I have oil pressure at an idle but when you give it gas it drops to 0 psi, there is no tic or knocking engine runs fine no smoke at all. I replaced the sending unit with no luck, the jeep has 93,000 miles, any ideas on what it might be.
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Re: 2000 jeep grand cherokee
You definitely need to put a mechanical gauge on there and check for ACTUAL oil pressure. It is possible that the passageway to the sending unit may be plugged with gunk. If oil pressure is not correct or if in doubt, do not drive it 'till you know for sure what's going on in there. No noises tells me that it is likely not serious but an engine is just too expensive to gamble!!!
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Chances are that the sending unit has a problem. Could also be a loose wire on it. Only way to test is to put a mechanical gauge on the engine and read actual pressure, or, just replace the sender and see if it helps. No noises from the engine is a good sign. If you had any tapping or knocking, putting a mechanical gauge on there would pretty much be mandatory.
the 1st thing to do is hook up a mechanical test gage and see what the pressure really is, the one used in the truck is electronic and u could have a sending unit problem, if the mechanical test gage show the same readings u will need a new oil pump, this assumes the engine doesn't have any bearing knock type noises
I am going to take a stab at this....as I think you may have a head gasket that has blown out. The head gasket will cause a lil white smoke, and make idling extremely rough. Sometimes water will fill up in the top of the cylinder in the compression chamber when this leak, even minor occurs. That would explain some of the compression issues. Obviously with no compression it will not run properly or even fire if there is water vapor pentrating into chamber mixing with fuel giving you that white smoke/steam.
These are somewhat time consuming to change, but not difficult. The backfiring is caused by the computer trying to compensate for the firing issue. The computer when you change the head gasket is easy to fix. After repairng gasket, try to start the car a few times but not allowing it to run as it will just continue backfiring. Turn key off, let the vehicle set about 30 minutes or so, then go back and the vehicle should run properly again.
First check the oil level and top up as necessary. If the oil pressure is at 0 , then it would very quickly sieze the engine, that not being the case, it sounds like you need to replace the oil pressure switch/sensor, which will be mounted either on the engine block or on the oil filter housing. Hope this helps
installation is pretty much tighten and plug in as described. if gauge goes to 0 with engine off u should be fine. 15psi idle 40 psi higher rpm is normal. it is possible new switch not as as sensitive as old.
You'll need to determine if the oil pressure is actually changing, or if the sending unit or gauge is lying to you. Be certain the oil level is up to normal, then check the actual oil pressure with a test gauge. If the pressure varies (drops) at engine idle, perhaps your pressure bypass is defective, or perhaps the oil pump is worn. Testing with a known good pressure gauge should lead you in the right direction.
PS to previous comment: i HAVE SEEN ONE OIL PUMP (IN A CHRYSLER CAR) DO THIS EXACT SAME THING I found the problem after tearing down entire engine: the pump driveshaft was actually spinning inside the pump gear.It actually was tight enough so it could not be finger turned but when shaft was secured in a vise, gear could be turned with little force using pliers.(first and only one I ever saw like that in thirty yrs...but it shows you...it can happen!
At idle, at operating temp is there any ticking from top end of engine? Are there any knocking noises brom bottom end? If no noises, change oil and add some Marvel oil to clean out galleys. If that dosent work, change oil pressure sendingf unit. Also, if you have a mechanical oil pressure gauge, hook it up and take a direct reading. Oil pressure (in any vehicle) at idle should NEVER be less than 15psi. Generally in 4.0 jeep engines it's never less than 30, with a high reading at driving rpm of about 40-60! (but, you did not mention what engine you have)