I have a 1992 Ford Explorer XLT.

The oil pressure guage started reading 50% on start up instead of 70% like it used to before. I replaced the sensor and for a bit it read around 60-70% but now is reading 50% again and sometimes even reads below 40% (on the O in Normal). What could cause this? I have come up with these conclusions:

1. Bad grounding of the guage clustor or sensor?
2. Old oil pump that needs replacing
3. Clogged oil filter or passages

Another thing to note is that one day I turned the engine on and the check oil light was on. I checked the oil three times in a row and it was down 2 quarts. This was very strange because the day ebfore it was at -1/2 quart and was not leaking. After adding just 1 quart of oil, the dip stick showed the engine to be completely full. I would guess this emans oil was somehow getting stuck up top. I switched to synthetic about a year ago, could the synthetic have loosened up the dino sludge and blocked passages? Could the oil filter need to be changed even though I changed it just 2 months/2000 miles ago?

Also, does anyone know how accurate the oil pressure guage is? Thanks.

 

There's actually quite a bit of info here on FTE about this issue. Do a search on the Explorer and the Ranger forums to get details. Basically, your sender isn't a sender at all but a simple switch. When oil pressure gets above a certain amount (it's unbelievably low...I think about 7 psi), the switch is made and voltage goes to the gauge. The "range" of the needle on the gauge is set by a resistor that limits the voltage and puts the needle to some mid-range value. In other words, your indication system is an "idiot light" with a needle, and not a variable reading pressure gauge. Without the resistor, your gauge would read full scale.

Having said that, there are modifications that some have done to convert this system to a variable reading gauge. If you desire this alteration, check the forums on how it's done.

 

Thas intresting I asked a Ford tech about it and he said that that wasn't true and that indeed it reads the true pressure. I guess he could have been lying though. But in any case should't replacing the sending unit fix the problem?

EDIT: I just asked another tech. He said it probably is just a switch since it has only 1 wire. Should I be worried about this. I havent noticed any change in performance. Does anyone have any ideas about why ths might be happening? How long do the oil pumps usuall last? Thanks!

 

If you want to prove the point, ground the sensor wire and see if the guage goes full scale, bet it doesnt.
we have a 92 and the pickup screen on the oil pump is gummed up, causing low pressure, have to drop the pan to clean properly.
If you tap into the oil circuit(at the sender) with a proper guage you can check the real pressure.

 

Oh boy, I am confused now. I thought the other poster was saying that the sending unit simply sends a "Yes" or a "No" pressure signal, nothing inbetween. So how would a real guage help? OR is it the guage itself that only reads on/off?

Anyway, I am more concerned about what the problem could be rather than if the guage is real or not. Any comments on the likely hood of a bad pump/gummed pickup at 175,000 miles and 15 years? It has had synthetic for the past year, but before was running on dino. Is the car known for gumming up pumps? Is it known as clean? Thanks!

 

the guage on the dash has a resister in series with the switch/sender, will not read "real time" pressure (ford's fix for too many customer complains of low/fluctuating oil pressure). By shorting the sender to ground you are proving the electrical circuit to the guage. I would be more interested in checking the real time pressure with a "real" guage, and if it is too low, look for the cause, gummed up screen or weak pump.
Or you can wait until it winds up the bearings and do a rebuild.

 

Hopefully this link will work.

http://www.autozone.com/servlet/UiBr...3d800d46de.jsp

It is clear that the "sender" is only a switch which is set at 4.5 to 7.5 psi. Anything above that will close the switch, grounding the circuit through the 20 ohm resistor. As the text says, the needle will read approximately mid-scale. If your needle varies, chances are that either the 20 ohm resistor, the resistor in the gauge itself, or the connections throughout the wiring are degrading. If the needle is staying somewhere in the scale, I wouldn't worry about it. One way to determine if you have this type of circuit is to watch the gauge on start-up. If the needle slowly climbs to normal indication, then you have something different than what I've described. If it immediately jumps to it's typical position, then you have this type of indication system.

Take a look at the circuit. Another thing you could do is ground the connector pin on the engine side of the switch. Your gauge should indicate pressure.

 

It goes from below Low (like the volt meter) to about 60% scale in 3-4 seconds, not instant (like the volt meter). Is that the speed you are refering to? I should replace the resistor, where is it located? Where is the resistor in guage, or must the guage be replaced? Thanks

 

I had the instrument cluster out of my 94 Ranger two days ago (for other issues) and noted the 20 ohm resistor is just crimped or soldered on the circuit board on the back of the cluster. I think the other "resistor" as shown in the diagram in the above link isn't a resistor at all, but a coil that the needle references to. If that's bad, you're looking at a new gauge. The last several pages of the Haynes manual tells you how to replace the gauge itself, as I recall. However, the movement of your needle indicates you have an actual pressure reading gauge. What does the sensor look like? If the sensor is more than a simple switch, you have something different...perhaps someone did an aftermarket modification. I would check all your wiring up to the cluster. (The cluster wasn't easy to get out).

Perhaps, you could tee in a direct reading pressure gauge obtained from the autoparts store. Then you would know exactly what pressure you're reading. I had an oil pump screen plug up from sludge on a different vehicle years ago. It gave me erratic oil pressure too.

 

No modifications. It is a stock 1992 Explorer with 4.0L and 5-speed. Maybe it is a strange 1992 thing because that year the engine also had 145hp instead of 155 and 160. Haha. The sensor/switch lookes like:

http://www.partsamerica.com/ProductD...pe=417&ptset=A

The website says it is a switch, and it only has 1 wire going to it. Maybe my guage is just lazy or something? Is it possible to make a sensor with only 1 wire? I guess it could be.

 

I've found that the only way my 92 ex will keep oil pressure is to use Napa Gold filters. Otherwise it will not keep pressure. I only use Napa Gold and Mobil 1 synthetic. 165K and still a smooth running engine.

 

Wow that is very strange? Why should the filter matter, hmm. Right now I am running a TG8A which is the nice version of Frams PH8A, it has the thing that stops oil from drainging back. I have the Mobil 1 synthetic that is good to 15,000 miles mixed with the normal synthetic Mobil 1. Intresting.