98' Ranger no oil pressure after valve cover gasket replacement

Hi all, I just joined up today and this is my first thread! I'm a novice mechanic working down list of suggested repairs from a local shop for a 98' Ranger 4.0L v6 OHV I recently bought off craigslist with 156k miles to be a daily driver.

I have completely lost oil pressure after swapping out both valve cover gaskets, new spark plugs, and wires. To my knowledge, I had no oil pressure issues before this repair. I decided to start with typical tune up procedures and then attempt more complicated repairs as needed.

Two weeks ago I ran motor medic MF3 flush, changed my oil and filter (Castrol synth 5-30w / Phram PH8A), my PCV valve (MicroGuard PCV375), fuel filter (MG 3595), and air filter.

Drove it around all next week with no issues what so ever.

Next I swapped out both valve cover gaskets with Fel-Pro's model VS50368T. This combo comes with a fuel rail gasket that I did not install as one wasn't there when I pulled off the upper intake manifold. Being this was my first time digging into my engine this far, I didn't take anything else apart past this point. The lower manifold wasn't touched nor was anything below the valve covers (except the spark plugs).

I cleaned the tops of the valve covers with brakeklean since they were caked with oil and dirt. I also cleaned the upper intake, the top of the fuel rail, and where I mounted the valve cover gaskets pretty thoroughly. I left the previous upper intake gaskets in as they didn't appear to be in bad shape. I applied Permatex between the head and the gasket but not between the gasket and the valve cover. I tightened the valve cover bolts and upper intake bolts to the torque specs listed in the Haynes repair manual I used to remove valve covers.

The old spark plugs were beat up and under gaped to about .042 (I forget the model). My replacement AP103 plugs said they were pre-gaped but they too were under spec. I gaped all six plugs to roughly .054-.055 (granted my cheap little gap coin is accurate..) I put on new Omni Spark 9572 wires (I now realize these guys might be cheapies) so I might put on the old motor craft ones because they look to be better quality and in ok shape. These are wired correctly according the Haynes manual and everything I've seen online for my engine and year.

I hook everything back up and when I turn my key to the on position, my check gauge light illuminates and I have no oil pressure. Everything else looks good on the dash. I tried starting it a few times (left it park) and the tachometer varies between 300-2000 RPMs. Initially the motor would die after a few seconds unless I gave it gas. It sounded normal, but as soon as I let off the gas, it would fall below 500 RPMs and eventually die.

Now that my bolts are correctly torqued, the RPMs still vary heavily between 500-2000 but will stay on without giving it gas. The oil pressure gauge floats around from 0-50% and the check gauge light goes off. After 1 minute of the motor being on, I see a small amount of smoke come out under the #2 spark plug on the passenger side valve cover. I cant quite tell whats leaking or where its leaking from. My first thought is oil is leaking on the spark plug since the motor isn't hot enough to smoke at that point? Just a guess.

Sorry for the long winded post but I am pretty stumped here! Any info, comments, thoughts are greatly appreciated!

Welcome to TRS! Not my area but just a couple questions, are you using the gauge on the dashboard or an external gauge for your oil pressure? Ford oil pressure senders are known to go bad often. Or, maybe just the wire came off?

If an engine hasn't been taken care of the running motor flush through it is a bad idea. If you start the process of loosening up big enough chunks and they fall into the oil they will float around until they get caught in the oil pickup screen and block it.

How much gasket maker did you apply? If you put an access amount it could have squeezed out the inside and stopped up the oil drain hole in your head. You probably do not have a leak around number 2 cylinder. Most likely it is just some carb and oil mixture left from cleaning the upper portion of the engine and it is burning off. I am just throwing potential causes that I have personally seen over the years.
Put a mechanical gauge on it and see what your actual oil pressure is.

@ Denisefwd93 - I am using the Ford gauge and I'm not sure if the oil pressure switch has ever been replaced. I assumed the sensor was good when I saw smoke thinking its trying to tell me something is definitely wrong!

@Craig0320 - Sludge was the next culprit on my radar, but I didn't realize the motor flush could have lingering effects after changing the oil. I applied a very thin strip of silicon around the head. I didn't see any seep out on the outside, hopefully none went inside. I don't think i applied enough to seep in.

Sounds like the mechanical gauge is a good place to start, thanks folks! Maybe another oil/filter swap and a new sensor while I'm at it could be an easy place to start eh?

On my truck sometimes it reads about 10 lb most of the time that reads normal to slightly high but sometimes it also jumps around so it's on the "list" with so many other things that are ahead of it like a brake booster

Maybe you just bumped the wire loose on the sensor. Not sure where that sensor is on the 4.0l. make sure the wire is firmly attached. That sensor is usually grounded through its threads in the block. So no thread sealant should be applied to its threads. Just a good clean threaded connection.

One other thing. It may not apply to your truck. But the older vehicles don't actually have an oil pressure sensor and guage. They have a pressure switch that closes at 5 or 6 PSI and makes the needle read near the middle of the guage no matter what the pressure is as long as it is above that setpoint. I don't know which year models are like that. RonD or Adsm would probably know if that applies to your truck.

This message composed solely of recycled electrons. Go green!

99 for sure has the on /off fake gauge, so almost certainly 98 as well.

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I'm having a heck of a time locating my oil pressure sender or gauge switch (I think they are the one and the same?). I bought a BWD S4110 oil pressure gauge switch that looks just like the one pictured below. However, my Haynes manual says it should be located by the oil filter. And many online forums and you tube videos show it being behind the engine on different years and models of the Ranger on the passenger side. Which coincides with what my Haynes manual says. But I just cant find this lil' guy!

I found this sensor at the front driver side of the car just below the power steering pump. Although they look identical, I feel this is the wrong sensor. I disconnected the wire and still got a check gauge light to illuminate. So i put it back on thinking it must be something else.

Is this the wrong sensor?

That looks correct to me.

I agree. That looks like it. I have the 3.0L and mine was originally at the rear of the engine near the top on passenger side and it doesn't have that 90degree elbow to screw into. Otherwise, the switch itself looks identical.

You were both correct! I spent hours looking in the wrong spot....

An oil pressure check from a mechanical gauge states that I'm running at a steady 51 PSI. I only ran the car for 2 minutes tops, it still varies from 500-2k RPM's. It sat at 1k RPM's for a while but its rough. According to Haynes, my PSI level should be between 40-60. So while that seems high, I guess I'm pleased with the test. I went ahead and threw the new oil pressure switch on since I was down there.

But!! I still have the check gauge light illuminated.

During my test I noticed that the smoke I was seeing on the passenger side above my #2 spark plug is coming from a tiny coolant leak in the heater control valve. I'll have to look into that further or replace the part, looks pretty affordable.

Unfortunately I'm now noticing smoke and a burning smell from the driver side exhaust manifold at as early as 1.75 minutes of run time. I'm not quite sure what my next move is, any thoughts?

Thanks everyone!

Oil pressure specification is between 40 and 60 psi warm, at 2000 rpm. it sounds like you may have an electrical issue that is causing problems with multiple things, might be best to check your grounds and all wiring connections for issues. The way i've always checked gauge sending unit wiring integrity is by grounding the wire out, this should peg the gauge with the key in the on position, if it doesn't, you're going to have to start checking wires. It is entirely possible that you spilled some oil when you changed your valve cover gaskets, check for anything contacting the manifold directly and if all is ok, run the engine for a bit and monitor it, it should dissipate after a few minutes.

Key on, ground that wire you found there and see if the gauge spikes. If it does not you have a bad wire or a bad gauge.

Grounding out the oil sending unit while the wire was attached to it spiked the gauge and did away with the check gauge light!!

What does this mean??

Means the wiring and gauge are good. Go buy a new sender.

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