lots of new information added (11-22-06)
additional information added (7-6-06)
Engine Starting Aid Tour
After much research, combining my own experience, the experience with others and the mass of confusing information in both early and late factory workshop manuals, factory service bulletins, training literature and various other manuals, here are some facts. This is still a work in progress but very much more complete and more comprehensive. Feel free to add information photos etc. wiring diagrams and more photos to be added soon I hope.
We can start a "tour" here to organize it for easier use. Our experienced group members will fill in additional information I am sure we have other are experts on the subject. We have volumes of information spread all over this site. Part numbers, photos, diagrams and text will be helpful collected in one place will be most helpful to others. The BBBs (early and late) have this information mixed in with dozens of other models and other subjects so sorting it all out can be a challenge even if you have the factory literature.
First of all the most important factor for engine starting is to have a good strong ignition and proper fuel supply. These items should be checked before diving into the complexities of the fuel injection system, having the engine in good tune and testing the fuel pressure and volume will often times solve starting problems.
Part descriptions can be confusing, the BBB is not entirely consistent on the terminology of these devices. Both starting devices ( intake starting valve and injection pump fuel enrichment solenoid) are actuated by a electrical solenoid controlled by an electrical relay. Engine coolant temperature sensors like the "thermo switch" and "thermo switch" sense coolant temperatures and send the feedback to the electrical relays. Some models had a "time switch which actuated one of the relays for a one second duration.
Part Descriptions
The "thermo switch" was a single terminal sensor which was used only on the earliest 230SLs and earlier sedan engines (described in the early BBB as version ll). The thermo switch was not used on any of the later versions. In fact a factory modification involved in disconnecting the thermo time switch and leaving it unhooked along with other modifications (more info. below). It functioned by providing ground (earth) to a relay at temperatures below 113 F. (45 C.).
(thermo switch photo soon here, anyone?)
The "thermo time switch", similar but different from the "thermo switch", senses coolant temperature and provides a time interval for it's feedback to a relay. Early 230SL systems, (version ll) had both a "thermo time switch" and a "thermo switch" along with two relays and a "time switch" !! The "thermo time switch" sensed engine coolant temperature and regulated the activation of these devices longer as coolant temperature decreased.
(thermo time switch photo soon here, anyone?)
The "time switch" was the little round relay mounted along side the rectangular relays. It was used on versions l and ll (230SL). Its function was to regulate the duration of the starting devices to one second under certain conditions. A time switch and wiring harness could be added as a factory modification to improve hot starting on some later W113s (see below). There are several different "thermo time switches" used on these W113 cars over the years of production. The main difference in function is the temperature range of when the device is actuated and how long (duration in seconds) it is actuated during the cold starting process.
( time switch photo soon here, anyone?)
"Relay l" and "Relay II" are standard electrical relays used to control positive current to the two starting devices. Only the early 230SL systems (version II) used both relays. These mounted next to the windscreen washer bag and brake booster along the fender apron. Don't be confused by the wiper relay also mounted with one or two of these starting aid relays.
The "Intake Starting Valve; this device on the intake manifold near right fender is most often called the "starting valve" in the BBB. It is also referred to as the Cold Start Valve (CSV). This device consists of a electrical solenoid and a valve which allows extra fuel to spray into the intake manifold at specific temperatures for starting. Here is some one's nice photo with text added by "iceberg" of the "intake starting solenoid". The W113 cars had two different size "intake starting valves" one was physically smaller.
The "injection pump fuel enrichment solenoid", was mounted on the rear cover of the injection pump. It is simply an electrical solenoid which moves the rack in the injection pump to full rich during certain starting conditions. It receives it's positive current via relay I. A second "shut off" solenoid (below the fuel enrichment solenoid) was added to the back of the injection pumps in later years it was not a starting aid. The last version, 1970 and later, had no fuel enrichment solenoid at all. Don't confuse the "shut off" solenoid on these models. Bosch had re-designed the ball valves in the injection pump and changed the intake starting valve so that the injection pump starting solenoid was no longer needed for starting.
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How They Function;
The earliest 230SLs used an early configuration referred to as "version II" in the Shop Manual. On this version the intake starting valve activates at engine coolant temp. of less than 113 F.. ( 45 C.) when the starter is activated. The injection pump enrichment solenoid activates for one second with the starter at coolant temperatures above 41 F. (5 C.). At temperatures below 41 F. (5 C.) this unit (injection pump enrichment solenoid) also activates and the activation period increases up to 17 seconds as the temperature decreases (up to 17 seconds at 0 F. (-20 C.).
A factory modification could be performed to improve starting as in version lll, by switching a couple wires and changing to the later 35 C. (95 F.)" thermo time switch".
Version lll; (includes the later 230SL. on this version the intake starting valve and the injection pump fuel enrichment solenoid both activate whenever the starter is activated. Above engine coolant temp. of 95 F. (35 C.) activation is only for one second. Below this temperature both units activate longer as the temperature decreases (up to 17 second at Zero F. or -20 C).
Two later versions were used on the 250SL and 280SL (1965- 1970) series cars which were similar but different.
Some time after 1965 the" time relay" was deleted. At engine temperatures below 95 F.(35 C.) the intake starting solenoid activated by the starter , increasing in activation period, with temperature, for up to 12 seconds at Zero F. or -20 C. The" injection pump fuel enrichment solenoid" activates at all temperatures with the starter. A factory modification (relay and small wiring harness) could be added to activate the intake starting solenoid for one second at temperatures above 95 F (35 C.).
After 1970, the fuel enrichment solenoid on the injection pump was illuminated by making other improvements on the injection pump and intake starting solenoid. The intake solenoid activates with the starter, at temperatures below 95 F. (35 C.). increasing in duration to up to 12 seconds at Zero F. (-20 C.). A factory modification (relay and small wiring harness) could also be added to activate the intake starting solenoid for one second at temperatures above 95 F.
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The easiest way to test these units is to use a test lamp on the electrical terminal of the solenoid during the engine starting process. If power is not delivered during starting, the electrical relay is not working or the "thermo time switch" is defective.
In many cases a non working relay can be restored by simply cleaning its electrical contacts.
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The very latest 280SLs were equipped with injection pumps with no injection pump starting solenoid. However, some of these injection pumps may be equipped with "fuel shut off solenoids". Be careful not to confuse the two. I will try to post pictures of the different configurations. The later BBB offers a lot of information on the later replacement pumps (later BBB 07-11/2 through 07-ll/6, and 07-16/1 and 07-16/2).
The last device, which is not actually a "starting device" is the "WRD" or the Warm Running Device" on the injection pump. It may effect cold starting if the device is stuck in the hot or lean position. This unit will change the fuel mixture and air intake of the engine at the injection pump. Engine coolant flowing through the unit changes the position of a slide valve and plunger via a "heat feeler" (thermostat). These do get stuck from inactivity. Dis-assembly and cleaning will often restore its function. Page 07-14/3 of the later BBB has some nice photos, diagrams and text on the later "WRD".
The unit is located on the top rear of the injection pump and can be identified by the engine coolant lines going to it. Listening for air rushing in the small cylindrical air filter during the warm up cycle of the engine can tell you if it is functioning. These air filters must first be checked to see if it is clear. Remove it and test it. Check the function of the "WRD" by listening for the suction at the "WRD" air filter by using a section of rubber hose as stethoscope.
Some of the earliest versions of the WRD had no separate air filter but had an air passage but had a separate air line plumbed back to the main air filter.
The early 230SLs had a injection pump and WRD which was different from the later W113 cars. The function was the same but many components were unique to these early cars.
Joe Alexander
Blacklick, Ohio
