Faulty Low Oil Pressure By-Pass Switch?

[Luffydog]

Guessing it does have correct oil level. I would have to check oil pressure with gauge and look in manual and see what pressure specs is and compare and go from there.

[KE4AVB]

The only thing in the service manual is that the oil pressure sensor switch opens and closes at 7-11 psi. No mention of a normal operating pressure range for a running engine. It would be nice to know what is a normal range so we have idea of the amount of wear on the bearings without having tear down an engine just to check for something on a hunch...

Just a few opinions of a fed up field mechanic.

Maybe one of these days these engine manufactures will get back to lettings us know what the norms are. It is so frustrating trying to do repairs when even the tech support can't answer our questions. I got a simple to answer question in with Briggs now that been waiting on an answer for over 2 weeks, No response at all other than they have received my inquiry. Not holding my breathe for an answer either. As I got another question with them that is over 6 months old. They simply don't care.

I am giving up on these manufactures ever treating us in the field as real mechanics. I use to attend training classes but they are most times just a joke and a waste of time to attend. Those trips from Alabama to Ohio was nothing but a working vacation just me to come back and have a two or three week backlog of work because the guy filling in just put things off. Boy was he mad when I gave him the same dose of medicine. Like the saying goes fool me once forgive, fool twice shame on you, fool me a third time shame on me. Most times there is no third time. Paybacks are heck sometimes.

BTW: I know there is no point in asking my questions here either as I rarely ever got a serious reply to my tough technical questions....Sometimes I wonder why I even try to work on some engines.

Going back in my hole in the ground it tornado season here....

[Fulltilt]

I have had the service manual since the day I purchased this unit more than 11 years ago and have referred to it many times. I have not found any diagram or description showing the low oil pressure bypass switch. Can you help me with this?

Well, the only thing that comes to mind is the oil sentry relay etc. must be part and parcel of the machines wiring/electrics. I would say peruse your machines wiring diagram and start probing with your 12v test light.

From the engine manual, it appears that ecu pin 25 is probably connected to the oil sentry circuitry, as it says " safety switch" w/o any further explanation. So, you may wanna start by disconnecting that wire and see what gives

[bgsengine]

Some of the tech support people themselves have no idea how their own engines work either. Have seen the same thing in the automotive field. Often it is left up to a few smart techs with a breakout box and DSO to find the root of the problem and figure out what exactly is happening in a circuit - it could be as simple as having used a wire gauge too small for the circuit or a weak or corroded connector pin.. I'd probably start by getting a graphing meter wave form of the oil pressure switch out put at the switch while the problem is happening and then another at the ECU connector where the input goes and do a little comparison work and come up with a theory as to what it should be expecting - Like I said it could be as simple as a sludged up bypass valve or just not enough pressure building up in time or it could be a resistance in a circuit giving a false reading to the ECU.. lot of things that could be wrong that would be within normal operating parameters otherwise, and they just didn't account for it in the engineering.

But without a diagnostic plan to figure out what it should be and what it actually is, it's just a "throw a new part at it and see what happens" diagnostic process, otherwise.

[Keystone]

So if the wire is disconnected from the pressure sensor the engine should start and run on initial crank, right? If it doesn't stay running until oil pressure is above 7-11psi then what should I look for?

[bgsengine]

IF the engineering made any sense, and the pressure switch is an input to the ECU then I would assume disconnecting the switch would cause a trouble code to pop up due to no input (out of range) however it would mean one of two things - If the switch is a resistance switch (resistance feedback to the ECU) then the resistance would be infinity and depending on which way the switch goes it'll either show as "no pressure" or "high pressure" - without a resistance range to test the switch (and it's input to the ECU) it will either start and run fine (with a DTC stored) or it'll do the same thing (with a DTC stored) - and again that all depends on if they engineerd the ECU to set code for an out of range input from the oil pressure switch.

if the switch feeds a relay ground circuit (assuming there is a relay and relay feeds back to ECU) then the relay would never stay closed (or open, as the case may be) and not set a DTC as the relay itself might be feeding an ECU signal either way. If that is the case and disconnecting the switch makes mo changes then you might try grounding the switch wire to ground bypassing the oil switch and see if that changes anything - But again that is all dependent on what the ECU is expecting to see

So I'd probably start by disconnecting the wire from the switch and do a resistance check of the switch with engine off, then crank and see if it starts and check switch resistance the whole time during crank and start-up and run (if it runs) to see what sort of output is coming from the switch, related to what your oil pressure gauge readings are showing.. and go from there.

[Fulltilt]

Look, you need to , as I said, go over your machines wiring diagram to figure what goes where.
You might try giving up the unit's information so that others know what machine you got, and can check out the wiring diagram, right?

[Fulltilt]

IF the engineering made any sense, and the pressure switch is an input to the ECU then I would assume disconnecting the switch would cause a trouble code to pop up due to no input (out of range) however it would mean one of two things - If the switch is a resistance switch (resistance feedback to the ECU) then the resistance would be infinity and depending on which way the switch goes it'll either show as "no pressure" or "high pressure" - without a resistance range to test the switch (and it's input to the ECU) it will either start and run fine (with a DTC stored) or it'll do the same thing (with a DTC stored) - and again that all depends on if they engineerd the ECU to set code for an out of range input from the oil pressure switch.

if the switch feeds a relay ground circuit (assuming there is a relay and relay feeds back to ECU) then the relay would never stay closed (or open, as the case may be) and not set a DTC as the relay itself might be feeding an ECU signal either way. If that is the case and disconnecting the switch makes mo changes then you might try grounding the switch wire to ground bypassing the oil switch and see if that changes anything - But again that is all dependent on what the ECU is expecting to see

So I'd probably start by disconnecting the wire from the switch and do a resistance check of the switch with engine off, then crank and see if it starts and check switch resistance the whole time during crank and start-up and run (if it runs) to see what sort of output is coming from the switch, related to what your oil pressure gauge readings are showing.. and go from there.

Well, from what the OP said, he replaced the switch with no change.
Also, according to the service manual, the oil sentry switch is a simple open-close switch, with no variable resistance. It also doesn't show up in the engine wiring diagram, and, like I said, the only thing showing in the diagram is wiring from pin #25 to a "safety switch" which more than likely means it connects to the machine's harness, so...
He needs to post his machines numbers.

[bgsengine]

Well, from what the OP said, he replaced the switch with no change.
Also, according to the service manual, the oil sentry switch is a simple open-close switch, with no variable resistance. It also doesn't show up in the engine wiring diagram, and, like I said, the only thing showing in the diagram is wiring from pin #25 to a "safety switch" which more than likely means it connects to the machine's harness, so...
He needs to post his machines numbers.

Yeah - another thing to consider - the oil sentry switch may not even be what is feeding back oil pressure data to the ECU - although unlikely but for example, some cars would have an oil pressure switch that is just for an oil light in the dash and second device elsewhere that feeds info to the ECU - Same for engine temperature (coolant sensor) - and the other thing is it could be a red herring entirely - Could be something else entirely that is feeding incorrect data to the ECU that is still *within acceptable range* and thus does not set a trouble code, but the data is still incorrect. There are other things that can be a problem at start up until the engine has been able to run a few minutes to build up (Fuel pressure comes to mind)

[Keystone]

This engine is in a manufactured carpet cleaning system. The manufacturer is no longer in business and never was very helpful. I do have a wiring diagram for the unit but I am not sure how accurate it is. I will see if I can post it here. It shows a terminal strip with 4 system shut downs, high system water temp, high waste tank level, high engine temp, low oil pressure. A wire from each of these switches comes in one side and a common wire off the other side of the terminal strip goes to the ECM.
I did find the part # for the oil sentry bypass which is install on this engine. The bypass includes wiring and a relay. A note in the description is " * Usable on any engine where the fuel system valve is controlled by a "normally open" oil pressure switch, typically found on gaseous fuel engines."