450 SL 1973 - D Jet. Trigger Points/MAP Rich Condition - Mercedes-Benz Forum

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post #1 of 19 (permalink) Old 03-18-2017, 08:50 AM Thread Starter
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450 SL 1973 - D Jet. Trigger Points/MAP Rich Condition

Hello,

I've finally gotten my 450 to run and I can see it is running in a overly rich condition.

The spark plugs are getting black very fast and the exhaust fumes smell very rich.

Where should I look first, MAP or the trigger points?

I've also read that the DME capacitors and resistance of the resistors can degrade over time also causing a change in the air fuel mixture.

Thanks in advance...from a fellow D Jetter

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post #2 of 19 (permalink) Old 03-18-2017, 09:36 AM Thread Starter
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Are the 280 SE MAP sensors interchangeable with the 350/450?

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post #3 of 19 (permalink) Old 03-18-2017, 12:21 PM
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The MAP sensors are not interchangeable..... there is a resistance check of the MAP sensor in the Djet section of the http://www.benzworld.org/forums/r-c1...ka-egv107.html. there sre several basic things to check, fuel pressure is one that I would check....

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post #4 of 19 (permalink) Old 03-18-2017, 03:25 PM Thread Starter
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Thank you.

Seems there are loads of things to check...Switch gear... Trigger points....MAP, etc.

Do you think fuel pressure can cause a rich condition?

Thank you

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post #5 of 19 (permalink) Old 03-18-2017, 05:05 PM
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Originally Posted by S320L1999 View Post
Are the 280 SE MAP sensors interchangeable with the 350/450?

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If you mean the 280SE 4.5 and USA 450SL with M117 engine, then engine and djet parts should be interchangeable. Same for USA 350SL which is of course a 4.5 but not for Euro 350SL or 450SL.
More important is to have ECU and MPS that match.
MB Part numbers are I believe:
ECU 0005452632 (Bosch 0280002005) and
MPS 0025422817 (Bosch 0280100100)

Re rich mixture, it could be caused amongst other things by:
- worn trigger points (check Comprehensive post in EGV107 for dimensions etc)
- faulty temperature and pressure sensors (check them using method in shop manual)
- high fuel pressure (29-30psig is normal)
- someone tying to adjust MPS without exhaust analyzer (check if epoxy seal over adjustment screw has been disturbed)

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

Last edited by MBGraham; 03-19-2017 at 01:43 PM.
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post #6 of 19 (permalink) Old 03-19-2017, 03:52 AM Thread Starter
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Great, thank you Graham and all others.

1. I will check the temp sensor and pressure sensors - do you have the shop manual to check these out?

2. I will remove the triggers and see if everything looks as it should.

3. How would I check for correct fuel pressure, connect a gauge on the fuel rail?

4. MPS looks to be untouched -

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post #7 of 19 (permalink) Old 03-19-2017, 07:20 AM
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Great, thank you Graham and all others.

1. I will check the temp sensor and pressure sensors - do you have the shop manual to check these out?

2. I will remove the triggers and see if everything looks as it should.

3. How would I check for correct fuel pressure, connect a gauge on the fuel rail?

4. MPS looks to be untouched -
1. Link to shop manual is in EGv107
2. Measure the rubbing blocks - see Comprehensive Djet post EGV107
3. Yes - tee in or use start valve connection.
4. Good.

1972 350SL 4.5L - MBGraham, near Kingston, Ontario
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post #8 of 19 (permalink) Old 03-19-2017, 01:39 PM
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Not up on the V8 but the M110, D-Jet ECU, has a knob to adjust the A/F ratio.
As stated don't try it without an A/F gauge of some sort.
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post #9 of 19 (permalink) Old 03-19-2017, 01:59 PM
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Not up on the V8 but the M110, D-Jet ECU, has a knob to adjust the A/F ratio.
As stated don't try it without an A/F gauge of some sort.
There is a knob on the ECU on V-8s. It only fine tunes IDLE A/F ratio. Has no affect on load A/F ratio which is controlled by MPS. Probably true for all D-jets. (This provided idle contacts in TPS are properly set up)

You can play with this knob to improve idle. Best with A/F or CO meter, but you can set in middle of it's range (11 clicks from either end), then try one click at a time in either direction and see if idle smooths out at some point (need to give throttle a little burst between adjustments) Clockwise is richer, counter-clockwise is leaner. Engine needs to be fully warmed up before adjusting.

1972 350SL 4.5L - MBGraham, near Kingston, Ontario
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post #10 of 19 (permalink) Old 03-19-2017, 03:23 PM
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When I'm following my personal guideline, "always check the easy stuff first", I ensure the knob is centered.
Sounds like it's good for V8's also.
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