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- Sent: Friday, February 25, 2000 11:04 AM
Subject: 1989 560sel - rough idle
Hi
I have a very good Mercedes mechanic but we have a problem with what I
will describe as a rough idle. The car starts good, runs good, but has a
slight miss in it at up to 1000 rpm then it clears up. It is slightly
worse with engine hot than cold. We have replaced the distributor cap
and rotor, spark is excellent, all wires are metered in proper ohm age
range, the fuse on the relay that might go if you jump start the car is
good, compression is excellent, fuel mixture is right on, it makes no
difference if air conditioner is on or off. The motor purrs but if you
look at the engine it has a slight shuddering as it misses. I love my
car, but this little problem is aggravating. By the way, we also checked
for vacuum leaks and found none. If you disconnect various vacuum hoses,
idle speed will vary, but the miss is still there. Yes, there are new
bosch plugs in it and the egr valve is working properly. Any advise
would be appreciated.
Maurice
- Sent: Tuesday, February 29, 2000 9:31 PM
Subject: Re: 1989 560sel - rough idle
Hello Maurice.
- Sorry it has taken me so long to get back to you. I worked on
a problem like this last week. One thing to try is the fuel distributor. I
know that these are very expensive but I have something for you or your
mechanic to try. What happens alot is that small particles build up inside
the distributor plugging the small screen inside each outlet port for the
cylinders. Remove all of the fuel lines at the top of the dist. leading to
the cylinders. Take a small wood screw and insert it into the top opening,
turn slightly to lock in and pull out the screen. This is very easy to do
and will not ruin the dist/ fuel flow etc.... Try it. I did and it works
great. Or you can buy a new one for a small fortune. Let me know if you do.
Another thing to do is to check the go/no on the hydraulic liters. A small
gauge ( available for about 45 bucks ) fits over the top of the hyd. lifter
and rocker giving the measurement. You can find out how to do this in the
116/117 engine manual for the 380/420/560. If you find one valve too far off
you simply change the thrust washer on the valve spring to compensate and
adjust for the difference. A cylinder time balance test will help you narrow
down the choices. I would check all the cylinders. I can get the tool for you if you would
like one. JON
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