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I have the idiot-light sensor fitted, but keeping it reading at all is the challenge. Over the years I've probably replaced the stupid thing three times trying to find a sensor that would either read correctly (the earlier transduscer sensors) or just center the needle (the later idiot switch type).
So the idiot light is just as bad (unreliable) as the transducer?
Glad I put a new transducer in then!!
Joking aside, I'm surprised the on-off switch has the same problems - I was talking to a friend about this problem and various theories about the failure rate and causes, many seem to think it's a heat/exposure/position issue as apparently the same system is used in MK3's and they don't have the same problems. Apparently some believe the location has an effect on the reliability of the units fitted to the 40's.
His solution? Move the sucker using an extension length of tubing/hose!!
Just the vibes coming off the oil gallery would drive any instrument trying to read it ,
NUTS!
Mine reads smooth,but came with a restrictor orafice installed.Also reads high.
Home now,work done,sleep time!
Will do Jag tomorrow,charging the cam,
Cheers,Jim.
Well,gorgeous sunny day,perfect for a little Jag time,wife distracted for the time being...
pulled the little port plug,3/16 inch hex bit,measured,it is a 1/8 inch NPT.
I installed my pressure guage ,it reads up to 60 psi,and it is without any restrictor.
I made up my variable resistor,0-500 ohm,ran one lead to the oil guage wire,and the other side to ground.
Start the car,oil pressure pinned the guage straight off!
I dialed up some resistance on the resistor and came up with...
230 ohms="2" on dash
170 ohms="4" on dash
75 ohms ="8" on dash
These reflect the resistance values straight to ground as if you would make up a resistor jumper straight to ground,or thru a "on-off" style sender.
Warmed up the car fully,oil pressure dropped to a low of 40 PSI gradually.
I took some readings from the sensor to ground,it's an airtex/wells I got from rockauto for 40 bucks or so,and it HAS a restrictor orafice to slow down the pulses in the oil rail.
Sooo,with the variable resistor in play between the wire and the sensor,all I had to do is dial up the correct "dash"reading and decide what I wanted the dash to read.
I chose BAR
1 bar=14.5 PSI
I read the variable resistor,and 75 ohms is the magic value,to go with my sensor.
I made the correct value from a combo of resistors(thanks Larry)
installed and re-warmed the car.
Start up=guage pinned,reads 7 BAR on dash,or 101.5 PSI pressure
Continued warm up until guade reads 60 PSI exactly,check dash,and bingo,just over 4 bar,Perfect!
Hot idle at 3 on dash,I now know what the engine is doing under there!
One thing to note,there is a LOT of pulse/vibration in the oil rail on these cars.
No wonder senders and senders do not last!
That wraps up my day for now,hope this helps,
Cheers All,Jim.
Out for a cruise today was looking at about 5.5 to 6.5 bar at around 85kph and high 4's to 5 at idle ..pretty close to pinning (7's) on cold start ...the other earlier numbers were obtained with the motor about a litre low (after we lost a bit doing the swap and driving her pretty hard down the island hwy)
...so gonna try the 75 ohm resistor to see what I get!
I've been waiting for oil change time to get to replacing those mick o-rings in the oil cooler bypass
When Jim *kindly* fitted my new oil pressure sender back in the spring he had to remove the oil cooler bypass to get at the sender. (believe me on the 94 it's no fun changing senders)
Anyway, the o-ring seals on the bypass union crumbled when we took it off and after driving all over town trying to get new seals, ended up compromising with not-quite-correct size o-rings and a squirt or two of gipe.
The union didn't leak all summer, so all was good - but over the summer I ordered some new o-rings and decided to replace them when I did the oil change.
Here's some pics:
the new bits
oil cooler bypass is located just under the oil filter and secured with one 13mm top-hat nut.
the old o-rings and silicone used for the get-me-home fix
New seals in place; oil pressure sender resistor assy shown at right
Hello..I am a new member and just had a new oil pressure sensor installed on my 91. Original one quit working. The replacement one is an old style that measures actual pressure. The new one says 8, and after the engines been running for a whole, it might drop between 5-6 at idle, but goes back up to 8 with acceleration. I enjoy all my gauges working, but I would like to have my oil pressure gauge tell me what my pressure is really doing
I found that the sensor that was installed was one that resembled the Airtex Wells 1S6678 (found on RockAuto). Bigger than the one that was taken off of the car. The Beck Arnley 2011505 (RockAuto) looks exactly like the original sensor that went bad (in fact, I can see it from the top of the engine. Was never able to see the old one), and I recall reading that the one I bought was also used on the XJ's around in the 70's (Series II, I think?), and they had 4.2L engines and another size I'm unsure of, and mines a 4.0L. Would putting the Beck Arnley sensor on change anything or would it need a resistor too? Am a little limited with tools right now
I've got the Beck Arnley one, needs a resistor too unless you like thinking your engine has huge oil pressure - see the pic further up this thread of the 75 Ohm resistor I made up.
I see! I also see how it connects between the wire and the sensor. Should be fairly easy to get one installed, I can reach down to the sensor and unplug it easily. I'm aware of a plug being on the side of the block next to the sensor to test pressure, am gonna try to contact someone who would be willing to test the pressure before I get a resistor, and help build one for me cause I am not very sure about how to make one
Last edited by dhatfield12; 02-11-2016 at 06:48 PM.
I haven't gotten her pressure tested yet, but from what I remember, the car always had great pressure, even on the hot days of summer (will be better once the dreaded oil cooler lines get changed, cause not only will I quit getting dripping, but I'll also quit burning oil when it gets hot, though it never blows out blue smoke when I drive, plus will be saving money on oil), so the next step is a resistor. I'm not very experienced with electrical and don't know how to make one, unfortunately, or what parts I'll need
You just need a 75 ohm resistor (I think the one I used was rated at 1/2 watt), some shrink tubing or electrical tape and two connectors, a male and a female spade type connector.
Then just solder the connectors to either end of the resistor and enclose the whole assembly in shrink tubing. Heat up the tubing and shrink it to fit, trim ends with a sharp utility knife and you're good to go.
Got the resistor made and installed. After fighting for 10 minutes, took off the hose for the idle valve and made it easier. Parts were readily available, thankfully. I got it on after a total of 20 minutes, and fighting with trying to get the connector and sensor prong lined up. Thanks to Jim and Lawrence for the useful information. Gauge works perfectly now (installed it this evening and went for a drive to test it). Car ever so slightly stutters at idle, and the idle speed is off, but I have a code for the EGR solenoid, Code44 (oxy sensor I believe, and an exhaust manifold leak, plus the intake has never been cleaned out, yet), but that can and will be fixed!
Mine has been acting up the last few days. Getting an oil can and 0 PSI reading and i can see oil being sent to the cams and after a cycle or 2 the sensor unsticks and starts working.
I just had a chance to get out and look and its already a replacement sensor so it looks like the replacement is taking a dive and its time for a new one. On the plus side its the new smaller style one so it shouldn't be a PITA to remove.
Im confident that's the issue as the car makes no more or less noise with the light on than off and after working on cars for so many years no oil pressure makes itself know pretty quick.
Oil Pressure gauge jumps to 0 after 20 mintues on the road
Thank you for the birthday wishes.. I do have a wish to find out why my J40 oil pressure gauge falls to zero after 20 minutes on the road and when idle.
I have to put in neutral at each stop to keep the pressure from falling to zero.
I just removed a factory installed "link lead" (pricey resistor) from my late '40 parts car's oil pressure switch (X300 on-off style).
The link lead part number is LMD3325BA. It contains a resistor that I just measured at 150 ohms - so if you fit the switch as an alternative to the sender keep in mind you might need to make up a 150 ohm resistor lead not a 75 ohm one.
Thank you for the birthday wishes.. I do have a wish to find out why my J40 oil pressure gauge falls to zero after 20 minutes on the road and when idle.
I have to put in neutral at each stop to keep the pressure from falling to zero.
Hi 1992sov,
Please do follow Larry's suggestion to read this thread from the start. It will answer your questions.
On a related note, using modern "thinner" grades of multi-viscosity oil such as 5W-40 will compound the false readings on the oil pressure gauge. Follow the Driver's Guide / Owner's Manual recommendations for the oil grade to use in your climate. In our area, the recommended grade is 20W-50 year round, though when our son had the car in Indiana I would change it to 10W-40 for the winter months for easier starting.
03-03-2015, 11:23 AM
fitted my new oil pressure sender back in the spring he had to remove the oil cooler bypass to get at the sender. (believe me on the 94 it's no fun changing senders) 
- see the pic further up this thread of the 75 Ohm resistor I made up.
I also see how it connects between the wire and the sensor. Should be fairly easy to get one installed, I can reach down to the sensor and unplug it easily. I'm aware of a plug being on the side of the block next to the sensor to test pressure, am gonna try to contact someone who would be willing to test the pressure before I get a resistor, and help build one for me cause I am not very sure about how to make one
) from my late '40 parts car's oil pressure switch (X300 on-off style). 
