No oil pressure at idle! (1995 E320) - Mercedes-Benz Forum

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post #1 of 3 (permalink) Old 11-30-2012, 07:12 PM Thread Starter
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No oil pressure at idle! (1995 E320)

Hi everyone--

I've got a couple issues with my 1995 E320 wagon which I can't figure out. I'm not sure if they're related, either.

First, and most disconcertingly, when the car is stopped and at idle or drive, the oil pressure indicator shows 0 oil pressure. When I put it in park it goes to "1", which I believe is a normal pressure indication. When I hit the gas in idle or drive the pressure rises to the top of the scale. When I am going fast and then put the car into idle the pressure slowly drops down.

Second, there is weird behavior when the car is at idle. Specifically, a lot of surging from the engine.

There are two error codes: Mass air flow sensor and air injection system.

I've been doing a bunch of work on the car recently. Just replaced the wiring harness. Have a MAF on order. Also, I need to get a neutral safety switch because it often doesn't start when in park.

That said, I am really mostly concerned about the lack of oil pressure. I don't know what's going on. Nor with the surging at idle. Any advice is appreciated!
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post #2 of 3 (permalink) Old 11-30-2012, 07:33 PM
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Date registered: Aug 2011
Vehicle: 95 E320 Special Edition
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Ok, problem 1:
The normal oil pressure for your car during idol is 2 kpa or above. I have heard accounts of some people's w124 getting down to 1.5 kpa, but never one or less. Just my 2 cents- I yield to other members. Secondly, at any RPM's over idol the normal pressure is 3 kpa. If you are driving and it is less than 3 kpa turn off your vehicle immediately (this line is in the owner's manual for the m104). I'd recommend taking a look at your oil pressure sensor and having a look at the thread linked below. Maybe a similar problem (and solution).

For your second problem I can only offer that the "air injection" code (or secondary air injection) is an air pump the injects air (ironically) into the exhaust to reduce emissions. You should have a check engine light with both of these codes.
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post #3 of 3 (permalink) Old 11-30-2012, 08:59 PM
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Date registered: Jun 2007
Vehicle: '95 E300 DIESEL, '91 600SEL, '92 600SEL
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Factory specifies that at full engine operating temp, 3+ bar must be established before 1500rpm. All 3 of my cars do at around 1200rpm or before.

These are the things that impact the oil pressure gauge.

1) Proper oil grade and engine + ambient temp. I use 15W-40 diesel grade oil (Chevron Delo400) as the factory recommends and that is what the factory put in during assembly. At high operating temps, the gauge WILL read lower during idle. 2 of my W124s read around 2 bar at full operating temp, the other one (with the original pressure sender and the least service history) always around 1.5. At high ambient temps (ex. 100F+) it is not unusual for the gauge to sit a little bit lower. The same goes for engine that run hotter than they should (100C on the dial vs. the normal 87C)

2) Proper oil service intervals. If the service gets neglected (i.e. oil service intervals beyond 5K), the little passage that drives the oil pressure sender can get clogged giving a low reading.

3) Oil pressure sender itself. When they get old, they show erratic behavior.

4) Positive (a.k.a. starter) harness which also connects to the oil pressure and oil level sensors suffer from eco junk wiring issues. Every 92 and up W124 has this issue and the best and easiest solution is replacing the harness. Cost is very reasonable from the dealer as long as you do the work yourself.

As far the surging goes, try the new MAF first. Can we assume you went with a new Bosch MAF??? Rebuilts aren't worth the box they came in and don't last very long. Both of my gassers still have the original factory installed MAF. They hardly ever go bad unless they get contaminated (using MAF cleaner or overoiling a K&N filter for example). BUT, the throttle body suffers from the same eco junk as the wiring harness. Find the green&white tag on the throttle body (no removal required) to verify it was made in 1998 or later. If not, your throttle body has eco junk.

Last edited by sbaert; 11-30-2012 at 09:23 PM.
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