Oil pressure dropping :(

Rebel_Frontier

Rebel_Frontier

New member
Hello all!

So, recently swapped my 4.0L for another 4.0L, (recently being like 4 months ago) replaced everything that was needed, and for a while she was running smoothly on me. I started noticing this a few weeks ago and didn't pay any attention to it. My oil pressure seemed to be riding on the low side, especially when I was on the beach in 4wd. Now it's starting to do it all the time. My engine kinda sounds like it's mis-firing when I crank her in the morning. Ill take off, switch to second and as soon as I press the gas the gas cuts off and you hear a loud pop comin out my muffler. This inly happens once in the morning. Ill be driving with the oil pressure at the mark before 40 and it drops to 0 everytime I turn or make a stop, and sometimes while I'm driving. It always dips then comes back up to that mark. The engine doesn't sound like it needs oil and there are no visible oil leaks anywhere. I'm assuming the engin would need to leak a lot of oil in order for the pressure to drop that low. Check engine light is on and I haven't gone to get the codes. Ill do that tomorrow. But any ideas guys?
 

Sorry to hear your jeep has the low oil pressure blues . Something for you to try in addition to getting the trouble code(s). Remove the oil filter adapter . Hopefully you have the cast 5/8" nut and not the T-60 screw as the screw is a real PITA , I heard and the cast nut is hassle enough to reach . First though , go to the parts counter at,a local Chrysler dealer and get the 3 piece O - ring kit for the oil filter adapter . When adapter is removed , verify the acquired kit has the correct size O-rings for your engine . When I did mine , I ordered the O - ring from Rockauto not realizing there are 3 and only got one with the kit , the largest one. Three are needed , largest one seals the adapter to the block , second largest seals the removeable shaft at opposite end and smallest one in the center. Pappa , momma and baby . The momma and baby seal internal pressure , especially the baby , which prevents oil from bypassing back to oil pan . If oil bypasses , that is where pressure is lost. The momma helps keep pressure too by avoiding an internal oil leak. Poppa helps seal external oil leak. When I did the job on my '92 XJ , I had to think quick and make use of a Dorman nitrile O-ring kit for the momma and baby as Rockauto only supplied me the o-ring, but that was my fault. I did not know I was to order the rings separate . Apparently , there are different sizes , different application ? Well , this is jeep for you , design change and change over from AMC to Chrysler to blame. Chrysler robbing AMC's parts bins and so forth . It is essential to have the correct O-rings to start with , I believe that is why we should go through the dealer , they will know where you can get the correct casting numbers to verify correct parts , I guess. When I changed mine , I immediately noticed no leaks , but vastly improved oil pressure at idle and acceleration , above 40 psi ! I cannot be sure the rings I selected , momma and baby , are right or even make a difference , but I am curious how the correct set will work for you . Hoping this will cure your low pressure problem , hope you may avoid oil pump replace as I think a good pump for the I6 4.0 is not cheap ! Try to furnish the most accurate info to get the right parts to do the job right , as you know. Boy , you would think this should be a no brainier , buy O-ring kit for a 4.0 ltr I6 , replace , done , enjoy . But lest we forget , it's a jeep and not always so easy. Best of luck to you and hope this helps cure your jeep's low oil pressure problem . We do not want problems after you just did an engine swap.
 
Forgot to ask , the predetonation you are experiencing , did you notice if the engine temperature rose prior to detonation ? That could set a code , but also wondering how is your oil pressure sending unit switch and also the coolant temp switch too . Coolant temp switch feeds back to ENGINE CONTROLLER (PCM) not sure if oil pressure switch does. Codes will tell . Really , best of luck as we want to see your hard work prevail . Best of luck , Greg92jeepxj
 

I have a tendency to immediately blame an oil pump when oil pressure is low . When I fixed the leak on my truck , I found the oil pressure immediately improved. I no longer blamed the pump and I figured that it was worth a try on the 4.0 in question . Hoping for the best and anxious to see the trouble codes .
 
Just got to the codes! But to me they really have nothing to do with the oil pressure. The codes are as follows:

P0303 - cylinder misfire detected-cylinder #3
P0302 - cylinder misfire detected -cylinder #2
It's saying this is because of a ignition system fault (but I just replaced spark plugs and wires about 2 months ago)

P0121 - throttle position sensor
This is also weird because I replaced this a month ago.

P0138 and P0141 - Says its heated oxygen sensor Bank 1 sensor 2
 
I agree , too many faults and all of a sudden. Now I wonder , is there really a oil pressure problem or is the engine idle become unstable like it is stalling and recovering causing the oil pressure to dip and raise back up . There is an obvious diagnostic problem that must be dealt with . I think since the o-ring kit is inexpensive , try getting the right ones as that seems hassle enough but once accomplished we can rule out oil pressure problems , or so we hope. Then we can go on to deal with the diagnostic problem now discovered. I once assumed a friends car had no problem with a mis fire and rough idle due to ignition components because he just tuned it up. I wasn't sure what to check next . He got a friend to put a scanner on it and found a misfire on a cylinder. Cracked spark plug. Problem solved , he broke a plug. Not saying you did anything wrong , we have changed plugs so many times . We know how to be cautious. But at this point , we have to rule out what could be and what isn't since these codes are coming up.
But at the same time , could there be a problem with two cylinders , a TPS, and both O2 sensors or could there be a computer fault ? Yes this is becoming interesting but not so unique.
Unfortunately , process of ILLimenation must be applied to find the fault. We know a good diagnostic shop would do it this way , I believe that is what will prevail.
First , double check tune up items , check TPS operation , harness , source and signal (input and output and ground) and o2 operation (open loop to closed loop and lean to rich cross counts ,etc.) computer grounds should be checked to make sure it is not flaking out because of a questionable ground. I have learned never to assume , check and make sure. This all sounds overwhelming , I agree , but I believe the only way to find and fix the fault(s) is the systematic approach. Yeah, that means breaking out the heavy guns. Computer safe test light , ten mega ohm impedance DMM , noid lights , spark tester , the works. I callin' all cars ! Emergency priority ! We gotta get this working right ! Don't mind my humor , but its time to take this jeep back to school and teach it how to act and stop wrecking all your hard work and accomplishment .
hang in there , it can be done , you can do it and the weekend is approaching. Make us proud.
 
I realize it would be so much easier if a scan tool with flight mode were available , or even a dyno session (money$$$) , but I guess we have to work with what we got . It's now sounds like a computer related issue more than a oil pressure problem , but it is better to go by process of illumination to find the faults rather than guess and throw parts at it (more money$$) . I would still start with the O-ring kit and replace all three as an engine with any mileage will no doubt need them . Besides , they're inexpensive. Hope you have the means to conquer this problem and get 'er done soonest ! Shame to have these problems after all the laborious engine swap ! Best of luck brother !
Hope to hear good news soonest !
 
As if you don't have your hands full now , I just discovered something that may very well apply to your problem. A member posted that he has a problem with his ASD fuse blowing repeatedly .
that is the auto shutdown relay circuit and controls ignition , fuel pump , O2 sensor(s) and maybe more but was straining my eyes looking at tiny diagrams and fine lines :cry:.
Ok , why this strange call in the middle of the night ? WIRING!!! ELECTRICAL SHORTS !!!
One or more of the driven components by this fuse and relay can be affected by short to ground.
since you are having codes pop up with O2 , and ignition , it is worth looking at your wiring harness under the hood to see if there may be any shorts , damage , opens and the like.
I say this because an engine swap has been performed recently and maybe, just maybe a wire or wires in any of the previously mentioned circuits could be affected. Oh , the fuel injector harness
is in line with this too . It just seems to fit and I think it is a good place to start by inspecting wiring harness under the hood . Stands to reason , old vehicle , brittle wiring , you never know.
besides , during the motor swap , wiring harness is handled quite extensively , as you know.
i really believe the diagnostics should start there as a lot of time probing wires and taking electrical measurements and values could wind up being totally inaccurate because of these dreaded shorts . I know you did not mention any fuses or relays blowing , but it just comes to mind and is worth a shot. We know anything can happen to wiring , so this is a good place to start. After all , we are supposed to inspect items of this nature including vacuum lines , etc. ,
any good service manual tells us to . They print this there for a reason , time after time,
like prove them right by repeating to myself , NEVER ASSUME , ALWAYS CHECK!
Hope you find the answer this way , tedious yes , but very cheap repair comparatively !
really hope this means something for your problem , worth a try .
 

If all the above checks out ok, I would look into the o2 sensors. Had a ford ranger a few years back that I had the codes read on, and it showed multiple cylinder misfires. Was both O2 sensors.
 
The more I think about it , realistically , I do believe it is probably just a glitch . Wiring from O2's or sensors themselves flaking out wreak havoc with OBD2 , happened to my dads '97 t-bird 3.8 .
Changed out all four O2's and running like new. I think Rebel will have it up and running by this weekend ! Betting myself $5 says he does !
 
69jeepcj said:
If all the above checks out ok, I would look into the o2 sensors. Had a ford ranger a few years back that I had the codes read on, and it showed multiple cylinder misfires. Was both O2 sensors.
Click to expand...

I like the ranger , but I think as good as a truck as it is , it dosen't compare to a well built CJ !
 

If it were me, Imight try changing the oil filter first especially if it's a fram. Then If that didn't cure it I might make sure it's not a faulty gauge or sending unit. I've never been in a 4.0, is it possible the pickup could be loose? Did you have the pan off? I know a previous owner of my Jeep really enjoyed silicone, I found a wad stuck to the pump screen on my 304.
 
Go down to AutoZone,pepboys or any chain auto parts store and rent an pressure tester. Free at 99% of stores, just leave a deposit. Buy a new oil filter and qrt of oil and fill the filter before screwing on. Replace your oil filter to take it out of the equation and screw the pressure tester. If your not getting any pressure, you can try to R&R the oil pump and retest. Most of the time its the sending unit.
 

It would be a good idea to monitor oil pressure from a direct connected pressure type not electronic oil pressure gauge when a glitch kicks in to confirm if the oil pump is bad or the dash gauge is reacting to the glitch as the dash gauge is electronic . That would be a good diagnostic procedure to find out if it is necessary to pull the pan off . Sure hope no one got happy with any silicone and some found its way to the pick up screen :shock:
 

No if it is showing full ,don't over fill it. Level has nothing to do with pressure unless it is low and sucks air into pick up tube. The pressure sending is cheap and easy to replace. Without running a pressure test its your first thing to replace blindly.
 
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