[R129 SL] finding engine problems after 4 months , concerning everybody

[Jan Kuylaars]

Hello All.
 
You know I send a mail last year about having problems with my M119 engine
R129 500Sl.
Nobody has given me an answer, but now I can help you to prevent the same
damage  and problems.
 
Last year I discovered that my car had no power at high rpm and  I was
thinking the fuel pump was not functioning good.
But most of the time I was cruising and driving slowly , so I thought it was
not such a big problem that I could not win from the younger guys in their
Volkswagen golf or some BMW.
 
Big mistake !!!.
 
After driving more than 1 year , supposing it was a fuel pump pressure
failure , or under pressure from gas tank , I had measure the pressure from
the pumps ( 2 pieces) and that was ok. So I thought maybe the pressure is
good, but the second pump for speeding up the fuel to the engine has not
enough capacity, but that will not stop the car.
 
Second mistake !
 
I discovered that by sunny weather with higher temperature the problems
started all even above 3500 rpm.
After some driving were I was happy to get home speeding 120km/hour on 2000
rpm I had taken the car for a drive with extremely high temperature like 38
degrees Celsius.
 
Driving home that day the engine stops running 4 times waiting at a traffic
light and I decided that I could not drive anymore in this condition..
Checking the fault indicator by the mechanic tells that the sensor in the
catalisator was defect and there were some bad connections in a connector.
Replacing did not solve the problem.
Testing with smoke if there was a leak in the fuel system indicated that all
was OK. 
Measuring the fuel and the air during driving indicated that the mixing was
ok, but the burning situation was not ok.
 
So we already checked and cleaned the distribution caps, replaced the spark
plugs but no result.
Measuring the sparkplug and bobbin cables indicated two fault cables and
taking out one bobbin gives a leak of cooling oil out of the bobbin.
That was the reason of the breakdown during high temperatures.
 
Replacing the cables and the bobbin was not solving the problem, so we going
to think there should be some problem with the exhaust.
Opening the catalysator , I don't know the English term, shows us that the
complete inner part of that was melted together, so the engine could not get
lost of the burned gasses. We take out both of the inner parts from the
catalysator and welded the exhaust so it was closed.
Only a little more noise , no problem, and because my car was from 1989/90
it was not necessary by law to have a catalysator.
We could align the CO on 1.4 what is the standard so no problem.
After that I heard there are replacement parts to put back into the
catalysator.
 
Driving at cold the problem was most gone, but sometimes it came back.
After a few days my cooling radiator started to leak on the above plastic
part where the hose is fitted.
So we replaced the radiator, and see that it took tens of minutes longer
before the engine become 80 degrees Celsius and 40 miles before it was 100
degrees Celsius.
 
After driving several days and put in injection cleaning fluid, the cars
start to drive better every day.
 
If you have 8 cylinders, you hardly notice if your 129 runs on 6 and a half.
It has so much power that you only see it if you are using maximum power.
So there was a problem with the sparkplug cables, if I had replaced them in
the beginning, it should be only that. 
But driving with 2 cylinders who have no 100% burning situation, fuel is
coming into the catalysator. The fuel is melting the chemical parts and
after a while the sensor brake down and no warning is made and the engine
cannot get lost of its exhaust power and heat, so the engine will reach
very quickly and always at 100 degrees Celsius. So the engine becomes very
hot and at least damaged the bobbin so you only driving on 4 cylinders and
the catalysator is melting complete so it becomes a worser every day.
Extremely heated engine damages at last the plastic parts of the cooling
radiator and the rubbers from cables .
 
This winter I will replace the outside rubber from the cables positioned
above the engine.
 
So let this be a warning, if your car has no power at the top, or is very
quickly at maximum heat, check the above points and save some money and
time. It costs me 2500 € and 3 months no driving , paying 270 € taxes.
 
Greetings from Jan the flying Dutchmen
 
 
 
Jan Kuylaars
 

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