280 SL Injection pump problem?

[gearjam]

I have a 70 280 SL with a fresh engine. When the engine warms up it drops cylinder no 5. I have gone over the basics to make sure that the problem is with the injection pump. If I pull the injection lines off at the pump and crank it over gas is running out of all but #5 fitting. Eventually it starts coming out of fitting 5 but not as fast as the others. I was able to switch the lines between 4 and 5 and the miss switched cylinders. I have about 8 psi of fuel pressure at the injection pump inlet. Seems like this is a injection pump problem to me? What do you guys think??

[Mike Hughes]

...or a partially clogged line.  Water in the gas can cause the line to rust internally and restrict fuel flow, just like plaque buildup in one's arteries.  I would take the slow flowing line off the car and ream it out with a length of stainless steel wire and see what debris you can dislodge - just think of it as a miniature sewer snake!  Then blow it out with high pressure air.

A friend had his original fuel lines cad plated during the process of restoring his Pagoda.  Darned thing wouldn't run right when he put it all back together.  Turned out that some shop debris was in a couple of the lines and the plating shop didn't flush them out thoroughly before starting the plating process.  So the debris was cad plated in place.  Reaming and blowing them out made the car run better, replacing all the lines with new insured that no more debris would be present to break loose later and ruin the injectors.

[Nate]

Did you have the injection pump rebuilt before you installed it with your fresh rebuild?  A tired inection pump struggles to feed fuel to a strong freshly rebuilt engine.  If you've spent the money on a correct rebuild, I would highly encourage you to spend the $1,200-$1,400 to have the injection rebuilt.

[ja17]

Hello,

The fix can be simple,  The 19mm fitting on top the IP must be torqued at about 20 ft. lbs on a 280SL. Do not under torque or over torque. If it is too loose it will not develope full pressure.

If this does not work, check the rack in the injection pump to make sure it moves freely and returns on its own. ( pump removal not needed, check from the access port in the front of the pump). If one piston in the pump is sticking, the rack will not move freely and that cylinder will not pump or will be irratic.