Oil pressure reading 0 (but it does have pressure) - PeachParts Mercedes-Benz Forum

pawoSD · #1 09-19-2007, 11:04 AM

A little over a week ago I replaced my old dying oil pressure sender with a brand new one from Meyle. Replacement worked great immediately, 2 bar at idle, pegged to 3 right away with throttle....etc. Until this morning. Started the car up. Sat at 0. Opened the cap, sure enough, oil squirting away. So I drove to work, when I got there I wiggled the connector on the sender, no go...still dead at 0. Perhaps the connector needs service, but other than that, what could have happened. It worked last night when I shut the car down, now today its dead?

I'll have to look into the connector later, but if thats not it....could the new sender have fried?

pawoSD · #2 09-19-2007, 11:48 AM

Anyone?

#3 09-19-2007, 11:57 AM

Can you reach the contacts on the sender and see if the resistance changes with oil pressure? It's possible you received a bad sender.

rrgrassi · #4 09-19-2007, 12:07 PM

Do what Craig said, and also check the wiring to the guage and the guage itself.

Johnt49 · #5 09-19-2007, 12:56 PM

Try removing sender wire & shorting it to ground with key on. If gauge pegs, it's a bad sender. If it doesn't move, bad wiring or gauge.

pawoSD · #6 09-19-2007, 08:09 PM

Quote:

Originally Posted by Johnt49

Try removing sender wire & shorting it to ground with key on. If gauge pegs, it's a bad sender. If it doesn't move, bad wiring or gauge.

Awesome, I never even thought of that. I will try it. Thanks! They'd better give me a new sender if it is indeed bad.

I'll also check the sender itself with a multimeter and see if the resistance changes....

DZL_Damon · #7 09-19-2007, 08:23 PM

????? Mine is mechanical... whats all this about a sending unit and wires.... is this an SD thing?

kerry · #8 09-19-2007, 08:40 PM

Quote:

Originally Posted by DZL_Damon

? is this an SD thing?

Yes. Also an MB van thing.

lonewolftek · #9 09-19-2007, 10:07 PM

Yep, SDs have electrical oil pressure gauges and speedometers.

My '83 does the same thing, 0 bar reading at idle and up to 2,000 rpm, then it pegs and jitters around for a while. I know I've got good pressure, based on hooking up a mechanical gauge in place of the sender.

PawoSD, have you switched to, or are you using, synthetic oil in your SD? I noted that my gauge only started acting funny when I started using Amsoil.

pberku · #10 09-20-2007, 08:30 PM

Quote:

Originally Posted by Johnt49

Try removing sender wire & shorting it to ground with key on. If gauge pegs, it's a bad sender. If it doesn't move, bad wiring or gauge.

Actually on these cars its the other way. If OPEN circuit, then gauge pegs at "3". If SHORT circuit then gauge show "0"

pawoSD · #11 09-20-2007, 10:24 PM

Quote:

Originally Posted by pberku

Actually on these cars its the other way. If OPEN circuit, then gauge pegs at "3". If SHORT circuit then gauge show "0"

??

Soo......when I put it to ground it pegged, but when I released the ground it stayed pegged.....turned the key off....it went back to 0....turned key on, stayed at 0. Grounded it, pegged to 3.

Sooo....is something wrong with the gauge or the sender based on that? Shouldn't it have gone back to 0 when I removed the ground?

pberku · #12 09-20-2007, 10:36 PM

Quote:

Originally Posted by pawoSD

??

Soo......when I put it to ground it pegged, but when I released the ground it stayed pegged.....turned the key off....it went back to 0....turned key on, stayed at 0. Grounded it, pegged to 3.

Sooo....is something wrong with the gauge or the sender based on that? Shouldn't it have gone back to 0 when I removed the ground?

From your description of events its not possible (at least for me) to tell what's going on. What I would do, is disconnect the plug at the gauge, and put an Ohmmeter on the wires leading to the sensor. I would then measure the resistance If open circuit then you have either a defective sensor or an open in the wiring.

In that case the gauge would have pegged at "3" If you have a dead short, then either a defective sensor, or a short in the wiring. In that case the gauge would have stayed at "0". If that checks out ok, I would then start the engine and see if the resistance to the sensor fluctuates when you rev the engine. If it does, then that's normal and I would then assume that the problem is with the oil gauge.

pawoSD · #13 09-20-2007, 10:47 PM

Also what I don't get is how it happened. Couple days ago, drove home from work, shut car off, was working fine when I did, next morning, dead gauge. Odd.

lietuviai · #14 09-20-2007, 11:46 PM

My 87 300D had an electric oil pressure gauge. I had problems with it too. It would drop to zero sometimes or not function at all or it would work erratically. Replacing the sender did nothing. A good whack to the top of the gauge pod would get it to work normally for a while. My guess you have something faulty with the gauge itself.

lietuviai · #15 09-22-2007, 12:44 AM

Good luck!
If that doesn't work, try giving the gauge pod a good smack.