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Thread: oil pressure problems

  1. #1

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    oil pressure problems

    Ok, I'm new to this forum. I've got a few problems with my motor. I have a 94 mighty max v6, 6g72. Im going to get this out of the way before someone says anything, Im not a idiot, Im just about done with a 2 year degree in auto system tech. AND yes i used the search function, but apparently "oil" and "low" are non existing. Anyway. Truck has 261k miles on it, this is the 2nd rebuilt ive got. I've got about 6-7k on the new rebuild. Up to about 3-4k in the new rebuild, oil light started coming on. I had just started smelling oil burning on the exhaust. Put it on the lift at school, diagnosed the real seal is leaking. Since this is my only form of transportation 90% of the time, I decided to fix it myself. This is my dads truck, which he paid someone to rebuild it since I would have took my time on it because of my classes and all, which really in the end he still had to wait. So, um, i was putting in a quart bout every week. oil light coming up, especially at idle. Past weekend, I put in the new rear main seal, dropped the trans all that good crap, I just happen to noticed there was a BOLT missing from the rear main seal housing, I was pretty pissed that who ever built it neglected this, But whatever, got new bolts, put them in. Got it all back together. Doesn't leak oil no more. But the oil light is still coming on, I also did a oil change in the process, I am using Valvoline synthetic 10-30. When I start the truck, it doesn't come on but after its been running aka gets up to operating temperature it lights up. I also hear the valves ticking, mainly at idle at a stop light, or at cruising speed. Give it gas, or put a load on the motor it goes away, the light and ticking. the light doesn't come on during actual driving. I would like to use obd to check for engine codes but my scanner tells me to check for power and I've done everything to get power to it, doesn't work. I am thinking oil pump, but I could be wrong. I am pretty sure it was not replaced. But I do know most of the parts that were replaced since I found most of them....unlike the shop that did it, apparently has no use of internet.

    What I found for the rebuild
    New crank or used but I mic'd it to be in great condition.
    Used heads/cams/valves etc. no crack in the heads.
    New rods. new rings, new bearings, I don't think the motor needed bored, it's already bored .040 over.
    gaskets, I'm not sure of the other stuff that was replaced. My dad got the list. I can get it if needed.

  2. #2

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    I had a similar experience when I got my '90 MM 4x4 with the V6. I talked to an experienced Mitsu mechanic and he suggested I replace the oil pressure sensor before doing anything else. I think it was around $20 and it turned out the sensor was the problem. That was about 70,000 miles ago and I just started having the same thing happening again, oil light coming on at idle after the engine heats up , especially if I have been pulling a trailer. I intend to replace the sensor again before looking for other causes. I'll let you know if it was the problem.
    1990 MM 4x4 3.0
    1991 MM 4x4 3.0 Diamonte
    1994 MM 2wd (work in progress)

  3. #3

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    Sounds like a good idea. I could pick one up next friday. Let me know how it works?

  4. #4



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    Or you can pick up a real gage and see what the pressure it. It could be the pressure relief valve spring is just worn out. Or they did not put in a new pump when they rebuilt the engine. If the valves are rattling then there is a low oil pressure problem. It's not uncommon for these engines to only have 20psi at idle.
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  5. #5

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    I'm assuming a oil pump is supposed to be replaced. Because to my knowledge, I would have replaced it regardless.

  6. #6


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    worst comes to worse you "might" have to machine the crank and put new bearings in. If the did a quick and dirty rebuild then they only polished the crank and went back to the original size bearings. This will also cause low oil pressure as the oil is leaking between the crank and bearings, which will not push enough oil up to the lifters and cam's at idle. As Lush said try the pressure switch first. The engine should be under warrenty with only 9K on it. They should cover it for 1-2 years and 20K unless they are a fly by night operation.I have all my machining done out of house but even I cover my rebuilds for a year.

  7. #7

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    Quote Originally Posted by Fordubishi View Post
    worst comes to worse you "might" have to machine the crank and put new bearings in. If the did a quick and dirty rebuild then they only polished the crank and went back to the original size bearings. This will also cause low oil pressure as the oil is leaking between the crank and bearings, which will not push enough oil up to the lifters and cam's at idle. As Lush said try the pressure switch first. The engine should be under warrenty with only 9K on it. They should cover it for 1-2 years and 20K unless they are a fly by night operation.I have all my machining done out of house but even I cover my rebuilds for a year.
    Which I already know all of that. But I mic'd the new crank myself, it was with in spec for standard sized bearings, and it was already polished. Even then, motor runs absolutely fine, no knocks. EVEN if the crank was under spec, and standard sized bearings were used, the oil light would have started coming on a lot sooner, the low pressure symptoms didn't start until after I diagnosed the rear seal was leaking oil.

  8. #8

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    Ticking lifters....seems that engine has those damnable hydros in it(?). Might be that either they weren't replaced, got a bad one or two when they were (it happens), or they weren't primed before they went in. They will theoretically self-prime under operation, but have had them not do it for whatever reason.

    Would definitely be going to a gauge over the idiot light. Not too spendy to put one in...and worth every penny to actually see what's happening!

    Idiot lights are justly named.

  9. #9



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    2 rebuilds in 261K? Though some folks drive their vehicles harder then others, this is kind of high for these trucks if oil is changed every 3-4k miles. I imagine the rebuilders are making money off your truck and doing a quicky job. Not paying attention to details and tolerances. Depending on area, oil viscosity usually falls in your environment. There is a viscosity chart in our wiki here that can help you with choosing oil wt. My truck has 275k and have not rebuilt bottom end yet. Compression good, but the noise that sounds like lifters in my truck is my wrist pins that can sounds very much like a bad lifter or un-adjusted rocker. Checking for a little too much side to side motion on the pistons when the heads off is a pretty good check done by pushing the piston forward and backward. My oil pressure drops too, usually after warming up and the oil thins out from heat. Get a needle gauge like it says here and no idiot lights. Depending on your oil pressure senders setting at factory (if it's the correct one for your truck) should be 2-7 psi approx. Sensor replacement first, oil pump second if your suspected oil problem is being diagnosed. You can see if oil is pumping well by taking the oil filler cap off during idle and look into the opening. Rev up engine a little look for oil splattering around, more as it revs.

  10. #10



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    Part of the issue could also be running synthetic oil on a motor with high miles, if they didn't return all bearings and such to factory specs. Do also understand that like you we are also knowledgeable about these trucks and are trying to help you here. There could also be an issue with lifter bleed down after running awhile - a new set of lifters bleed properly could solve that if the sender is not the problem. Remember, just because a garage says they replaced parts, unless you see them do it and hand you the old ones, thay could be what was there to start.
    Last edited by pennyman1; 06-02-2013 at 05:09 PM.
    Pennyman1
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  11. #11

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    Yeah, the 1st rebuild was done at about 230k......we know that garage did a horrible job. However, I do feel if I found a bolt missing from the rear main seal housing, (requires 5 bolts, I could tell new ones were installed, this was no mistake) but I wonder what else was neglected as in the process of dropping the trans last weekend, I found numerous of loose bolts, you just don't 'forget' one. They also didnt clean a lot, maybe had the block dipped but that's about it, which imo, is very unprofessional. Like i said before, the motor runs fine. I will get the gauge this week and check though.

  12. #12



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    Quote Originally Posted by Rivals Inc View Post
    I'm assuming a oil pump is supposed to be replaced. Because to my knowledge, I would have replaced it regardless.
    It could be the relief valve spring is bad or plunger is stuck in it's bore. That is the first place to start looking, after you put on a real gage for testing you will know for sure. You should have one in you tool box just for this type of complaint. I don't know how many time a customer told me there light was on and with a quick test it was something else. 80% of the time it was the oil pump relief valve. When a filter clogs it will make a retched noise as the oil is forced through the by pass in the filter when cold, it will also vibrate and you can see it.
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  13. #13

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    What oil pressure gauges do you guys recommend?
    1990 MM 4x4 3.0
    1991 MM 4x4 3.0 Diamonte
    1994 MM 2wd (work in progress)

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