(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

 

I have not ever rebuilt the 4.0 SOHC, so my comments here will mean nothing to you. Just sayin' that ahead of time.
Just a few comments from me, but it won't be anything you like.
First, I would avoid the DNJ brand, especiallly on something as critical as your oil pump. A RockAuto special, I presume? I've heard too much bad press about that brand. Seriously, though, I don't think the pump is your problem.
Second, I would have used plastigage. I don't care how much experience a person has, I don't trust anybody else to make critical measurements.
Third, nobody uses non-detergent oil on a break-in engine. I'll get some flak for saying this, but the factory doesn't use non-detergent oil on a break in and the only good place for non-detergent oil is your air compressor.
I'm not there and I'm not getting my hands dirty, but I predict that your engine will eventually get pulled again.
Just my $.02 worth.

 

I think I would be looking for a missing or mis-placed part on the cylinder head. I am not real familiar with the OHC 4.0, but thought it had chains that were equipped with tensioners. If the tensioners were installed wrong, or there was a plug that was taken out at the machine shop to clean the head, and then left out you'd have the kind of symptoms you report.
Take a good look at your shop literature{I HATE DVD manuals. They charge just as much as paper, and are hard to use} and look for the head parts breakdown. You might find an obvious place. If there is an oil gallery illustration, or a 'blow up' of the head/block, look for a gallery plug that could have been left out.
The pump you installed should work as long as you want it to. You can replace it, but I really doubt it could be so bad as to cause the low pressure you report. If the relief valve were stuck wide open, the pressure would change with temperature, and your readings are very close to constant. The numbers, to me, indicate some part of the oil system is wide open, dumping the oil where it should not.
One last thought is that in most engines, the oil to the heads has to cross the block-head gasket. Is there any possibility of having the gasket flipped or flopped such that the oil is allowed to leak from the transit passage to the crankcase? Most gaskets I have seen will be labeled "Front". This marking will be visible on one bank, and face down on the other. If flipped, it is possible the sealing needed between block & head is not happening.
My thoughts on oil pumps begin with the statement that it, the pump, is the best lubricated part of the engine. It should just work. The only problems would be wear on the driving and driven faces of the gear, fully submerged in oil, and the gear-end wear leading to leakage, but those are loooong term things. Again, fully lubed from the instant the engine starts... should last. I'd bet most pumps in boneyards would pass factory tests for output volume and pressure. May be wrong...
tom

 

if your bearings had excessive clearance you would have a noisy engine. Especially on cold start. I always use high volume pumps. A pump change may be good plan. I have had the pump bypass be bad. Also if the pickup tube is sucking air. (a hole or warped mounting surface) the will make low to no oil pressure.

 

The 4.0L is to use 5W-30, Not 5W-20, as its oil pump never got upgraded to be able to pump enough Volume of the lower hot viscosity 20wt oil, so make sure your using a XW-30wt lube in your 4.0L crankcase.