I have a 97 4x4 4.6 f150 with 205k miles on it.
Occasionally I have a minor annoyance not really a problem just annoyance of when idling, mashing the gas, then quickly stopping as in stop and go traffic or backing a trailer the engine rpms drop really really low and stall or almost stall.

Well today my oil pressure dropped with the rpm! When I was slowing down form high speed coming off the interstate at about 8 mph while coming to a stop the oil pressure dropped very low, the needle fluttered around frantically and the light(red oil pressure light beside the gauge) would come on.

I checked my oil level was low but i still have oil. Took the cap off didn't notice any water in the oil or oil in the coolant.

After a few times in a row of the oil pressure dropping and fluctuating wildly I decided to keep a tiny bit of gas on while I was stopped. Power braking at 1k rpms. Just to keep the oil pressure up at normal pressure.

On the interstate on the way home I was driving very hard, running the engine hard(this is how i normally drive the truck) And there were 0 issues while doing this.

For a couple of months now I have had a "lean" code and a check engine light. I have not gotten around to doing anything about this since there have been no issues. Some one told me that a lean code could mean a vaccum leak. And I know in the past sometimes low oil pressure could be associated with a vaccum leak.

Please ya'll tell me somethin about my oil pressure! I can't afford to loose my truck much less have it leave me in between work and home!

Thanks!!!

 

Hello zman764, I don't know how to quote anyone from the FAQ's on page one of this forum so I just copied and pasted the Question and the answer here... I think the thread is closed now for quotes. But here is what I found there.

Q: My truck idles roughly or stalls at idle. What could be the problem?

A: A fairly common idle related malfunction in these trucks seems to be the Idle Air Control valve motor. This valve sits on top of the throttle body and holds the butterfly valve open at idle so the engine can breathe. A sluggish or malfunctioning IAC will prevent a constant idle. The problem sometimes only presents its self when the engine in cold. This certainly isn’t the only thing that can cause a rough idle, but If you find yourself having to keep pressure on the gas pedal to keep the engine running, this may be a place to start. Typically, just cleaning doesn’t offer any improvement, if the IAC is faulty, it usually needs to be replaced.
For some pictures of the IAC take a look at Fordman311's gallery at https://www.ford-trucks.com/user_gal...7&albumid=14860 If you want to go to this web site, You'll have to copy and paste the http because it isn't a link.

If this doesn't help you I would suggest that you start with the simple things first. Add oil to your truck until it is in the proper range or an oil change if not recently done. Also, check the wiring at the oil sensor (sender) to see if it may be loose. I really don't think that the wiring is the problem but it would be my next step. I am inclined to believe after reading the links directing me to some of the IAC problems that this would take care of your problem.

 

Thank you,

I have read that before, and its not exactly the problem I am having. The stalling and dropping of the rpms is very very rare.

This thread was about my oil pressure fluctuating and going to 0 and the light for that coming on.

That is my ocncern.

 

Ok, but remember that when your rpm's drop so too does the output from the oil pump. If your rpm's drop enough and the oil pump output drops too then the sender gets the impression that it needs to let you know...So, the gauge bounces or drops and the light comes on.

 

I have got to know about how this oil pressure fluctuation is going to hurt my engine. I drive form home to school to work. I use my truck at and for work and my college classes and my work are very demanding. I will check for any replies in the morning before I leave.

But how negative is this going to be to continue to drive my truck like this until i can take it somewhere or figure something out?

Well normally no matter what the oil pressure stays at the same rate. When I first noticed this today the drop in rpm & oil pressure coincided. But by the time I got home the oil pressure would fluctuate and drop while stopped in drive at a steady normal rpm for idle.

So at last note the oil pressure was fluctuating and dropping with foot on brake in drive at a normal 600-800 rpm idle.

 

You could simply have a oil pressure sensor. Or it could be more serious.
But yes, the crappy idle is directly related to crappy oil pressure.

and it is probably an IAC motor, these go in and out to regulate air flow while the throttle plate is closed.

Think about it, when you are cruising on the free way(or stomping on it in your case) and you let off the gas and the throttle plate slams shut, there is going to be a lack of air and an excess of fuel going through the manifolds into the cylinders, so the IAC valve or motor opens up to allow additional air flow. Plus dumping gas down the exhaust is a good way to clog up a cat, they dont like gas, they like 14.7:1 air fuel mixture-a theory that your motor is built around. since 1996 a LOT of it has to do with emissions rather than power... but thats another story.

You can unbolt the IAC motor, leave it plugged in, and it should move when you start the truck. if it doesnt, its crap- or the wiring is crap, but most likely the IAC is crap.

IAC is extremely important at idle, it makes all the fine tune adjustments.

 

The end result of low oil pressure in any engine is less oil being circulated to throughout the engine to all of the essential spots. Due to gravity the top end (cam/cam bearings, lifters) usually suffers first. And if left to run it's course the big stuff (main bearings, timing chains, tensioners) gets damaged. And ofcourse the end result is engine failure. In older pushrod engines if the pressure drops at idle thats usually a sign that some damage is already done. Usually this starts by running with the oil level low or overheating the engine or a combintion of both. If it's not knocking yet your best bet is to do an oil change and maybe step up to 10W-30 oil (I like motorcraft syn blend). I would probably add some Lucas oil stabilizer. But regardless of what brand you use, in my opinion the most important thing you can do is change the oil regularly and keep it full. Oh, and if your already having oil pressure problems, maybe be a little easier in the throttle. Good luck.

 

Well bad news about the knocking. I bought it with 168k miles on it, and it has always knocked. But I have been running 93 in it and it didn't knock for a while but recenlty it has started knokcing with the 93 octane.

 

93 isnt going to help rod or lifter knock, it will only help spark knock.

 

Well this morning I started up the my truck, made my morning drive in to school then work then, home in the evening. With 0 fluctuation in the oil pressure. The needle stayed in the exact same spot that it normally does.
Do I just say that yesterday was some weird fluke? Or is there probably a more serious underlying problem? I make the same 32 mile round trip drive too and from work everyday. On the weekends I may do some light towing a little playing in the mud. I have a heavy foot but I don't think I really abuse the truck.
I figure this weekend I will change my oil just to be on the safe side. It's been about 5k miles anyways which is about how often I normally change it.

 

I changed my oil the other day in my '97 Scab, 4.6, 229,300 miles and the same day while idling in park the oil pressure needle began fluctuating wildly.
It fluctuates a little bit in drive while at a stand still, but more when in park. It seems to happen after it's been running about 30 minutes or so. I do regular oil changes with Motorcraft 5W-30 and Motorcraft FL-420S filter.
Any ideas as to the cause? The rpms are fine.

 

If it were my truck I would install a manual oil pressure guage from the local parts store to get a true reading of my ACTUAL oil pressure.
I would not keep driving the truck untill I knew what my oil pressure was!

 

As you can see I last posted Jan 25 2007 Now its May 2008 my oil pressure will still drop to 0 when I come to a stop and it fluctuates wildly 218000 miles so its prolly just a short or bad sendin unit but either way its obviously fine... g/l w/ yours

 

I had this on a Jeep with a 4-cyl and it would just drop at idle. If you kept it rev'd up a little the pressure would be fine, but if you let it go to idle it would drop to nothing. In the end, we believe it was the bearing in the bottom end of the engine - I don't know if it is rod or main (sorry, but that is past my technical expertise). According to a friend that rebuilt the engine, the bearings can get so worn that the oil slips past them and doesn't make it up to the sending unit until there is enough pressure to compensate. Sounded like a good story to me and rebuilding the engine did the trick. I had tried a new oil pump - no effect - a new sending unit - no effect. So, with the miles on yours, it might be those bearings are worn.