Misfire

[rob walker]

Despite much work to solve this problem I am still troubled my an intermittent misfire.
She normally runs without a problem, but sometimes when run at motorway speeds, I get a hesitation at between 2,000-3,500 rpm on medium throttle. If I use full throttle the misfire is not there.

The car has had the following with a UK or European specialist over the last 2 years.
Top end rebuild
Rebuilt injection pump
New distributor
Electronic ignition
New coil, plugs and leads
New fuel filter

I run the car on super unleaded with an additive.

It does appear that 1 injector has been changed also noticed the seal on the gas cap is completely perished so will replace this.

As usual the car runs great for weeks after any work then the misfire reappears, unless I am trying to show the mechanic!

Any helpful suggestions would be appreciated.

Rob Walker

1968 280SL papyrus white/green leather
2004 230 SLK silver

[lurtch]

Hello from Calif,    

Hey Rob - -  your mssg did not indicate which spark plug you are using. The heat range rating can make a big difference with these engines.   I had mis-fires all the time with  Bosch WR7DC.   Changed to WR8DC (hotter) and saw some improvement.  Now I am running the hottest non-resistor version W9DC with good results. I use middle grade RON 91 with no additives, but have no knowledge about your Spanish gas. Also make sure you have the highest quality wire set - - my engine was very finicky about the wires also. Good Luck - - -Larry Hemstreet

[rob walker]

Larry, thanks, I have installed new leads (supposed to be the best) will check on plugs but think they are WR8DC.
Any other suggestions welcome, how can you tell if an injector is failing and which one, would this give the same sporadic effect?

Rob Walker

1968 280SL papyrus white/green leather
2004 230 SLK silver

[A Dalton]

Get rid of the Resistor plugs...
 113 ignition systems like regular, non- resistor , copper core plugs.