ZERO oil pressure, What can I expect to find??

Hey all. First off...this is on a 97 Grand Cherokee. But since they motors are the same, Im sure someone in here can give me some help. Im also no stranger to working on stuff...so Ill probably figure it out. I just want to hear some opinions before I have to start to work on it...

I was driving my mom's ZJ this morning, and I noticed a weird noise. Sort of like an exhaust leak kind of sound. Jeep has a flowmaster, so I just figured it was a weird drone at first. Then I realised the oil pressure was at zero. As soon as I saw it was at zero I shut it off. Coasted alittle ways. Came to a side street and traffic was coming. So I had to stop. Then I had to fire the engine again, just long enough to bump it into gear and get me goin again, then immediatly shut it off.

If I had to guess...I would say I drove for about a mile for issues. Didnt notice the zero oil pressure at first. I went about 7/10s of a mile on zero pressure. Some of that was coasting with the engine off as well....

The jeep has plenty of oil. No holes in the block that I can see. And was running fine earlier when I left for work. My first thought was the oil pump blew. Then I got to thinking that a bearing spun. Even if a bearing didnt spin...Im wondering how much damage has been done to the engine. It has somewhere around 120,000 miles on it. Never a hiccup.

Any advice or help as to how I should proceed would be appreciated. Ive never had to track down an internal engine problem...but Ive torn them down plenty of times. So Im not scared of the work. I just dont want to waste my time doing something pointless. Thanks in advance for any help!!

Justin

The key question is was your engine making any knocking sounds when the oil pressure was zero? If not, it's unlikely you spun a bearing because if you did, the engine would have been knocking pretty loudly.
I think you'll have to pull the oil pan off, inspect the rod/main bearings, and replace the oil pump. I suspect that by pulling off the pan you'll find the reason for the zero oil pressure.

has your mom ever noticed this before?(prob not because women dont look at guages) just asking because I was on a friends gc all last week and it would constantly drop to zero and go back up so do you think it could be a bad oil press sender? I also have a vw with a bad oil press sender so this is why I bring this up.

ps I am no exper on this matter. just my 2cents

I was also thinking bad sender. I know they're common on the 4.0's on XJ's to go bad, and I'm assuming that the engine in his mom's ZJ is a 4.0.

The sound of an exhaust leak could very well be a cracked manifold....my old neighbor has a 98 with about 110K on it with a cracked manifold. You can really hear it roaring when she first fires it up cold...but once it warms up everything quiets back down.

What brand oil filter ? check the sender connection but BEFORE firing it up mark and pull the distributor, using a drill and a long piece of metal steel spin the pump up with the key in the run position, have someone watch it and see if you have oil pressure. If you do that eliminates the gauge and sender, if not pull the sender and put a mechanical gauge on it and repeat. If you have pressure it may just be the gauge/sender. If no pressure you will need to pull the pan for a closer look. If for some reason you need to turn it over pull all the plugs and give the cylinders a few good squirts of mobil-1 or other synthetic, this will at least get some lube on the cylinder walls and rings.
I have had issues with Purolator filters in both my 4.0XJ and my 2.5TJ, I only run Mobil-1, K&N and Mopar OEM's. I have been tempted to try NAPA, only problem is they keep bankers hours and are closed before I leave for work and when I get home so I never have.

Hmm...not sure about what filter is on it. Motor is a 4.0...

Jeep has never done this before. I drive it often and there wasnt any issues. I would agree on bad sender...but it started making noise first. Which then caused me to check gauges. Alittle too much of a coincedence for the sender to crap out just as the engine was acting up.

The noise it was making sounded more like a sick engine than an exhaust leak. Its hard to describe. When I had to crank it back up to turn onto the side street, it didnt sound like it usually does. Alittle sluggish, which Ide expect if there wasnt oil pumped around everything.

Dr. Dyno: As for noises before this happened, there was a slight ticking/knocking noise. I wouldnt even really call it knocking. But I could tell it was mechanical. Now...my 94 XJ 4.0 makes lots of noises. They are noisy motors. And it wasnt loud at all. It wasnt even audiable to people not listening for it. If a bearing spins, do you loose all oil pressure? Or does oil pressure just get low? Because the gauge was PINNED over on zero. Like the Jeep was shut off.

I think my course of action is going to be something like this. Pull the dizzy and spin the oil pump up. See if I get any pressure. If not, my first move will be tearing the pan off to replace the oil pump. IF I get the pan off, and find a handful of metal...Ill start pulling caps off to see which bearing, if not all of them, took a dump. If I find enough damage to where Ill need to do all new bearings or have crank work done, I think Im going to just grab a short block. I kind of need to get it done in a timely manner, and Ide rather stab a short block in, and swap everythign onto it than rebuild a motor.


Not sure when Ill get to start messing with it. Probably this week at some point. Thanks for all your help so far! Keep it comin!

Justin

Justin, like RichP says, filters can make a difference.

Does the engine overheat? Do you get any loud knocking sounds when the engine is running for a bit? When you restart the engine after it has cooled down, do you get any oil pressure on the gauge at all? It may be worthwhile to troubleshoot the oil sensor and oil pressure gauge first before replacing oil pump.

As old_man says in post http://www.naxja.org/forum/showthread.php?t=74620&highlight=troubleshooting+oil+pressure "... hook up a mechanical pressure gauge. Don't trust the dash gauge." That'll tell you whether or not the oil pump is putting out. If it is, then either your oil pressure sensor or your gauge or something in the middle has failed.

Yucca-Man says in http://www.naxja.org/forum/showthread.php?t=72228&highlight=troubleshooting+oil+pressure that "... A disconnected sender will immediately peg to 80psi " So if you disconnect the sender wire from the sender, and the gauge pegs with key on, it seems to me that your wiring from sender to gauge and the gauge itself are likely ok. That leaves a faulty sensor. I'm sure other more knowledgeable members can provide additional troubleshooting methods for these gauge-related components. Good luck tracking down the cause. Rick

Also at http://www.naxja.org/forum/showthread.php?t=47820&highlight=troubleshooting+oil+pressure HoratioTheJeep points to a link for specific troubleshooting of oil pressure sensors and gauges: http://www.olypen.com/craigh/pressure.htm Fyi, Rick

Rick,
Thanks a lot for the posts... The engine made absolutely no weird noises prior to this. It ran great last night..just like it has since we got it new. The filter is the same style filter we always put in it. I think it might be a mobil 1...but I cant remember. Engine doesnt overheat. In fact I just replaced the water pump due to the weep hole spraying coolant out. Oil pressure was always great in that jeep. Always at or around 40psi...even when idling. Seemed to be a real healthy engine.

And again...the oil pressure didnt just drop, and then I thought I heard noise. I heard noise and the motor felt weird...which caused me to look down at the gauges. At which point the oil pressure gauge showed zero. On cold start up...great oil pressure. Hot start up...great oil pressure. Alawys fires right off. Always cranks easy. Thing still got 16mpg avg around town. Its NEVER had anything major wrong with it. Literally the only things that Ive replaced have been tires, brakes, and tune up stuff. Then the water pump at 122,000 miles. It now has 127,000 on it.

Im starting to think a bearing might have spun. Because the oil pressure seems to have just dropped all of a sudden. Within the 8 minute drive from my house to work... I would think the oil pump would start to drop pressure little by little and not just blow out and stop working. But again, Im not an internal engine wiz. The pressure was dropping in my 94 and I replaced the pump and pick up and its been great. Im wondering if something got sucked into the pick up tube??

But Im prepared for the worst...Im prepared to deal with the fact that I toasted the engine. I just gotta start to dig in to see for sure what it was.

J.

Justin, I guess when I wrote the following I was referring to now, not yesterday or previously, but *after* the pressure-went-to-zero event:

"Does the engine overheat? Do you get any loud knocking sounds when the engine is running for a bit? When you restart the engine after it has cooled down, do you get any oil pressure on the gauge at all? It may be worthwhile to troubleshoot the oil sensor and oil pressure gauge first before replacing oil pump."

Have you restarted and run the engine to check for these engine symptoms?

If it were me, I probably would. Just briefly, though. And I'd be careful to shut it off before any damage is done. Then, before I even considered tearing into the engine, I'd try to do the simpler things first - like test the oil pressure, sensor, wiring, and gauge.

Like you say, you'll just have to dig in to see for sure what it is. Have a good one, Rick

Rick..yeah I guess I probably read what you wrote wrong. All I know is it definetly wasnt running right when I noticed the pressure at zero. I shut it off and coated down the road a ways. Wanted to just turn into a side road...but there was traffic. So I had to fire it again just to get enough momentum to take the turn and get onto the side road. When i did re-fire the engine, it started slower and it was pretty rough sounding. So I just dont think I can blame the gauge/sender. BUT....I know there are some simple tests to check that stuff so I will start there. Thanks for the advice!

Justin

Best of luck Justin and I hope for the best for you....but from what you're saying I fear that it may not be what you want it to be.

Definitely keep us updated.

Thanks for clearing that up. So you did restart it and it did run for a brief period, though harder to start and running rough. However, if the engine isn't overheating, it's likely getting oil. It doesn't sound like you ran it long enough to determine if it is overheating, though. So, I might do that, if it were my rig. I might run it now for a period of time. Or, maybe it would be more prudent to do as RichP suggested and spin the pump with a drill to make sure the oil pump is working. I'm sure you are fully aware that lack of oil not only causes overheating, but a more immediate effect would be knocking and clicking sounds associated with lack of lubrication to the valve train components, bearings, etc. A "rough sounding" symptom as you describe the engine performance when you briefly restarted it could also be due to some sort of electrical problem that happened all of a sudden and might also be effecting your gauges. But I can sure see where your coming from... you hear unusual engine sounds, look at the oil pressure gauge and see zero. It's natural to connect the two and assume right away that the oil pressure is gone, and that's what is causing the problem. And, very likely it is! You did the right thing in pulling over and shutting off the engine right away. At least that bought you some time to diagnose and fix the problem before it caused major engine failure. Let us know what you find out. Rick

haha... Thanks man. It honestly doesnt matter to me what it is... I wont be paying for the parts lol. I found a long block for $1000 after core charge. So if I determine that the bearings are all toast, and if there is some other damage that a crank kit wont fix, I might just go that route. We'll see. Judging by the noise i think I might find some ugliness in there once I start taking bearing caps off. Once I find the main problem, Ide like to know what caused it because that jeep is well taken care of. Not really beat on. My jeep on the other hand has 200,000 miles, modified all over, beat on regularly, I miss my oil changes frequently, and it runs great. I hope its something obvious like the oil pump stopped working. Even if the motor is toast, atleast it'll put my mind at ease about the "how/why".

I appreciate all the responses so far. I know its tough to do the "internet mechanic" thing especially since I havent torn into it yet and dont have a lot of info. So thanks! Ill definetly let you guys know what I find once I start checking things out.

J.

If you can, take some pictures. It would come in very handy in the future incase others run into a problem such as this...

99XJSPORT06 said:

If you can, take some pictures. It would come in very handy in the future incase others run into a problem such as this...

Click to expand...

Definetly man. Ill be snapping some pics and maybe taking a video of the way it sounds when running... Like you said, it would be great if it could help someone else.

J.

ghettocruiser said:

Definetly man. Ill be snapping some pics and maybe taking a video of the way it sounds when running... Like you said, it would be great if it could help someone else.

J.

Click to expand...

I like videos even better!

-Tim

ghettocruiser said:

I think my course of action is going to be something like this. Pull the dizzy and spin the oil pump up. See if I get any pressure. If not, my first move will be tearing the pan off to replace the oil pump. IF I get the pan off, and find a handful of metal...Ill start pulling caps off to see which bearing, if not all of them, took a dump. If I find enough damage to where Ill need to do all new bearings or have crank work done, I think Im going to just grab a short block. I kind of need to get it done in a timely manner, and Ide rather stab a short block in, and swap everythign onto it than rebuild a motor.

Click to expand...

Don't bother trying to spin the oil pump with a drill. Just go straight to removing the oil pan. Since your engine was runnign rough and making noises with zero oil pressure, I guarantee you'll find something wrong.
It's quite possible that the oil pump shaft broke first, causing a sudden loss of oil pressure, starving the bearings of oil, so now you've probably toasted the bearings and scored the crank journals. You might also find some scoring of the cylinder walls caused by the piston rings because there was no oil to lubricate them.

Yeah...Im not going to bother spinning anything. Ill be pulling the oil pan and checking everything out. Im not too worried about the cylinder walls being scored, because I was under the impression that oil got into the cylinders from the crank slinging oil up there. I man, oil doesnt get "pumped" into the cylinders under the pistions right? And the rings wipe the cylinder walls alitle bit on the way down. So I thought they'd be ok.

Since I know I already did some damage, I decided to give it a crank today to see what happens. I also took video and the sound came out pretty good... Ill post it along with an explanation of what happened after youtube approves the video.

Justin

OK...looks like the vid is up.

So here is what happened. I know I did some damage to the bearings. Just by the amount of noise it made and how rough it was running. So I decided to fire it up for a few seconds just for the heck of it. And to get you guys some video. Well, it fired right up, made a lot of noise, then to my surprise quieted down. You can hear it in the vid... You can see how surprised I was because I went to look at the gauge. Sure enough..oil pressure. The motor was still making a racket. After the video, I watched the gauge as I revved the motor to about 2000 rpms real quick and let off. Oil pressure went right to zero for a few seconds, then slowly back up to ~35. Shut her down after that.

My thoughts are...the oil pump failed. That would explain the fluctuation in the oil pressure. I can hear something weird too...that sounds like a whirring noise. I kinda of thought maybe since the oil was so cold and thick from sitting, that it was thick enough to have oil pressure at first. Which is why it had pressure, but was really unstable. Anyway... the only way Ill know how much damage is to tear into it. But Im hoping that I might be able to get away with a crank kit at this point...

Here is the vid... Ignore my stupid commentary. haha.

http://youtube.com/watch?v=-GlQsYMI5RQ

Justin