Injection problem?

[JJD]

Since a few days my 1970 280SL developed a funny problem.
When driving above 40 MPH keeping the gaspedal in the same position the engines revs go up and down a couple of times per minute (the car accelarates or slows down a bit). It does it when the engine is cold or hot. The engine starts okay and does not stall. At low speeds you don't notice.

[Cees Klumper]

Could this be in the ignition (vacuum advance/retard behaving erratically for example)?

Cees ("Case") Klumper in Amsterdam
'69 white 280 SL automatic

[BHap]

sounds like fuel starvation....  fuel pump beginning to fail, fuel filter or inlet screen on fuel pump would be my first suspects...

[jeffc280sl]

In the event Cees is on to something, disconnect the connector from the base of the two way valve and go for a drive.  If the problem continues its not the emissions control stuff.  If it goes away let us know and we can work on fixing the problem.

Jeff C.
1970 280SL 4-speed

[rwmastel]

Could it be in the distributor?  Broken springs, worn shaft, etc.?

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[blairwag]

Hummm, I think that the distributor retard should be fully engaged by or before 40MPH.  I'm apt to suspect fuel delivery, too. I'd replace the fuel filter first. If it persists, I'd find a way to measure the fuel pressure.

--
~~~~~~~~~~~~~~~~~~~~~~~~~~~
William Blair Wagner: blairwag@earthlink.net
Education is not always knowing the answer,
...but rather knowing where to look for it!
1971 280SL US Automatic
~~~~~~~~~~~~~~~~~~~~~~~~~~~

[hands_aus]

I agree with Rodd,
possibly the distributor springs gone soft or broken.
A cheap quick test to eliminate this suggestion...remove the distributor cap and turn the rotor clockwise and let it go. It should spring back easily and quickly.
While in there check the points gap and clean the inside with a dry cloth.
See if the felt wick in the top of the distributor shaft is dry. If yes give it an oil with 2-3 drop of oil and then add 2-3 drops to the oil point on the outside of the distributor.
What have you got to lose?

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[JJD]

Just to finish this thread.
I found the issue. It was the emmission reduction electronics (Relays) that didn't work properly.