Oil Gauge Problem revisited

Several weeks ago I wrote about my oil gauge, and I received some great suggestions from this forum. At first I thought the problem was solved, but apparently not, so I am appealing once again to your collective minds as to my next steps.

To recap:

When I start my car (and it is below about 40 degrees) and accelerate, the oil gauge drops to 0, causing the check gauges light to illuminate. I take my foot off the accelerator and it goes up. This continues for about 15 minutes or until the car reaches about 210 degrees; then it runs perfectly until it cools down. We have tried:

1. Replacing the sending unit (twice)

2. Cleaning the sludge out of all of the areas around the unit;

3. Replacing the alternator (that appeared to work for awhile, but not now)

4. Checking all contacts

5. Checking all grounds (just did that yesterday).

It is cold today, and when I picked it up from the shop, the gauge went to zero every time I accelerated until the car was heated. It has been fine since.

The car is a 99 Jeep Grand Cherokee with 127,000 miles on it. If this were your car would you:

1. Replace the gages?

2. Replace the oil pump?

3. Do something else, and if so what?

Thanks for any help you can give.

Try an after market gauge…for experimental purposes if nothing else

It is a 12 year old car. Unless it sounds like it has no oil when this happens ( it would get clattery ) I would put a piece of black tape over the light.

At this point my main goal would be to get this out of the false/true report area. You can ask an automotive electrician “how clean is my DC” (he will know you are looking for ripple). In reality with the new alternator things should be good. I have done an extensive TSB check (meaning several years above and behind yours also) and not a hint of any known technical issue provided by EBSCO (EBSCO is where I go to look for TSB’s). After it is determined that this warning is in error I would give the schematic a really good looking over to see if I could come up with an idea of what would have to be failing to cause this situation. Let me look at what I have as a schematic and see if there is a BCM involved(EBSCO schematics are pretty brief). If we are lucky it is and if we keep getting lucky the oil pressure can be displayed on a scanner and with the scanner hooked up and the failure present we can see if the scanner value changes along with the dash gague. Yes it does sound a bit time consuming.

At this time I can’t say if the gague is telling us the truth or a lie,it could go either way based upon what information you have provided.

EDIT: Have you told us if this is the 6cyl or the V-8? I do not have a wiring diagram on the 6 until 2001 but I do have one on the V-8 in 1999. The oil sender reports to the PCM and of course the BCM talks to the PCM,a scanner should be able to see the oil pressure.If this is the 6 cyl I can not say the same thing until the 2001 year model.

From your description it sound like a loose connector or break in the wiring. The engine moves left/right when you use the accelerator, (accel/coast) moving the engine wiring harness. Connectors and wiring are also affected by temperature. The oil pressure sensor connector (P/N 5014007AA) should have been replaced on the second visit just to insure a good connection. If a break in the wiring can’t be found in a short amount of time new wires could be run. This would take less than an hour and rule out the very basics of an oil gauge problem before anybody starts throwing computers or an instrument cluster at the problem.

A mechanical oil pressure gauge should have been put on this engine long ago to establish beyond a doubt whether or not this is a legitimate oil pressure problem. Since it apparently hasn’t been done yet, it shoud be the first step moving forward. And it should be done very soon.

This involves simply installing a mechanical oil pressure gauge temporarily, by inserting a “tee” where the current sending unit is, so that both the original sending unit and a separate mechanically driven gauge can be installed. The mechanical gauge relies on nothing electrical, uses nothing but oil pressure to drive it. This way you’ll know beyond any doubt if you really do have oil pressure problems. Up until now you’re still guessing if this is oil pressure, electrical, gauge or sender. If you have legitimate oil pressure problems, you need to know that and get that resolved before you render your engine unrepairable.

Thanks for all of the suggestions. I will visit with the mechanic working on this. I believe (but don’t know for sure) that he ruled out that there is actually an oil pressure problem, but I don’t think he put a mechanical gauge on it. I will discuss that, along with the other suggestions. We hope to get rid of the car this summer, but can’t sell it or trade it until this problem is fixed. And we are running out of cold weather in which to test it . . . so will let you know what we find out!

Oh, and by the way, it is a V-8 engine.

The mechanic did say that he has put a mechanical gauge on it twice, both times indicating good oil pressure. We discussed the wiring harness idea. He is thinking perhaps it is the gauge panel, but doesn’t think we should pay that much for a car as old as ours. So we are working on the new wiring idea . . . will keep you posted.

I strongly discourage “hacking up” your main underhood harness (or any harness for that matter). You mechanic is most likely correct with his cluster diagnosis, you could figure it out with a scan of the BCM, but if you feel better hacking up your harness, it is not my business.

You advice has been solid so far, so I will certainly pay attention. He didn’t seem to like the idea, but was willing to look at it if nothing else worked. Unfortunately, once it gets warm, we won’t be able to replicate the problem after it warms up. So I may never find out what the problem actually is, though he is leaning to the instrument cluster as the problem. I may take it to the Jeep dealership, just to check with them. Maybe they know something that none of the rest of us know.