View Full Version : Quick help needed with oil pressure sensor

11-29-2003, 07:22 PM
Just finished filling car w/ coolant and burping after a motor mount change. At first when the fan came on, and now even w/o, the oil pressure guage will drop to 0, go back up, drop part way, go back up, and repeat. The check guages light will illuminate with the oil gauge drop, not the check engine light. It did not do this until the first time the fan came on.

The plug for the oil temp/level sensor was unplugged when I started the job. I plugged it back in b4 starting. When I sw this, I unplugged it again, to no effect.

Any help is appreciated...

11-29-2003, 08:59 PM
Hmm, when Check Gauges was on for my car, it turned out to be the connection to the lower right coolant temp sensor. It had crumbled apart.

11-29-2003, 09:19 PM
Ok after looking at it further; I have isolated the event to specific conditions: It occurs after the first time the cooling fan comes on, & every time it comes on, occurs if I hold the brake and let out clutch to drop RPMs from idle slightly, and occurs and random after the first or second cooling fan cycle. It did not happen while test driving.

I watched it flicker around the first 1/4 of the guage for a good minute with the check guages light on. No change in running.. I have to assume it is not oil pressure. If the oil pump was failing, could it first produce less pressure before stopping completley?

The connection on the oil temp sensor was moved around and slightly removed, could not come off completely due to accessory bracket. It only had the effect of causing the oil pressure guage to read low for a while, rather than flicker. It appears to be in good condition.

11-30-2003, 09:35 AM
If it was actually the oil pump, you'd be having issues beyond just check gauges.

Sounds like some sort of wiring problem or sensor problem. I'm not sure what drives the Check Gauges light to come on, but it must be some anomoly in the voltages it is expecting to get back.

Double check all your connections and make sure your ground straps are attached.

Keep in mind, that unless you have modified the oil pressure gauge wiring, the stock sensor is an idiot light. When it senses pressure, the gauge goes to a default spot. When there is no pressure there is nothing. It doesn't have any range. It's either pressure, or ZERO pressure. So if it's flopping around, and keyed with the engine fan. I'd just double check all the wires. I'd also wonder if the Alternator is performing properly. The engine fan could be pulling enough amps to cause low voltage in the system, screwing up some of the sensors. I'd check system voltage with the fan running to see if your alt isn't outputing enough.

Yeah, lots of thoughts. Sorry can't be more specific.

11-30-2003, 02:16 PM
It is indeed a strange problem. Apparently the check gauges light comes on when the oil guage, fuel gauge, or termperature gauge are out of range.

The car once overheated when I first acquired it do to a failed low speed fan. The heat gauge was out of range, and the check gauges light was on. This is essentially the same but for the oil pressur guage.

The sending unit was replaced before I purchased the car, about 8k miles and a number of months ago. I had the connection off when replacing the motor/transmission mounts; it seemed ok but I bet its related due to its appearance now, after completion. A friend moved the wire connection around the top of the sensor while I watched, got the oil gauge to show low for about a minute.

Definately an electrical problem, the car is now flawless after the finished mount/plug/thermostat job.. drove it over an hour.

Strangest aspect of this problem is that it will not occur until after the first time engine warms up enough to engauge low speed fan. Then it comes on every time with the fan, or if I drop the RPMS below idle with the clutch, or even randomly. The guage continues like this until the next time car is restarted.

Before the temp is sufficient to activate low speed fan, the gauge acts perfectly fine, even if I activate fan w/ a/c compressor or drop RPMS w/ clutch to almost dead.

I was hoping to remove the oil sending sensor wire completely, but it looks like the accessory bracket is now in the way. lol.

As mentioned, no other running symptoms.

Thanks for your help thus far..

11-30-2003, 09:06 PM
I experienced similiar problems with my oil gauge. The first thing I checked was the connection at the sender (behind access bracket driver side). It seemed tight, but I took it off cleaned it with qtip and electrical cleaner. Then I squeezed the connector slightly with pliers to make it fit the post on the sender a bit tighter. I applied some dialetic grease and put it back on. That was several thousand miles ago and problem hasn't reappeared. John

12-01-2003, 01:49 PM
Excellent, thats what I was hoping to read AnnivSpeCpe. I will attempt to try that with the accessory bracket in place & see if it works. Then again, I have also considered just cutting the connector and wiring it directly.

12-19-2003, 01:11 AM
Ok I could not disconnect the sensor plug entirely due to the alternator bracket, but I was able to mostly remove it & shoot electronics cleaner into the contact area. I also tightened the contact with needle nose plyers.

Unfortunately this had no effect.

The gauge/light still drops/illuminates after the engine warms when engine decelerates to idle.

As time goes by, it occurs at a higher & higher RPM until it hits a limit at about 1500.

If there was only about 5 psi of oil pressure at idle or slightly above, how obvious would it be?

12-19-2003, 07:10 PM

12-23-2003, 04:50 PM
Can anyone tell me what type of sensor this sending unit is, and how it goes about sensing for a given oil psi?

I have a feeling due to the regularity of this event, and the conditions of low idle + heat, there is a true low oil pressure problem.

Can a gauge be attached to the engine w/o removing the power steering bracket?

Thanks again;

MIKE 38sc
12-23-2003, 05:53 PM
Every engine I've ever worked on that does what you describe has had worn out rod and main bearings.
See when the engine is cold the pressure will appear to be normal. But after the engine warms the oil thins and all the bearing clearances increase. That increase of clearance allows the bearing to leak off more oil so pressure drops and since the crank and rods are the first things in the oil system to get oil, thats not a good place to have problems because a loss of oil flow at that point reduces oil flow to the rest of the engine so now all those parts are wearing at an accelerated rate.

12-23-2003, 06:08 PM
Are you sure you have the wires in the right location? Should be a red tipped plugin for the oil and black for the water temp. I reversed these once and had same kind of problem. Cant remember what happend tho.

12-23-2003, 06:28 PM
scbird1; They are in the correct location.

Unfortunately I was afraid of something like what MIKE 38sc said, as this problem is just too regular. This and I have just read about 1800 threads on other forums with the same problem and either bad bearings, rare oil pump slow failure, or clogged pickup screen.

Now I want to know, what would cause this on a 93k engine with regular oil changes?

I have owned the car since 83k and used mobil one syn 5w30. It did not do this for about 7000 miles prior to a motor mount change (and other things). The night the mounts were in and it was ready, this happened after the engine warmed. 300 miles later, still there.

I also need to know how I can diagnose for bearings w/o pulling the engine. I'd like to assume about the low oil pressure for now until I can test it.. I think its a pretty good assumption.

Lastly, how long will it last and what can I do to make it last longer?


12-23-2003, 06:31 PM
I also have what may sound like a strange question I meant to also post:

Could sawdust entering through either the intake or crankcase cause a slow bearing failure like this? What would it do?

Thanks again

12-23-2003, 06:39 PM
Best bet would be to get a manual guage and find out for sure your oil pressure is low before tearing it down. I dont think saw dust in a small amount would hert it. I know they used to use it in motors and trans years ago to dummy up a car to sell it. I wish you luck. Mark

12-28-2003, 05:04 PM
One last thing I am concerned w/ before I stall until getting a manual check;

This problem occured very suddenly after performing maintenance to the car. I drove the car for 6k miles before changing mounts + more over a 2mo period, oil was changed twice in that time, once again after mounts were done.

I am wondering, if it is the described drop in oil pressure/volume, why would this problem have occured so suddenly?

12-28-2003, 06:20 PM
Ok I have just found an interesting article @ bobistheoilguy.com. The article (http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=4;t=000141) discusses oil pumps.

From what I understand of this article, only the oil pump could cause an actual loss of oil pressure @ idle, and then oil pressure would increase with RPMs. This would apparently be due to a sticking oil pump relief valve.

Who can tell me about a relief valve on our pumps, how it might work specific to our application, and any experience you may have with it?

12-28-2003, 06:29 PM
All of that is behind the front cover of the engine. The relief valve's purpose is to bleed off excessive oil pressure when opened. If that valve has failed and is stuck open, and the pump is functioning otherwise properly, you'll see low oil pressure.

12-28-2003, 06:30 PM
It is possabe but oil pressure is built by the resitance of oil clearnce though the bearings as well. did you get a real guage on it?

12-29-2003, 08:48 PM
Ok I have acquired a mechanical gauge and will be recording pressures asap.

I searched many stores looking for a mechanical diagnostic unit, but I only came across one and it was expensive. Therefore, I purchased a Napa brand unit intended for installtion on or below the dashboard. It has 2 or three couplings, and markings appear to be in increments of 25 with 4 markers in between. Will this gauge provide useable results? Also, if anyone has experience w/ these units, I need to know if the included couplings will fit my oil port.

How exactly do you access the port for installing the oil guage coupling? It seems the alternator bracket is in the way. Can it be installed with the bracket in place? (I hope so!) Are there any other places I might not be aware of to screw this into?

Lastly, what procedure should be used to take measurements? What RPMS should I record, and how long should I keep it there to do this?

Thanks for your help!

01-02-2004, 11:03 PM

01-04-2004, 08:27 PM
Ok just recently changed the PCV valve and this problem seems to be noticeably reduced, but still there.

Any information my previous post about checking oil pressure would be helpful..

01-06-2004, 02:50 AM
I thought the oil pressure guage acted like an on off switch, not so much an actual oil pressure guage.

Mine regularly go's down to nothing and up...and when it gets down the check guage light i think comes on...then it will go off when it comes back up.

I was of the understanding that this was just a bad connection somewhere which completely makes sense....but i don't know that much about cars n stuff to know where this connection may be located in my car

01-06-2004, 04:18 AM
The stock gauge is a pressure switch; activated @ 5 psi.

When does yours go down? What is happening in the vehicle at this time? Randomly, or with certain RPMs? This information will help diagnose it.

There is a red plastic/rubber socket connection at the pressure sensor switch which goes over a small screw thread. Sometimes this connection becomes corroded or contaminated and random behavoir occurs.

Unfortunately I don't have a picture to show you, but it is near the bottom left of the alternator bracket (looking at engine from front), below the thermostat. It is fairly deep, around the water pump I believe? There is a metal pipe coming out of the block or intake manifold with a screw socket; the sensor screws in there. You can see the small red rubber elbow connection on top of it.

01-06-2004, 04:37 AM
mine go's randomly...but just about guaranteed to drop when stepping on it after about 2500-3000rpm.

I've pretty well learned to just not pay attention to it....just the red guage sometimes scares me...until i'm positive it's just the oil guage.

01-06-2004, 04:45 AM
If its random, try removing & cleaning that sensor connection. Then apply dielectric grease, such as the kind available from Autozone; see if that helps.

I could still use some assistance here..

02-28-2004, 11:23 AM
I found this pic in another thread searching for this problem. It's not the clearest pic, but it does show the locations of the sensors we're looking at.

I've been having issues with the Check gauge light coming on for no apparent reason I could see. The only other odd thing I noticed was that on the highway the temp gauge rarely even touched the bottom line of the NORM range. The longer the car is driven, the sooner the check gauge light pops on under acceleration. Starts coming on above 4500 RPM and eventually comes on by 3000 RPM. This is even more of a concern for me as O/D is pretty much gone in my tranny and 3rd keeps me at or a little above 3000 RPM. I also noticed last night on the way home from work that my oil pressure would drop as soon as I went above 3000 RPM, so I limped it home keeping everything but me as happy as possible till I can figure out what's happening.
If anyone comes up with more ideas, please post them. This thread is one of the closest to my problem I've found.

02-28-2004, 11:52 AM
Here is picture of the oil pressure sender(switch) from my 90. It is tight, but you can get to it.



02-28-2004, 12:05 PM
Just as a good practice. Even if you suspect your sensor or guage has a problem, double check the oil level anyway. Like most SC owners, I had leaky valve covers and over time the oil level would drop. One day, when stopped on a hill, the light came on and the guage dropped to nothing raising my anxiety just a bit. I pulled over and checked the oil only to find nothing on the dipstick :eek: It took a bit over 2-1/2 quarts to bring it back up which means I was running on about 2 quarts of oil :eek:
So, check it out. Oh, and I've since fixed the valve cover leak and I keep a very close eye on the oil level.

02-28-2004, 02:31 PM
redknight, through numerous searches at bobistheoilguy.com and other places, I was able to find extensive info about varying oil pressure under different conditions. Unfortunately, what you describe, loss of pressure under higher RPMs, seems to be common to those with mechanical engine problems. However, the oil sensor on our cars does cause problems, and it is worth replacing for 6 dollars.

dbd, thanks for the useful pic. Unfortunately the end of my sensor butts right up against the accessory bracket, making removal of even the wire impossible w/o removal of the bracket.

TbirdSCFan, it seems this has been the case for numerous people. Apparently if the oil gets low enough, it can splash around in the pan and evade the pickup line under certain conditions, leaving the top end dry.

I have since isolated my original problem to a leaking oil pressure sensor. It leaks right at the threads, resulting in a registered loss of oil pressure. It was replaced before I purchased the car, and apparently not correctly:rolleyes: lol.

Thanks everyone!

02-28-2004, 05:59 PM
Originally posted by Digitalchaos
redknight, through numerous searches at bobistheoilguy.com and other places, I was able to find extensive info about varying oil pressure under different conditions. Unfortunately, what you describe, loss of pressure under higher RPMs, seems to be common to those with mechanical engine problems. However, the oil sensor on our cars does cause problems, and it is worth replacing for 6 dollars.

I keep a close eye on fluid levels, especially with my tranny slipping in O/D pretty bad. I'll plan on replacing the sensor anyway. As for engine problems, I seriously hope there aren't any!!!!! The engine only has 25,239 miles on it. On second thought, maybe I am screwed. This is the 3rd engine for the car. The second engine had ~5,000 miles on it when I bought the car and died with a little over 34,000 of a snapped crank. Thankfully I have my truck to use as a daily driver. I only drive the SC a few times a week to keep everything lubricated and in running order.

02-28-2004, 07:14 PM
Where have you been acquiring your new SC engines? Were they Ford rebuilds? It seems some have had terrible luck with those.. I think I may get a Jasper should the time come.

02-28-2004, 08:07 PM
Originally posted by Digitalchaos
Where have you been acquiring your new SC engines? Were they Ford rebuilds? It seems some have had terrible luck with those.. I think I may get a Jasper should the time come.

I got my engine from CREBB Engineering. Formerly Custom Race Engines By Bob. It was probably a little pricey but I paid $1926 with shipping. It's been good so far. I had the same problem with detonation I had with the other engine, but for now I don't seem to hear it anymore.

03-10-2004, 03:32 AM
In my case AnnivSpeCpe hit it right on the nose. Both the Oil Pressure sensor and the upper ECT sensor had loose connections. All the readings are back where they should be (at least for stock "gauges") with NO warning lights. Hopefully Scott's and the other problems will be as easy to diagnose. Good luck.

Now the only major problem left is a tranny rebuild
:( , but that's for another thread. Thanks for all the help and suggestions guys.