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Originally Posted by 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.
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KE system injectors have check valves that require a minimum opening pressure and these are "chatter valves" in that once line pressure is sufficient to open the valves, they rapidly open and close. This helps promote fuel atomization, however, if these valves begin to leak they will tend to flood the affected cylinders, which can cause hard hot starting and/or rough running for the first few seconds until the flooded condition clears up. Also, leaky injectors can cause excessively rich mixtures in the affected cylinders, and since the lambda system reads the average A/F ratio across all cylinders it will bias lean, which could cause some cylinders to get into enough lean misfire to both increase idle roughness and drive up the HC count.
Achieving good idle quality with continuous flow injection systems is problematic (The Rochester FI system used on Corvette and some other GM engines from '57 to '65 is an example.), and is probably one reason why Mercedes finally abandoned the system and went with electric solenoid injectors.
It's my belief that KE injector "wear" that leads to leaks is a primary cause of both the idle roughness that KE engines tend to develop as they age and also contributes to the generally higher HC emissions that KE-equipped engines exhibit relative to solenoid injector engines of the same vintage.
These injectors can be cleaned, leak, and flow tested, but the cost may not be much less than just replacing them with new parts.
Your observation of no fuel in two lines indicates that these injectors were probably leaking. The others are probably serviceable. It takes only one leaky injector to cause increased idle roughness and a higher HC count, particularly at idle.
Duke