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Registered
1988 560 SEC
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32 Posts
Discussion Starter #1
Hi guys

My 560 SEC engine surges and seems to hunt the mixture. At idle a multimeter on pins 6 and 3 of the diagnostic plug show that the car starts about 5.5 and then reduces to 2.8 and the straight back to 5.5 or so.

This causes the car to loose rpm as the number decreases and then jump up again when it goes back to 5.5. Rpm drop is maybe 150 or so.

It has a new idle controller and valve, injectors and EZL unit.

Any ideas ? Am I measuring these number the right way with a multimeter ? What should they be ? How can I adjust them and how can I get them to stabilize ?

Cheers
Daisy
 

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Premium Member
1991 560 SEC 1994 E500 2014 E350 Cab
Joined
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7,029 Posts
smoke check the manifold for leaks, I had 17 and replaced all the rubber and vac lines. Seats seals and injectors gor r/r as well. Your fuel fuel filters might need a swap as well.
 

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Registered
1988 560 SEC
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32 Posts
Discussion Starter #3
Hey there. Thanks for the reply.

Have checked most of this. New rubber manifold skirt, new injectors and seals, and smoke test found no leaks.

I have looked at the rubber air piping around the engine but didn't see anything wrong. Vac lines I have not looked at. Fuel filters are new.

Does the engine fuel computer fluctuate the mixtures for some reason ? It seems to start rich and run down to lean then straight back to rich again, over and over. And not just at idle either, but at low to mid throttle too.

Thanks
Daisy
 

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Premium Member
1991 560 SEC 1994 E500 2014 E350 Cab
Joined
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7,029 Posts
Yes it does, if rpm will go from about 520 to 760 but drop down to 520 after it warms. *O2 sensor maybe, usual issues Icv and the fuel flow regulator. *Mcclare is a great source, review his threads. *My surging idle issues caused me to get new tranny so don't neglect it or band aide fix it. *Spending 800 might save 8k lol.

Louis
 

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Premium Member
1991 560 SEC 1994 E500 2014 E350 Cab
Joined
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7,029 Posts
smart phone repeat, sorry
 

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Registered
'82 Euro 500SEL, '85 Euro 500SEC AMG WB Cabriolet,'86 Euro 500SEC RUF
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9,487 Posts
Have you had the Air/Fuel ratio checked on a CO machine? Sometimes that mixture is off a bit and will cause a surge. As said above the O2 Sensor could be bad, Also the EHA could be wonky.
 

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560SEC / 850CSI / 525i
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73 Posts
Just to add to the above, Ive been fighting high idle (1000rpm) and some minor surging since I bought it couple months ago. I found and fixed many vacuum leaks (hoses) and tested for more around the injectors.. problem was I tested with a Penetrating Lubricant (some 3M stuff) which indicated no leak around injectors.

Today on a whim I bought Carb Cleaner and retested and I was nearly able to make the engine cut out by spraying on 2 particular injectors! The rest seemed a bit leaky too. To test even further, I used some spray grease, its sprays like WD40 but sets to a sticky film, much thicker than WD40/3M stuff and should fill rubber cracks (temporarily) . Sure enough, for the first time ever my idle dropped from 1000rpm to 800rpm and maintained it. It had a fairly uneven sounding idle however, but maybe Euro SECs are like that (I heard they idle like old American V8s)?


Regardless, Ive ordered new injector upper seals and lower orings (hope I can re-use the holders). Everyone else, dont use WD40 or a penetrating spray for testing!
 

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Registered
1988 560 SEC
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32 Posts
Discussion Starter #9 (Edited)
Hi again guys

Have done a fair amount of work now to my engine. Still have problems.

Car now has a new CIS-E box, new EHA, O2 sensor and alternator. I have tested all the wiring associated with the alternator, have done a full check for vacuum leaks and done a gas analysis/mixture check and set mixtures correctly.

Timing about +8-10 at idle and up to +35 at high RPM. Car has a new EZL, crank sensor and vacuum for the EZL comes from a source that has low vac at idle and increasing vac with RPM (From out of the side of the guard, not from a direct engine source. Direct from the manifold set the timing very high)

Car still has the following problems.

1. A test on pins 2 and 3 of the diagnostic plugs shows about 3.6 volts with ignition on and then about 2.2 with the engine running. This 2.2 does not fluctuate as it should ??

2. Alternator is only charging to 13.2 volts.

3. Dashboard temperature guage over reads dramatically (no change to other guages) and electrical drain - say, attempt to raise a window with already up, or, turn on the A/C - and the engine changes note at idle (drops RPM) and the temp guage changes reading.

4. Idle RPM is all over the place still too. 1200 - 800 (New idle controller helped a little) But still wanders.

Having said all that - the car run great ! No hesitation on first throttle crack and good power. At cruise RPM engine is smooth and steady. Hard to keep the wheels from spinnng !

But, I would like to fix the above dramas. Any ideas ? On any of it ?

Cheers
Daisy
 

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Premium Member
1991 560 SEC 1994 E500 2014 E350 Cab
Joined
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7,029 Posts
K I will not pretend to draw a effective conclusions, but after I had my work done, similar to yours, I started to have electrical problems. After driving, with the a/c and radio with amplifier, radiator fan on etc, my car would begin to die. the fan on the inside would slow at low idle, the radio would cut out etc. I replaced the alternator with a 150 amp alternator and voila, no more issues. A NAPA check had me at 869 CCA on the battery, but the alternator was at 13.2, and then at 13.6. So the conclusion for me was that the stock alternator could not keep up with the more powerful a/c I had installed running at full blast, with the radio/amplifier and opening, closing the windows....oh yes I forgot, the foglights on as running lights. So that all came about after I fixed the idle issues and you must spend time with the air flow/fuel mix to get it right. Again, just what happened to me, not what could be with yours.
 
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