It looks like the posts are working again,
Hello Dana,
I agree with Bob, the relay is most often the problem.
Check all your fuses first. Do not depend on just visual checking, use your test lamp. These fuses tarnish on their ends and sometimes loose connection, even though they are not blown.
Tools;
You will need a 12 volt test light or a voltmeter and a jumper wire.
The System;
These mechanically injected engines have four or five versions of starting systems. The exact location of the relays varies depending on year and W113 model type.
There are two or three relays often nestled together. These should be in the engine compartment, between the brake booster and the left fender on the W113 cars. One should be for the intake starting valve, sometimes another for the injection pump starting solenoid and often times a round time relay for the activation period of the starting device.
Function
This is how the cold starting systems work on your 1969 model year 280SL;
During cold starts (below 95 deg. F. eng coolant temp.) The intake starting valve should activate for a time period. The time period increases with decreasing coolant temperatures. The time period can be up to 12 seconds max. at temperatures below 0 degrees F .
The power to the intake starting valve relay’s coil comes from the starter . The 12 volt power is delivered through fuse #6 when the starter is engaged. The thermo time switch also controls the relay telling it when to activate and how long depending on coolant temperature by controlling the negative ground going to the same relay‘s coil.
The injection pump starting solenoid is mounted on the rear of the injection pump. It moves the injection pump rack to full "rich" position during all temperatures when the starter switch is activated. Use the 12 volt test light to see if it is activated during all starting. ( later cars after 1970 may not have this starting solenoid, also some cars have another solenoid below this one, and it is unrelated to cold starting.) Many of the earlier versions with this system had a round time relay which limited the duration of the starting solenoid to 1 second. Later versions deleted this round time relay and activated the starting solenoid during the entire starting period. Sometime in 1970 improvements were made to the injection pump and the intake starting valve and the entire injection pump starting solenoid system was not installed on these cars from the factory..
Identification of the relays;
These cars may have two or three rectangular relays. The starting device relays have four electrical prong sockets, which are labeled . #85 is the negative ground to the relay’s coil. #86 is the 12 volt positive for the relay’s coil. #30 is the “work line” (12 volt positive). #87 is the switched work line which delivers 12 volt positive to the starting device . Identify the relay by taking a jumper wire from the positive battery and touch it momentarily to the #87 prong hole in the plug. You should hear a device activate, either the intake valve or the injection pump solenoid. Now you can identify the relays by which device actuates. Inside Doing the same test on the other relay will confirm that the devices are actually functional and will identify which relays does what.
A larger relay with five electrical prongs sockets is the wiper motor relay.
You can work backward from each starting device using a 12 volt test lamp.
The “intake starting valve“, as you know is the unit on the intake manifold.
A factory modification kit was available to improve this version. Most engines did not need this modification. It consisted of adding a time relay and some wiring. After installation of the kit, the intake starting valve is activated for one second even during warm starts.
Diagnostics;
First of all check each device during a cold engine start to see if they activate. Hook your 12 volt test light to negative ground and the other end to the intake starting valve and activate the starter. Do the same on the injection pump starting solenoid.
The light should illuminate on each device during any cold start. If one or the other does not actuate, check it‘s relay first. It has contacts inside which can tarnish or stick from lack of use. Before opening the relay hook your test light to battery negative, and the other end to the # 86 plug socket. It should illuminate when the starter is activated during a cold start. If the light illuminates then the problem is most likely in the relay.
Open the relay and clean the contacts.
Re-test your intake starting valve again during a cold start. If it still does not activate (test light) your problem could be the thermo-time switch.
The thermo time switch is in different places on different engines and different years. There were two versions and locations for the thermo time switches. The early versions were located in the "pod" near #2 and #3 spark plug and has two screw-on wire connections. The latest version had the thermo time switch in the cylinder head itself and had a plug in wire connection. On your 1969, you will see the "pod" mounted between the injection pump and cylinder head, near spark plugs #2 and #3. It has a coolant hose going to the WRD, the sending unit for the engine temperature gauge, and lastly the infamous thermo time switch. The thermo time switch has two wires connected to it. They may have the original black rubber boot over them. If you pull the black rubber boot back you will see that the terminals are labeled "W" and "G" on the metal. There are two small different size hex bolts holding the wires in place. the "G' side is the smaller of the two.
The "G" wire comes directly from the starter and is hot when the starter is activated. The "W" wire supplies the ground for the relay coil of the intake starting valve!! I know this does not really make sense at first. It can be a real puzzle. After dissecting some of these thermo time switches year ago I realized what was going on.
The thermo time switch looks like just a small sensor from the outside. However the insides are much more complex. Inside are an electric coil wrapped around a bi-metallic leaf with contacts at it's end. The tiny assembly is housed in a fairly small brass cylindrical case with the "W" and "G" wire terminals on the exterior.
When the starter is activated 12 volts goes to the "G" terminal which heats up the wire coil and bimetallic leaf now bends from the heat of the two dissimilar metals, which expand at a different rate.
The bending movement closes the contacts and the negative ground is supplied to the relay’s coil. Yes, the ground to the relay's coil is "switched on" by the thermo time switch activating the relay!! Now since this tiny assembly is incased in brass and screwed into the coolant system, the coolant temperature will effect when and how long the device activates by changing the internal temperature of the whole assembly thus altering the bi-metallic leaf position. This all happens in this tiny little device with no electronics!
The other relay for the injection pump solenoid has a constant ground.
Hook your test light to negative ground and the other end to the "G" terminal. It should illuminate anytime the starter is engaged.
Next re-hook your test light to the positive post of your battery and test to see if the "W" terminal goes to ground and illuminates your test light when the starter is activated during a cold start. If it does not your thermo time switch may not be functioning. You can verify the diagnosis by connecting a jumper wire from any negative ground to the "W" terminal of your thermo time switch. This jumper ground by-passes the thermo time switch and should activate the relay to the intake starting solenoid during any start.
You can leave the jumper ground on the "W" terminal to try some cold starts. This should activate the devices at any start. You should notice an improvement in cold starting.
At PUB 2007 we diagnosed a brand new relay from Mercedes as bad in Bob Possel's pagoda. The contacts in these relays can tarnish and not make contact when the relay activates. So don’t take anything for granted.
Also make sure the injection pump solenoid is activating during any (hot or cold) start. It is the top solenoid if you have two. Latest pumps have none or just a lower one!
Looks confusing, but just take one step at a time. Consider there are many more starting systems on these mechanically injected engines. It took me quite a long time to learn them all.
****Note, this procedure applies to this particular version of W113 (250-SL, 280-SL 8-65 to 1970), and may not be completely applicable to the other versions.
Joe Alexander
Blacklick, Ohio
