oil pressure gauge dropping out, again, 2002 XLT 4.6L 4WD

[LMHmedchem]

Hello,

I am having trouble once again with my oil pressure gauge. For history, the gauge dropped out in about 2011. My mechanic back then replaced the sensor and the oil pickup tube but that didn't fix the issue. He was convinced that I had pressure and that it was a wiring issue. I figured that it was the issue discussed here,

Have a 4.6L? Here's a problem I bet you all have...

since the oil pressure sender connector wire is one of the wires in the harness that is affected. I drove for a while without the gauge working. When I had all of the power steering components out for repair, I decided to tackle this issue while I had the area exposed. As expected, the white wire that runs to the oil pressure sensor was worn completely through. I fixed that, and also the yellow wire that goes to the AC clutch, and put it all back together. I also replaced the sensor again with Motorcraft SW8368 since I didn't know what part the mechanic had used and they are only $10. I had to replace the oil filter adapter gasket anyway so I just re-replaced the sensor while it was out.

When I got everything back together, I had my oil pressure gauge back and everything looked fine.

It has been very cold recently so I have been going out and starting my truck and letting it run a while to keep the battery fully charged. On one of these occasions I noticed that the "check gauge" light was on and my oil pressure gauge was dead flat. I checked the connector again and zip tied it up and away from the engine because I thought it might be getting too hot. I am a little unsure about where I got the wire harness put back.

The short version is that the gauge reads good pressure when I start up, but if I leave it for a while at idle the gauge drops out to flat. The engine temperature is fine, the engine oil looks good, and the engine sounds good so it seems like it must be an instrumentation fault. I am not sure enough of that, however, to just let it go.

I have an analog oil pressure gauge, so I will hook that up to see what the pressure is really doing. I saw a video where the mechanic used a 3 way block (or T) adapter so he could connect both the analog gauge and the sensor at the same time and compare readings with the engine running. This seems like a good idea so I would like to know the size and threading for the sensor going into the oil filter adapter. I believe that the sensor is 1/4" but I don't know the threading.

I guess if I just get a 1/4" NPT 3-way barstock T and a 1/4" NTP male straight connector, that would be all I need but it would be nice to know if the size and threading are correct before I spend all day running back and forth to the hardware store. It's amazing how difficult it has become to search for such things on websites now and how many of the search results have nothing to do with what you are looking for.

The engine only has about 155,000 easy miles on it (no towing, off-road, etc) so I generally don't think much yet about the internals of the engine wearing out.

LMHmedchem

 

[LMHmedchem]

I have circled back to this again and today tried to hook up my oil pressure gauge to see if I have actual oil pressure loss or not.

My question at this point is if anyone knows of an even marginally reasonable way to unscrew the oil pressure sensor without removing the engine, or the front differential, or something equally idiotic like that?

One would think that for a sensor that often needs to be replaced, not to mention a gasket that often leaks, there would be some moderately reasonable access to the area. Yet another example of an engine that was not designed to be repaired I'm afraid. One of the videos I watched on this was done on a Ford from the 1970s. The mechanic just opened the hood, reached down into the bay, and un-clipped the harness. I swear he could have been standing in the engine bay between the engine and front suspension. It must have been nice to be a mechanic back then.

I can see the sensor and wire harness from underneath but there is no where near enough room to reach it. Maybe if I was 10 years old I would be able to get my arm in there but that was a very long time ago. After removing the oil filter drip tray I am able to reach in from the front and feel the sensor. I cannot see anything but I suppose that I might be able to blindly un-clip the harness and get a box wrench on the sensor to remove it. I don't think there would be enough room for a deep well socket. I am not looking forward to trying to get the manual gauge hooked up if I have to do things that way.

The only thing I can think of to improve access would be to drain the oil and remove the oil filter, either that or remove the rack and pinion, drivers CV axle, etc (meaning things I am not going to do). When I removed the adapter to change out the gasket, I did most of that through the drivers wheel well and a bit from the engine bay. At that time I had the power steering pump, hoses, rack an pinion, intermediate steering shaft, fan, fan shroud, oil filter, radiator hoses, etc, all removed so there was allot more room to work in. I have no idea how I would remove the adapter to change the gasket now when I can't even un-clip the wire harness.

Does anyone know how to do this? Am I missing some trick or way to get in there?

I could remove the intermediate steering shaft again if for some reason it was easier to get to from the top.

Thanks,

LMHmedchem

 

[LMHmedchem]

I spent another 2+ hours on this idiotic nonsense yesterday. I was able to make some progress.

I was able to get the wire harness detached. I removed the oil filter drip tray (3x bolts) and then you can see the sensor behind the oil filter. I was able to reach back in with my left hand and feel the tab but I couldn't depress it enough to remove it. Then I reached back with a long flathead and was able to depress the clip and push off the connector. I still don't know exactly what I did but it did come off. Possibly a tool like the ones that are used to remove plastic retainer button clips would have worked better because of the angle at the tip. If the part of the connector that you press on to release the clip was not facing forward I have no idea how I would have got it off. This is something to remember when re-installing the sensor.

I couldn't see any way to get a wrench on the sensor to remove it from the front so I went underneath and used a long handled hinge-head ratchet with a 21mm deep well socket. I first tried a long extension with a universal joint but there wasn't enough room to get the socket onto the sensor with the U-joint. I was able to get the ratchet around the front drivers side of the differential and my hand around the back side and get the ratchet over the sensor. There is only enough room for 2-3 clicks of the ratchet, so I was only making about 1/8 turns. It took a long time to get it loose, so bring a pillow for your neck. Once it loose enough that the ratchet would not engage, I went back to the front to try and remove the sensor by hand. I just couldn't get a grip on the sensor to turn it. I ended up having to drain the oil and remove the oil filter to be able to get to the sensor.

I didn't want to do this but I figured that if I couldn't get the sensor out, there was no way I would be able to get the analogue gauge screwed in, or the sensor reinstalled. There is a benefit to having the oil out in that I won't have to find and install the correct fittings for the analogue gauge with oil pouring out the sensor port. I cleaned out my oil pan very well so I can just pour the oil back in, though I will pour through a strainer.

After removing the oil filter, I was able to remove the sensor. I tried with 2 of the fittings from the kit but was not able to get either of them into the port. I used a caliper to measure the sensor and picked the fittings that were the closest. One of them seemed to be the same dimensions and threading but I couldn't get it threaded in. I gave up for the day and will take the sensor to the hardware store to make sure I have the right fittings. This is where it helped that I have removed the oil.

Looking at the setup through the drivers wheel well, you may have access if you drain the coolant and removed the radiator hose from the oil filter adapter. It's hard to tell but you might be able to get to it from there.

It's annoying that I may end up removing both the oil and coolant when I had both out when I replaced the gasket on the adapter.

LMHmedchem

 

[LMHmedchem]

Well I was able to get the analog oil pressure gauge hooked up today. The main thing was finding the correct fittings. I didn't get everything quite tight enough and it dripped a bit, but I was able to get some numbers.

Here is what I recorded,

 engine start: 75 PSI @ idle 900 RPM
               80 PSI @ 1500 RPM
               85 PSI @ 2000 RPM
       +2 min: 72 PSI @ idle 900 RPM
       +4 min: 70 PSI @ idle 900 RPM
-> engine thermostat registers about here
       +6 min: 68 PSI @ idle 800 RPM
       +8 min: 60 PSI @ idle 800 RPM
               78 PSI @ 2500 RPM
      +10 min: 50 PSI @ idle 800 RPM
      +15 min: 45 PSI @ idle 800 RPM
               70 PSI @ 2000 RPM
      +20 min: 37 PSI @ idle 600 RPM
               65 PSI @ 1500 RPM
      +25 min: 33 PSI @ idle 700 RPM
               65 PSI @ 1500 RPM
      +45 min: 33 PSI @ idle 700 RPM
               65 PSI @ 1500 RPM

Sorry that my measurements were a bit erratic. The pressure was almost 80 PSI at startup where the engine idles at around 1000 RPM. The pressure dropped steadily over the first 20 minutes or so, but the idle RPMs also drop to around 600 over that time. I assume that the pressure drop is due to the oil thinning as it heats up. It never dropped below 30-32 PSI and always went up to 65 PSI or so when I ran the engine up to 1500 RPM. I don't have any references but these numbers seem fine to me.

Does anyone think that these numbers represent a problem?

If I am correct in that these numbers are good, I am left with the puzzle of why the oil pressure sensor cuts out after about 10 minutes and drops to 0. I don't have the correct set of fittings to hook up both the analog sensor and the pressure sensor at the same time so I don't know the actual pressure when the sensor cuts out. Based on the above data, the pressure would be between 45 and 55 PSI when I loose the sensor input. That seems plenty high enough for the sensor to register. Also, in all of the above tests, the pressure jumps up to at least 65 when I rev the engine. No matter how high I pushed the RPM, I can't get the sensor reading to come back once I loose it after 8-12 minutes.

I find this very odd.

If the sensor isn't working, why does it work for 10 minutes or so and then die out?
If the pressure is dropping below the detectable limit of the sensor, why doesn't the reading come back when I rev the engine?

If I forgot to mention, this is a Motorcraft sensor and is more or less new.

Does anyone have any suggestions?

LMHmedchem

 

[LMHmedchem]

Well I think I am done with this for now. I have come to the conclusion that the issue is that the oil pressure sender is overheating and this causes it to shutdown.

I got information at another site indicating that the hot idle oil pressure should be between 25-30 PSI. Mine is above 30, so I think that it is fine. Around 70 is also the correct pressure at startup so that is good as well. The booklet that came with the oil pressure gauge lists two different 4.6L Ford engines. Both of these are older than mine, but the values listed are 40-60 PSI at 1500 RPM. My pressure is 65 PSI at 1500 RPM (after warmup), so that also sounds fine. I would appreciate knowing if anyone disagrees with those numbers.

For some background about my suspicion that the sensor is overheating, my drivers exhaust manifold heat shield has crumbled. Ford does not make this anymore and I wasn't able to find any aftermarket parts available. I find this odd since I would expect that nearly every one of these that is still on the road is likely to need a new one by now. I thought about making one but I decided instead to look for a part from a later model Ford 4.6L engine that would still be available.

I ended up getting this one, which is for the 2009 4.6L Explorer,

Ford 6L2Z-9Y427-AA Drivers Side Exhaust Manifold Heat Shield

Other than the mount holes being in the wrong places, it seemed to fit fine. The cutout for the intermediate steering shaft was in the right place and after drilling some new holes it went on without issue. I drilled the new holes so that there was the same amount of space between the heat shield and the engine as there is on the passengers side.

My only thought at this point is that the heat shield does not fit well enough on the bottom resulting in a build up of heat in that area, which is where the sensor is. I only mounted the heat shield with bolts on the top, so maybe there are supposed to be some on the bottom, I don't know.

I think that the sensor is overheating because it consistently works fine for about 10 minutes and then dies. I can't think of anything that would cause this on a consistent time table other than heat, since the heat off of the engine should increase at a predictable rate at idle.

As a fix, I decided to fabricate a heat shield for the sensor out of 24 gauge galvanized sheet metal before putting it back on. This is what it looks like,

I installed this with the open side facing down in the hope that if there was any excess heat coming off of the exhaust manifold, this would protect the sensor and allow it to keep functioning. It should also allow good airflow to the sensor once the truck is moving.

I installed this today and found some limited success. The oil pressure sensor kept functioning for 20 minutes (instead of the usual 10) before the gauge dropped out and the "check gauge" light came on. Though it is far from certain, I think this is good evidence that heat is the issue. I suspect that once I am driving, there will be enough airflow to keep the sensor cool. If I have a chance, I will try to add some reflective heat shield tape to the outside of the heat shield to see if that helps.

Whether or not the excess heat causes other issues remains to be seen. There is nothing much else in the area, so hopefully it will not.

Since no one replied to this thread, I guess that this is not a common issue. Still, I have attached a PDF template and instructions for the heat shield in case anyone else ever needs to make one.

LMHmedchem

 

[mountaineer2004]

Wow, you do detailed work, that's good. Good luck.

 

[Supercharged281]

Nice write-up. I have the same problem, been doing it for a while I'm going to give this a try. Thanks!

 

[LMHmedchem]

Nice write-up. I have the same problem, been doing it for a while I'm going to give this a try. Thanks!

Just a few suggestions.

1. If you have the v8 and have not already done so, you will want to look at doing the repair outlined here,

Have a 4.6L? Here's a problem I bet you all have...

The first thing to go with this issue is the connector wire for the oil pressure sensor. I don't think that this issue would cause the dropout after working for a several minutes but just having to take the wire on and off will likely break the wire if it is already damaged. This isn't an issue with the v6 so you can ignore if that is the case.

2. Even for the Motorcraft part, the oil pressure sensor is $15-$20 (last time I looked). Since you will have it off, you may want to just replace it. If you have the same issue I did replacing the sensor will not fix the problem but everything on a 20 year old truck will need to be replaced eventually so now is a good time to do it if you can.

3. If you have 4WD, the area where the sensor is located is difficult to access because of the front differential. It can be done from underneath with a long handle flex head ratchet and deep well socket. It is much easier to access the area if you remove the oil filter and the oil filter drip tray. With both of those parts out, you can remove the sensor from the front by reaching over the cross-member. If you do that, you may want to change the oil at the same time if you are due. Otherwise, use a really clean oil pan so you can reuse the oil. It's a pain but not too bad.

4. If you have, or don't mind getting, some self-adhering heat shield tape I think this would be a helpful addition to the sheet metal. You should be able to pick that up for less than $10. Just make sure that it has a reasonably high heat rating. I wouldn't pay allot for something like that but if I had some, or could get some cheap, I would add a couple of layers to the outside.

Let me know if you have any other questions,

LMHmedchem

 

[LMHmedchem]

Also,

5. When you have the oil pressure sensor off, this is also a good time to hook up an analog gauge and read the actual oil pressure instead of the idiot light version. A pressure tester kit is about $30. This is another job that is a pain because of the limited space but if you have removed the filter and drip tray you are most of the way there. It's nice to know that your oil pump is still working. It its not, you need to worry about more than the sensor overheating.

LMHmedchem