73 450 sel. no injector pulse - Page 5 - Mercedes-Benz Forum

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post #41 of 52 (permalink) Old 03-14-2016, 08:41 PM Thread Starter
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I'm still baffled. Now it's only sputtering a little while cranking again. I'm at the end of my rope with this thing. Help.

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post #42 of 52 (permalink) Old 03-14-2016, 09:12 PM
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Figuring it out is part of the fun. You will be more proud when you figure out what's been wrong and how to fix it.

Don't let a hobby frustrate you. It's supposed to be fun. Right?

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post #43 of 52 (permalink) Old 03-14-2016, 09:19 PM Thread Starter
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The fun factor went out the window on this one a while ago. It's electrical and I just can not seem to trace the issue and parts are too expensive to just throw at it until it works.
I'm thinking those trigger points are shorting across or something. So correct me if I'm wrong. Is it one common positive wire going to the points and 4 outputs? Or is it 4 positive feed wires and 1 ground?

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post #44 of 52 (permalink) Old 03-15-2016, 06:17 AM
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Do you mind summarizing your symptoms once again? We are on post 43, and I'm sure there is lots of information pages back, but most readers probably won't go all the way back. If you can say what is, and what is not working, I bet that would help.

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post #45 of 52 (permalink) Old 03-15-2016, 08:02 AM
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Do you mind summarizing your symptoms once again? We are on post 43, and I'm sure there is lots of information pages back, but most readers probably won't go all the way back. If you can say what is, and what is not working, I bet that would help.
I was thinking the same way. Summarizing symptoms and just what has been done so far, would probably help you (as well as us) in trying to figure out what the problem is. A number of suggestions have been made. It would help if you indicate which ones you have acted on and what the results are.

Regarding the trigger points. Terminal 12 is a ground. It connects to pin 11 of the ECU internally which is the ECU ground. This is a diagram of a 4-cyl Djet, but principle is the same. Trigger points are on left hand side.

http://www.pelicanparts.com/914/part...rical/ECU1.jpg

1972 350SL 4.5L - MBGraham, near Kingston, Ontario

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post #46 of 52 (permalink) Old 03-15-2016, 12:15 PM
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... Is it one common positive wire going to the points and 4 outputs? Or is it 4 positive feed wires and 1 ground?
No. The trigger-points work on connecting to ground. Injection pulse is started when the points get closed.
The 'main' ground wire is in the middle, the other ones switch the ECU when they get grounded.
You can check this using a LED continuity-tester. It has to blink intermittendly when the engine is turning.
You can't test this with a modern multimeter because it reacts too slow.

Best way to check and adjust the points is using the tool I developed. You can produce it by yourself if you have a lathe. Ask me for the figure by PM.

I ship the tool all over the world, too. 20.- US$, payment via Paypal. shipment will last about 10 days. Contact me via PM.

MBGraham owns the tool - don't know he now has got experience using it.

Have a look at it here: https://oldtimer.tips/en/forum2/jetr...er-gebiss#2346

Download the instruction here: https://oldtimer.tips/media/kunena/a..._en_ver3_1.pdf

Regards
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post #47 of 52 (permalink) Old 03-15-2016, 01:19 PM
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You can't test this with a modern multimeter because it reacts too slow.

Norbert
Hi Norbert,
An ohmmeter is a very useful tool for checking the trigger points when the distributor has been removed from the car. I use a non-digital needle type. I have not tried this without removing distributor, but provided engine can be turned over slowly by hand, it should still work (I must try that when I get back to Canada)

The method involves checking the angle the rotor must be turned through in order to open or close the points. We do this for each set of points using 12 as the common ground point. If the points stay closed for something in the 110-140deg range, then that shows the rubbing blocks don't have excessive wear. But if we see something over 150deg, then rubbing blocks are getting near end of life. We also see poor performance (usually rich mixture) when they are like that even although they are still opening and closing. This is the method I used successfully some time ago when I had very poor engine performance (before I knew about your tool). You should try it

I do believe your tool makes it easier to check and adjust the points. I have used it to check a brand new set of points as well as for adjusting one of my spare sets. It worked well. Brand new points had smaller gap than you suggest adjusting to, but your number is good. Unfortunately, not everyone has the patience to wait for the tool to come from Germany when they are frustrated and anxious to get their car going! And not many have a machine shop to make one. But for $20, they should just get one of yours on order! It is a much quicker check than setting up to use my method above.
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1972 350SL 4.5L - MBGraham, near Kingston, Ontario

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post #48 of 52 (permalink) Old 03-15-2016, 03:50 PM
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Hi Graham,
thank you for having my tool described so positive and recommended.

What now concerns my recommended setting - it refers to the old NOS sets that were available to me. Possibly Bosch has reduced the gap at the newly produced versions. But this is not functionally crucial. The recommended value of mine considers all possible tolerances and establishes the exact average.
New pulse generators have certain tolerances, too.

Of course I also know the electrical measurement method that you describe and yet another that works in operation.

But for me, it is the best to remove the pulse generator out of the distributor, clean, visually inspect, re-grease and afterwards reassamble it. This really helps to maintain the reliability and minimize wear.

One then can leave this for many years or miles in the distributor without thinking about it...

Regards
Norbert
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post #49 of 52 (permalink) Old 03-16-2016, 09:04 AM
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But for me, it is the best to remove the pulse generator out of the distributor, clean, visually inspect, re-grease and afterwards reassamble it. This really helps to maintain the reliability and minimize wear.

Regards
Norbert
Certainly agree with that for most of us DIYers.

However, not everyone is comfortable with removing the distributor. And from personal experience, on the V-8 Mercedes, it takes some care to get the distributor back where it was and with correct timing. (and not drop the clamping screw!)

I want to try checking the closing angle of the trigger points in-place. This would be a way of doing a quick-check of trigger point wear without having to re-time the engine.

1972 350SL 4.5L - MBGraham, near Kingston, Ontario
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post #50 of 52 (permalink) Old 03-16-2016, 04:52 PM
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I want to try checking the closing angle of the trigger points in-place. This would be a way of doing a quick-check of trigger point wear without having to re-time the engine.
Hi Graham,
BOSCH describes a procedure in doing a dynamic test in the manuals meant for the use with the EFAW228-tester.
Without this tester, you can do exactly the same using a multimeter:

- run the engine at 2000 rpm.
- read the Voltage between the center pin and the (4) points pins.
- the readings should not differ by more than 1.5 Volts - else the points have to be replaced.

Testers other than Bosch have a special function for testing the points dynamically. Because the Janbo, the Ditron and the Kent-Moore testers all replace the ECU (ECU is NOT connected when testing, fuel pump is switched on by a separate switch) they have an adjustable function for driving the injectors without any influence of sensors or the trigger points. With the engine running without the ECU the dwell can be measured.

Regards
Norbert
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