Hello all,

I've posted before about a problem with the oil pressure sending unit on my 2013 F150 4wd, 5.0l V8. I had to have the oil pressure sending unit replaced about a year ago because it went bad.

About a month ago, I start getting the same symptoms on the replacement unit: the needle on the analog gauge would fall down to 0, the warning light with the little oil bucket would come on, and the pleasant little bell thingie would go off.

My assumption was that it was the same problem again. There's a thread on it, which I just commented on as well.

So what I did was to first make sure that I wasn't getting stuck with parts made in Afghanistan or somewhere. So I went to the Lincoln dealer and got a replacement sending unit, and also the pigtail that it plugs into. The sending unit itself was about $7, the pigtail was more...

Took it to a professional shop and had the guy install it. I picked the truck up, after closing hours, and by the time I got it home it was doing it again.

So the obvious question: Really, what is it?

Could it be, 1) A bad sensor unit out of the box, 2) Imperfect installation on the part of the guy who put it in, (didn't get it plugged in right?) or,

3) Uh oh... what if it's the oil pump? I've never had an oil pump go out on an engine so I don't know how it does it if it does. But this problem has always been happening at low RPM. I give it some gas and then it starts showing pressure again.

The next obvious question is what's the procedure to replace the oil pump? It's a 4WD... does that require dropping the transfer case, etc? If that's the case what's the damage likely to be?

TIA

 

The next step is to get your mechanic to install a mech gauge temporarily to verify what the pressure is.

 

That makes sense but that's gonna be a good trick. The sensor is located behind the alternator...

 

One would think that if the oil pressure really is dropping to zero, the hydraulic cam followers would start making a racket. Mechanical gauge is needed.

 

More information:

This only happens at low RPM. What this tells me, at least right now, is:

1) It can't be a problem with a faulty install, because if it were it would be failing consistently regardless of engine speed. For example, if the pigtail isn't plugged in correctly, the unit would not send a signal regardless of engine speed.

2) At least according to what I'm able to tell, the oil pump is working correctly. I've sat in the driver's seat and seen the failure happen exactly as the engine speed slows to about 600 RPM, and then continue for however long, (several minutes), I'm willing to sit and watch the alarm go off while the engine is at idle speed, about 500 RPM. Once I give it some gas and the engine speed crosses over about 700-800 RPM, the gauge perks up and the alarm stops.

3) What would make it do this, at a particular RPM range, especially low RPM? I think the obvious choice is the oil pressure sending unit. The one that came with the truck went bad and I had to have it replaced. The replacement unit that was installed back in January went bad just now... the replacement unit, a new Motorcraft unit that I bought myself, made in a factory in Spain and shipped here and sold for less than $7, was defective straight out of the bag. It will translate oil pressure to an electrical signal at about, let's say, 700 RPM. Once the speed goes down to idle speed, 500-600 RPM, it fails predictably.

So this is the deal... I didn't have this repair done at the dealer. I bought the parts at the dealer and had them installed at a local shop. Obviously I can't go the the shop for a solution, at least not without paying for it, because the continued problem has nothing to do with the way he installed the sending unit. If I take it to the dealer I bought it from, they'll probably refund the part or give me another one, but they'll want to do the repair there at the dealership and charge me for it.

So I suppose the question becomes how do I approach this at the dealer's? I don't think they're going to be interested in doing the repair for me all over again for no charge. At this point I don't have any confidence I have in this particular Motorcraft part anyway. Why do I want another one if my experience tells me I'm likely to have the same problem with it?

Hmm... it does just fine at about 800 RPM, but fails 100 per cent of the time once the engine speed falls below about 600 RPM... Hmm... what to do...

 

Remember, the oil pressure gauge is not linear, it's a glorified idiot light. It sits in the middle till the pressure drops below a certain threshold, then it drops to zero. This is why a mechanical gauge is necessary to see what the pressure actually is. I'm guessing the threshold is around 7 psi or so.

What exact oil and filter are you using? How many miles on the engine?