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1973 450SL, (Previous 2008 ML350,2002 E320 Wagon, 2000 SLK230)
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56 Posts
Hi Hans,
try to change the electrical connectors between cylinder 5 injector and cylinder 6 injector.
The time the injectors 'fire' doesn't matter much, and you can check if the error moves to cylinder 6.

Try to interchange the spark plugs between the cylinders, too. A good spark in free air doesn't mean they function properly in the engine under pressure.

The spark plugs mounted are 'suboptimal'. The 'R' means 'resistor' and originally no resistor plugs were used. Resistor plugs tend to get bad.

Using resistor plugs is not a problem on most engines, but the M116 is quite sensitive.
Buy the Bosch spark-plugs directly from Mercedes <not the maybe fake aftermarket scrap> or try NGK BP6ES.

Regards
Norbert
I just want to thank you for this suggestion. My '73 450SL has been missing/loping/running rich since I bought it. I was at my wits end, even looking at potential replacing the distributor or trigger points when I came across this. I pulled one of the plugs that an indie installed (plugs, points, wires, cap, rotor, etc - $1000 and still had the lope). They installed Bosh R6 plugs. I replaced them with what was immediately available - NGK BPR5EGP, and after the smoke and colorful language cleared I turned the key. No stuttering, no loping, no drop in idle. It followed from cold to hot and ran perfectly - the best this has ever run. I took it for a ride and it was a pleasure, without having to pull off the gas, overexert the pedal - just drive. I'm hoping this is definitely the fix, but doing so absolutely improved the performance. Thank you!!
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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10,766 Posts
Glad to hear your car is running well!.

Just wanted to mention that the plugs Norbert suggested were NGK BP6ES . Many of us use these. They are non-resistor plugs. The ones you have are resistor plugs (R in number) - they have a 5kohm resistor built in.

Many owners feel the resistors are detrimental to performance, but my own experience with Bosch resistor plugs over many years was good. I now have the NGK BP6ES in the car, but only because someone gave me a set!

Another issue that may be brought up, is that the plugs you have (BPR5EGP) have platinum centre electrode. These are not usually recommended, although I can't recall reasons. BPR5EGP $3.08 NGK 7082 Spark Plug - Best Car Spark Plug Replacement

The NGK BP6ES plugs are inexpensive - probably worth putting a set in, even if only for peace of mind :)
 

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1973 450SL, (Previous 2008 ML350,2002 E320 Wagon, 2000 SLK230)
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56 Posts
Unfortunately these were the only ones available locally, and my window to work on this was tight, so I rolled the dice and bought them. I was becoming so frustrated with this situation, that I was considering selling the car, but now I can pause, breathe, and enjoy for the moment knowing the hard work and frustration was worth it. I'll take you your advice and order a set for the long term operation of the vehicle - thank you.
 

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1973 SLC 450
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26 Posts
Hi Norbert,
I am presently replacing the Trigger Points (in my 73 Mers 450 SLC) that I bought from Volker. I just wanted to check that all is ok before I put it back in the car ( I set the gap to app. 0.5 mm but it is hard to get it exactly 0.5 mm). I rotated the distributor checking with a multimeter and and marked on the top of the distributor the range when each of the 4 points were 'firing' when there was a circuit. Using a protractor I measured this time period as a degree.
1/. Is this time period when the contact points are closed / contacting?
2/.My range was approximately Red 147 Dg, White 150 D, Green 150 Dg and Yellow 140 does this seem reasonable? MBGraham in this post Trigger Points Cleanup & Adjustment recommends that they should be between 100-120 degree??? What are your thoughts?
Regards
Peter
Distributor.jpg
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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10,766 Posts
You were asking Norbert, but I happened to see your post. If you can readjust and get those angles down by 15-20deg, (say 125deg) you will be better off. Otherwise, it won't be long before the fiber blocks wear more and you will start having problems.
There is no exact angle. We just want the points to open and close reliably and not bounce and send multiple signals. Anything from 100-140 deg seems to work, but if you are adjusting, go for the lower end of the range.
 

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1973 SLC 450
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26 Posts
Ok thanks - They are new so I want to get it right. To close the angle do you open or close the cam gap? Thanks Peter
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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10,766 Posts
Peter,
I am surprised a new set would have that large a closing angle and need bending. I had a brand new set and they were
higher than I would have guessed. But still 122, 140, 139, 120. I suspect that depending on just how the points fit against the distributor, they could go in slightly to one side and result in these type of varying readings. I left them as-is and the car runs well.

Norbert has made changes in his tool design from the early version I have. Assuming you have his tool, it would be best if he explains how best to decrease the closing angle. I may be wrong, but my guess is that you would use a larger gap. Maybe use 0.6mm or 0.025" following Norberts' instructions and see what angles you then get?
 

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W212 E350 vanagon
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75 Posts
Hi,
I don't adjust the trigger points with an oscilloscope but use my tool(s).
This adjust the points to maximum reliability - the middle between 'not closing anymore' and 'not opening anymore'.
As I <and Graham> wrote before, an absolutely exact timing isn't neccesary.

The unit has some 'play' when being installed into the distributor, therefor you will very seldom find absolute same readings when checking with an osci.

Volker Huck from jetronic.org <former oldtimer.tips> owns a distributor-test-stand and prefers measuring / controlling using an oscilloscope.
He says the optimal value for the closing time is between 140 to 150 degrees, but I by myself can't verify this.
Never used my oscilloscope to check this...

You increase the closing angle by using a larger gap.

Regards
Norbert

Add: I just noticed Peter crossposted his questions to the jetronic-forum. Here is the link and the answer from Volker :Link to the Posting
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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Hi Norbert,
Volker Huck from jetronic.org <former oldtimer.tips> owns a distributor-test-stand and prefers measuring / controlling using an oscilloscope.
He says the optimal value for the closing time is between 140 to 150 degrees, but I by myself can't verify this.
You increase the closing angle by using a larger gap.
On oldtimertips, he at one time had a number of 135deg :) As I am sure you know, there is no magic or optimum number. We just want to get one pulse! So any number will do up until the points start bouncing and sending multiple pulses. Because the fibre blocks wear, it just makes sense to start with a low number. So if closing angle is say 125deg to start, it will be some time before it gets to those 'optimal' values ;) A lower number maybe even longer life :)

You said use larger gap to increase the closing angle? That gap is the one between your tool and the rubbing block?
I am a bit confused :(

This is from your post in another thread:
Using my tool, the points will work at a gap between 0.004 in <less = points opening no longer> and 0.04 in <more = points closing no longer>.
The gap of 0.5 mm (0.02 in) is the median and allows the highest tolerance the unit in positioning or the distributor-camshaft could have.
So small gap, points closed for longer. Large gap point closed for less time.

If present closing angle is 140-150deg and we want to reduce it to 125deg, we would then need a larger tool gap - perhaps something between 0.02" and 0.04"? Maybe try 0.025-0.03" and see what the angle is?

Norbert, please correct this if I am wrong. I haven't looked at trigger points since I installed my new set :)
 

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W212 E350 vanagon
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75 Posts
Hi Graham,
the larger the gap between fibre-blocks and bottom of the distributor-camshaft, as longer the points stay closed <and as smaller ist the points-gap>.
The smaller the gap between fibre-blocks and bottom of the distributor-camshaft, as shorter the points stay closed <and as wider is the points-gap>.

The points are closed as long as the blocks are not touched and lifted by the cam.

We adjust the points for the best reliability - maybe one could adjust them a little bit different for prolonged life.
But why? Correctly greased, the trigger points will have a life of about 100k miles - and then you could still readjust them most likely.

Rubber blocks show wear only when they are not greased or the distributor-cam ist rusty maybe because the car has sitted for a long time.

Maybe you, Graham, are a little bit confused because you own one of the very first of my tools.
I designed this first version before I got knowledge of the plastic-shielded points I hadn't seen before at this time.
Yes, this tool is suboptimal for adjusting plastic-shielded trigger-points.
You have to measure the points gap, not the fibre-blocks-to-the-tool gap.
Using the early tool, adjust the points gap like the spark-plugs-gap <compare it by eye> and all will be o.k.

I would like to send you the later tool, but Corona makes it impossible for me as I wrote before.

Regards
Norbert
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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Add: I just noticed Peter crossposted his questions to the jetronic-forum. Here is the link and the answer from Volker :Link to the Posting
As you know, for a long time, many of us here have adjusted trigger points by setting the closing angle.
Trial and error at first.
When you later produced your tool, it made things easier!
Over time, we learned that at above about 150deg, bad things start to happen. Usually rich mixture that many could not explain. 100-140 deg and there are no problems. If I was Peter, I would aim for 125deg. The exact number is not so important.

Having said that, I will stay out of any further discussion of Peter's points.. Good Luck Peter!
 

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W212 E350 vanagon
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Hi once more,
  • long closing time (150°) means :
  • wide play between tool and fibre blocks
  • points opening late, closing early
  • small points-gap
not much reserve for fibre-blocks-wear.

  • short closing time (100°) means:
  • small play between tool and fibre blocks
  • points opening early, closing late
  • wide points-gap.
high reserve for fibre-blocks-wear, but maybe probs with fluttering points.

Consider adjusting using my tool... you will get reliable adjustments and the trigger points life will be as long as if they were new.

Understanding and simplifying problems is the real art of engineering... not the use of hi-tech-equipment.

Regards
Norbert
 

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1973 SLC 450
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Thanks all,
For an amateur I really appreciate the way you have explained the situation. At the moment I have set the gap to 0.5 mm (rather tight 0.5mm) which gives me all 4 at 143° of closed points.
Thanks all.
 

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1973 SLC 450
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Peter,
I am surprised a new set would have that large a closing angle and need bending. I had a brand new set and they were
higher than I would have guessed. But still 122, 140, 139, 120. I suspect that depending on just how the points fit against the distributor, they could go in slightly to one side and result in these type of varying readings. I left them as-is and the car runs well.

Norbert has made changes in his tool design from the early version I have. Assuming you have his tool, it would be best if he explains how best to decrease the closing angle. I may be wrong, but my guess is that you would use a larger gap. Maybe use 0.6mm or 0.025" following Norberts' instructions and see what angles you then get?
Hi Graham,
I needed to adjust them as I had already adjusted them for the old worn set.
Thanks
Peter
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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Norbert - from experience, we know that rich running problems occur when rubbing blocks are worn and closing angle is high. This is cured when the points are adjusted so that closing angle is reduced. This has been proved over and over. We don't know for sure, but Porsche and other owners attribute the richness to multiple pulses (fluttering?)

Didn't you just said the opposite of that when you said "high reserve for fibre-blocks-wear, but maybe probs with fluttering points."

One thing you could add to your instructions, is to recommend checking the opening/closing angles after completing adjustment. (that is what we usually do) If closing measures in say 120-140deg range, then users would know they have made a reasonably good adjustment. Using numbers in your instructions, the angle should actually come out to 135deg (1/2 way along ramps between larger and smaller diam of cams.). It is a lot easier to measure angles than points gaps.

Anyway, we know from experience what works, so no need to keep this discussion going.
 

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1973 SLC 450
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Sorry to be a pain,
I put the distributor back on and noticed that it was only running on 4 cylinders 2 pairs (1 and 5 and 4 and 8 are NOT working). It has spark - my fingers can testify this but I put a multimeter across the connection on the Trigger Point terminals using the black as the common- I got around 2.6 volts on the red and Green but next to nothing on the White and Yellow ( I'm pretty sure these are the banks not firing).
The question I have is this a Trigger point issue or an ECU issue or something else? Remembering these are a new trigger points
Regards
Peter
2649279
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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Maybe first check resistance between ground and each other wire using ohmmeter. Should see it swing from 0-infinity as you rotate engine. You can use starter (maybe pull coil wire so it does not start.) Covered in Section 07.4 of manual section 040-13. Do you know which wire is ground?
This will confirm that problem is not in trigger points or their internal wiring.

The trigger points don't carry the injector voltage. They just provide pulses. You can check injector voltage at the injectors or back at the ECU.

If you have the original trigger points and cable connector, compare the wiring on the plug. I don't have that type of connection, but others have had trouble with the wiring to that plug when making changes.
 

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'72 450SL, 107.044-12-000422
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That continuity check would verify proper operation of the points, but if I'm understanding correctly, he's only seeing signal voltage (2.6 volts) to two of the four points. That signal voltage comes from the ECU so could be a problem with the ECU or in the harness. However, I'm not sure if the ECU provides a constant signal voltage to all four points. Maybe try rotating the engine and check the "dead" points again.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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10,766 Posts
That continuity check would verify proper operation of the points, but if I'm understanding correctly, he's only seeing signal voltage (2.6 volts) to two of the four points. That signal voltage comes from the ECU so could be a problem with the ECU or in the harness. However, I'm not sure if the ECU provides a constant signal voltage to all four points. Maybe try rotating the engine and check the "dead" points again.
EDITED: Memory coming back! If you measure voltage from each trigger point harness contact to ground while engine is running or being spun with key on, You should get a voltage. It is not a very useful one, but if all are the same, that is a good sign. If you don't, do the other checks to help find out why. (What you will measure is a sort of square wave alternating voltage. 12v on then off. Voltage on DVM is approx the average.)

Checking voltage at the triggers as above, may help a little. Continuity at distributor (points open and close), and then continuity again back on ECU plug (to check harness wiring) will help in trouble shooting. If the points can be shown to open and close in both those locations and still no voltage signal goes to 4 injectors, then there must be a problem elsewhere.

It would then be just as well to check the injector wiring. Using method in FSM 07.4 40-16. Pull plug at ECU and measure resistance for each pair of injectors in turn from pins 3, 4, 5 & 6 to ground. That will give you combined resistance of two injectors in parallel (~1.25ohms). If you don't see that, pull one of the pair of injector plugs and you should see ~2.5ohms for the single injector.

Once you have done both of these checks successfully, but car still only runs on 4 cyl, then ECU might be the problem. Try to borrow a spare for testing!

 

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W212 E350 vanagon
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Hi,
measuring the Voltage at the working trigger points is a testing method Bosch describes in the special D-Jetronic manual describing the testing procedure using the EFAW228-D-Jetronic tester.
@MBGraham, I think I sent this to you some years ago?
The Voltages are not so important - but they should be similar on the different 'channels'.
-------------------------------------------
Having injected a channel, the ECU needs the signal of a second <paired channel> trigger-point before it allows the first channel to inject again. This function is realized by some flip-flops in the ECU.
Therefore - when only one trigger-point isn't functional or the wire is broken, the corresponding channel of the ECU will not be functional anymore.
Two channels will fail.

Regards
Norbert
 
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