Fuel injectors

[hbofinger]

I learned an interesting lesson yesterday.

My 1989 560 SEL had been running a bit rough when completely warmed up. Also, it usually started within two to three seconds when cold, but had a bit more trouble when starting warm. And after it started, it would take a few seconds before it had all the power it should.

So I rounded up the usual suspects - OVP valve, Accumulator, etc. Somewhere I had read that injectors contain springloaded moving parts and wear out, and should also be replaced - I talked to a Benz dealer in my area, and he said that "usually on a Benz with 98k miles nobody replaces them..." I already had bought them, though, and since the accumulator is hard to get to without ramps, I decided to do the injectors (with new insulators) this weekend.

As soon as I removed the fuel lines, I noticed something interesting. All the injectors had fuel resting in them up to the top of the fuel line attachment, except for nos. 4 and 8. They were dry. Could this have been the cause of the fuel depressurization and hard starts?

After reassembling the injection system, and getting the engine going again, I noticed that it now starts within a second (approx. 1 turnover), hot or cold. Also, it now runs a consistent and ever so slightly rough - obviously because somebody in the past had readjusted the mixture trying to get rid of the roughness caused by the bad injectors.

Moral of the story - replace the injectors on a regular basis (maybe 100k miles?), no matter what the dealership may say.

The accumulator is going into the spare parts bin.

Notes fo doing the job:
You'll need injectors, injector seals (buy two more than you need - they are fragile, and I broke one while putting it on), injector insulators (the seats), and two air supply hoses. Plan on cutting away the old air suppy hoses from the injector seats - they are stiff and briddle, and trying to pull them off broke one injector insulator in half. I had a bear of a time removing the broken seat from the head. Use the plugs from the old hoses at each end of the new hoses. You may also want to replace the vacuum line from the fuel pressure regulator while you are at it.