Engine starting aid failed and confused

[K-Jet]

And I assume that is not at all uncommon as there is an entire "Engine Starting Aid Tour" page, with multiple versions and multiple quirks.

I. Current situation (pun half intended)
I have spent part of two days (work until frustrated, think until frustrated, come back to it later) trying to understand what I have and how it should work. Part of the challenge was that I have two relays lined up along the inside fender, but only the back one seems to be related to cold starting. One was that the car has been apart, with a different engine installed with different components, but now has a stock 2.8.

What I might correctly understand...
1. In a one-relay system, the back relay is the one that operates the cold start valve on the intake manifold.

2. The relay terminals are numbered in the manual and on the relay bottom.
      30: key on power from fuse___
      85: Switched ground from thermo-time switch G terminal to ground the relay when below 95 degrees.
      86: Power from terminal 50 (starter); also connection to thermo-time switch W terminal to warm the thermo-time switch
      87: Output connection to the cold start valve

3. When 12V is applied to  the cold start valve, it gives a hearty click indicating good.

4. When 12V is applied to terminals 85 and 86, the relay clicks and there is continuity between terminals 30 and 87 (12V would be supplied to terminal 87), indicating good.

5. The thermo-time switch does not connect the W and G terminals, so getting the right wires connected to the right terminals is essential.
- Relay terminal 85 must be connected to the G terminal of the thermo-time switch to provide ground to the relay when the thermo-time switch is cold.
- Relay terminal 86 / starter terminal 50 must be connected to the W terminal of the thermo-time switch to provide voltage to heat the bi-metallic strip inside.

6. After trading my terminals 85 and 86 in the relay connector, I do get an instant of voltage to the cold start valve. The circuit functions!

II. What I don't understand

1. The only source of switching signal to the relay is terminal 50, so the starting circuit in my car is only powered for a fraction of a second when first turning the key. Once the starter begins turning all the current goes there and the voltage on terminal 50 drops to near zero. Is that all the enrichment I should be getting? If not, where does the voltage come from?

2. If there is only power to the starting aid circuit when starting, what is the point of the thermo-time switch? When the motor is warm it will disconnect the ground at the G terminal, but there will never ever be 3 to 5 to 12 seconds of "on time" for electrical current to heat up the bimetallic strip. This doesn't seem right. If terminal 50 was "on when running" rather than "on when starting" that would make sense. But it's not.

3. What is the second relay- in front of the starting aid relay- for? It is an identical 4-pin relay. I lost hours trying to understand what it did for starting enrichment to no avail. Given the voltages I measured, I suspect some of these pins are also in the wrong places.

4. My injection pump has the enrichment solenoid, though the car (being a 71) does not have the wires for it. There is a red/yellow wire hanging around down there- was that for the shut-off solenoid, or does it belong somewhere else?

Many thanks,

[BobH]

Hello, have you looked at the colour wiring schematics in the tech manual?, these will clarify a lot of what you're asking

It seems that your car may have some starting aid components that are no longer required

1. The only source of switching signal to the relay is terminal 50, so the starting circuit in my car is only powered for a fraction of a second when first turning the key. Once the starter begins turning all the current goes there and the voltage on terminal 50 drops to near zero. Is that all the enrichment I should be getting? If not, where does the voltage come from? What makes you think this, have you measured the voltage when cranking?  The TTS should receive power all the time the key is turned and the engine is cranking

2. If there is only power to the starting aid circuit when starting, what is the point of the thermo-time switch? When the motor is warm it will disconnect the ground at the G terminal, but there will never ever be 3 to 5 to 12 seconds of "on time" for electrical current to heat up the bimetallic strip. This doesn't seem right. If terminal 50 was "on when running" rather than "on when starting" that would make sense. But it's not.

3. What is the second relay- in front of the starting aid relay- for? It is an identical 4-pin relay. I lost hours trying to understand what it did for starting enrichment to no avail. Given the voltages I measured, I suspect some of these pins are also in the wrong places. The starting aid relay, number 20 on the schematic, provides power to the intake starting valve, as long as the engine is cranking, until the TTS has warmed up and removes the ground feed to the coil.  The second identical relay, number 21 on the schematic is fed from the starting switch, the duration being dictated by the cranking time, not affected by the TTS. You say this isn't currently wired, assume the loom didn't have this wiring when your car was built, so i'm not sure if this is now redundant or if you need to reinstate this wiring if you have starting problems?

4. My injection pump has the enrichment solenoid, though the car (being a 71) does not have the wires for it. There is a red/yellow wire hanging around down there- was that for the shut-off solenoid, or does it belong somewhere else? Can't see any red/yellow wires on the schematic in that area, the feed from relay 21 should be a black/pink.  You may need to trace this wire out, or hope someone else can comment on this?  Again, it may be redundant now, always slightly difficult to assess when different engines are installed in a car

EDIT - Apologies, senior moment, i was referring to the relays on a 230SL, which are the opposite to the later cars, i've changed the reference numbers above and also changed the description of the operation

Actually irrelevant now that we know your car is a 280SE, which may have different wiring colours and relay set up anyway

[Pawel66]

I am not a mechanic, so take it accordingly.

Before answering your points, make sure you study the relevant chapters of the Technical Manual (you are a Full member, you can use all resources):

https://www.sl113.org/wiki/Engine/ThermoTimeSwitch
https://www.sl113.org/wiki/Restricted/Engine-starting-aid-tour#startingaids
https://www.sl113.org/wiki/Electrical/WiringDiagram

where the colour digram shows all the connections you need to see.

a.d.1. Yes, the Cold Start Aid system gets power during cranking only. That is why it is a Thermo TIME switch, it provides ground for certain time, not just for an instant, depending on temperature. It actually works not only for cold start. It works for all starts, just works shorter if engine is warmer. Thermo Time switches have descriptions about how much time they provide connection depending on temperature. Some owners, experiencing difficulties with proper functioning of the Thermo Time switch, install manual switch to have control over time the connection is provided.

a.d.2. The Thermo Time switch function is to enrich mixture o help start for certain period of time that depends on how warm is the engine. It is activated with crank signal and then keeps connection for some time depending on temperature. G is not ground! This is critical. G is + to heat it up, then ground is provided from TTS housing to W to activate relay. Yes, ground is provided to W for several seconds depending on temperature. If your TTS does not do it, it is shot.

a.d. 3. I think you have starting aid system where this second relay operates fuel enrichment solenoid on your injection pump. In some cars it is not connected, e.g. I do not have that solenoid on my injection pump. It works in a very similar way as relay for cold start valve, but it works only when you crank the engine, not longer.

a.d. 4. I see on the diagram that wires to the enrichment solenoid are balck/pink for signal (from relay pin 87) and brown for ground.

Note on the wiring diagram:
20 - relay for Cold Start Valve
21 - relay for enrichment solenoid on injection pump
31 - Cold Start Valve
32 - Thermo Time Switch
33 - Enrichment Solenoid

On your points:

a.d. 2. Relay terminals
30: correct
85: NO! Ground from TTS is from W terminal! Be careful there.
86: Power from starter - yes; but TTS connection - NO! goes to G terminal to warm up TTS, not to W. Do not swap these - you may cause fire, the circuit 50 is not fused!
87: correct. To Cold Start Valve on one relay, fuel enrichment solenoid on the other relay.

a.d. 5 Connecting relay.

It does not matter if you trade sockets in the plug to change 85 to 86. But it does matter that you do not connect + from fuse or starter to W. 

[Bshaunessy]

K-JET
  I too spent many frustrating hours troubleshooting my cold start system (70 280 SL, auto, North American spec) as my car was very cranky in both cold start and hot start modes……more than one flat bed trip home because it wouldn’t start.
  I have tamed the savage beast and it starts reliably almost always now……once cold start system sorted out.

The only helpful hints I would offer over and above the very sage advice above by PAWEL and BOB H would be:
(1) draw up your own dedicated sketch of the relevant wiring diagram and components ( relays, TTS, injection valve etc).  Annotate a chart beside each connection time with specified voltage ( and separately resistance) at that connection under all  four possible conditions  : IGN OFF; IGN ON but not running; CRANKING; RUNNING ( yippeee!). 
   Then test and note on same diagram YOUR voltages and resistances under same scenarios.  The faulty bits will become clear.
NB: it wasn’t until I did this that the twisted logic of how this system was designed became clear…..ah ha!  ( it is a very elegant design once understood).

(2) In my case, my OEM TTS functioned (sort of ) but not to spec.  Replaced with a new TTS from a reputable supplier that also was faulty!  Finally after the third TTS I got the system sorted out.   HINT: bench test your TTS ( ie out of the car) both cold and warm ( hot water bath) .

(3) After all of above, system now functions as designed and car starts reliably ( cold and hot and in-between) almost all of the time.  HOWEVER,  I did put a TTS over-ride temporary switch discretely under the dash that activates the cold injection valve when pushed.  There are times of no start where this manual fuel injection at drivers discretion will get the car to start. Very occasional use but comforting to know it’s there.  ( several threads in this forum on how to do it….highly recommended).

[K-Jet]

Hello, have you looked at the colour wiring schematics in the tech manual?, these will clarify a lot of what you're asking

It seems that your car may have some starting aid components that are no longer required

1. The only source of switching signal to the relay is terminal 50, so the starting circuit in my car is only powered for a fraction of a second when first turning the key. Once the starter begins turning all the current goes there and the voltage on terminal 50 drops to near zero. Is that all the enrichment I should be getting? If not, where does the voltage come from? What makes you think this, have you measured the voltage when cranking?  The TTS should receive power all the time the key is turned and the engine is cranking

2. If there is only power to the starting aid circuit when starting, what is the point of the thermo-time switch? When the motor is warm it will disconnect the ground at the G terminal, but there will never ever be 3 to 5 to 12 seconds of "on time" for electrical current to heat up the bimetallic strip. This doesn't seem right. If terminal 50 was "on when running" rather than "on when starting" that would make sense. But it's not.

3. What is the second relay- in front of the starting aid relay- for? It is an identical 4-pin relay. I lost hours trying to understand what it did for starting enrichment to no avail. Given the voltages I measured, I suspect some of these pins are also in the wrong places. The starting aid relay, number 21 on the schematic, provides power to the intake starting valve, as long as the engine is cranking, until the TTS has warmed up and removes the ground feed to the coil.  The second identical relay, number 20 on the schematic does a similar thing, this is fed from the other relay, number 21, and provides a feed to the FIP starting solenoid, but you say this isn't currently wired, assume the loom didn't have this wiring when your car was built, so i'm not sure if this is now redundant or if you need to reinstate this wiring if you have starting problems?

4. My injection pump has the enrichment solenoid, though the car (being a 71) does not have the wires for it. There is a red/yellow wire hanging around down there- was that for the shut-off solenoid, or does it belong somewhere else? Can't see any red/yellow wires on the schematic in that area, the feed from relay 20 should be a black/pink/white.  You may need to trace this wire out, or hope someone else can comment on this?  Again, it may be redundant now, always slightly difficult to assess when different engines are installed in a car

Thank you for your knowledgeable, encouraging replies. Let me see if I can answer all your questions.

The car does start better now than it did before I set out on this journey, so we’re already ahead, though maybe not yet to the finish.

I am not sure at which points my 280SE differs from your 280SLs. Documentation is sometimes murky on that.

BobH,

1. I only get 12V for an instant on my multimeter- the instant the starter begins to engage. After that, the voltage drops.

2. If I understand what I’m reading and seeing, the TTS’s only function is to turn off the enrichment function after extended starter application.

3. I have the sedan, so things may be different. The 280SE wiring diagram in the manual shows only one relay, and this relay supports the intake enrichment solenoid.

According to the two diagrams in my original post, the two-relay system would have the intake enrichment on relay number 2, toward the front of the car. My intake enrichment relay is relay number 1, the back relay.

Further, the wires going to my relay 2 (red/black, brown/blue, brown, brown/white) don’t match what’s on the 280SL 2-relay wiring diagram.

So I think my Relay 2 (front) is for something else.

[K-Jet]

I am not a mechanic, so take it accordingly.

Before answering your points, make sure you study the relevant chapters of the Technical Manual (you are a Full member, you can use all resources):

https://www.sl113.org/wiki/Engine/ThermoTimeSwitch
https://www.sl113.org/wiki/Restricted/Engine-starting-aid-tour#startingaids
https://www.sl113.org/wiki/Electrical/WiringDiagram

where the colour digram shows all the connections you need to see.

a.d.1. Yes, the Cold Start Aid system gets power during cranking only. That is why it is a Thermo TIME switch, it provides ground for certain time, not just for an instant, depending on temperature. It actually works not only for cold start. It works for all starts, just works shorter if engine is warmer. Thermo Time switches have descriptions about how much time they provide connection depending on temperature. Some owners, experiencing difficulties with proper functioning of the Thermo Time switch, install manual switch to have control over time the connection is provided.

a.d.2. The Thermo Time switch function is to enrich mixture o help start for certain period of time that depends on how warm is the engine. It is activated with crank signal and then keeps connection for some time depending on temperature. G is not ground! This is critical. G is + to heat it up, then ground is provided from TTS housing to W to activate relay. Yes, ground is provided to W for several seconds depending on temperature. If your TTS does not do it, it is shot.

a.d. 3. I think you have starting aid system where this second relay operates fuel enrichment solenoid on your injection pump. In some cars it is not connected, e.g. I do not have that solenoid on my injection pump. It works in a very similar way as relay for cold start valve, but it works only when you crank the engine, not longer.

a.d. 4. I see on the diagram that wires to the enrichment solenoid are balck/pink for signal (from relay pin 87) and brown for ground.

Note on the wiring diagram:
20 - relay for Cold Start Valve
21 - relay for enrichment solenoid on injection pump
31 - Cold Start Valve
32 - Thermo Time Switch
33 - Enrichment Solenoid

On your points:

a.d. 2. Relay terminals
30: correct
85: NO! Ground from TTS is from W terminal! Be careful there.
86: Power from starter - yes; but TTS connection - NO! goes to G terminal to warm up TTS, not to W. Do not swap these - you may cause fire, the circuit 50 is not fused!
87: correct. To Cold Start Valve on one relay, fuel enrichment solenoid on the other relay.

a.d. 5 Connecting relay.

It does not matter if you trade sockets in the plug to change 85 to 86. But it does matter that you do not connect + from fuse or starter to W. 

Pawel,

I am not a mechanic either, or I'm sure I would have figured this out already! Thank you for the links to the technical manual. I had read them before, but made it a point to reread them again, and learned some things that I will try.

I am definitely wrong about the terminals on the thermo-time switch. That said, the two diagrams I included with my original post disagree- the first connects terminal 85 to G and terminal 50 (starter), the second shows terminal 86 connected to G and 50.

Both wiring diagrams show (and the SL113 technical manual agrees) terminal 86 connects to G and 50, and terminal 85 connects to W. I was wrong about this.

Having said that, I think I need to test my TTS as the technical manual describes.

As an aside, my family has a very soft spot for Poland. We adopted a sibling group of kids from Warsaw Orphanage Number 1 back in 2002. They are all grown now.

[K-Jet]

Bshaunessy,

Thanks. I am a big fan of being systematic and writing things down as I go. The attachment below shows some of my notes that got me to the level of understanding that I have. Yes, you read that right; I am on page 68. Lots of work done, lots of things I've come to understand a bit better.

Fortunately, my car has always started, and does start better now than it did two days ago even though I mis-connected some things.  First thing after fixing that is to follow the local technical manual testing procedure for the thermo-time switch.

[ja17]

Don't try to identify the function of your relays by their location. The plugs are exactly the same and can easily be switched without consequence since the relays are identical also. It is critical to identify which version your starting aids are so you can look at the charts and diagrams so you can diagnose your issues. What year is your car? How many solenoids are on your injection pump? What is the "R" number of your injection pump?

[K-Jet]

Sometimes you just don't know what you don't know (or have forgotten).

The pump is an R20 in a 1971 280SE (108 018 12 68_---- (I don't remember the rest, though I used to know)). The pump came to the previous owner separately from the engine, so may not match. He sought out this particular version of the pump. I don't remember why.

PE S6KL 70B120 R20

I did think about the identical relays / connectors, but the wire lengths would make it difficult to swap these two. Then again, one of the diagrams in the manual had the thermo-time switch wiring backwards, so maybe the location of relay 1 and relay 2 could also be wrong. Or changed.

[K-Jet]

The resistance on the cold thermo-time switch looks to be in spec.

W to battery ground 0.2 ohms
G to battery ground ~23 ohms
W to G ~23 ohms

Starter and G connected to terminal 86, W connected to terminal 85.

I think all of this is correct.

I see 12V on the meter at the enrichment solenoid on the intake manifold for a fraction of a second before it drops to zero. On restart it stays at zero, though temperatures are in the 80s here today so that may be why.

Not sure where else to look.

[ja17]

Does your injection pump have a solenoid on the back?

[K-Jet]

It does. One in the upper position.

[ja17]

Ok, so it looks like you have Version Four (lV). Check the voltage going to the solenoid when the starter is activated. It should activate at any temperature during the entire starting period. Your intake valve looks like it is working properly and should only operate at temperatures below 95F or 35C for an instant (longer when colder). It will not normally re-activate until the coil in the tts cools down and/or the engine temperature cools. Are you having issues or just checking the system?

[K-Jet]

I dug into this after a professional vintage Mercedes mechanic drove the car and said there was no cold start enrichment happening at all. I have made some progress, as I there is a moment of enrichment at the intake manifold at cold start, and that makes starting easier.

Please describe Version Four, or tell me where I can read up.

Thank you!

[Bshaunessy]

K-JET
 It’s important to test the TTS :
- on the bench…ie disconnected from wiring harness…both hot and cold
- excerpt from Tech manual / engine starting aid/ TTS testing:
The resistance value between "G" and ground should be:

At a temperature below 35 degree C: about 20 Ohm.
At a temperature above 35 degree C: about 60 Ohm.
The resistance value between "W" and ground should be:

At a temperature below 35 degree C: 0 (zero) Ohm.
At a temperature above 35 degree C: about 100 Ohm.
With the switch installed on the engine the same procedure can be used but both wires on terminals "G" and "W" must be disconnected!

If you are testing the TTS "in car" with it connected to wiring harness, you will get mis-leading resistance readings. ( I did this when trouble shooting and was chasing my tail). I also concluded the TTS was fine…and then bench tested per above….it wasn’t FINE!
 Strongly suggest you remove the TTS from car and bench test per above.  Also…read carefully the test procedure in Tech Manual / Engine starting aid/ testing the TTS.
 I will bet you $1.00 🇨🇦 that your TTS is faulty. 
  Also read about suitable substitutes…I wound up getting a Porsche equivelant for 1/4 the price of a TTS from MB or other supplier. Albeit, you need to change the electrical connector but other than that…has performed as intended for two years now.
  Good luck

[K-Jet]

I did test in the car with wires disconnected, as listed on the tech page here. I didn't test it warm because I'm not having warm problems.

Could well be that the TTS is defective.

[ja17]

You might be off track here. Maybe your mechanic was talking about the "WRD". (warm running device) on the injection pump?? If it is stuck in the warm position, you will not get any fuel enrichment with a cold engine.

[ja17]

You might try searching "Version lV Starting Aids". There are charts, diagrams and descriptions, which will make it clear.
Otherwise "Version IV" has three devices which effect starting. First is the WRD (warm running device) which enriches the fuel mixture during the warm up period. It is mounted to the top back of the injection pump and it has three hoses going to it. A slide valve in the unit can get stuck, especially during long periods of storage. Although this is not dedicated just for starting, it will make the engine more difficult to start if it is stuck.  There is a lot posted already on the "WRD" about diagnosing and fixing the problem. The WRD is regulated by coolant temperature and regulates fuel and air during the warm up period. Next is the "CSV" on the intake manifold. With version IV, this "CSV" device will squirt fuel When starting, when the engine coolant temperature is below 95F or 35C. The colder the engine is the longer it will activate up to 12 seconds max at -20F. It's signal comes from the starter switch and the "thermo time switch" TTS via a relay. The next starting device on version IV is the injection pump starting solenoid, which is on the back end of the injection pump. With version IV, this starting device is activated whenever the starter is activated. When the starter is activated the solenoid is energized regardless of engine temperature. This solenoid moves the rack in the injection pump to "full rich" for starting. It also uses a relay to control its operation. With this information you should be able to test each starting aid. If you find that one of the starting aids is not working properly, we can track the problem down from your test results of each. I am tending to believe that your WRD might be the issue! Keep us posted. You don't have to "over educate" yourself on all the fine, complex workings for now if you can just do the diagnostics. Believe me only a few here have a true understanding of these complex and various starting aids.

[BobH]

Hello all, don't forget K-Jet's car is a 280SE, do the starting aid components differ from the 280SL's?

[ja17]

No, they do not differ. The 280SE uses versions 4 and 5, and are the same as the pagoda's versions 4 and 5.

[K-Jet]

As recommended, I continue to test, measure, and figure.

1. Jumpering thermo-time switch (TTS) terminal W to ground gives voltage to intake enrichment circuit as long as the key is turned. Since I only got voltage for a split second at the beginning of starting before, I think this means my TTS is toast.

2. The red/yellow wire that is connected to the pump solenoid originates in the relay at the front left corner, A000 542 93 19. Not sure what this relay does.

3.  Investigating Relay 2 (front relay inside driver’s side fender).

a.  Resistances (OL means no continuity)
Terminal   Wire color   TTS G   TTS W   Pump solenoid   Ground
30                 Bn         0.7      0.7              OL            0
85                 Bn/Bk      70      70              OL            13
86                 Rd/Bk      3.6      3.6              OL            3.4
87                 Bn/Wh      OL      OL              OL            OL

b. Voltages
      Key off      Key on
30      0         0
85      0         12.7
86      0         12.7
87      0         0

c. Applying 12V to terminal 86 causes the fuel pump to run and something in the back right portion of the engine bay (air conditioner relay?)

Questions
1. Given this information, what is Relay 2 supposed to do?
2. What is the correct wiring for Relay 2? I don't think what I have currently could possibly be correct.
3. Where is the red/yellow wire connected to my pump solenoid supposed to go, if not there?
4. What other wire is supposed to go to the pump solenoid?  The brown/white wire from T87 seems to be connected to nothing, so seems like a candidate.  I haven't traced it yet.

[ja17]

You should get voltage for only a split second in high ambient temperatures. Your TTS is probably good. Those relays in your pictures are emission timing relays. They should not effect starting. The WRD is probably your problem, did you check it yet?

[K-Jet]

I have not yet looked at the WRD, though I know Herr Fritzsche adjusted it when he went through the pump. It did sit on the shelf for three years before installation, so it may need some cleaning

[K-Jet]

On to the WRD!

Having now read a slew of threads, my WRD is clearly not working. There is no bump to 1000 RPM on cold start. There’s just a lumpy 800 always. The video here https://www.youtube.com/watch?v=F6sxlOFmoYw was very useful just to see the components and to get a sense of the system.

The unit came off and came apart fairly easily, which is as it should be as it was professionally gone through a few years ago (then sat on a shelf for 3 years). It had one oval shim between the unit and the injection pump.

Upon disassembly, I find that I have a spring-wound shaft rather than a tapered shaft. I haven’t seen that in threads here or in the video. Normal?

I used a meat thermometer (my cheap IR thermometer went down yesterday- bad timing) in a pan on the stove, with a stout piece of wire to hold it all together. Measurements, especially for temperature, are undoubtedly imprecise.

Temp F      Distance (mm)   Change      Total
         shoulder to  ring   (mm)               extension(mm)
70         15.6                  
90         15.7                  0.1         0.1
100         17.2                  1.5         1.6
110         18.0               0.8         2.4
120         18.4               0.4         2.8            
130         19.2               0.8         3.6
140         19.2               0.0         3.6
150         19.9               0.7         4.3
160         20.9               1.0         5.3
170         21.2               0.3         5.6
180         21.6               0.4         6.0
190         25.9               4.3         10.3
195         26.2               0.3         10.6
200         26.2               0.0         10.6

When at max temp, the shaft would cause the pump shaft to be fully extended, plus a few mm extra as seen in the last picture.

[ja17]

Just make sure the sliding piston is not seized and is able to move.