Help with idle circuit

[Ian]

I have a 1971 280SL a 113.044 chassis with a 130.983 engine. I have straightened out all of the fuel injection and it runs very good.
I I’m working on the cold starting. I have it all figured out. Except for the high idle. My vehicle has the two black boxes with a switch over valve mounted behind the L/S headlight. It uses a temperature switch on the lower part of the engine block behind the injection pump.
I have fixed the system back to its original working order. It uses a single wire to the temperature switch in the block that I described
above when the wire is a closed circuit to ground the idle is high when the wire is an open circuit the idle speed comes down to normal. This is all done with
the vacuum switch over valve controlling the ignition timing and it works perfect. My problem is the temperature switch in the block is stays open circuit because the switching point is 17c equal to 60F. This causes the vehicle to constantly have a normal low idle when I need it to be high while warming up.     We are located in south Florida and the temperature is almost always above 60f so the switch constantly stays open. What I need is a temperature switch that starts off closed to ground and opens at 30c equal to 88F or close to it. Also could use help in the way of a wireing diagram for the idle solanoid on the intake manifold.

[glenn]

Ian, Welcome to 'The Wonderland of MB Fuel Management and Pollution Control'.  Your '71 probably has pollution control.(?)   The car is probably not in the same state it was when it left the Homeland.  The thermal expansion, timing, condition, etc of all the parts have changed.  Circuits could have been altered.  The WRD, CSV, start relay, pollution circuits, FIP shaft adjustment, linkages, etc are all suspect.  With all due respect for our Forum(the best source, period, of help), we have yet to come up with a single, all encompassing solution method.  WE can help, bit by bit, of info.   First, 'idle solenoid on the intake manifold'- you mean the CSV?  Next?

[Ian]

Please define what WRD, CSV stand for. I have been working on Mercedes since 1979 at the dealership my experence is very strong starting with CIS fuel injection i have worked on early 1974 Mercedes EFI with trigger points but am limited when it comes to mechanical fuel injection and all the old timers who i have worked with that would be able to help me are dead. i know what im doing i just need some guidence. This 1971 280SL is in exalent condishin and has never been tampered with it has all of the origanal equptment. So just a little explanation on how the idle solanoid works and what parts work with it.

[66andBlue]

Please define what WRD, CSV stand for. ....

Here is a short list of abbreviations:
http://www.sl113.org/forums/index.php?topic=16112.0 - see first entry!

[stickandrudderman]

Use the search Luke, sorry Ian.
Don't make the mistake of assuming that the contributors on here know less than you because you are a professional. You'll find them very helpful and very knowledgable and that knowledge is openly shared rather than being closely guarded like it would usually be within a dealership environment.

[pagoden]

Welcome, Ian -

When you mention anything electrical on the intake manifold we think Cold Start Valve, a spritzer to give a fuel shot like that from a carburetor's accelerator pump, powered by the IP as long as the starter circuit energizes it and a timer/thermometer allows it.  CSVs often leak into the combustion mix as a result of needle valve issues, not often the electrical circuitry.  The only other solenoid-like device on the intake manifold would appear only on cars with automatic transmissions, an early idle-speed maintenance device energized when the drive gears are engaged but not in neutral.  This one is a solenoid.
I won't try to play expert much beyond this, as my experience is pretty much limited to my own 1969 model with a little different, and nearly as complex, circuitry than yours.  I made a living as a mechanic myself, but it was a long time ago, quite a ways from here and not on this iron.  There are guys here who can run rings around both of us on this stuff, and the collective knowledge -- both written and remembered -- is considerable.  I agree with Glenn: for the mechanical injection era, there is likely no better place on the planet than this group.  But we don't often get folks with your type of experience, and some of the best information around here -- especially that which is in people's heads -- is packaged differently than you're probably used to, so it may take a bit of getting used to on both sides.
I see Alfred has a link to terminology for you, a good beginning.  Stick said it well and he's a pro in his own right.  Settle in Ian, take it easy, and welcome.

Denny

[twistedtree]

Ian, if I follow your original post correctly, it sounds like you have done an excellent job of returning your car to it's original configuration and set up.  Most people rip out all the pollution controls rather than make them work correctly, so I applaud your approach.

That said, the control I think you are working on impacts timing advance by switching the vacuum on and off.  I was under the impression that it was strictly about emissions, and not in any way an idle speed control.  If it appears to be the key to proper idle speed, then I think you still have another problem lurking somewhere.

Take a look through the linkage tour and other parts of the Technical Manual on this site.  It includes a wealth of info that I think will help you.

[glenn]

OK, First the CSV solenoid is powered by 12v.  It opens a valve squirting gas from the electric fuel pump in the rear of the car(not the FIP) into the intake manifold feeding all 6 intakes.  It squirts on 'Start' until a temp/timer scheme(different on different years/cars) expires.
   I've worked on CIS Bosch stuff.  Totally different, but useful.  Mechanical injection systems a la 1963-1971 are different.  Mostly meaningful- there is no control feedback such as rpm, no computer versatility, lambda, etc.  
   Not to insult you, but...  the humble opinion of most of us on this Forum who have been humbled by our initial over- valuation our 'superior knowledge' is legend...Pride goeth before the fall.  I've had my share of humble pie.
   Sorting out your situation will add to your and our collective knowledge.  Welcome

[Ian]

Guys, so far each and every one of you has given me great insight into my problem. This web site is the best thing I could have found. What a wealth of knowledge! The dealership, with ties to Mercedes and even the classic center didn’t have near the depth of resources I have found on this site. We have access to all of the Mercedes literature. The old stuff that is offered on Star Tekinfo has been scanned in to the computer by Mercedes. When you view it, you can't even make it out it's so poor it becomes useless.

Ok now for my issue. The real problem I’m looking for is a high idle until the engine warms up. I have read a lot of stuff on this web site and understand it very well. What I thing is wrong might not be the real problem. I’ve learned on this web site that the 17 degree switch and the vacuum switch over valve that controls the vacuum to the ignition distributor for retarding and advancing the timing which raises and lowers the idle speed. This function is for emissions not for warming up the engine. I know the system itself is working properly because I have replaced some of the components. When I ground or open the wires on the 17 degree switch the vacuum changes and so does the idle speed. If I start the engine with the wire grounded it has a high idle it starts and runs perfectly. If I open circuit the wire at the 17 degree switch once the engine warms to 60c or above. The idle comes down and the engine sounds like a wrist watch. What a sweet sound. The younger technicians are amazed to see how nice this thing sounds at the tail pipe. I though all along this was the way it was suppose to work, but after reading the below paragraph I’m not sure and need HELP. IS THIS THE COLD HIGH IDLE CIRCUIT OR IS THERE SOMETHING ELSE?       



















 

[ja17]

Hello Ian,

Since you are having warm up running problems. Check the WRD (Warm Running Device). This is comparable to a Warm UP Regulator on a CIS car except it is all mechanical.  It is located on the top rear of the injection pump. It has a round canister attached which is a air filter. Do not confuse the barometric compensator with this. The barometric compensator is the larger  round can. The air filter is the smaller round can which is mounted sideways.  This WRD unit also has two water coolant hoses attached to it and one air line attached to it which snakes around behind the engine and eventually makes its way go the intake manifold (near the left shock tower) where it feeds additional air into the intake manifold during warm up. Engine coolant circulates in the unit as the engine warms. A "heat feeler" thermostat type device opens and closes the air passage for the additional air as well as changing the quantity of fuel to the engine during the warm up period.  These units get stuck from long periods of storage. It is easily diagnosed and fixed. Diagnose the unit by removing the small round canister (air filter) and observe that air is sucked into the assembly while the engine is cold and also observe that the rush of air stops after the engine is fully warm. After you complete this check we can move onto other possibilities. We can try to post some photos for you while we wait to hear back from you.

Keep us up to date. Its nice to have another "tech"  on board even though you are from a more modern generation!

[Ian]

Joe,
This was one of the first things I remembered from watching the old timers. When I started out we use to have an old Hungarian guy, Eugene and man he knew these old M130 engines. I worked under him years ago. He would do all of the older stuff and give me the newer ****. Well not that new now but he did teach me some good stuff. This warm up thermostat was one of them. When cold it is sucking good. As the coolant temp comes up it starts to shut down until it is fully closed. I’m so puzzled at this point if I only had a coolant switch that would be grounded up until about 60c and then go to an open circuit my trouble would be history. I could screw it in where the 17c switch is in the block and my engine would have a high idle when first started. When it reaches 60c the idle speed would drop and I would be all set. What do you think? Every hear of anyone doing that? Can some one get me a part number for a sensor ? I’m getting desperate!!!!!!!!!!!!!

[twistedtree]

A couple of things:

- Which distributor do you have?  Stock would be an 062.  We should be clear which one we are dealing with.

- Where exactly is the thermo switch that you are working with?  From a quick read of the BBB there should be a 100 C switch (seems high, but that's what it says) in the thermostat housing (not the block, and not the head) to control advance and hence idle speed.  Here's the passage from the BBB.

After the adjustment, slip on cable connector again
and check vacuum ignition change-over from retard
to advance, by grounding the 100 C thermostatic
switch at the thermostat housing. The speed must
then increase from about 800 to 1300 - 1500 rpm.

- It sounds to me like you are hooked up to a switch that is a) the wrong temp rating, and b) in the wrong location on the engine?

[glenn]

Ian, Does your 983 head(later version) have the two tapped holes in the head at No. 6 plug for, 1) the dashboard readout temp sensor and 2) the temp s/w?

[twistedtree]

Ian, have you checked out this section of the Technical Manual http://www.sl113.org/wiki/Electrical/EmissionControlSystem

[Benz Dr.]

There are two thermo switches on this version. The one on the thermostat housing controls ignition advance when the engine gets hot. grounding this switch will make the ignition advance below 2,200 RPM or at idle speed.
The other switch advances timing when the erngine is cold to aid cold running. It shuts off at a fairly low temerature and will be ble to hear the RPM's drop when it does. Engine will run about one minuet before it switches.

[Ian]

Dr.Benz,
You nailed it!!!!! You have the perfect wording for the problem I have. I have copied and pasted it below for everyone to read.

(The other switch advances timing when the engine is cold to aid cold running. It shuts off at a fairly low temperature and will be able to hear the RPM's drop when it does. Engine will run about one minute before it switches.)

Ok now I need some of the true thinkers to help me with modifying this circuit. The other switch that Dr Benz is talking about is the 17c switch in the engine block on the left hand side right behind the injection pump. It too has control over the vacuum to the distributor. Like Dr Benz says it shuts off at a fairly low temperature you will be able to hear the RPM's drop when it does. Engine will run about one minute before it switches off.
 
THIS IS MY PROBLEM TO A TEE. IT SHUTS OFF TO EARLY. REMEMBER THIS 280SL LIVES IN NAPLES FL. BUT IT STILL  NEEDS TO HOLD A HIGH IDLE FOR AT LEAST FIVE MINUTES. IF I COULD ONLY REPLACE THE 17c SWITCH WITH ONE THAT IS 30c MY PROBLEMS WOULD BE HISTORY. ANYONE THAT MIGHT KNOW A PART NUMBER FOR A SWITCH THAT WOULD HELP ME? 

[twistedtree]

I think you are fixing the wrong thing.  The other contributor to fast idle is the Warm Running Device.  It sounds like the ignition advance controls are all working properly, so if the warm up idle speed is still unsatisfactory I would think that the WRD isn't contributing as much as it should to the fast idle.  Its progression relative to engine temp can be adjusted with shims inside the WRD between the heat feeler and the valve spool/plunger.  Removing shims will open it up more and cause more fast idle at lower temps.

[pagoden]

And the WRD is adjustable for the length of time of it's contribution to warmup running as well.  Maybe it's dropping out too soon.  I think ja17 was going to get into that next.