Dickinson County Comanche Posted June 29, 2020 Share Posted June 29, 2020 Hello all, when I got my Comanche back on the road back in march and put ~20 miles on it before putting new oil in it. After that change, the oil pressure drops to less than 20 when warm. It has very little response to throttle and it makes a ticking (most likely valve/lifter) it has 60psi upon cold start and doesn’t tick when cold. Engine only has 126K on it. It doesn’t smoke and doesn’t have any other noises except for maybe one small exhaust leak and a EGR quack. I do not have a mechanical gauge to test actual oil pressure, and I can drop the oil pan if need be on a lift. in the video, most of the noise is from the countershaft bearing in the BA10/5. I’m eventually going to put an AX-15 in, I just haven’t got there yet, and thus, the noise persists. IMG_3079.MOV Link to comment Share on other sites More sharing options...
jdog Posted June 29, 2020 Share Posted June 29, 2020 I would get a gauge just to make sure, you just need an aftermarket gauge, nothing fancy ie: https://smile.amazon.com/Sherco-Auto-Chrome-Mechanical-Pressure-Gauge/dp/B0844S18VX/ref=sr_1_16?crid=8LSLCOZS29CE&dchild=1&keywords=mechanical+oil+pressure+gauge&qid=1593464408&sprefix=mechanical+oil+%2Caps%2C196&sr=8-16 and just hook into the oil pressure sender spot. the factory gauges are not always accurate. the other thing ill ask is what oil and filter? Link to comment Share on other sites More sharing options...
Eagle Posted June 29, 2020 Share Posted June 29, 2020 Below 20 psi at idle, or at road speed? Factory spec for il pressure is only at normal operating temperature (meaning both the engine and the oil). The spec is 13 psi minimum at 600 RPM, and 37-75 psi at 1600 RPM. It doesn't sound like you have anything to worry about. Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted June 29, 2020 Author Share Posted June 29, 2020 1 hour ago, jdog said: I would get a gauge just to make sure, you just need an aftermarket gauge, nothing fancy ie: https://smile.amazon.com/Sherco-Auto-Chrome-Mechanical-Pressure-Gauge/dp/B0844S18VX/ref=sr_1_16?crid=8LSLCOZS29CE&dchild=1&keywords=mechanical+oil+pressure+gauge&qid=1593464408&sprefix=mechanical+oil+%2Caps%2C196&sr=8-16 and just hook into the oil pressure sender spot. the factory gauges are not always accurate. the other thing ill ask is what oil and filter? I think it’s a Fram filter, and 10w30 oil, which is what the Haynes manual called for. Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted June 29, 2020 Author Share Posted June 29, 2020 1 hour ago, Eagle said: Below 20 psi at idle, or at road speed? Factory spec for il pressure is only at normal operating temperature (meaning both the engine and the oil). The spec is 13 psi minimum at 600 RPM, and 37-75 psi at 1600 RPM. It doesn't sound like you have anything to worry about. Below 20psi at 2000-2200 rpm. I usually like about 10 psi for every 1,000 rpm. It will sometimes drop completely to 0 at idle. Rpm seems to have no effect on oil pressure, except when cold. Link to comment Share on other sites More sharing options...
Minuit Posted June 29, 2020 Share Posted June 29, 2020 You say this started after an oil change. Take that Fram filter off and put it in the dumpster where it belongs. Anything but Fram for oil filters. Then go from there. There are multiple accounts on this very forum of sudden low oil pressure on otherwise healthy engines attributed to Fram oil filters. If that doesn't fix it... Minimum spec or not, If I ever saw less than 20 psi oil pressure on a 4.0 I'd be planning my next move. A healthy 4.0 should put up at least 25-30 at hot idle. Even a worn out engine should have no trouble getting above 40 from a cold start. My 91 with 189k bottoms out at 35 psi with the oil fully warmed up, verified by mechanical gauge. The factory gauge is relatively accurate if and only if all connections are clean, the sensor is an OEM unit, and there is no sealing compound on the threads for the sensor. If in doubt, verify with a known-good mechanical gauge. Preferably not one rented from a parts store. As for your sound clip, that's exactly what my '89 with a completely shot bottom end sounds like once it's warmed up (with a lot more random knocks and clacks than yours has). The oil pressure gauge on it rests on "0" once fully warm. Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted June 30, 2020 Author Share Posted June 30, 2020 39 minutes ago, Minuit said: You say this started after an oil change. Take that Fram filter off and put it in the dumpster where it belongs. Anything but Fram for oil filters. Then go from there. There are multiple accounts on this very forum of sudden low oil pressure on otherwise healthy engines attributed to Fram oil filters. If that doesn't fix it... Minimum spec or not, If I ever saw less than 20 psi oil pressure on a 4.0 I'd be planning my next move. A healthy 4.0 should put up at least 25-30 at hot idle. Even a worn out engine should have no trouble getting above 40 from a cold start. My 91 with 189k bottoms out at 35 psi with the oil fully warmed up, verified by mechanical gauge. The factory gauge is relatively accurate if and only if all connections are clean, the sensor is an OEM unit, and there is no sealing compound on the threads for the sensor. If in doubt, verify with a known-good mechanical gauge. Preferably not one rented from a parts store. As for your sound clip, that's exactly what my '89 with a completely shot bottom end sounds like once it's warmed up (with a lot more random knocks and clacks than yours has). The oil pressure gauge on it rests on "0" once fully warm. The bad bearing noise is the transmission. It doesn’t make any other noise than that tick when warm. I wouldn’t think the bottom end would be gone, it only has 126k on it Link to comment Share on other sites More sharing options...
Minuit Posted June 30, 2020 Share Posted June 30, 2020 Just now, AwashCascade said: The bad bearing noise is the transmission. It doesn’t make any other noise than that tick when warm. I wouldn’t think the bottom end would be gone, it only has 126k on it That tick is what I'm talking about. And mileage has very little to do with it. The '89 I mentioned has roughly 140k on it and the engine is completely shot. Change the oil filter. Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted June 30, 2020 Author Share Posted June 30, 2020 14 minutes ago, Minuit said: That tick is what I'm talking about. And mileage has very little to do with it. The '89 I mentioned has roughly 140k on it and the engine is completely shot. Change the oil filter. Just the filter? Or should I change all the oil as a precaution. I just changed it less than 100 miles ago. Link to comment Share on other sites More sharing options...
Eagle Posted June 30, 2020 Share Posted June 30, 2020 12 minutes ago, AwashCascade said: Just the filter? Or should I change all the oil as a precaution. I just changed it less than 100 miles ago. Just the filter. He is guessing that you installed a Fram filter, and they are known for screwing the oil pressure. Just throw on a good Wix or Purolator filter, add a quart to make up for what was in the filter, and check your oil pressure again. Most 4.0L engines run at 50 to 55 psi at around 65 MPH -- when brand new. If you're anywhere in the 45 to 50 psi range, you're good. But the pressure should not be below 13 psi at warm idle. (I don't like to see lower than 20, but the book says 13.) Link to comment Share on other sites More sharing options...
silvertwinkiehobo Posted June 30, 2020 Share Posted June 30, 2020 The book was written by the engineers at the #4 automaker. SAE standard is 20 PSI hot idle and 5-7 pounds, IIRC, for each 1000 RPM minimum. And I agree, check the pressure with a gauge at the sender port. Also, the filter housing could have an o-ring problem. When you go to change that filter (Yeah, Fram ain't what it used to be), go ahead and plan to replace the square ring and hollow bolt O-rings, in case one or both have fallen apart/cracked or whatever happened. Better yet, find the Chrysler unit on a later-model engine and install it, so you don't have to chase down filters for AMC Jeeps with the metric threads. The Chrysler filter has SAE threads and are much more common to find. Anyway, good luck on getting this sussed out, as your engine needs its life blood to flow and be up to pressure. Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted July 16, 2020 Author Share Posted July 16, 2020 A bit of an update on this, oil pressure acts normal and is good (40-60 psi when driving, 40 at 2,000 rpm) but once it hits 160°, or the midway line on the gauge, the oil pressure drops. I have seen, however, that it does react to throttle, so it isn’t the oil pump, but I didn’t get it all the way up to 210° (what I’d call “normal” operating temperature, so I’m not sure how it reacts there.) If it’s the bottom end bearings, how hard is it to replace while it’s still in the truck? I don’t want to have to pull the motor if possible, but I’ll have it apart when I do my AX-15 swap. Link to comment Share on other sites More sharing options...
87Chief Posted July 16, 2020 Share Posted July 16, 2020 Bottom end bearings? Take the motor out to do those, you don't want a crankshaft falling on top of you, I would just wait until you do your transmission. Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted July 16, 2020 Author Share Posted July 16, 2020 Also, as I was reviewing this footage to check for knocks, I hear this noise apon shutdown. It is the starter staying engaged? It had the tendency to run with the key off right when I got it, but it’s gone away with time (and I’m guessing, usage) FullSizeRender.mov Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted July 16, 2020 Author Share Posted July 16, 2020 2 minutes ago, 87Chief said: Bottom end bearings? Take the motor out to do those, you don't want a crankshaft falling on top of you, I would just wait until you do your transmission. I meant more on the rod bearings, but I guess while I’m down there I might as well do all of them. I hate this oil pressure issue. I never had it and then it just showed up. It makes me upset because it runs just so good, other than a backfire that is (most likely) from a quacking and probably dirty EGR. Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted July 16, 2020 Author Share Posted July 16, 2020 I think I figured it out. There is a tiny bit of gas in the oil. What would cause gas to get in the oil? I just replaced the injectors so I wouldn’t think it’s that. Link to comment Share on other sites More sharing options...
Eagle Posted July 16, 2020 Share Posted July 16, 2020 3 hours ago, 87Chief said: Bottom end bearings? Take the motor out to do those, you don't want a crankshaft falling on top of you, I would just wait until you do your transmission. They can be done one at a time, while the engine is in the vehicle. Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted July 16, 2020 Author Share Posted July 16, 2020 Does anybody know why there’d be gas in the oil? Does the Renix run at a lower pressure than the HOs do? I put in the later style sender. Also, what could be the damage that that would have caused? Should I consider putting a new motor in? Link to comment Share on other sites More sharing options...
Dickinson County Comanche Posted July 17, 2020 Author Share Posted July 17, 2020 So, I made the startling discovery that there was gas in my oil when I went to swap my oil filter. It isn’t too much, but it is gassy-smelling, has a foul taste, is way too thin to be 10W30 (I had a bottle on hand and compared), and doesn’t smell, taste or even look similar to other oils in some of my other vehicles. I’m guessing one of my brand new injectors has failed and is causing the excess fuel pressure to run out into the cylinder after I shut it off. I’m going to pull plugs and see which one is washed. (Or, at least, see if one is washed.) to find the culprit. But, the damage has been done. I just recently changed the oil and the oil pressure didn’t recover. What kind of damage would this cause? If it’s too bad, I have another 107K Renix motor I’ll swap in, but I’m a bit afraid to since it was in a rollover accident, and it smoked pretty good the last time I saw it run, which, I suppose, could be oil he put in the cylinders, but I highly doubt it, but It’s probably stem seals, which I could just swap over my head since it doesn’t leak or smoke. Link to comment Share on other sites More sharing options...
Eagle Posted July 18, 2020 Share Posted July 18, 2020 Duplicate threads merged. Link to comment Share on other sites More sharing options...
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