Hesitation at low rpm

[Ari.g.123]

Hello pagoda family.

I am a new member with a 69 280SL. I have read extensively about the cold start issues etc but my problem is a bit different. Cold starting is not difficult, starts after about 3 to 4 seconds of turnover. Ideals at about 1200rpm and when warm down to about 800rpm. The problem is that when I drive hot or cold as I accelerate at the low rpm around 2000 the car sputters or hesitates. As I press the accelerator through that rpm the car takes off.  Warm starts are a bit difficult even with pedal on floor.  Plugs and wires new, valves adjusted. Fuel line from tank replaced.

Any help would be great! 

Thank you for your time.

[ja17]

Welcome!

It could be as simple as a plugged main fuel filter.  You should do a fuel system pressure and volume check. It is not that difficult, read up in the tech manual on it. Sounds like you have a lean running condition at low speed range. I would not adjust the injection until you checked the fuel pressure and volume, timing, linkage. Go through the linkage tour also, if the pressure and volume check is OK. You can verify my diagnosis of a lean running condition by doing a "split linkage test" at idle and low speed. The hot starting is also related to the lean running condition most likely. Check to see that the electric fuel feed pump in back is original type. Substitutes usually cause problems. If this all sounds difficult and confusing, just ask more questions and we'll fill in the blanks.  

[Ari.g.123]

Ok!

The pump was tested by the shop that did the "tune up" but I will ask for the detailed explanation now that I know it could be a material detail that has been overlooked.  Fuel filter was replaced, and the car was timed.  I will go through the list of items myself, and get back to the group with any questions.   

Your help is much appreciated.

[kampala]

I had similar symptoms, specifically sputtering and hesitation at low RPM. After chasing the problem, eventually found a frayed wire connection on the coil -- hidden under the little rubber boot --- the thin wire that runs from the coil to the side of the Dizzy.  Problem cured once the connection was made proper.   It's an easy wire to damage, especially when changing and bleeding the fuel filter.

[Ari.g.123]

Ok. Thanks for the heads up. I will look at that as well. It makes sense.

I will update the group with my findings.

[Ari.g.123]

Hello all,

Just an update on the problem.  Sorry for the late response but here it is.  I ended up cleaning the fuel tank and having it acid washed because I found about half an inch of rust flakes on the bottom of the tank.  The step by step for the uninstall and install of the tank on the site was great.  The fuel sending unit along with the tank plug filter were also changed.  A great deal of better running so far but not fully solved.   The fuel pump is an after market "universal" that will be taken off and replaced with a new correct Bosch short pump this weekend.  The plumbing was changed to fit the universal so that all will be changed at the same time to factory hose diameters etc.

I will update you on my progress, and then will advise what my findings are before I dare touch the injection pump adjustments.

Thank you all for the help and positive direction.   

Peter

[Ari.g.123]

So I completed the fuel pump instal along with all the plumbing fuel out and return.

Car starts and runs infinitely better. Start right away when warm and very well when cold.   No hesitation at all on low rpm etc.

Put several hundred miles on it.

Just rescently tryied to start it when warm after sitting about an hour on a hot day and a hard drive and it would not start till cold - 4 hours.

Any ideas or help?

[66andBlue]

When the engine is hot you are supposed to press the accelerator petal while cranking as described in the user manual; are you doing this?
If you do and the problem persists then perhaps the info here might help:
http://www.sl113.org/forums/index.php?topic=17829.0
http://www.sl113.org/forums/index.php?topic=16345.0
http://www.sl113.org/forums/index.php?topic=9423.0
http://www.sl113.org/forums/index.php?topic=7503.0
http://www.sl113.org/forums/index.php?topic=4591.0

in addition to this: http://www.sl113.org/wiki/Restricted/Engine-starting-aid-tour

[ctaylor738]

Here is my solution using a timer relay to fire the cold start valve with a hot engine.  This has been in place on a 250SL for over a year and has worked very well.

http://www.sl113.org/forums/index.php?topic=17329.0

Cheers,

CT

PS - Geez Alfred, I thought you would have cited this!

[66andBlue]

...
PS - Geez Alfred, I thought you would have cited this!

It is a mod, not original - sorry can't do!  

[Ari.g.123]

Just another update for you all that may be interested.
The lead to the positive terminal was look on the fuel pump so it was not pumping. Once rectified all is good.