QUESTION: Why stalling when oil pressure drops when car comes to rest

[Fdevita]

Tried searching and while there are a lot of posts on the subject I am not sure they are specific to what I am seeing, so let me try and please let me know, maybe my question has already been answered. Thanks in advance

1967 230SL Automatic.  Recent tune-up, changed points, plugs about 1,000 miles ago.  81,000 miles. Has reproduction fuel pump, most everything else is original.

Engine runs strong, oil pressure pegged when running in gear, no overheating issues, heat gauge steady.

After the engine wars up and runs for 15 - 20 minutes, especially on a warm day, when the car comes to rest, the oil pressure drops and the car stalls. Stalling occurs in gear, if I put it into park or neutral, the old pressure stays pegged and constant.

Fuel issue or something else likely?

[Cees Klumper]

Sounds like your idle speed solenoid is failing. That's the electro-magnetic widget that raises the idle speed in automatics/AC cars, over time they lose their 'oomph'.

[Fdevita]

Thanks Cees,

I will reference the linkage tour and give that a try and see what happens.

Is there a way to test to see if the idle speed solenoid is working correctly?

[Cees Klumper]

What you should see when you put the car in gear, with the engine running, is the solenoid engaging and pushing the linkage such that the idle RPMs are maintained at the same level as when the car was in neutral. The solenoid should be adjustable. I had to replace my solenoid a couple of years ago (expensive) when it had lost its 'strength'. It was still engaging, but not pushing the linkage far enough. Good luck with the diagnosis.

[Benz Dr.]

I would check the ignition timiing. If it's late the engine will stall in gear at a stop light even though everything else is working normally. You should have at least 38 degrees full advance by 3,000 PRM.

[Fdevita]

Thanks Cees but I think I can now rule out the CSS as the culprit. With an assistant with their foot not he brake and car in gear, I check that the CSS is operating. However, the oil pressure drops and car stumbles and eventually stalls regardless of whether the CSS is fully extended or not extended.

I also checked all the linkages while it was idling at 8,000 rpm is was running rich so I adjusted the Venturi stop screw. I then readjusted the linkage rod from the injection pump to about 237mm rather than 233mm to get back to 8,000 rpm idle with   In so doing, the CSS is more engaged than it was previously; when the rod was 233mm, the rod pushing the CSS stop needed to be at its furthest adjustment and still barely made contact.

Distributor is clean, plugs are clean, starts and runs with no hesitation at all.

Thanks Benz Dr. , I will check the timing in next day or two and report back.

Has there been anything like these symptoms from fuel pump or fuel filter?  I ask because I had a full tune up done several months ago (about 1,000 miles) by an older mechanic who had several pagodas and seemed to really know his way around them. And the PO had this issue before the tuneup and linkage adjustments, etc. and the car has a reproduction fuel pump and I have not replaced the fuel filter yet.

thanks

[stickandrudderman]

The oil pressure is dropping as a result of the engine stopping. It is not the cause of the stopping.
Read the linkage tour again.

[Benz Dr.]

Go back to the things that you recently worked on and in many cases this will be a clue of what to look for. I would check the dwell angle of your points and timing. It may very well be a fuel issue but until you rule out any ignition problems first you will chase your tail for a while.

[Fdevita]

OK, will do

[ctaylor738]

You can also try going a couple of clicks richer (clockwise) on the idle adjustment on the pump.  The engine may not be be getting enough fuel to keep in running in gear at a stop. 

You might also check that the throttle position switch is working properly.  Easy - turn the ignition on, you should hear a click.  Depress gas pedal, you should hear a click.  Release pedal, you should hear a click.  All this is the transmission solenoid moving from "idle" to "driving" position and back.

Cheers,

[badali]

I had a similar problem and it turned out to be the points.  If they are too close then it ran well until your foot was off the gas.  I set them a 16 thousandths and now it runs fine.  Too close of a gap made it run bad and lower idle.

[Benz Dr.]

Idle speed on our cars is a combination of air, fuel, and timing. Get any one of these wrong and it won't idle properly. Point gap adjustments change your ignition timing and since you changed the points, this is the first place I directed you to.