warning lights will come on, then go out one at a time. Usually, we just swap out the gages if they are in question. But, that is an expensive option, and I think the gage is OK..
I am leaning towards thinking your oil lift pump is getting weak. I suppose we could kind of test a little further by removing the sensor lead from the oil pressure switch. But, I can not remember if the switch grounds when it sees pressure or opens. Now, that I think about it, I feel confident that the switch grounds when pressure is low. An easy way to test would be do disconnect the lead and connect an ohm meter between the terminal and ground while the engine is not running. Seeing a reading close to zero would indicate that the switch grounds when no pressure is present. Unfortunately, seems like this is an intermittent problem, so this approach could be very frustrating. Please don’t run the engine at high RPM with the pressure switch disconnected. I suppose you could wait for the alarm to sound then disconnect the switch terminal while it is running. If this silences the alarm/puts out the light, then I would feel comfortable saying the alarm if accurate and you have some sort of oil pick up pump issue. Once again, keep in mind that even a brand new oil pump is not going to operate properly if there are internal issues causing poor vaccum/pressure signal to the pump. Again, you might want to do a compression test. Yes, I realize that great compression readings does not mean you have great crankcase pressure vacuum signals. But, low/ uneven readings, probably mean internal troubles that are affecting the signals to the pump.
Sorry, alot of conjecture here. I will have to review some of my old manuals to see how that pressure switch is activated. And yes, I realize it is not easy to remove the intake cover and get at that switch while the engine is running. You want to make up a little wiring extension allowing you to make or break the switch connection more conveniently than trying to remove everything while the engine is running. Above all, please be careful. My methods are somewhat unorthodox, and could cause you to fall in the water or get injured. Always have a helper along just in case something happens. Safety first.
Finally it is important to remember how that system check gage works. Even a fault that lasts for only a few seconds will cause the alarm to sound for at least 30 seconds along with the corresponding light. Once the alarm shuts up, the light will stay on until the problem is resolved. The alarm is there to get your attention so you will look at the lights. Not understanding how this gage functions can create more frustration and inaccurate assumptions.
Sorry to ramble on here, I will try to rustle up one of my old service manuals and reviews troubleshooting procedures. D
.
