1981 mercedes 380sl STALLING - PeachParts Mercedes-Benz Forum

dima4855 · #1 04-19-2006, 08:38 PM

Greetings once again,
An ongoing stalling problem.
The car has already had a tune up, timing is set to 5bdc, new spak plugs and wires. Changed fuel filter and all fluids.

When I am driving in the parking lot at about 1500rpms and let go of the gas pedal the car occasionally stalls. Also if nuetral you rev the car up to 1500rpms and hold it there for a few seconds and then drop it, the car will stall or try to stall.

As far as I know the Idle Control Valve has been replaced, but the vacuum line coming out of it (the black tube that's connected to it) wasn't connected to anything, so I connected it to the intake manifold (??). In addition, there is also a red sensor 3-4 inches away from the idle solenoid screwed into the intake manifold with two port for vacuum lines, one of them is is not connected. The mechanic also told me that I have problems with the vacuum lines, but I don't have a diagram because my cd's from mercedes are on backorder.

Let me know if I picture would help.

Any help or drawings are appreciated.

Any ideas would be appreciated.

dima4855 · #2 04-20-2006, 06:18 AM

I got some pictures and circled the switch and lines in question. Hope this helps?

dima4855 · #3 04-20-2006, 08:44 PM

Please see the attached vacuum diagrams. I redid my vacuum routing and vent for a test drive and it almost didn't stall. Almost would be the key though.

The only thing wrong now is the distributor advance does not hold vacuum. Could that be causing it. The advance unit bottom hose is what's not holding the vacuum, the top one holds it just fine.

Anyway the only way I can stall this thing is by cruising at 1400 rpms and dropping the gas pedal. Half the time it starts itself back up but the other times it does not. What do you think could be causing that problem?
It almost feels like whatever lets the rpms drop down gently does not work. On the modern cars I've replaced the idle solenoid to fix the problem.

Dmitri

dkveuro · #4 04-20-2006, 09:32 PM

There are other things to check first.

Cam timing...older vehicles needs checking.
Fuel pressure control unit....again, pressures need checked.
Fuel accumalator...would be checked for operation when checking all fuel pressures....rest/run/pump stall/volume...etc.

Injector/s....dribble and spray pattern.

Air flow ratio....with c/o setting screw, after all tests indicate everything working within factory spec's.

One more thing...Run the timing with out any vacuum applied set to 10 to 12 degrees BTDC at 700 rpm.
Watch for smooth advance from the mechanical advance weights and also smooth decay back to idle speed....weights wear and get irratic...they have a tendence to hang up, so settings get thrown off. Weight springs get weak and do not pull advance back to basic after engine speed returns to idle.

This help ?

PS...If memory serves...that vac' switch turns on either egr, charcoal canister or vac' advance and switches off at 50 degrees C coolant temperature. It is a vacume switch valve. If it's plumbed into the distributor advance via a three way connector then it's for emmision control.(Purge canister.).. the vac' lines for the other switch go to the control pressure regulator and the intake manifold prior to the throttle plate, it's also a 50 degrees C switch. This vac' signal causes a little extra fuel when throttle opened .

.

.

dima4855 · #5 04-20-2006, 10:51 PM

So, you're saying to do all those things (which I have never done before on any vehicle) to fix my idle problem?
How would I check the cam timing without pulling of the front cover and looking at the marks on the chains?
Fuel pressure, I don't think that I have any evidence of fuel starvation, of course I could be wrong...... There is no log during accelaration or etc..
I don't have the tools to do the fuel pressure testing anyway.

Thank you for the response.

dkveuro · #6 04-21-2006, 09:24 AM

I'm replying to your cry for help...if you don't want to check, or have these basic settings checked, all the help you may get may be usless unless these are okay.

Chain timing is checked by removing the valve covers and turning the motor over untill the timing marks align.

If you would like to be walked through the basic settings you can do, I'll try to help you, but blowing off help as too complicated tells me you may be looking for an easy fix.

Have you increased the timing to 10 degrees BTDC ?
Have you checked for false air ?

Does your idle valve connector show 12 volts dc.?

There are still other things to check but if you don't wish to do so, please save me the time helping you by saying so..

BTW.....Your post of 03-01-2006, 07:56 PM says "..............everything is working cherry"....so what's the story ?

.

Tomguy · #7 04-21-2006, 02:33 PM

If this is like MANY other MBs of its time frame, and most other m116/m117 engines I've seen, getting those vacuum lines right is CRUCIAL to running right at every RPM - it will run rich at all RPMs if it's leaking, and it will show symptoms of low idle and possibly stalling. If I pull vac lines from my car while it's running, the idle drops a lot EXCEPT if I pull the one running to the distributor. ANY manifold vacuum leak will cause a lower idle. BEFORE adjusting the timing and everything, make 100% sure all your vac lines are connected, and connected PROPERLY. After doing that, check for vacuum leaks. The intake manifold is two halves, and the seals between them can crack over time and start to leak. Spray carb cleaner around it at idle and see if it sputters or stalls or changes the engine's tone at ALL. Do the same around the injectors and throttle body. Spraying anything on the outside of the intake areas should NOT change engine RPMs or tone, if it does, you have leaks!

AFTER (And only AFTER) you are sure EVERYTHING is hooked up right, you should set the timing. If your distributor's vacuum line is hooked up to the wrong source, or if your switch for it is bad, this WILL cause your timing to be WRONG so setting it before checking your vacuum lines is like balancing bald tires - A waste of time.

Get vacuum diagrams any way you can. Someone here has GOT to have them for you!