yet another 4.0 oil pressure post -
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post #1 of 4 Old 10-12-2017, 12:13 PM Thread Starter
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1999 TJ Wrangler 
Join Date: Aug 2016
Location: peterborough
Posts: 29
yet another 4.0 oil pressure post

hey all! I understand there are numerous 4.0 oil pressure problem posts on all the forums.. But for some reason I cant find one unique to my issue.
So I have a rebuilt 4.0 in my 99 tj. runs great, no knocks or anything. when I fire it up the gauge will rise slightly but never increase or decrease with temp, rpm, etc. Unplug the sensor and get the check gauge light and a reading of zero. Done the gauge self check as well and it sweeps with everything else. swapped the sensor to another 4.0 I have and it reads normally. Has anyone had a similar issue and if so what ended up being the culprit? thanks in advance!

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post #2 of 4 Old 10-12-2017, 07:14 PM
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mukluk's Avatar
2000 TJ Wrangler 
Join Date: Oct 2010
Location: Clyde
Posts: 5,218
Could be an issue with the wiring to the sensor, or a problem with the cluster itself. I'd inspect the sensor wiring, looking for any areas that are kinked, abraded, melted, or otherwise damaged, as well as checking the connector pins for corrosion or looseness. Verify you have low resistance to ground at pin 3 (BR/YL) of the sensor connector, and with the ignition on verify you are seeing 5 volts to pin 1 (VT/OR). If no faults are found with the wiring, remove the instrument cluster and verify all the screws holding the circuit board are tight, but don't overtighten them. Reinstall the cluster making sure the connectors are well seated. A common complaint on the earlier TJ's concerning erratic issues with the cluster has been found to usually be effectively dealt with by slightly twisting the pins for the cluster to ensure they achieve good contact when the connectors are seated.

2000 TJ SE
2005 LJ Rubicon
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post #3 of 4 Old 10-14-2017, 08:21 AM
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2003 TJ Wrangler 
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If you really want to know the precise oil pressure and be confident in the reading, put a manual gauge in the cockpit.

I have a 50-year-old Stewart Warner manual oil pressure gauge with a 270-degree sweep, and it gives me the precise oil pressure value every time, all the time. It is not dependent on voltage or wiring or sensors or anything but oil pressure. The only aggravation is stringing a little nylon hose from the engine to the gauge, which is really not much of a problem.

That same gauge has been in several vehicles through the years and is still ticking in my ole TJ. It's a lifelong investment if you want to take the time to install and reinstall the gauge as you change vehicles through the years.

I also have the factory's electric oil pressure gauge operating in the '03 TJ connected with the manual gauge via a brass "T", but it does not accurately track what the oil pressure is doing except in a general fashion. It basically reads in the center of the gauge, whatever that means. I understand that earlier models do show what purportedly is the more precise oil pressure, but they are dependent on the electric system and the wires and the sensor.

Sometimes the old fashioned way to do things is the best way.

Sorry about the rant. I just had to brag on my faithful ole Stewart Warner that I grew up with.
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post #4 of 4 Old 10-17-2017, 06:24 AM
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1971 CJ5 
Join Date: Jan 2002
Location: Eagle Point
Posts: 8,212
X2 on the gauge.
All oil pressure issues should be verified with a gauge.
You don't need to install one, but should at least screw on in to verify the actual pressure.

The duty of a patriot is to protect his country from it's government
Thomas Payne
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4.0 , jeep , tj , xj

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