(Sorry for the lengthy post--I wanted to provide as much information as possible in hopes that someone can help)


P { margin-bottom: 0.08in; } OK, here is the background: I purchased a 2003 Ranger Edge project last winter. The engine is the 4.0 liter SOHC. The vehicle has 157K, and I bought it from the previous owner because the timing chain guides went, causing the timing to jump, and that was it for that engine. I decided to rebuild it myself (first rebuild FWIW), farming out the machine work to a highly-rated machine shop in this area. When I disassembled it, there was almost no wear on the bearings, and I trusted the machine shop to get the right bearings. According to them, everything was in standard limits, and the only work done was a polishing of the crankshaft. They did the heads, which included replacement of the bent valves.


I have an official shop manual on DVD, so I did everything “by the book” when I disassembled then reassembled the engine. I purchased a new DNJ brand oil pump. I used engine assembly lube when reassembling it. Finally, we got the engine back in the vehicle, and lo and behold, it started right up and sounded good.


However, I have an oil pressure issue. I am sure most, if not all of you, know that the oil pressure gauge is nothing more than an “idiot light”, and the pressure sender is a go-no go pressure switch. When I started the engine cold, the oil pressure gauge showed normal, but after the engine reaches operating temperature, the pressure gauge went to “zero” (same as an oil light coming on) at idle. I did not want to run it with a “low” reading, but there were no noises that indicated the engine was starving for oil.


I finally got my mitts on a professional-grade oil pressure tester so I can get the precise oil pressure readings at different RPMs both cold and hot. Below are the readings.


(BTW, the shop manual states that there should be a minimum of 20 PSI at 2000 RPM, but no other pressure readings).


COLD READINGS:


1000 RPM: 8 PSI
2000 RPM: 18 PSI
3000 RPM: 19-20 PSI (highest reading)


HOT READINGS:


Idle (800 RPM): 4 PSI
1000 RPM: 5 PSI
2000 RPM: 11-12 PSI
3000 RPM: 19-20 PSI


So, as you can see, the oil pressure is below normal both cold and hot (and worse when hot).


I am looking for some advice. I obviously do not want to pull the engine out again. When I assembled the engine, I did not do any plastigage readings because I trusted that the machine shop did all of those tests (and one of the people who recommended that machine shop said that he had them do quite a few of his engines, and he stopped doing plastigage readings because he trusts them so much). Nevertheless, I am beating myself up for not doing that as a matter of insurance that the bearings were in proper tolerances.


In desperation, I changed the oil and filter. I decided to use a straight 30-weight non-detergent oil for initial break-in, but when I changed the oil I used 10W30 detergent oil.


But I have been thinking a lot about the oil pump. As previously mentioned, I purchased a new DNJ pump (standard, not high volume), and despite the american flag and eagle head on the box, the pump is made in China. I did an initial prime of the pump prior to install by pouring a bit of oil into the inlet then spinning it. Initially, it was very hard to spin. After the engine was assembled and installed, I made a makeshift oil pump primer (it uses a star shaft rather than a hex shaft so I had to make my own). I used a cordless drill to spin it until oil first came out the pressure sender port, then I installed the pressure sender then primed it until I got a pressure reading on the gauge.


I am open to suggestions. I would really love to hear from someone who may have built a 4.0 SOHC. What do others think about the pump? I know the basics of oil pumping and how pressure is developed, but could there be a possibility of a bad pump? Has anyone ever experienced issues with DNJ pumps? I am thinking of purchasing a Melling high-volume oil pump; will that possibly cure the issue? As for replacing the oil pump, I may be able to swap it out with the engine still in the vehicle (getting the cradle out will be a bear, but according to the shop manual I would need to lift the engine a inch or so and remove one or more cross members).


After all of this work, I am extremely depressed over this situation. I would greatly appreciate any advice that can be given by others.


Sean
Lansing, IL

 

Hi

I am having exactly the same problem with my 05 Ford Ranger 4l v6. I fitted all original Ford parts. Did you come right with your problem..can you offer some advice maybe?

 

Thankfully, I found the problem--probably miraculously. It turns out that the machine shop messed up when they did the block--they failed to reinstall one of the plugs for the oil galleyway. That led to a lack of buildup of oil pressure ("No resistance, no pressure"). Fortunately, the bearings were getting enough oil to prevent metal-to-metal contact, though I only chose to pull one bearing cap to check and make sure the bearings and crank did not get messed up.

It was not easy to troubleshoot. After changing the oil pump (which was new) with a high-volume pump, it still would not build up much oil pressure. I was suspecting that perhaps one of the galleyway plugs was missing, so first I pulled the front cover and used my homebuilt primer to see if any oil was coming out the front. No such luck. So I reluctantly pulled the motor out again, put it on the engine stand, then ran my homemade primer, and lo and behold--I found oil pouring out from a passageway down into the sump (I had the front cover off so I could see it). Sure enough, one of the threaded plugs was missing. I went back to the machine shop, and he was very apologetic, even to the point of giving me a partial refund, and he found a plug I could use. After installing it, I spun up the oil pump, and I had over 50PSI of pressure. Problem solved--but not without a lot of time, sweat, and colorful words I would not use in church :-)

As for your issue, first I would recommend hooking up a real oil pressure gauge to your engine--either a test unit or a consumer-grade gauge, and read the pressure when the engine is at idle and at 2000 RPM. Do not use the "gauge" in the instrument panel because it is just an "idiot light" disguised as a pressure gauge. I think the minimum pressure should be 25PSI at idle (I don't have my shop DVD with me now). If gauge reads low (under 25PSI) then you will need to do some serious troubleshooting. Did you replace the oil pump with a new one? Try replacing the oil filter--that is a cheap (and quick) troubleshooting step.

If you wish to check the oil galleyway plugs, it is possible to drop the oil pan and lower cradle with the engine still in the vehicle--if you have 4 wheel drive you will need to remove the engine mount nuts and lift the engine about 10 cm in order to be able to remove the cradle. If you took photos of the engine before you rebuilt it you can compare the pictures with how it looks now--if there is a galleyway plug missing you should notice it. While you have that cradle out, you can pull the oil pump if you wish to either check or replace it.

If you cannot find anything out of the ordinary, then you may need to pull the motor. Once it is out and on the stand, you can remove the oil pump drive and try priming it. Unfortunately, I could not find a spline that will fit this oil pump drive shaft so I made my own--hopefully you will have better luck with finding one. If you can prime it, first pull the front cover, then while you prime it see if you notice any oil pouring down into the pan or out the front. There will be some oil seeping down past the bearings, up to the heads, and out into the timing chain, but if you see a large quantity pouring out from one or more locations, you may have a problem there.

One other thing you may need to check is bearing clearances. it is possible that you may have gotten the wrong bearings, leading to excessive bearing clearance. When I rebuilt my motor, I had enough trust in the machine shop that I did not do the Plastigauge clearance check when I installed the bearings, so when I had the low oil pressure issue--and before I found the true cause--one of my thoughts was that I had the wrong bearing sizes.

Hope this will help. If you need any more advice don't hesitate to ask.