Erratic oil pressure gauge during full throttle only

[CDW6212R]

The odometer is very difficult to change, keep your speedometer if at all possible.

The cluster has three main sections in it, the outer four gauges come out separately, easily, and the tachometer plus spdeometer go in the middle part. Removing the three sections is fairly easy, they pull out, and push in, once the front cover is removed.

 

[BadaBingM3]

The 'sensor' is just a pressure-operated switch: open below 5psi or so; closed above that pressure, creating a connection to ground (engine block). If it jumps rapidly between these two positions, the gauge needle will be erratic. If I understand correctly, you already tried three different ones, and they did the same thing, while a mechanical gauge reads normal. That leaves the wiring (or, much less likely, the gauge) as a suspect. I'd get a test light and tape it to the windshield. Then connect a couple long wires, hook one end to the battery plus; the other to the sensor, and go for a ride while (carefully) watching the light. It should be steady on all the time. If so, you have bad wiring or a bad gauge. If it's flickering or steady off, you have low oil pressure -- for one reason or another. Good luck!

So hooked up a 6v-24v test light as you instructed. Light stayed on entire time. I didn’t go drive it but ran it idle and few throttle inputs to warm it up, ran for about 20 minutes to operating then drove it. To recap, my dash gauge will jump around at +4,200 rpm and flutters then drops to zero kicking on the check gauge light at idle while in D with brake applied. At high WOT, light stayed on, at idle in D while stationary, a/c off, light test light stays on. Checked bunch of times idle in D which drops the rpm’s to about 950-975. Stayed on entire time. So I’m down to a wiring issue from the switch to the gauge cluster I suppose?

one question is, I connected my volt meter to the leads, red to the wire off the pressure switch at the test light, black to the chassis ground. With ignition off, I got a reading and if my test light is 6-24v, had to be above 6v, but if I start the engine, I got no reading but the light is on. I’m not an electrician so puzzled why with engine running, there was to voltage on the wire from the switch but ignition off, there is a reading.

 

[1998Exp]

So hooked up a 6v-24v test light as you instructed. Light stayed on entire time. I didn’t go drive it but ran it idle and few throttle inputs to warm it up, ran for about 20 minutes to operating temp. Checked bunch of times idle in D which drops the rpm’s to about 950-975. Stayed on entire time. So I’m down to a wiring issue from the switch to the gauge cluster I suppose?

I would still go for a ride.

 

[BadaBingM3]

I would still go for a ride.

I did, actually. I updated my post and I wasn't logged in. But yes, I did drive it and light was on entire time, WOT to idle in D at dead stop.

 

[1998Exp]

I did, actually. I updated my post and I wasn't logged in. But yes, I did drive it and light was on entire time, WOT to idle in D at dead stop.

Just to make sure: the test light that you hooked up is off with ignition on and engine not running, right?

 

[BadaBingM3]

Just to make sure: the test light that you hooked up is off with ignition on and engine not running, right?

So the light was off with ignition on, light is on with engine started. But talking to one of my tech's who's a CAT diesel tech and electrician said that light test doesn't conclude anything other than there is power applied all the time. He said what needs to be determined is if the switch is a open-loop or closed-loop switch because the one-wire lead going to the oil pump switch is actually a signal wire, not a hot wire. The light test only provides a hot signal. So I had tested the switch with a meter in ohms. This switch is designed as a open-loop. Meaning there is no connectivity while the there is no pressure on the diaphragm inside the switch to close the loop and send a resistance to the PCM signal and then to the instrument cluster gauge. When there engine is running and oil pressure pushes on the diagram in the switch, creating a contact to the signal wire, then there is resistance and that is what sends a signal to the PCM, then onto the gauge.

So the big question is since I tested two new Motorcraft switches, if 1.) The oil pump/crank, etc. is not providing enough pressure at idle AND high rpm's to hold the diaphragm in the switch closed (creating a signal to the gauge to be showing pressure), 2.) the gauge is somehow going bad in the cluster and low and real high resistance causes the resistor or PCM to make the gauge erratic at high rpm's and turns it off at low rpm's, 3.) The new Motorcraft switches that have had updated p/n (per Ford), do not hold the same predetermined pressure calibrated settings within the switch, meaning, the high and low pressure does not equal the resistance in the switch that it should to put out a proper amount of resistance in the circuit to keep the gauge on and steady in the cluster.

This sort of actually makes since that possibly the pump or crank (worst case) at real high rpm's is loosing pressure causing a break in the circuit at the switch on & off rapidly, and at low idle in D, the pressure drops off the switch, opening up the loop and now there is no resistance in the wire to the PCM to the gauge. My next step will be to ohms check the loop with the engine running and see if at idle it actually shuts off and kills the ohms signal. If that is the case, then the switch is opening the circuit at around 11-12 psi, which is what I saw on the pressure gauge. He also mentioned that on a pressure gauge, I may not be able to see the small variations in pressure that may be causing the cluster gauge (switch) to rapidly shut on/off causing the erratic behavior of the cluster gauge at real high rpm's at WOT. What a pain in the ass to deal with.

 

[CDW6212R]

These engines shouldn't ever lose oil pressure at any upper rpm's with a nearly new pump. They don't turn enough rpm for windage to be a problem, or for the pump to run out of capacity to pump at high rpm's. So just assume you have pressure at top rpm's, and concentrate on the lower rpm pressures.

Test the sensor while running, at idle, and low rpm up to about 1500 max. If there is an oil pressure issue, that's where it will be. Only a very old wore out oil pump might have issues at high rpm(which for these is only 5000rpm).

What you described sounds correct, the sensor is just a switch to stop current flow through it, or to let it pass. Measure the resistance when off, at idle, and rpm's around 1000 to 1500.

 

[BadaBingM3]

So talking to my local Ford dealership service rep and he said minimum oil pressure should be 17psi with no hesitation. He said either crank bearings have slack in them or the pressure regulator in the pump is taking a dump. Now if powertrain products will honor the warranty I got with this engine because it can be a full engine pull to replace the bearings worst case. great.

 

[1998Exp]

So the light was off with ignition on, light is on with engine started. But talking to one of my tech's who's a CAT diesel tech and electrician said that light test doesn't conclude anything other than there is power applied all the time. He said what needs to be determined is if the switch is a open-loop or closed-loop switch because the one-wire lead going to the oil pump switch is actually a signal wire, not a hot wire. The light test only provides a hot signal. So I had tested the switch with a meter in ohms. This switch is designed as a open-loop. Meaning there is no connectivity while the there is no pressure on the diaphragm inside the switch to close the loop and send a resistance to the PCM signal and then to the instrument cluster gauge. When there engine is running and oil pressure pushes on the diagram in the switch, creating a contact to the signal wire, then there is resistance and that is what sends a signal to the PCM, then onto the gauge.

So the big question is since I tested two new Motorcraft switches, if 1.) The oil pump/crank, etc. is not providing enough pressure at idle AND high rpm's to hold the diaphragm in the switch closed (creating a signal to the gauge to be showing pressure), 2.) the gauge is somehow going bad in the cluster and low and real high resistance causes the resistor or PCM to make the gauge erratic at high rpm's and turns it off at low rpm's, 3.) The new Motorcraft switches that have had updated p/n (per Ford), do not hold the same predetermined pressure calibrated settings within the switch, meaning, the high and low pressure does not equal the resistance in the switch that it should to put out a proper amount of resistance in the circuit to keep the gauge on and steady in the cluster.

This sort of actually makes since that possibly the pump or crank (worst case) at real high rpm's is loosing pressure causing a break in the circuit at the switch on & off rapidly, and at low idle in D, the pressure drops off the switch, opening up the loop and now there is no resistance in the wire to the PCM to the gauge. My next step will be to ohms check the loop with the engine running and see if at idle it actually shuts off and kills the ohms signal. If that is the case, then the switch is opening the circuit at around 11-12 psi, which is what I saw on the pressure gauge. He also mentioned that on a pressure gauge, I may not be able to see the small variations in pressure that may be causing the cluster gauge (switch) to rapidly shut on/off causing the erratic behavior of the cluster gauge at real high rpm's at WOT. What a pain in the ass to deal with.

At first I thought that your engine has marginally low oil pressure or - much less likely - there is a loose connection somewhere, and naively tried to help you sort this out. Now comes the story of the diesel tech and the open loop (or perhaps closed loop) switch reporting its resistance to the PCM, which in turn... It finally dawned on me that you are pulling our leg. Enjoy!

 

[BadaBingM3]

At first I thought that your engine has marginally low oil pressure or - much less likely - there is a loose connection somewhere, and naively tried to help you sort this out. Now comes the story of the diesel tech and the open loop (or perhaps closed loop) switch reporting its resistance to the PCM, which in turn... It finally dawned on me that you are pulling our leg. Enjoy!

What? For real? lol! I think I'm the one going around in circles. I'm just providing my findings and what I'm learning. Why the carcasim bro? And why would I waste my time reporting back? Give me a break bro.

 

[fast_dave]

@BadaBungM3

If I remember correctly, you have a 4.0 OHV

I can't tell from your post if you have an original engine, or a rebuilt one.

But - I'll just throw this out there for you to take a look at - it can't hurt.

Check out this link: How to: - Replace Gaskets On The 4.0 OHV Oil Filter Adapter / Mount

Posting #2 of that thread shows a original factory Black O-Ring that over the years cooked and broke into 3 Pieces

In short, that Lil' Black O-Ring is responsible for keeping oil pressure in the block.

After that repair, in addition to no more leaking oil from the "adapter", my Oil Pressure Needle was rock solid stable, and I picked up about an 1/8" of Positive/Upwards Oil Pressure Movement to where the end of the needle touched the "Oil Can" handle (on the dash gauge).

Hope that helps -

 

[1998Exp]

What? For real? lol! I think I'm the one going around in circles. I'm just providing my findings and what I'm learning. Why the carcasim bro? And why would I waste my time reporting back? Give me a break bro.

Sorry, I know you tried your best, but the story was just too fantastic with all the twists and turns, and perhaps well-meaning "advisers" talking nonsense instead of taking a look at the manual and trying to understand how that very simple circuit works. We all want to believe that the thermometer is broken when it shows that we have fever, and then keep looking for the one doctor who will tell us we're not really sick. Hope the company that sold you this engine stands behind its warranty. Good luck!

By the way, for the benefit of those who may be pursuing a similar problem: in the 2nd generation Explorers the PCM does not have any information of oil pressure and will not turn the engine off, even if it drops to zero.

 

[BadaBingM3]

@BadaBungM3

If I remember correctly, you have a 4.0 OHV

I can't tell from your post if you have an original engine, or a rebuilt one.

But - I'll just throw this out there for you to take a look at - it can't hurt.

Check out this link: How to: - Replace Gaskets On The 4.0 OHV Oil Filter Adapter / Mount

Posting #2 of that thread shows a original factory Black O-Ring that over the years cooked and broke into 3 Pieces

In short, that Lil' Black O-Ring is responsible for keeping oil pressure in the block.

After that repair, in addition to no more leaking oil from the "adapter", my Oil Pressure Needle was rock solid stable, and I picked up about an 1/8" of Positive/Upwards Oil Pressure Movement to where the end of the needle touched the "Oil Can" handle (on the dash gauge).

Hope that helps -

yeah I have a Powertrain products rebuild 4.0 ohv. It's got 20,000 miles on it and I installed it back in July of last year. I remember having to put new O-rings for that oil filter mount and actually had to go through some searching to get one of the O-rings as it was not in the engine rebuilt gasket kit. My engine though is pretty clean and I've not noticed any leaks coming from the outer ring, but this is interesting to know it could be the issue. I think last few things I can do is check the instrument gauge with a new cluster since I have one on the way, if it's not that, I'll pull the exhaust cross manifold off and pull this oil filter bowl mount off and put some new O-rings. I'd hope with only 20,000 and 11 months time they didn't deteriorate already though, jeez, garbage. I'll report back on that if I go down that route. I may just bring it to the local Ford dealer since this engine is under warranty by powertrain products and have them replace it, IF they do have to tear into the oil pan.