Well, phooey. For those of you following my fluctuating oil gauge issue, when the alternator was put in yesterday, it seemed to resolve the problem. Unfortunately, this a.m. when we drove the car totally cold, the oil gauge once again went to zero. The alternator was part of the problem, as the oil gauge was not “misbehaving” as badly nor as often, but there is obviously still something else wrong.
Yesterday, another person suggested using another electrical meter, which I will suggest to the mechanic. Any other ideas? I thought we had this fixed.
I still give Rod Knox the A+ because the alternator was going bad, but I am hoping someone else can get an A+, too!
I’d Like To Try And Help, But . . .
. . . in all 3 discussions I can’t seem to locate the Model-Year Of this Jeep Grand Cherokee. Knowing which engine is in the Jeep would possibly help, too.
Thanks,
CSA
I’ve Seen Strange Results Of Poor Grounding Of Electrical Devices, But This May Be Too Much Of A Stretch (Grasping Straws ?).
Some Jeep Grand Cherokees Have a myriad of different electrical complaints caused by poor dashboard grounds. The two bolts (one on each end) that secure the right and left lower instrument panel to the side cowl panels are also the ground connections between the two pieces.
The mating surfaces have to make good contact, but sometimes just re-torquing (loosening and retightening) the bolts could supply a good connection. Looks like they’re really easy to access just below the dash.
I’d have a hard time believing that a poor ground here could influence the behavior of only the oil pressure gauge, but hey, I’ve seen ground problems cause malfunctions that I wouldn’t believe if I didn’t see them myself.
CSA
My husband will be delighted with your thoughts, as he has contended all along that it is a ground wire somewhere! We just haven’t been able to find it. The car is a 1999 Jeep, so it is old. It has 127,000 miles on it, and contrary to our multiple experiences with Jeeps (though we keep buying them), it has been fairly maintenance free.
I talked with the mechanic this morning, and he was really surprised the alternator didn’t work. When he disconnected the alternator, the oil gauge functioned perfectly, so we really thought that was the only issue. I am still convinced that the alternator was part of the problem, as this morning although the oil gauge went to zero and brought the check gages light on, it only did it once, and we could continue to accelerate and it went off. Prior to replacing the alternator, I had to decelerate to get it to go off.
The difficulty of trying to diagnose anything within the ten-minute “warm-up” window complicates the situation. Once the car gets warm, it doesn’t malfunction the rest of the day, even if it sits most of the day (unless it is really cold out, which it isn’t right now.)
I will have my husband check the ground wires you suggest . . . we are all ears!
I Believe They Aren’t Wires That Do This Grounding, But Rather Just Metal On Metal Contact Between The Dash And Cowl Panels Held By The 2 Bolts, No Wires.
CSA
Well, some problems are more difficult than others, Karen. It sounds like your man will go the extra mile for you and if he doesn’t mind suggestions from the peanut gallery I would suggest that if the problem persists after all grounds are verified, disconnect the wire to the oil pressure gauge and test the line voltage from the meter under the conditions that failure occur. Also inspect the wire at the connector for indications of corrosion under the insulation.
Throwing Out Ideas . . . I See There Has Already Been Some Discussion Of The Actual Oil Pressure (As Opposed To Indicated Pressure). Here’s A Link To A Discussion I Ran Across . . .
http://www.alldatadiy.com/techtips/Jeep/20060131a.html
Also, I had to put links here to your two previous discussions on this oil pressure gauge problem.
http://community.cartalk.com/posts/list/2243998.page
http://community.cartalk.com/posts/list/2241794.page
CSA
Great! You are right; we have been very loyal customers for a lot of years, and he treats us as such. He has also appreciated all of the suggestions from this forum. I suspect he will begin following this forum, as it is up his alley. I will talk with him about all of the suggestions made, and if we come up with something, will keep you posted.
As you can tell from the A+ you received, I am a former educator and love handing out A grades. I hope someone will get another one 
Very interesting. I hope it is a ground wire, as this sounds much more complicated, but it certainly is an option! Although we are going to be getting rid of the car within a year, we think this needs to be fixed before we unload it on anybody . . . so I hope we find out soon what it is. Appreciate all of your positive suggestions. Will let you know when we figure it out!
Excellent link. This is the first time I have looked at this post, I had a similar problem with my gas gauge. The computer mentioned in the link may or may not be the main computer that drives your engine. In my case, it was a separate computer called the Body Control Module. Mine is a GM so Jeep may have another name for it if it is separate.
It might be cheaper just to put in a mechanical gauge an be done with it.
Does this Jeep have a D’Arsonval meter or the digitized model that GM has developed?
I believe it is the D’Arsonval meter. If Google is right, that means my oil gauge is circular with a pointer, rather than digital, right? Mine is on the right-hand corner, circular with a pointer that goes left to zero or right to over 50 or 60.
I had a feeling the champagne cork got popped on this one a bit too early.
Perhaps a little, but I think there is more than one issue. I do believe the alternator was part of the problem, as when it was disconnected, the gauge worked perfectly. And this morning when the car was cold, it did go down to zero, but only once (as contrasted with eight or ten times on the same drive every other time). So, it is better . . . just not totally fixed. I did mention your idea but didn’t have the exact wording, so the mechanic wasn’t certain about what I was talking. He did use a voltmeter, but I need to read him your exact words. I am collecting everyone’s ideas and will take them all to him. Will let you know what we find out.
If he replaced an alternator due to a “rectifier” failure the he certainly knows about AC ripple in the DC. This firms up my idea that the alternator was replaced over some concern with the voltage regulator not rectifier.
A bit about repairs that seem to make the problem a little better for a little while, this is wishful thinking, not a repair at work.
Maybe you should disconnect the alternator again. If the problem is totally eliminated then you can narrow your search somewhat.
And D’Arsonval meters and digital meters look identical. But the D’Arsonvals are basically analog volt meters and the digitals are stepper motors operated through the computer.
I will have to ask which one I have. Interesting sidebar this morning . . . it worked perfectly. But it is very warm here today, so I don’t think the car got cold like it has been. This is leading my husband down the ground theory, since he says the dash is possibly still warm. So we are going to see what happens tomorrow, when it is cold again, and then try to figure out where the grounds are if it malfunctions tomorrow. This is similar to vet medicine, isn’t it? You know something’s wrong, but the car can’t talk back
This is a digital instrument cluster.
That would be mine!