[TJBaker]

What does the switch (above the oil filter) actually do?

The switch is an on off switch, opens with whatever they deemed "adequate" pressure and closed below that point. I suspect the PCM looks at engine temp, RPM and other pertinent parameters and generates a theoretical oil pressure to display on the cluster gauge. It does thie by sending a message on the serial data bus that the cluster processes and displays on the oil pressure gauge.

I intend to pull one or more switches at the yard and test them to see where the setpoint(s) are.

 

[MD TBlazer]

I think others already know this, but there is a spin on tool in place of the oil filter, that measures oil pressure. Of course it is just for test purposes not kept on full time. But that does seem to point to oil pressure vice oil flow as a parameter.

 

[MD TBlazer]

^this is what i was referring to, however looks at the specs it doesn't say for GM 4.2.
Fits GM 4.8L, 5.3L, 5.7L, 6.0L engines, 1996-Present
• Similar to J-42907

 

[mikejenner972]

The switch is an on off switch, opens with whatever they deemed "adequate" pressure and closed below that point. I suspect the PCM looks at engine temp, RPM and other pertinent parameters and generates a theoretical oil pressure to display on the cluster gauge. It does thie by sending a message on the serial data bus that the cluster processes and displays on the oil pressure gauge.

I intend to pull one or more switches at the yard and test them to see where the setpoint(s) are.

It's interesting that GM decided to engineer a sensor that a) requires a special socket for removal, and b) threading too large to match standard pressure gauge kit adapters so that another specialty tool is required. (see MD TBlazer contribution above, as well as, info I found in a YouTube Trailblazer MAY03LT video:

All this to deliver a binary Press/No Press switch, and a cooked readout for the gauge...
lol

 

[mikejenner972]

It's interesting that GM decided to engineer a sensor that a) requires a special socket for removal, and b) threading too large to match standard pressure gauge kit adapters so that another specialty tool is required. (see MD TBlazer contribution above, as well as, info I found in a YouTube Trailblazer MAY03LT video:

All this to deliver a binary Press/No Press switch, and a cooked readout for the gauge...
lol

And yet...
I'd STILL like to have a oil gauge on my simulated dashboard. Despite the readout, Press/No Press information is valuable.
TJBaker, is there a User-Defined PID that you are aware of that I can add? It turns out the dashboard file can be shared to other OBD Fusion app users that I'd be happy to post, oil gauge or no.

 

[TJBaker]

I will see what I can do. I have a PID for the switch, it sets a single bit of a multiple parameter byte.

I also have had some success in Torque Pro using a non-standard method of data retrieval. Instead of requesting a data parameter by PID (Parameter ID) using service 22, I use a standard class 2 J1850 message to request data from a functional address as is done with normal operations of the various modules in the truck. The oil pressure seen in the cluster is sent this way by the PCM. I haven't yet tried to do a request for the oil pressure. I have requested odometer, ambient air temp and some others. The bad news is I have only succeeded with Torque Pro. OBD Fusion or the Car Scanner app don't recognize the reply although they will display it in the test in their PID editors. I was recently thinking of contacting them to see if we can get that resolved.

 

[mikejenner972]

I will see what I can do. I have a PID for the switch, it sets a single bit of a multiple parameter byte.

I also have had some success in Torque Pro using a non-standard method of data retrieval. Instead of requesting a data parameter by PID (Parameter ID) using service 22, I use a standard class 2 J1850 message to request data from a functional address as is done with normal operations of the various modules in the truck. The oil pressure seen in the cluster is sent this way by the PCM. I haven't yet tried to do a request for the oil pressure. I have requested odometer, ambient air temp and some others. The bad news is I have only succeeded with Torque Pro. OBD Fusion or the Car Scanner app don't recognize the reply although they will display it in the test in their PID editors. I was recently thinking of contacting them to see if we can get that resolved.

As a suggestion, can the response merely be a binary display e.g. Green or Red light or some other Yes/No indicator? Since the analog display is contrived for the sake of 'print pretty'.

 

[TJBaker]

As a suggestion, can the response merely be a binary display e.g. Green or Red light or some other Yes/No indicator? Since the analog display is contrived for the sake of 'print pretty'.

This is an example of the more functional equation editor of Torque Pro. In Torque I can isolate the one bit I need of the reponse byte, then substitute some text for the values returned such that I can have my display read "OK" or "Low".

 

[TJBaker]

And speaking of oil pressure... I just did something I have wanted to do for some time. Test the setpoint of the oil pressure switch. I've only tested one unit thus far, a used one, but it reliably switched at....ready for this?? Just under 3 psi.

 

[MD TBlazer]

Only 3 psi? I’d say thats beyond the point of engine damage. It is disappointing GM engineered the sensor that way.

 

[MD TBlazer]

With the weather being how it is, I haven't really a chance to explore the possibility, but if this part is threaded maybe an aftermarket sensor can be screwed on? Just a idea

 

[mikejenner972]

And speaking of oil pressure... I just did something I have wanted to do for some time. Test the setpoint of the oil pressure switch. I've only tested one unit thus far, a used one, but it reliably switched at....ready for this?? Just under 3 psi.

Alarming indeed! I haven't seen any issues regarding engine seizure in the reliable 4.2 so the troubling setpoint may not be a real world issue.
What controls the 'Check Gauges' light? In video 1 of 2 from MAY03LT on YouTube, the oil sensor plug is jumped resulting in a zero, 0, pressure reading and the 'check gauges' light coming on.
I must agree with your experience that the CS support from OBD Fusion is very good; I got a response back same day on three separate questions. To qualify, it wasn't that my issue was resolved so much as getting a timely response.
At the end of the day Torque Pro is also at the $5 price break.

 

[mikejenner972]

With the weather being how it is, I haven't really a chance to explore the possibility, but if this part is threaded maybe an aftermarket sensor can be screwed on? Just a idea
View attachment 56587

Disclaimer: I am NOT this guy's agent, so here goes...
Check out the YT link I provided above. This very approach is investigated to a degree.

 

[TJBaker]

With the weather being how it is, I haven't really a chance to explore the possibility, but if this part is threaded maybe an aftermarket sensor can be screwed on? Just a idea
View attachment 56587

I have an old school aftermarket mechanical oil pressure gauge installed to that point. It's a close fit to the tensioner though.

 

[TJBaker]

Alarming indeed! I haven't seen any issues regarding engine seizure in the reliable 4.2 so the troubling setpoint may not be a real world issue.
What controls the 'Check Gauges' light? In video 1 of 2 from MAY03LT on YouTube, the oil sensor plug is jumped resulting in a zero, 0, pressure reading and the 'check gauges' light coming on.
I must agree with your experience that the CS support from OBD Fusion is very good; I got a response back same day on three separate questions. To qualify, it wasn't that my issue was resolved so much as getting a timely response.
At the end of the day Torque Pro is also at the $5 price break.

I also have not heard much of engine seizure but see a lot of owners on popular groups on Facebook who experience rod knocks.

I must say I don't even look much, if at all at the cost of todays apps. I still remember when we would pay hundreds or more for good softwares and now these apps are less than the cost of a decent burger!

 

[MD TBlazer]

Thanks for the pic, TJ. Thats a pretty neat install. I have to wonder why gm has that tap if its unused by the vehicle, but its not for nothing that gm is known for design idiosyncrasies.

 

[TJBaker]

Thanks for the pic, TJ. Thats a pretty neat install.

I used an Autometer adapter and standard hardware store type fittings.
I secured the nylon tubing frequently with double-wrapped zip ties, running it up the dipstick tube, then across with the A/C line, back by the fuseblock then in with the main harness through the firewall.

 

[mikejenner972]

Nicely done, Sir! What readings did you find?

 

[TJBaker]

have to wonder why gm has that tap if its unused by the vehicle

There are actually a number of places like this in the casting. Some performance builders even route an additional oil feed back to the rear of the main oil gallery using these points.

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[mikejenner972]

Wow...Turbo.
4.2L Turbo Kit

4.2L Turbo Kit?

Does anybody make a turbo kit for the 4.2L....... As far as i no nobody does!!!!

www.trailvoy.com