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Possible to convert '03-'06 oil pressure gauge to display actual oil pressure?

11K views 40 replies 19 participants last post by  Red_ 
#1 ·
Atleast it seems like it is the '03-'06, '97-'02 had the "real" oil pressure gauges, later TJ's had the dummy gauge. Is it just the sending unit, or the PCM is different? What would be involved in the conversion?
 
#2 ·
I have not found any information, but what I can tell all that is needed to be done is install the older pressure gauge sending unit. If you do a gauge test on the dash the oil pressure gauge shows that it can show all ranges of pressure. That points to it supporting a real sensor and not just a switch.
 
#3 ·
Sometimes manufacturers make changes to avoid unnecessary scrutiny. While I don't know if it is the case here, the oil pressure gauge may have switched in the later years because the previous gauge which read actual numbers may have been inaccurate. No numbers = no scruitny.

Oil pressure readings should be used more for comparison day in and day out than an actual number anyhow. If you know it runs at a certain level and all of a sudden it drops below that level, time to investigate. Sometimes people get too hung up on a number - an engine can survive right nicely with much lower oil pressure than most people think.
 
#5 ·
Sometimes manufacturers make changes to avoid unnecessary scrutiny. While I don't know if it is the case here, the oil pressure gauge may have switched in the later years because the previous gauge which read actual numbers may have been inaccurate. No numbers = no scruitny.

Oil pressure readings should be used more for comparison day in and day out than an actual number anyhow. If you know it runs at a certain level and all of a sudden it drops below that level, time to investigate. Sometimes people get too hung up on a number - an engine can survive right nicely with much lower oil pressure than most people think.
It's not just about numbers, the '03-'06 is a dummy gauge, while the '97-'02 is a real oil pressure gauge. I am not auto-dumb, and I want to know what the actual oil pressure is, you can know alot about the engine via oil pressure too - low oil level, high engine temp etc...
 
#7 ·
Ah, so it appears it can't be done. Even it was said here:

Ever try giving the stock gauge a real sender (i.e. a variable resistance). Might the gauge move linearly - might it work like a real gauge?
No good, it's driven off the data buss. Fun trick to try: Leave your sender hooked up, start the jeep, THEN disconnect the sender. The gauge still reads normally, and even rises and falls with RPM. Now there's NOTHING TELLING THE GAUGE THE OIL PRESSURE AT ALL!!!!. If you shut down, then restart, it'll put the light on.

The switch MUST ground before a crank signal is seen. Then the PCM must have the tach signal first and then see the switch toggle from closed to open. Once it does, it'll simulate a gauge reading. If it doesn't toggle (either stuck open or closed) the gauge cluster will light the lamp, but ONLY on startup, OR if the switch closes again with a tach signal present.
Basically as it is now, the gauge reads "normal" unless there is 3-7psi oil pressure, which is when the switch trips. All this mod does is change the trip point to 17-20psi. Much more useable, but its still a dummy gauge. I want an actual oil pressure gauge.
 
#8 ·
Not sure if its similar to Fords set up. but I know there was a write up for my 96 F250 that I believe involved changing the sending unit and/or adding a (or mabey more) resistor to the gauge, then it would read real pressures. I'll see if I can locate it again.
 
#24 ·
This has been interesting to read. I find it disappointing that the manufacturers have to dumb-down their vehicles (installing a dummy gauge that displays readings based on engine RPM and only shows trouble when a switch trips below 7 psi) to match the ignorance of buyers.

This may explain the oil pressure readings on my '94 F-350. Ever since I bought the truck eight years ago, the oil pressure gauge needle has remained between the 'N' and 'O' in the word 'Normal', regardless of the engine temperature, ambient temperature, cold start, long trip, idle, high revs, etc. If the engine is running, the gauge has remained at the same reading for years. I won't rest easy until I temporarily install a gauge to find out what's really going on in there.

Reading the below post makes me think this is the case (a dummy gauge).



I'll dig around on The Diesel Stop and other Ford forums to see what I can find out.
 
#10 ·
Real, factory oil pressure gauges in cars are nightmares for dealers because people are generally stupid and hound service departments to check why the engine oil pressure drops when the car idles. Mazda eliminated in the Miatas because of the "warranty" checks...
 
#11 ·
What are you guys talking about? I don't understand.

I had a 96 XJ and now an 06 LJ Rubi and the gauges seem the same to me and read similar pressures.

So what's the problem about? I must be missing something here, but my guage appears to show actual oil pressure. It drops when idling, and all the other stuff my 96 XJ guage did, except that my LJ has a slightly more/better pressure (probably because LJ has 23K miles while my XJ had 96K miles).
 
#12 ·
What are you guys talking about? I don't understand.

I had a 96 XJ and now an 06 LJ Rubi and the gauges seem the same to me and read similar pressures.

So what's the problem about? I must be missing something here, but my guage appears to show actual oil pressure. It drops when idling, and all the other stuff my 96 XJ guage did, except that my LJ has a slightly more/better pressure (probably because LJ has 23K miles while my XJ had 96K miles).
The sensor in the LJ is simply a switch that turns on above 7 PSI and tells the computer there is pressure. Then the computer just moves the gauge in the dash according to how much RPM the engine is doing. The gauge is entirely simulated by the computer and can be fooled into thinking there is always pressure.
 
#14 ·
INteresting.
Do you thing there would be enough interest in a retrofit oil pressure gauge (right in the cluster - looking factory) to make it worth coming up with a kit? It can almost certainly be done.

I have a spare 98 F150 gauge cluster (left over from the changover when I brought the truck down from Canada) and the oil pressure gauge is quite small, I'd bet there's room inside the TJ cluster for it, have to figure out how to anchor it. Add a hard wire out to a sender and you're good. Kinda...
 
#15 ·
I've been interested in doing this mod myself. I have the 2 gauge pillar on my A post, and have an open spot (the other one has my OBA air pressure gauge). How hard would it be to install a sender to a separate oil gauge in the pillar?
 
#16 ·
Bringing this thread back from the day - I started to think about this again. I understand it cannot be modified to work with the pcm. Can the gauge be wired directly to a sender? I had the cluster out and there are screw terminals on the back of the gauges. The gauge can display full range of movement, so there's gotta be a way to bypas the gauge from the PCM bus and wire it directly to a variable electric sender.
 
#19 ·
I would guess the gauge itself probably didn't change, just where it received it's signal from (now the PCM, rather than the sender). We could compare part numbers of the cluster for starters (old vs. new) Or just drive-in; like you implied, run a seperate sender/lead directly to the gauge, and see if that would work. :thumbsup:

It would annoy the hell out of me to have to run another gauge to get a real oil pressure reading...
 
#18 ·
You can put all the oil pressure gauges in your Jeep as you'd like. The factory "gauge" in our Jeep's is nothing more then an oil pressure idiot light that dances around with RPM to look good.

I could just install a real oil pressure gauge, but for the sake of less stuff and keeping a clean look, I'd rather just find a way to get the oil pressure gauge on the instrument cluster to display true oil pressure, like it did on the early TJ's.
 
#30 ·
You can put all the oil pressure gauges in your Jeep as you'd like. The factory "gauge" in our Jeep's is nothing more then an oil pressure idiot light that dances around with RPM to look good.
While that is true with your 2005 and others that are 2003 or newer, that is not true with early TJs like my previous '97 that showed the true oil pressure. :)
 
#20 ·
That's exactly what I was thinking. Get an oil pressure sender for an early TJ 4.0 and wire it up directly to the gauge, bypassing the PCM.

I had the cluster out. Each of the 6 gauges has 4 screw terminals for the various signals/ground going to the gauge. It wouldn't be very hard to isolate that from the printed circuit board and run some wires to those terminals.

I wonder what in the actual gauge/cluster changed between the two, or if like you said, the gauge is the same, just where it got it's signal from.

I'm not exactly up to date on my electronics stuff, but I'm sure we'd have to match the ohm range of the gauge to that of the sender, or play with adding some resistors. That probably sounds rather dumb, it's been a while since I've been on that side of things.

I'm gonna go to the parts store and compare part numbers to TJ 4.0 oil pressure sending units over the years.
 
#21 ·
I posted another thread for intell. If the gauge clusters are the same between <'02 and >'03 that would confirm our suspicion that only the signal source is different (PCM, rather than sender).

Does anyone have the part number to gauge cluster for an '02 and earlier TJ?

My 2004 Parts Manual lists:

56010678AE
56010679AE
56010680AE
56010681AE
56010682AE

It's doesn't list much for differences other than all are 4cyl/6cyl and the last two are 2 door
 
#22 ·
The sender is in fact different. '97-'02 is $45 and is labeled "with gauge", '03-'06 is around $20 and is labeled "with light".

I bought an oil pressure sending unit for an '02 TJ 4.0.

I haven't checked if its the same plug, I'm thinking it will not just plug in and work. Its good to know the clusters are the same - I was wondering about that.

The best thing to do next is find a schematic for '02 and see how it is wired up. The '02 sending unit has 3 connections but none are labeled.
 
#23 ·
I figured the sender was different, really a oil pressure switch. I haven't got confirmation on the gauge cluster yet. 'Hoping someone will answer my other thread.

Has anyone had any difficulty with the engine running without the oil pressure switch connected. Is there an idiot light too?
 
#25 ·
From what I heard, if you disconnect it when the engine is running, the gauge will be unaffected - still moving up and down with engine RPM. If you shut the engine off, then start it again with it disconnected, the gauge will not read anything and the check gauges light will come on.

That's all it does. Normally it does it's preset dance, if oil pressure ever dropped to 3-7psi, it goes all the way down and the check gauges light comes on along with the chime. Between the two, that is the "idiot light"
 
#31 ·
Interesting read, Stretch. I don't think our jeeps are wired the same way though. I believe our OP gauges are getting a signal from the PCM to mimic a real OP reading. Seems like Ford took the easy way and let the OP switch give you the resistor reading :laugh:
 
#27 ·
Why do you guys care what the oil pressure is? Sure its stupid to dumb it down, but I don't see much point in caring what the actual pressure is, as long as its not low. I have 8 after market gauges (digital output to 3 actual gauges) in my mustang and I didn't bother with an oil pressure gauge, but i do have an oil temp gauge.
 
#29 ·
An oil pressure gauge can give you an indication of oil temp, but an oil temp gauge will not give an indication of oil pressure ;)

To the untrained eye, an oil pressure gauge may be nothing, but when you know what to look for, and know the normal behavior of your engine, it'll warn you of all sorts of problems.
 
#28 · (Edited)
A change in oil pressure that would be readable by a real gauge could indicate a problem that's fixable before the engine grenaded itself. For instance, a reduction from the normal operating pressure for your particular engine might indicate a partially clogged oil pump intake screen, a clogged filter, a spun bearing, or other such problem...

"Dang, the gauge is showing lower than it usually does. I'd better investigate this."

With the idiot gauge, you'll think everything's hunky-dory until the pressure drops so low as to trip the switch. By then it's most likely too late to do anything but rebuild the engine.
 
#34 ·
I didn't get a chance to mess around with the oil pressure sending unit today - worked on getting the recently installed lift dialed in better.

But if what I see on the back of the block, passenger side, is the oil pressure switch, there is only one wire going to it. The new sender has 3 wires, so the sending unit would be wired directly to the gauge. The gauge had 4 screw terminals on the back of it.

I need to get ahold of a wiring diagram to an '02. Did the '02 wiring go from the sending unit directly to the gauge or did it go thru the PCM? If it went right to the gauge, I wonder what, if any resistors were in the path, and how it was wired up at the gauge.
 
#36 ·
Did the '02 wiring go from the sending unit directly to the gauge or did it go thru the PCM? If it went right to the gauge, I wonder what, if any resistors were in the path, and how it was wired up at the gauge.
I have the Chrysler Factory Service Manual set for my 2001. I quote:

"The PCM continually monitors the engine oil pressure sensor to determine the engine oil pressure. The PCM then sends the proper engine oil pressure messages to the instrument cluster."

The sensor itself has three wires:

5-volt supply, Violet / Orange

Sensor signal (to PCM), Gray / Yellow

Sensor Ground, Black / Light Blue
 
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