Ackkkk! How do I replace the Oil Pressure Sending Unit - Page 2 - Mercedes-Benz Forum

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post #11 of 32 (permalink) Old 06-30-2011, 02:40 PM
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The logic behind your thinking is correct, but the execution is off.

If you look in the right places, you can get genuine MB parts at discount prices.

If you're comparing to a domestic car, then yes there will be a adjustment period when it comes to parts pricing. However, UNlike a domestic car where the parts become unobtainium after 5 years or so (a.k.a. no longer available) parts for these cars will remain available for a long, long time.
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post #12 of 32 (permalink) Old 07-06-2011, 03:51 AM
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Smile not so easy

after 3 different attempts to locate my sending unit (and some research in between each attempt) i finally found it. (1995 mercedes E320 w M104 engine)

that thing is crammed in the cramhole! (dodgeball anyone?)

someone mentioned that getting the wire on and off would be hard. It was very hard to get off, not that bad getting on. really difficult to pry a screwdriver where you can't see. speaking of seeing it i do agree you can see it somewhat better from the top of the car. it is behind/ under/ more toward the center of the car from the oil filter.

i have a very long 17" wrench, which didn't help as there was no room to turn it. in the end i actually made the final tightening push from the top. that wasn't easy as you have to be careful of wires and hoses.

thanks a BUNCH for everyone's help on this.

also - look out for the other wire that needs to come out just so you can get a wrench on this thing from underneath.

now my oil presure gage isn't bouncing all over, it's just pegged at 3! onto the next troubleshooting task. Oil pump? going to start with scrubbing the engine ground cable and re-connecting w some electro static grease.
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post #13 of 32 (permalink) Old 07-06-2011, 03:55 AM
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It will stay at 3 for about 15 min, If its staying pegged longer than that may see if the wiring harness is shorted/degraded/cracking or your new unit is bad. That happens quite a bit.

Good Luck.
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post #14 of 32 (permalink) Old 07-06-2011, 04:11 AM
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interesting. it stays at 3 for 15 minutes? then what happens? does it just start giving a good reading?

i didn't get to really test drive it. it's too late. that and when it started at 3 the "good feelings" of a job well done killed any incentive to properly test drive at midnight.

it's got a good (newer/ replaced) wiring harness. defective replacement part is a good explanation. hadn't thought of that. thanks
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post #15 of 32 (permalink) Old 07-06-2011, 10:52 AM
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The wiring harness which connects to the oil pressure sender, starter, etc is called the positive harness.

While your car likely has the replacement engine wiring harness already installed, the positive harness is often overlooked. R&Ring the oil pressure sender with the original treehugger positive harness will usually render it beyond repair. Looked for cracked insulation on the small wiring loom that goes down/around the oil filter cap.
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post #16 of 32 (permalink) Old 07-08-2011, 12:41 AM
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positive harness looks to have been replaced too. wich is great. except my oil pressure is still pegged.

i'm going to check to make sure that the pinhole on the valve cover isn't blocked. i saw that in another post.

what else could be causing such a high oil pressure reading?
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post #17 of 32 (permalink) Old 07-08-2011, 08:51 AM
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"what else could be causing such a high oil pressure reading?"

migraines

1999 ML320

the oxidizer...
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post #18 of 32 (permalink) Old 12-08-2015, 03:55 PM
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Quote:
Originally Posted by kvorka2003 View Post
..............
i'm going to check to make sure that the pinhole on the valve cover isn't blocked. i saw that in another post.

what else could be causing such a high oil pressure reading?
Landed here searching to fix strange movements in my oil pressure indicator needle on dash... anyone know of a "pinhole" on the valve cover (mentioned prev post here)....??? M104 engine. Thanks!
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post #19 of 32 (permalink) Old 12-08-2015, 06:41 PM
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No knowledge of a pin hole on the valve cover of a M104 or how it would have anything to do with a jumpy oil pressure gauge. Has the lower harness on the car been replaced?
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post #20 of 32 (permalink) Old 12-09-2015, 03:46 AM
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if the wire to the oil pressure sender is BROKEN and disconnected, it reads always pegged at 3. my wife's E320 wagon came that way, and I drove it quite gingerly for a couple weeks til I got under there and fixed that stretch of crumbling corroded wire, and phew, her oil pressure is fine as was the sender... maybe 1.5 on a hot day with a fully warmed up engine at idle, and immediately goes to 3 with any RPMs at all....

the 1 pin plug on the sender was pretty easy to diassemble and solder a new stretch of automotive oil-resistant wire to, which I spliced onto the existing harness where the original wire wasn't disintegrated. this sender is on the back left corner of the engine, directly below the oil filter.

if the wire is shorted to ground, it will always read 0, btw.

the lower harness probably should be replaced but everything else seems fine, so cross-my-fingers-and... I know I know...

. . . . . . . . . .
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