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 wrote: 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.