Engine Missing and Eventually Dying

[gstorek]

I am a new owner of a 1971 280SL.  When we bought it, it ran ok, but as it warmed up, the engine started missing, getting progressively worse, and then, when it came to a stop, it would not idle and the engine just died.  Would not restart, but if left to sit for several minutes, it would start and run again.  Then the missing and dying problem would repeat.  Sent it into a MB shop for a general check up.  Much work was done to the car; including: cleaning out and flushing everything; installing a completely rebuilt fuel injection system from a very reputable source; new rebuilt fuel pump; removed points and converted to electronic ignition; valve adjustment; torqued the head (engine has very good compression); new plugs; transmission adjustment; plus many other mostly non-engine improvements.  Brought the car home after a month in the shop, supposedly with it running well; however, after two recent test drives the original problem is still there!  It starts right up when cold, runs fine, but after a while the engine starts to miss and eventually won't idle and dies.  The problem certainly seems to be correlated with the engine heating up, but the temperature gauge reads normal.  Oil pressure is good too.  Any suggestions or advice will be greatly appreciated.  Thanks! 

[Mike K]

Welcome to the Group and sorry to hear about your issues.
Have you replaced the spark plug wires? I recently had similar running issues with my '71 280SL.  Yesterday I replaced the ignition wires to the spark plugs and the wire to the coil. Problems all solved.
 
Another thought, I assume the fuel tank's been checked and cleaned out as well as the fuel lines and tank filter & fuel filter? I say this because I also had this issue when I bought my car, which displayed similar symptoms.

Best,
Mike

[Jordan]

You could have a dirty fuel tank and it is clogging up your filters preventing/restricting fuel flow to the engine.  It's starts and runs well initially until the dirty fuel eventually clogs the line.  When the car dies the fuel slowly seeps back into the line so you are able to start and run it, until the line gets clogged again and the car dies.  There are 3 filters, one in the tank (this and the flower pot can get plugged up if there is a lot of rust in your tank), one in the electric fuel pump next to the fuel tank and the large main filter in the engine bay.  You can also check to see if you are getting full volume fuel flow at the return line where it goes back into the tank, should be about 1 litre every 15 seconds.

I'm not sure if the 280SL tank is vented as that may also be plugged if it is.  Maybe someone with a 280SL can comment on that.

[rgafitanu@gmail.com]

From my own experience; I had this problem with clogged fuel filter for a while and while chasing it I changed, modified, adjusted and readjusted pretty much everything from IP fuel mixture to resistors, points and capacitors. The best thing to do to isolate fuel problems is to plumb a $4 fuel pressure gauge right before the IP (I did it at the CSV). I mounted a "previously enjoyed" tank that was stagnant for years and when I started cycling gas and running it a lot of fine rust particles became loose and are clogging the fuel pump screen every 1-2 months. Now when I see the fuel pressure drop below 6PSI I know that I have to clean that screen. What is different is that after the engine stalls it starts right away with no hesitation. The gas flow pushes the rust particles against the screen clogging it. When the engine stalls and there is no gas flow the particles fall to the bottom and there will be a few minutes before they get pushed by the flow against the screen again.
The fact that the engine runs well cold may point to mixture adjustment, air flow screw and IP mixture screw.
Use the search feature on this forum and you will find hours of reading other people's experience on this precise subject. Also as a full member you have access to the technical manual which is very good.

Radu

[ctaylor738]

Sounds like the classic fuel tank issue, the passages in the "flower pot" in the tank are constricted.  When the car sits, enough fuel drains into the pump and lines to keep it going, so it will start run for a while.

To fully diagnose, let the car run to the point where it won't start.  Unhook the fuel return line, slip a piece of hose over it and lead it into a container.  Turn the ignition on to run the fuel pump.  My guess is you will see only a trickle of fuel rather than the healthy flow (a liter in 15 seconds?) that should be there.

However, I will say that I once saw fuel starvation like this caused by a blocked return line (the Attractive Asian Woman's car).  Without circulation, the pump was overheating and its output was greatly reduced.  It would then cool down and run OK for a while.  So when you have the line apart, you might want to hit it with some compressed air and listen for "burbling" in the tank.

[gstorek]

Thank you so much to Mike, Marcus, Radu and Chuck for your very kind and helpful responses!  The car is now back in the shop and I have passed on your thoughts and suggestions to our mechanic.  Again, much appreciated and very glad I joined this group. 

/ Glenn
1971 280 SL