False Oil Pressure Gauge?

[rbattelle]

In the `03 service manual, where it discusses operation of the factory oil pressure gauge, it says it will read minimum until the pressure rises to 6 psi, after which the needle will jump to approximately the center of the gauge and remain there until the pressure goes above some value (75 psi, I think).



My point is, it looks like this is a false gauge that is calibrated to read in the center (40 psi) no matter what the actual pressure is, as long as it's above 6 psi. In fact, the manual specifically states that the gauge is designed to indicate a pressure "consistent with the owners expectations".



I've heard that the 2nd gen oil gauge was programmed similarly... am I reading this correctly?



If so, good justification for installing an aftermarket gauge.

 

[Badunit]

I read the same thing but it doesn't appear to me to actually work that way. Mine has at least three places it hangs out. It is below center when idling warm and above center when cold and around center when warm and going down the highway. I haven't watched it to see if or how it moves with respect to RPMs.



This programming is one of those "customer expectations" things. Kind of like the fuel gauge that stays near full for so long then drops like a rock.

 

[JWerkheiser]

I believe the range is something like 5-80 psi actual with a gauge reading based on voltage from alternator so it "fluctuates". It definitely has no direct relationship to actual oil pressure. Oh well, there's always the idiot light...

 

[Rosco]

Originally posted by JWerkheiser

I believe the range is something like 5-80 psi actual with a gauge reading based on voltage from alternator so it "fluctuates". It definitely has no direct relationship to actual oil pressure. Oh well, there's always the idiot light...

I am not sure this is true unless the alternator puts out more "juice" when the engine is cold. On my truck when I start it up cold I have a much higher reading than when the engine is warm. Also the oil pressure drops gradually as the oil warms up. In my opinion if the gauge in my truck is a "Idiot Gauge" then Dodge wasted alot of time programming the truck to make it act like a real gauge. I surely don't want to step on any toes so I have to say this is just what my truck does and maybe yours are programmed different

 

[sag2]

See my post in Warm Up Time



https://www.turbodieselregister.com/forums/showthread.php?threadid=63981



I was just curious as to how the sender worked after I read the service manual.

I guess in the long run, as long as I have over six PSI, nothing should get hurt. I've had a couple of cars that when I actually knew the pressure, it just worried me!

 

[Evan A. Beck]

This really isn't relevant to the ISBe trucks, but on some non-Chrysler ISB engines, Cummins had a kit to convert the oil pressure gauge to an non-functional gauge. Came with a new wiring harness and an oil pressure switch--not a sensor. You have to reflash the ECM when doing this "upgrade. " Perhaps Cummins has the same thing on the ISBe used in the Dodge truck?

 

[nickleinonen]

Originally posted by Evan A. Beck

This really isn't relevant to the ISBe trucks, but on some non-Chrysler ISB engines, Cummins had a kit to convert the oil pressure gauge to an non-functional gauge. Came with a new wiring harness and an oil pressure switch--not a sensor. You have to reflash the ECM when doing this "upgrade. " Perhaps Cummins has the same thing on the ISBe used in the Dodge truck?

shouldn't the red highlighted part be the other way around? kit comes with a sensor, not a switch?

 

[Badunit]

I think this is just a case of poor technical writing. I watched my gauge yesterday and it varies with engine RPM just like I'd expect it to. Maybe what they meant was that the gauge doesn't budge until it gets at least 6psi then it jumps up to the "okay" range and operates like it's supposed to. And above 75psi it will go above the "okay" range. That's my take on it.



Or, as an alternate explaination, maybe since it operates like I'd expect it to I've been suckered into their "customer expectaton" trap!

 

[PCline]

what's this "customer expectation" nonsense?



My expectation is that the gauge tells me the engine oil pressure. I don't want some "feel good" display! DUH! What are they thinking?



On the other hand I find it hard to believe that it's programmed so good that it emulates startup, cold temperatures, warmed up conditions, etc.



I think the sender and gage are really continuous output devices.

 

[Badunit]

I think it does operate like a true "continuous output device" with the one quirk where it stays at zero until it hits 6psi. Since it does not have numbers on the gauge they could also make it non-linear (but still continuous) so it stays closer to the center more of the time, keeping with the "customer expectation" that that's where it's supposed to be. I don't know if they do that or not but they could.

 

[gthiessen]

Just so all you 03 owners know that the oil pressure gauage is not a manual gauge It is a virtual oil pressure gauge. It is basicly a idiot lite. I found this out from one of our best diesel tech in our shop. He just went to a DC class on the updated cummins motor. Also they don't want the public to know that. The guage wiil show normal even with a minimal pressure of 3 to 5 lbs.

Greg:-{}

 

[DIESELMAN]

My brothers trucks mechanical gauge agrees with the Oil Pressure on the dash exactly, only that the dash gauge is damped, is dual regressive, and is very slow to react. The oil pressure mechanically snaps up almost immediately yet the dash gauge takes a second then slowly rises to the real pressure. Same when slowing to an idle. Same cold / high and hot / low.



The Speedometer is the same, a computers representation of the processed data used to control the vehicle, then displayed for appropriate action by the operator. Note that when you stop at a light, look down real quick and you are going 3-5MPH for another second, then it drops to zero. It assumes a California Stop every time.

 

[sag2]

I verified the gauge is in fact a virtual light. When I got home tonight I looked in the wiring diagram and it is in fact a single wire switch. It is normally closed (grounded) and opens (not grounded) when the pressure gets above six PSI.

I unplugged the sensor wire, and the gauge worked exactly like it was before, because there was no path to ground. I then pushed a jumper wire into the connector and grounded it. After a short delay, the gauge went to zero and the check gauges light went on accompanied by a chime. Removing the ground returns the gauge to normal.

Contrary to PCline's comment, it is programed exactly like a real gauge, delays on start up, goes higher when cold, and moves between low and high with engine RPM.

BTW, I put my test gauge on it at the same time, and it reads 40 PSI hot idle and 70 PSI at 2000 RPM.

Based on how my gauge reacts, I would have sworn it was an electrical gauge.

 

[Rosco]

I am totally irritated by this. Here I was thinking that the Dodge had one up on the Ford boys with a real gauge. I would rather have a transmission temp, boost, or egt gauge, in it's place but they would probably just do some B. S. programming on those also.

 

[rbattelle]

This is why I'm ordering a new electric oil pressure gauge and installing it 1st thing.

 

[Badunit]

Just so I understand what tests you did, when you had the wire disconnected did you run the engine and



1) See that the gauge read higher when cold and lower when warm?



2) See that the gauge varied with RPM?



Being a one-wire sensor does not determine whether it's a switch or a variable resistor. The wiring diagrams show it as a variable resistor (but they call it a switch). The test above would prove it to me.

 

[Terry]

Ford has had a "FAKE" gauge for years. It reads higher cold because the battery temp. sensor lets the alternator charge harder when it reads cold battery's. The teacher at the Ford tech. school said it was done to reduce customer complaints of low oil pressure at a hot idle.

 

[sag2]

Badunit

Disconnected the wire at the sensor, and the gauge reads exactly the same as when connected. That is because the cluster thinks it has oil pressure because with no actual pressure, the sensor takes the circuit to ground.

If you want to try it on yours, just reach down and first slide the little red safety catch to one side, and then depress the tab on the connector. Let the wire hang and fire it up.

 

[Big MAK]

Good Info. Now when I install my gauge cluster I know what I'm putting in the third spot. EGT+Boost; Fuel Pressure; Oil Pressure.

 

[VietDoc]

Originally posted by Big MAK

Good Info. Now when I install my gauge cluster I know what I'm putting in the third spot. EGT+Boost; Fuel Pressure; Oil Pressure.

ditto!!



doc