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  #1  
Old 07-12-2000, 11:23 PM
dsantos
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Hello all,

Can someone please tell me WHERE the oil pressure sending unit is on my 1992 400E.

I don't think it is functioning since I the gauge always reads MAX oil pressue. Even during the initial start from an oil change. At no time does the oil pressue gauge move at all. Then only time is is not at max is when the car is off.

Please help.

Thanks!

David
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  #2  
Old 07-13-2000, 01:48 AM
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Join Date: Mar 2000
Posts: 528
On the right side of the engine, below the oil filter housing; has a single electrical line connected to it. Moderate failure rate; easy to replace.
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  #3  
Old 07-13-2000, 10:56 PM
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Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
Also, be VERY careful. The harness here likes to crack. I have seen a few harness problems cause this.

The sending unit is the most likely problem though.

------------------
Benzmac:
Donnie Drummonds
1991 GMC Syclone
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM
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  #4  
Old 09-13-2000, 06:22 PM
dsantos
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Thanks to all that answered the location of the sending unit. I just replaced it with a new one from the dealer. Pretty straight forward job. Now I need some more info.

When I replaced the sending unit and turned on the car, I didn't start it, just turned the key to the on position, the oil gauge read '0' for the first time I have had the car. Great, this is what I expected to see. I started the car and within a few seconds, the gauge read full oil pressure. I drove the car around the block and checked for leaks.... Nothing. So I buttoned up the job.

Well about 1 hour later, I needed to go to the store and noticed that when I turned on the car, the oil gauge read 3 still.

My question is: Is it normal to have the engine HOLD oil pressure? Is there some check valve that keeps the pressure high so there is no oil starvation during startup?

I will see if the pressure is still high after the car sits for a while, maybe overnight. But can someone please help me out here. Could it be that my new sending unit went bad afer 1 hour of use?

Thanks all!

-David
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  #5  
Old 09-13-2000, 07:18 PM
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Join Date: Jan 2000
Location: New Bedford, MA USA
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David, try this.. Disconnect the lead from the sending unit, turn on the key, check the reading, start the engine, check the reading. If it reads max all of the time, then you have another problem. May be the gauge itself or a short in the wiring. You can also try grounding the lead wire to the block. If this changes what you are seeing, then it may in fact be the sending unit. The sending unit presents a variable resistance to the gauge, however, I am not sure at which end of the scale this occurs.

------------------
Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE
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  #6  
Old 09-13-2000, 08:29 PM
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Join Date: Jun 1999
Location: Los Angeles, Calif, USA
Posts: 521
On my 87 300D (W124), the oil gauge reads MAX when the wire is disconnected.

David
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  #7  
Old 09-13-2000, 09:47 PM
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Join Date: Jan 2000
Location: New Bedford, MA USA
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OK, oops!! if I got them backwards sorry. Ground the lead first, turn the key on. The gauge should read zero. If not, problem is in wiring or gauge itself. If open circuit produces max pressure reading, then resistance is scaled from high to low, ie open=infinite resistance=max reading, not open=intermediate resistance=some other in between gauge reading, grounded=no resistance=zero gauge reading. If you get this response from the gauge, then it's wiring or the sender.
BTW, engines do not hold oil pressure after they are shut off and yes, it is possible for the sender to be defective that quickly, especially if there is some wiring gremlin at work in there..
------------------
Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE



[This message has been edited by jeffsr (edited 09-13-2000).]
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  #8  
Old 09-13-2000, 10:25 PM
dsantos
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OK,

I just got back from under the car.

Removed lead, MAX oil pressure.

Grounded lead, NO oil pressure.

So this tells me that the gauge and wiring are fine.

Its hard for me to believe that the new sender went out. I know that it was working since I had no pressure during the initial startup. Oh well. I will pull the new sender and see if there is anything plugging the opening. DAMN I hate it when this type of stuff happens.

Thanks again for all the input

-David
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