[private]

Thank you for that post, I didn't know about that little trick.:thumbsup:

I do believe 02/03 up are all "idiot gauges". Anything below, albeit, not a true mechanical gauge, actually does its job.

 

[TJRHD]

Mine is doing the same thing. Interested to see what you find.

 

[The_Trooper]

I do believe 02/03 up are all "idiot gauges". Anything below, albeit, not a true mechanical gauge, actually does its job.

Interesting, so if they aren't even true gauges should I just get mechanical ones? I am confused then on how they even show the proper guage...

 

[Black05Rubi]

Interesting. My oil pressure gauge changes with rpm changes. At idle it's a hair over center of the gauge, 26-2800 rpms it's about 2/3 up between L and H. I wouldn't think an "idiot gauge" would do that.

 

[jkp]

The computer moves the gauge around based on RPM. Notice that it does not change position based on hot or cold oil. A real gauge would. This is a result of people comlaining that their oil pressure is "low" or "high."

From the FSM:

​

​

​

​

Engine Oil Pressure Message - Each time the
cluster receives a message from the PCM indicating
the engine oil pressure of a 2.4L engine is above
about 0.2 kg/cm2 (3 psi), or of any engine other than
a 2.4L is above about 0.4 kg/cm2 (6 psi), the cluster
moves the gauge needle to the middle of the normal
range on the gauge scale to represent the engine oil
pressure. The gauge needle will continue to be positioned
at the middle of normal range on the gauge
scale until the cluster receives a message from the
PCM that indicates the engine oil pressure is low, or
until the ignition switch is turned to the Off position,
whichever occurs first.​

​

​

​

​

Engine Oil Pressure Low Message - Each​

time the cluster receives a message from the PCM

below about 0.2 kg/cm​

​

​

​

2 (3 psi), or of any engine other
than a 2.4L is below about 0.4 kg/cm2 (6 psi), the
gauge needle is moved to the graduation at the far
left (low) end of the gauge scale, the check gauges
indicator is illuminated, and a single chime tone is
generated. The gauge needle remains at the left end
of the gauge scale and the check gauges indicator
remains illuminated until the cluster receives a message
from the PCM indicating that the engine oil
pressure of a 2.4L engine is above about 0.2 kg/cm2​

(3 psi), or of any engine other than a 2.4L is above
about 0.4 kg/cm​

​

​

​

2 (6 psi), or until the ignition switch
is turned to the Off position, whichever occurs first.
The cluster will only turn the check gauges indicator
on in response to an engine oil pressure low message
if the engine speed message is 300 rpm or greater for
more than about five seconds.​

My '92's gauge actually reads in PSI and it will peak our at 75 PSI on a cold morning, which is the point at which the relief valve opens. On a hot GA day it will be down around 20 PSI at idle.

 

[TexTJ]

Your YJ should have a real gauge, my 91 did and it would change with a hot or col motor and rpm. My TJ doesn't move much oat really just stays in the center.

 

[jkp]

Yep, it does, see above.

 

[TexTJ]

I understand that the gauge only has two set positions, the question is if it takes longer than a few seconds to read a good pressure why does it just stay at zero instead of checking again and bumping the gauge back to the middle.

 

[ChaseB]

Interested in knowing what's causing this issue.

 

[DanZ51]

The "oil pressure gauge" in your '05 is nothing more than an idiot light. The "sending unit" is a switch that closes at something like 5 psi. When computer sees the switch close, it moves the needle to mid-scale.

Base on that logic, I guess I would disconnect the switch check for continuity and have someone start the engine. See "if" the switch is actually closing. 'Might want to also re-check the part number of the new switch-sender and see if it's the correct one they sold you.

 

[Black05Rubi]

Still not getting why my oil pressure gauge seems to move all over the spectrum with rpm changes if it's just an idiot gauge. Not only that, but how does oil temp affect what the gauge reads as pressure? Pressure is pressure regardless of how that pressure is generated, isn't it?

Sorry if this seems like a couple of dumb questions, I am generally wondering, not trolling.

 

[TexTJ]

The sending unit is good and the I have swapped the instrument cluster also and still the same problem. If it just stays at zero when I start it hoe do I know that if I loose oil pressure while I'm driving it would actually tell me? That is if I restart it and get it working prior to it loosing pressure. It sounds simple that the computer would constantly check the pressure but it sounds like it only checks it at start up.

 

[TexTJ]

Your oil pressure will drop the hotter the engine gets because the hotter the oil the thinner it becomes.

 

[jkp]

Still not getting why my oil pressure gauge seems to move all over the spectrum with rpm changes if it's just an idiot gauge. Not only that, but how does oil temp affect what the gauge reads as pressure? Pressure is pressure regardless of how that pressure is generated, isn't it?

Sorry if this seems like a couple of dumb questions, I am generally wondering, not trolling.

The computer will move the gauge around slightly based on RPM.

If it were a true oil pressure gauge, it would be on the far right when the oil was cold (approx 75 PSI). When hot, at idle, it would be fairly far to the left (20 PSI or so). When hot and revved the oil pressure would vary from 20 - 60 or so with the RPM. You will never see one of these newer TJ gauges near the right peg, no matter how cold it is.

Hot oil is thin, therefore less pressure for a given RPM. Cold oil is thick, and hard to pump, higher pressure for a given RPM.

 

[DanZ51]

The computer moves the gauge around based on RPM. Notice that it does not change position based on hot or cold oil. A real gauge would. This is a result of people comlaining that their oil pressure is "low" or "high."

From the FSM:

​

​

​

​

Engine Oil Pressure Message - Each time the
cluster receives a message from the PCM indicating
the engine oil pressure of a 2.4L engine is above
about 0.2 kg/cm2 (3 psi), or of any engine other than
a 2.4L is above about 0.4 kg/cm2 (6 psi), the cluster
moves the gauge needle to the middle of the normal
range on the gauge scale to represent the engine oil
pressure. The gauge needle will continue to be positioned
at the middle of normal range on the gauge
scale until the cluster receives a message from the
PCM that indicates the engine oil pressure is low, or
until the ignition switch is turned to the Off position,
whichever occurs first.​

​

​

​

​

Engine Oil Pressure Low Message - Each​

time the cluster receives a message from the PCM

below about 0.2 kg/cm​

​

​

​

2 (3 psi), or of any engine other
than a 2.4L is below about 0.4 kg/cm2 (6 psi), the
gauge needle is moved to the graduation at the far
left (low) end of the gauge scale, the check gauges
indicator is illuminated, and a single chime tone is
generated. The gauge needle remains at the left end
of the gauge scale and the check gauges indicator
remains illuminated until the cluster receives a message
from the PCM indicating that the engine oil
pressure of a 2.4L engine is above about 0.2 kg/cm2​

(3 psi), or of any engine other than a 2.4L is above
about 0.4 kg/cm​

​

​

​

2 (6 psi), or until the ignition switch
is turned to the Off position, whichever occurs first.
The cluster will only turn the check gauges indicator
on in response to an engine oil pressure low message
if the engine speed message is 300 rpm or greater for
more than about five seconds.​

It really pisses me off that this was Jeep/Chrysler's solution to customer complaints of low oil pressure. Seems to me, a blurb in the owners manual explaining how oil pressure reads at different temperatures and RPMs would have made more sense.

I wish it was warmer out, and I'd go outside and play with my oil pressure switch to see when the PCM samples the switch open/closed readings. What I'd REALLY like to do is find I way to convert my gauge panel back to a real oil pressure gauge!

 

[EarthRunner]

So how does one go about swapping the idiot gauges to actual working gauges? Is there a write up on this?

 

[Katahdin]

I'd suggest making sure your battery terminal connections are tight, the gauges in my 93' GMC would do screwy things when they started to come loose.

 

[DanZ51]

So how does one go about swapping the idiot gauges to actual working gauges? Is there a write up on this?

Easy enough to add an additional (real) gauge. So far, no one has figured out or posted up how to convert the "idiot" gauge to a real one. The other option would be ....

http://www.scangauge.com/

 

[TexTJ]

Even if you replaced the gauge with another, the check gauges light is still going to come on.

 

[goofus]

I am having the same exact problem on my 2005 4.0l with 101k. This was happening occasionally over the past few years, but now is daily. Every morning, start it- reads zero pressure. I kill it and start again- it's perfect. In the afternoon driving home from work, after sitting still for 8 hours, no problems. I have always used a Napa Gold (WIX) filter and Valvoline 10w30.

A few times I keyed to run, but not start, and let it sit for 15 seconds. Then off, then start and it would read pressure- albeit a little slower to get to the normal range.

I'm going to get some dielectric grease on the connector today, also have a new pressure sensor coming.

And exactly as the OP stated, there's definitely actual oil pressure. This is not related to an OPDA issue.