ECM oil pressure

[CarlsonR]

I understand the oil pressure gauge is only telling me what the ecm calculates that the oil pressure should be based on several different sensor outputs,and in my service manual it shows the only actual oil pressure sending unit is just a six psi switch which turns on the ecm circutry to activate the dashboard oil press gauge needle. My question is how does the ecm know that i've changed oil from 5-40 to 15-40 thereby giving me a 10psi increase. this happened today in approx 1hr. period when i dumped my winter oil and refilled with summer grade. Any ideas on how the ecm could calculate this??

 

[Pawpaw]

One of the inputs it uses to "fake you out" is coolant temp. During that 1-hour period, your truck may have cooled down below the magic threshold temperature (whatever that is), that tells the ECM the engine is cold.



Cold oil = higher pressure in the real world, so the ECM tries to fake the same thing.



Just a guess.



Bob

 

[nickleinonen]

One of the inputs it uses to "fake you out" is coolant temp. During that 1-hour period, your truck may have cooled down below the magic threshold temperature (whatever that is), that tells the ECM the engine is cold.



Cold oil = higher pressure in the real world, so the ECM tries to fake the same thing.



Just a guess.



Bob

spot on there bob. . the ecm looks at iat [manifold and air box] & coolant temp and does its figuring to give you a guesstimate as to what the oil pressure is.

 

[p-Bar]

They call them idiot gauges

 

[CarlsonR]

that would be true but the difference was at the same temps. 10psi difference when cold and about 5psi when hot(200). Any other thoughts?

 

[sag2]

PFM or a vivid imagination

 

[nickleinonen]

PFM

:-laf:-laf:-laf

 

[Missouri Mule]

Thicker oil will have a higher pressure reading.

 

[nickleinonen]

Thicker oil will have a higher pressure reading.

true, but when the ecm only sees a signal from a glorified 6psi hobbs switch, the ecm doesn't know if you have 50w in the sump or diesel fuel. as long as there is more than 6psi, it will read what the ecm wants to show

 

[JasonCzerak]

I don't get how the programming for this "idiot gauge" was cheaper then just a real pressure gauge? . . mind boggling.

 

[y-knot]

Thats because you are looking at the problem from a consumer stand-point and not a manufacturers stand point.



The hole ideal behind the estimated oil pressure readings and not using a true oil pressure reading is they wanted to eliminate UN-necessary (and maybe even some legitimate) service calls. There are just to many worry worts, old timers and first diesel users that would freak out if they seen how much the oil pressure fluctuates. It's bad enough when everything is new but after a few years and when everything gets loose, the oil pressure does suffer some. Just put yourself in Dodge's shoes, you have so many buying these trucks and many are first time diesel, and first time truck owners. The trucks go for a premium, which makes many fret over every little problem or squek. So if you could design a system that would circumvent the many service calls, which by the way equals a huge amount of money, maybe just maybe you would do the same thing??? This little Trick, has saved dodge millions. And I'm sure there are many other little tricks like this we don't even know about.

I have been telling people about this problem for years, but most were set in denial, thinking good old Dodge wouldn't do such a dirty trick, not to there precious Cummins!! Well it's true, and you can live with a truck that constantly lies about it's most important engine function, or do as I did and install you own oil pressure gauge and pull your head out of the sand.

 

[AKaiser]

Wonder if you could connect an electric sending unit into the dash oil pressure gauge?

 

[nickleinonen]

Wonder if you could connect an electric sending unit into the dash oil pressure gauge?

probably could be done, but much cheaper/easier to add an aftermarket one

 

[JasonCzerak]

Thats because you are looking at the problem from a consumer stand-point and not a manufacturers stand point.



The hole ideal behind the estimated oil pressure readings and not using a true oil pressure reading is they wanted to eliminate UN-necessary (and maybe even some legitimate) service calls. There are just to many worry worts, old timers and first diesel users that would freak out if they seen how much the oil pressure fluctuates. It's bad enough when everything is new but after a few years and when everything gets loose, the oil pressure does suffer some. Just put yourself in Dodge's shoes, you have so many buying these trucks and many are first time diesel, and first time truck owners. The trucks go for a premium, which makes many fret over every little problem or squek. So if you could design a system that would circumvent the many service calls, which by the way equals a huge amount of money, maybe just maybe you would do the same thing??? This little Trick, has saved dodge millions. And I'm sure there are many other little tricks like this we don't even know about.

I have been telling people about this problem for years, but most were set in denial, thinking good old Dodge wouldn't do such a dirty trick, not to there precious Cummins!! Well it's true, and you can live with a truck that constantly lies about it's most important engine function, or do as I did and install you own oil pressure gauge and pull your head out of the sand.

As dumb as that sounds, you are 100% right. That makes perfect sense. I do it in my line of work to a point as well. :-laf . It's retarded, but smart. Whaadya gunna do.

 

[brods]

Not 100% right, its not a diesel or Cummins or first time owner conspiracy! Dodge has been doing such things across the board. Customer complains about the water temp on a Cherokee, a little ecm tweak and the gauge reads "within customer's expectations"! I would not be surprised if most other manufacturers do the same or at least severely dampen the gauge response.



Why do you think most manufacturers' gauges have vague markings? High, Low and a wide middle ground. Because with old analog gauges having numbers clearly labeled, when two owners got together and compared numbers, inevitably a call to the dealer followed asking why one had lower readings than the other. This is a very old problem for the manufacturers and not limited to Dodge or the CTD.



Ryan's fake gauge thread https://www.turbodieselregister.com/forums/showthread.php?t=141311



AKaiser, answer to your question https://www.turbodieselregister.com/forums/showthread.php?t=153168

 

[p-Bar]

Well put Brods. The only thing I trust on that instrument panel is the tach and speedometer the rest is gloried idiot lights.

 

[AKaiser]

Well put Brods. The only thing I trust on that instrument panel is the tach and speedometer the rest is gloried idiot lights.

Well, I guess I know what I'm putting in my truck when I put my bypass filter in, don't I?

 

[p-Bar]

Funny thing is that my stock gauge doesn't hiccup like Amsoil says they do.