1982 240D Euro idle & oil pressure - PeachParts Mercedes-Benz Forum

indybenz · #1 05-18-2023, 10:19 AM

Hello,

Anyone help with this one? Here are two videos.

Ever since I replaced the head gasket, which included replacing the front crank seal and water pump and a few other bits, the oil pressure drops randomly at idle, usually after it's warmed up. Then lately the idle will also fluctuate, sometimes in sync with the oil pressure but other times the oil pressure will stay at 3 bar and the idle will drop very low and almost stall.

Hopefully these videos will play
https://photobucket.com/u/northy_polk/a/130a4e88-2b57-41af-a8da-daaae7b03ead/p/5272c917-6553-426f-881e-12212de3f90d
https://photobucket.com/u/northy_polk/a/130a4e88-2b57-41af-a8da-daaae7b03ead/p/5272c917-6553-426f-881e-12212de3f90d

Sugar Bear · #2 05-18-2023, 02:44 PM

What is the ambient air temperature? What weight oil?

1 bar oil pressure at hot idle is common. The gauge should peg as soon as it is accelerated.

Good luck!!!

t walgamuth · #3 05-19-2023, 11:09 PM

verify oil supply in engine.

indybenz · #4 05-24-2023, 11:10 AM

Quote:

Originally Posted by Sugar Bear

What is the ambient air temperature? What weight oil?

1 bar oil pressure at hot idle is common. The gauge should peg as soon as it is accelerated.

Good luck!!!

Not sure the exact temp but it fluctuates this time of year in Indiana 50-80F. The air temp does not seem to have any impact one way or the other. The engine temp, however, does seem to have an impact. When it is warmer the oil pressure and idle are both more erratic.

The oil pressure is always at 3 under load, but at idle it varies from 1.5-3 and goes up and down erratically.

Oil is 15w40 of some sort. I change the oil frequently and often get what is cheapest 15w40.

indybenz · #5 05-24-2023, 11:11 AM

Quote:

Originally Posted by t walgamuth

verify oil supply in engine.

There is oil in there.

indybenz · #6 06-06-2023, 09:29 AM

The car still has this surging/dropping idle issue. Anyone else care to take a guess? The videos in the first post show from outside and inside. Thanks!

*UPDATED the links so hopefully vids will play now

hercules · #7 06-09-2023, 08:17 PM

Pop off linkage to injection pump, ck. if pump is on stop.
Ck. fuel pressure.
How much fuel is in tank?
Fuel lines connected to proper places.
Oil by pass valve could be sticky
Water in fuel or algae blocking fuel strainer.
injection pump inner adjustments.

Diesel911 · #8 06-10-2023, 01:55 AM

1.5 bar at hot idle is an OK oil pressure in the factory service manual.

The question is it the engine speed that is causing the fluctuation or is the engine speed reacting to some load that the oil supply system is putting on it and bogging the engine down.

Way back in 2007 when I first became a member, I believe I read something about sticking oil pressure relief valves in the oil pumps. I also read the relive valve springs occasional break.

If you have an oil cooler there is a thermostat in the oil filter housing as well as the mentioned oil bypass valve.

The fuel pressure relief/overflow valve controls the fuel supply pressure. In time the springs become weak, and they don't hold pressure well at idle speeds. Also, a ball bearing is used as a valve. If here are rough or rusty portions on the ball, you get erratic fuel pressure.

The fuel supply/lift pump on 240Ds have disc valves in them. It could be they are worn there is build up on the tiny springs.

Air leaks can cause surging as well as the mentioned clogged filtration to include the tank screen.

indybenz · #9 06-13-2023, 11:16 AM

Ooft.

Looks like I have some investigating to do.
1. fuel pressure relief/overflow valve controls the fuel supply pressure
2. oil pressure relief valves
3. air leaks are unlikely from my experience but won't rule that out
4. I put a larger capacity fuel filter on and eliminated the small 'primary' fuel filter and the problems started after that so perhaps should go back to the original set up.

indybenz · #10 09-06-2024, 10:47 AM

I realize this is an older thread but I'm attempting to revive it as I've not sorted this out yet.

Could something that happens be related to this? Sometimes, I'll check the oil level on the dipstick when the engine is cold and it reads lower than I know it should because I know there is oil in there as I've checked it at another time and it reads the amount it should and I know that much oil hasn't just disappeared, and perhaps the oil is 'stuck' in the oil filter housing and there is a valve in there that is either stuck open or closed? Perhaps someone mentioned this already and I did not recognize the language used to describe it. Thanks!

indybenz · #11 09-07-2024, 04:26 PM

So I removed the fuel pressure relief valve and it is clean and the ball and spring are working and clean and no rust on the ball. I put it back together and same issues. It idles erratically for 3-4 minutes and then, all of a sudden, it just idles normally! Something to do with it being warmed up. But then I can drive it, and come to a stop, and it will start the issues all over again intermittently.

I did notice that when using the primer pump, it was leaking diesel all over like crazy. Not sure if there might be an air leak due to that but perhaps I need a new one of those. Add it to the list haahhaaha!!!

hercules · #12 09-08-2024, 02:31 PM

The hand pump can suck in air and cause idle changes ,replace it, retest, it is needed,
may just fix your problem

indybenz · #13 09-09-2024, 12:39 PM

Here is the rough idle

3 minutes or less later...it is smooth!

I have also ordered a lift pump rebuild kit that includes a new old-style primer pump. I'm not convinced this is the issue....but really have no clue!

hercules · #14 09-09-2024, 01:46 PM

Engine surge, can be caused by injection pump not on idle stop, pop off linkage, set idle
making sure not too slow, readjust linkage making sure pump remains on stop.

indybenz · #15 09-09-2024, 04:14 PM

Quote:

Originally Posted by hercules

Engine surge, can be caused by injection pump not on idle stop, pop off linkage, set idle
making sure not too slow, readjust linkage making sure pump remains on stop.

I don't 100% follow.

I have removed the 'piston' that was connected to the pump that helped control the idle. It made no difference when I did.

I also removed the idle cable that goes to the dash as it was inoperative. It is still on/in the car but disconnected.

I have adjusted the idle using the screw on the back (firewall side) of the pump on this car. You loosen the larger 13mm nut, then you can use an 8mm wrench to tighten or loosen the smaller part that sticks out.

There is a chance that I have buggered up something along the way, but it has not always done this idle hunting/surging, only after doing the head gasket has it behaved this way.