Oil pressure and temp issues

[G8orFord]

2001 4.0
Two separate issues but figured I'd cover them both in one thread.
First, the oil pressure switch/gauge in the cluster is way off. It "sweeps" when you turn the ignition on but the needle sits at about 5:00 and completely off of the gauge markings. I haven't worried about it too much since I know it isn't giving a true oil pressure reading anyway, but figured if it's as simple as pulling the cluster and tweaking the needle, I'd go ahead and fix it. Anyone have this problem before?

Second, I replaced the t-stat housing due to the housing being spilt and leaking. I went ahead and rolled both both temp sensors while I was at it. I assume one of these sensors works the gauge and the other talks to the PCM. The problem is, the dash gauge reads normal temps and checking the hoses, housing and even the sensors themselves reads normal temps as well (~190° +-), but reading the temp with Forscan or TP through the PCM usually reads about 10°-20° higher and it's very erratic and changes too quickly for it to be an accurate reading. I figure it's a bad out of the box sensor, but which one? The harness looks ok so I figured I'd change the sensor again first. Am I right on the need for two sensors? Which one goes to the PCM?

 

[Curious Hound]

Ok. On temperature, the 2-wire sender is what feeds the PCM.

On the oil pressure, it sounds to me like the resistor for the gauge is shorted. Not sure how that would have happened all by itself. Resistors usually fail "open" and break the circuit so it doesn't work at all. I wouldn't "tweak" the needle. The only way that would fix it would be if it got messed up by someone tweaking it.

What's the history on the truck? Has someone else maybe been messing with this stuff before now?

 

[91stranger]

I would start with replacing all three sensors. They should be around $10-13 for each one and are all really easy to change. Once you replace the sensors and sender then you can at least eliminate these as the issues. I wouldn't touch the needle. That sounds like a recipe for disaster. The oil pressure gauge is a dummy gauge so it's either working or not working. Since it's not working properly, the easy and cheap fix is to replace the sender. I would take it off so you can match it at the parts store. the last time I replaced mine they gave me an engine coolant temp sender.

 

[G8orFord]

Ok. On temperature, the 2-wire sender is what feeds the PCM.

On the oil pressure, it sounds to me like the resistor for the gauge is shorted. Not sure how that would have happened all by itself. Resistors usually fail "open" and break the circuit so it doesn't work at all. I wouldn't "tweak" the needle. The only way that would fix it would be if it got messed up by someone tweaking it.

What's the history on the truck? Has someone else maybe been messing with this stuff before now?

From what I can see, without removing anything, both sensors appear to be two wire. I'll dig in deeper later. Working on the mud race truck right now.

I doubt the PO messed with anything. He wasn't very mechanically inclined. The truck had sat for three years when I bought it. I'm pretty sure It had been ran hot because of the housing leak. Along with the t-stat housing and sensors, I had to replace the fuel pump, radiator and a few other sensors to get all the codes cleared. The trans cooler had ruptured in the radiator. So I've also been flushing the trans here and there too.

 

[Uncle Gump]

I will never understand the throw new parts at it until it's fixed... absolute nonsense.

I agree with eric... The resistor for the oil pressure gauge is shorted. Disconnect the oil pressure switch and jumper it to ground... key ON... read the gauge. If it sweeps to the 5 o'clock position... the circuit to the sender is good and the gauge is broken.

As for the coolant temps... I wouldn't worry about a small difference in the readings between the two. You say it's erratic... erratic by a couple degrees? Or erratic by 50 degrees? Scan tool data is constantly being calculated and updated.

 

[RonD]

Coolant temp SENDER(for gauge), has Red/white stripe wire, sand black/white as ground, this is a 12volt sender

ECT sensor for PCM uses light green/red stripe wire, and Grey/red, this is a 5volt sensor


Oil pressure switch is 12v, Grounded when pressure is above 5psi, ungrounded under 5psi
It uses a single dark green/white stripe wire
If you unplug and ground this wire, then turn on the key gauge should show 1/3-1/2 depends on resistor inside gauge
Unground this wire and gauge should drop to 0 pressure, key still on

5:00 doesn't help since I don't have a 2001 Ranger to look at, 1/4, 1/3, 1/2, 3/4 can be applied to any gauge

 

[G8orFord]

Maybe this will help with the oil pressure gauge issue.

Is that a resistor issue?


I'm not sure if the "throwing parts at it" comment was directed at me, but I have not "thrown parts" at anything. Each part replaced, with the exception of the two coolant sensors, was diagnosed prior to the replacement. I did the sensors for good measure when replacing the t-stat housing since the existing ones were likely 18 years old and the o-rings appeared to be seeping. They are not quite so easy to replace on a 4.0 as other engines since they are located under the intake manifold and there is limited room to get them in and out. It's doable, but not "easy".

 

[G8orFord]

I checked the sensor output cold this morning and it showed 74° for ECT and 72° for TFT, so that looked believable. However the ECT went from 74° to 148° in roughly 2 minutes with little to no load. That seems a little quick to me, but even if it isn't, once warmed up, the ECT will go from 192° to 218° in a matter of a few seconds maybe a minute at the most and will fall back down just as quickly. The ECT is never really stable and jumps around quite a bit. 192, 198, 204, 196, 192, 210, etc. << Those are not actual recorded values, just a for instance.

 

[RonD]

Oil pressure is 0 so replace the sender, or Ground its wire first then turn on key, should go to 1/3 to 1/2 on gauge, if it does then replace sender

You could try and diagnose ECT sensor with OHM meter and hot water but for the price of the sensor, $15, I think your time could be better spent.

And you do need to fix that temp issue as the Computer relies on that sensor for many things, including fuel economy, so having it working correctly saves you $$

 

[G8orFord]

Yes, that's exactly why I want to get the ECT figured out and working correctly. The PCM has to be confused by the erratic readings.

I'll replace the oil pressure sender/switch and see if that fixes the problem. It's 18 years old too so it can't really hurt. If that doesn't fix the gauge, I'll troubleshoot from there.

 

[Uncle Gump]

My throw parts at it comment was not directed at you...

I was thinking the oil pressure gauge needle swept the other way. I would ground the oil pressure switch wire and see where it puts the needle. As Ron said it should end up in the normal range (near 1/2). However it does look as if the gauge needle is off when the key is off. It shouldn't hang that far down... you may just have two issues here... both the switch and the gauge.

As for the ECT... a 30 degree swing is probably excessive. If it was just a couple degrees either way... no big deal.