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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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

hobfinger

replaced my injectors on my 300E two weeks ago resolved my warm start problem, idles smooth, hard to tell if the engine is running.

it solved some of the problems I had, but not all. In fact, is is now a bit rougher all around, but more consistently so, i.e. it's rougher when cold and smoother when warm, but still slightly rough. I suspect the idle mixture had been messed with to compensate for the bad injectors, or I may have bad timing due to a worn out timing chain... (at 99K? I don't know)

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

Thanks for your installation tips. I am deciding if I can do this job myself. I have a 560 SEL and I have not messed allot with engines in the past. Do I need special tools for this job? Any additional tips are very much appreciated.

Thanks

Would doing a heavy duty fuel injection service through http://www.bgprod.com/ give similar results? I only ever changed the injectors once which was on my ex - the W201. I think I may try the BG first and measure my results. I'm curious about these products.

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1989 300CE Astralsilber/Schwarz
1992 300CE Schwarz/Schwarz

justt took a look at the prices for my s500 injectors and the best price i could find was $233.00---EACH!!?
IS THAT RIGHT?

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'95 s500 (bought for wife but can't bear to share!!!) 125kms
'92 legend 180kms
'88 tbirdturbo(fantastic car-only regular maint.)120kms
'87 mustang gt(gone)
'86 tbirdturbo(gone)
'85 mustang gt(gone-but not forgotten)

I just checked with one of my suppliers and they don't have them for you car so I don't know how much they cost. The supplier I deal with specializes in Mercedes and BMW parts. The have almost everything. The only time they don't have a part is when it's very expensive and/or a low demand on that part.

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1989 300CE Astralsilber/Schwarz
1992 300CE Schwarz/Schwarz

I had the same problem with mine. After installing the injectors your mixture needs to be adjusted with a gas analizer. Mine was very lean. Runs like a champ now.

John

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President Minuteman Section MBCA
www.mbca.org/minuteman

You might find them a little cheaper but probably not by much. Surprisingly dealer prices are often competitive - don't know why that is. There are two basic types of injectors - the old style and the new style. Only the old style, which tend to run about $25 to $30 each can be replaced on a preventive maintenance basis. The new style, i.e. $150 to $250 each, you don't replace just because they've got some miles on them. You clean and refurbish instead. The good news is that the expensive ones rarely go bad.

The good news is that the expensive ones rarely go bad.

well that's good to hear!!!!

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'95 s500 (bought for wife but can't bear to share!!!) 125kms
'92 legend 180kms
'88 tbirdturbo(fantastic car-only regular maint.)120kms
'87 mustang gt(gone)
'86 tbirdturbo(gone)
'85 mustang gt(gone-but not forgotten)

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