Help! I am about to give up on my R107 350SL

Dear all,

It has been a godsend to find this forum.

I don't want to overcomplicate things, so will summarise my problems here in point form. I hope someone can help; I am tempted to just dump this car because I have already put in thousands to this car and it has not run properly.

Car:

1973
350SL
Mileage: unknown, reset recently. Now approx 15k km
Restored sometime in 2011
Am using the aircon quite a lot, based in tropical country so this is needed
I have owned it for about 2 years.

Problems:

1. My car cannot idle properly.
It will die unexpectedly both when car is stationary and also when moving. It will do this without warning, and usually happens when car is warm. But sometimes, it happens when it is cold too.

2. There is severe loss of power, heavy jerking and stalling while driving.
This has happened 6-7 times now over the course of the last 1.5 years. Sometimes it is not so bad so I can still drive to the workshop. Sometimes, it's so bad that I have to tow it. I am good friends with the tow truck company now. When these things happen, I usually observe a lot of black smoke from the exhaust.

3. My engine has difficulty revving past 3,500rpm.
It feels like I have hit a rev limiter when i rev to 3,500rpm, cannot really go past that. Unsure why again.

4. Engine seems to run very rich.
I have gone through already 4 sets of spark plugs with a mileage of only 2-3000km.

What is done so far:

1. Fuel pump replaced (W124 pump)
2. MAP sensor replaced
3. Several sets of spark plugs
4. Fuel tank cleaned
5. Wiring checked
6. Vacuum checked

Workshop recommendations:

Workshop 1: Replace ECU.
Workshop 2: Replace ICU

Can anybody shed light on my car's woes please? Will answer any questions as detailed as possible to get to the bottom of this.

Thanks,

M

Hi,

it would be great if you signed with your first name, that would make it easier to greet and welcome you.

Anyhow, let us look into your case:

Let me ask some questions:

1. Is idle-run also bad when A/C is off
2. How high is CO % in idle-run? Can you change it by potentiometer on ECU?
3. Why a W124 fuel pump? That is designed for higher pressures in KE-Jetronic. Better use an L-Jetronic pump or even better a refurbished D-Jetronic pump
4. How high is fuel pressure on running engine?
5. When you swapped MAP sensor, did you do leakage test as described in video in chapter 4? The 0 280 100 012 tend to have torn diaphragm.
6. Was ignition timing tested at idle, 1500/min and 3000/min plus vacuum retard?
7. ECU should be the last thing to test.

Volker schrieb: Hi,

it would be great if you signed with your first name, that would make it easier to greet and welcome you.

Anyhow, let us look into your case:

Let me ask some questions:

1. Is idle-run also bad when A/C is off
2. How high is CO % in idle-run? Can you change it by potentiometer on ECU?
3. Why a W124 fuel pump? That is designed for higher pressures in KE-Jetronic. Better use an L-Jetronic pump or even better a refurbished D-Jetronic pump
4. How high is fuel pressure on running engine?
5. When you swapped MAP sensor, did you do leakage test as described in video in chapter 4? The 0 280 100 012 tend to have torn diaphragm.
6. Was ignition timing tested at idle, 1500/min and 3000/min plus vacuum retard?
7. ECU should be the last thing to test.

Dear Volker,

Please excuse my manners! I'm James, hailing from Singapore. My 350SL is probably one of only less than 5 in our small little island, and I am very fond of it! But it is also the reason why no workshops here know how to work on it properly.

Thank you so much for running this forum and sharing so much of your knowledge, it has helped a lot!!

Here are my responses to the best of my knowledge:

1. Is idle-run also bad when A/C is off
Yes.

2. How high is CO % in idle-run? Can you change it by potentiometer on ECU?
Unfortunately I am not so technically inclined to answer you. But I will check with my workshop and get back to you. I believe yes, this can be adjusted via the ECU. I've seen my workshop insert a sensor at the exhaust several times to measure the CO2 and adjust this.

3. Why a W124 fuel pump? That is designed for higher pressures in KE-Jetronic. Better use an L-Jetronic pump or even better a refurbished D-Jetronic pump
It was a stop-gap solution as there wasn't parts available. But then the W124 pump seemed to run OK, so I did not identify this as an issue.

4. How high is fuel pressure on running engine?
As above, beyond my gullible non-technical mind, but I can check with my workshop.

5. When you swapped MAP sensor, did you do leakage test as described in video in chapter 4? The 0 280 100 012 tend to have torn diaphragm.
Will check with my workshop.

6. Was ignition timing tested at idle, 1500/min and 3000/min plus vacuum retard?
I believe so, yes.

7. ECU should be the last thing to test.
Agreed...

Hi James,

I spent some time working in Singapore a few years ago, I know how hard it is to find expertise on the older cars there.

If your engines loses power but still runs, I would check the D-Jetronic trigger points, it sounds as if half of the injectors are intermittently not firing which would account for the power loss (i.e. only running on 4 cylinders).

I do not believe the W124 pump is an appropriate exchange due to the higher pressure this pump provides, but it maybe accounted for by the pressure regulator, I am not sure.

Is your car silver with blue trim? I used to see a lovely 350 SL in this colour parked under the Fullerton Hotel occasionally when I was there in about 2011, it was a lovely sight next to the boring black S-Class and 7 series!

Good luck with your project.

Carl

Hi Carl,

Good to know somebody been in Singapore and know my situation!

Yes, the trigger points are also mentioned elsewhere and I will definitely check this.

Yes exactly, it's a silver car with blue trim. I wonder if it's the same car parked at Fullerton, as back in 2011 I did not own the car. But it was about the time the car was restored! So there is a high chance that it is.

James

Hi all,

Here is an update.

After visiting the workshop, the car now runs noticeably better.

However, the engine still died once while I was parking it at a tight garage (lots of low speed manoeveurs).

Now I got a new additional problem however. My engine runs great when cold, but when hot it seems to get rough and also has a high idle (around 1300rpm). What is wrong with my car.

Hi James,

sounds to that your workshop has increased idle-rpm to overcome rough idle of your car. If we shall help you, you should answer questions 1-7 from above. Otherwise I should have magic telemetric hands to heal what is wrong.

Hi Volker,

Am trying my best to get all this info from my workshop however they really aren't competent enough to provide these!

Anyway, after so many months of troubleshooting, now the workshop recommends changing the ECU as part of the connector is burnt. Please see the pics here: www.facebook.com/groups/MercedesR107/per...k/10154891174294801/

What could cause this, and is it salvageable? I need a replacement urgently to get my car road legal so if anyone here has one to ship to Singapore please let me know... I need a 0280 002 004 but I think if it ends with a 001 or 002 it works too.

Merry Christmas all... Cheers! (despite dreary times with my R107)

Hi James,

I cannot look at your picture as I am not registered on Facebook.

If ECU connector is burned, how does wiring harness look like? There should be a reason for that. I could give you another 0 280 002 004 ECU or test and repair yours but I fear that such a failure will happen again. Wiring harnesses tend to break and loose isolation. That can create shortcuts. Other than that I can right now not think why connectors should burn.

Hi Volker,

Apologies, please see the pics below. Hope this is clearer.

I too am so puzzled why this has happened. I have virtually chased every possible lead and left the ECU to the last. And I was quite sure it was functioning OK. More importantly, I don't want the problem to surface again so I want to be sure what the problem is.

Hi James,

that is severe damage ! What I see it is pins 11 and 12. They are shortcut on ECU. 11 is ground IN, 12 is ground OUT to trigger contacts and throttle switch. When they are so burnt, I can only assume that somehow 12V were applied to the cable connected to 12 and thus caused a heavy shortcut. It looks like it has damaged both connector contacts and ECU. In worst case also your wiring harness. It can also have damaged more on your ECU. Being so far away I would definitely recommend you to

1. swap ECU
2. swap 2 contacts in connector housing (you are so lucky that I have just found such contacts after years of searching)
3. verify wiring harness, especially path from pin 12 to T.C. and throttle switch Remove both connectors and measure 12 to ground and +12V on your car. Both should be open. Verify with both connectors applied function of throttle switch and T:C. Still there should be open end to +12V.
4. I can also have a look at your broken ECU whether it has caused the problem. but I do no think so. In that case you need to send it to me DECLARED AS A GIFT. We have such an embarassing customs duties process.

and someone has also opened your ECU. I can see that from missing sealing on those screws.

Hi James, hi Volker,
does the M116 wiring harness (or this car...) have a connection from lead 12 to the ground at TPS or somewhere else? I believe the M116 doesn't have this in original, but other cars have...
Maybe someone made such a connection to make a better ground connection for the D-Jet-system.

This then could be the reason for the damage: Bad earth from chassis to engine. When high current flows (esp. when starting) insufficient engine-earth would cause such a damage - engine would try to 'get' earth via the grounded (at the engine) lead 12 and the grounded lead 11 (grounded at the chassis).

Just an idea

Norbert

Hi Volker,

Sigh, yes it is severe, and this is only maybe 10% of the issues I have faced so far elsewhere in the car...

I have conveyed your instructions to my mechanic. I am ordering a refurbished ECU from Australia. The workshop is fixing the wiring harness - can you explain further what you mean by swap 2 contacts in the connector housing?

How shall I send you the ECU?

And yes, my mechanic opened the ECU out of desperation, as he could not trace to any other issues already.

Norbert - I have no idea actually whether lead 12 has a ground or not. I am totally not technically inclined, this is all very difficult to understand for me.

Hi Volker,

An additional question from my mechanic - is this existing injector on the car correct for the 350SL?

Cheers,

James

Hi James,
two answers I can give, too.
- This injector isn't an original one. It's similar only, has the same fit. A type 'EV1' injector, manufacturer and type unknown..
Maybe it fits - one had to compare impedance and the flow tables.
But maybe it's totally wrong... try to find out the make / type.

---

Your workshop can easily check out the possible problem I described before.
They can check both damaged wires for continuity towards the chassis (ground)).
One (PIN 11) has to be resistance of 0 Ohm towards the chassis - it is the ground wire.
The other one (PIN 12) has to be isolated from the ground, endless resistance towards the ground.

Regards
Norbert

Hi James,

those are the wrong injectors, they look like L-Jetronic injectors. You need yellow D-Jetronic injectors and they are hard to find. If you find nothing in Signapore, I should still have new ones.

The 2 contacts in connector housing to ECU are very special, not normal receptacles. I've recently managed to get hold of some after hunting every Bosch service and other workshops for years. That is why I recommend you to replace these 2 burnt contacts. If the fail temporarily you will have no injection.

You need to find the reason for the wiring harness or workshop failure. If you look at chapter 10 of my compendium , you can find all necessary material for rebuilding a wiring harness.

Thank you both!

I'm shocked to find out that my injector is non-original, but because replacements are so expensive and hard to come by I think I will stick with the current ones for now. After all, my car did seem to run fine for a while with the current injectors.
I suspect my current ones are for the 450SL, but I am not sure. There is no make or type indication on the injector.

As for Pin 11 and 12, strangely the workshop checked and their grounding is correct, there is no issue with them. I wonder what else could have caused the burning? I fear, could it be water leaking and therefore causing a short circuit? I did not show it on this forum before, but my ICU was actually found to be completely drenched before, with water inside. I have since replaced it.

So far I have already replaced a water pump, fuel pump, distributor cap, rotor button, trigger points, distributor, ICU, air temp sensor and throttle valve switch.

Hi James,

original injectors have a yellow body with no. 0 280 100 034 . I cannot comment on yor injectors other that they are non-original.

Talking of ECU: Was the current ECU full of water? That could of course cause a shortcut. However I still believe that it came from wiring harness pin 12. If someone or somethind had accidentially applied +12V to the cables leading to Pin 12, then I would expect such a burn on Pin 11 and 12.

Hi Volker,

No, the ECU was dry. Hopefully, we will get to the bottom of it in 2017. Happy new year!

Best,

James