Rich running 4.5 any advice? - Mercedes-Benz Forum

 
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post #1 of 7 (permalink) Old 03-27-2016, 11:53 AM Thread Starter
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Rich running 4.5 any advice?

Hi All
I just fitted the petronix ignition module (1885). The car starts right up and runs lovely. But ever since I fitted it, the car is running to rich. The gas mileage is not good at all. Can anyone tell me the steps to check to dial it in properly? The car always ran very nicely before, with good spark plug color and reasonable gas mileage for a 4.5.
Happy Easter.
Cheers John.
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post #2 of 7 (permalink) Old 03-28-2016, 10:16 AM
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Hmmm, looks like my previous reply didn't stick...

The thing that hits my mind immediately is the air temp sensor connection. Without it, the car runs more rich. Is it possible you broke a wire or connection while removing the air cleaner (assuming you removed it?)?

At idle, the mixture adjustment is on the ECU itself. Under load, the mixture is adjusted at the MAP sensor. When I installed my pertronix, the mileage actually improved ...
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post #3 of 7 (permalink) Old 03-28-2016, 01:18 PM
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Checking the temperature sensor wiring is a good start (bad coolant sensor can cause rich mixture).

Higher than standard fuel pressure will cause rich mixture.

Perhaps timing is off? Hook up a timing light, and first check that you get fast advance from about TDC to 25-30 BTDC as you rev from idle to ~3000rpm. It's possible that the Pertronix may be preventing the centrifugal advance from working by binding on something.

If advance is working properly, set timing so it is at about 27 BTDC at 3000rpm - at idle it will be at TDC or even 5BTDC.

In order to adjust mixture using ECU (for idle) or MPS (for load), you really need an exhaust analyzer or AFR gauge. Before doing this, I would check:
- both temperature sensors
- fuel pressure
- timing
- all vacuum lines are connected.

BTW, did you install 1885 just as points replacement or did you also bypass the switchgear?

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post #4 of 7 (permalink) Old 03-28-2016, 04:47 PM
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Originally Posted by Grubeguy View Post
Hmmm, looks like my previous reply didn't stick...

The thing that hits my mind immediately is the air temp sensor connection. Without it, the car runs more rich. Is it possible you broke a wire or connection while removing the air cleaner (assuming you removed it?)?

At idle, the mixture adjustment is on the ECU itself. Under load, the mixture is adjusted at the MAP sensor. When I installed my pertronix, the mileage actually improved ...

I like mbgraham's timing suggestion. That's one thing that's pretty much guaranteed to change when moving from points to pertronix.

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post #5 of 7 (permalink) Old 03-28-2016, 10:46 PM
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Pertronix igniter unit does change the timing and requires advancing the ignition quite a bit ,first noticed that on my M130 engine .
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post #6 of 7 (permalink) Old 03-31-2016, 08:49 PM
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I have the same issue after a Pertronics install. MBGraham recommends checking both temp sensors. Is this done by measuring resistance? If so, what should they read?
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post #7 of 7 (permalink) Old 04-02-2016, 10:22 PM Thread Starter
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Hi Guys.
I did go back in to check and adjust the timing. I set as you suggested MBgraham. It seems to have done the trick Before my plugs were very dry, sooty and black. I cleaned them, did the adjustment, then drove around for about 25 miles. Now they have a very nice sandy color. The car seems to run very smooth. I am checking gas mileage at the moment but so far it seems heaps better
Thanks everyone for the suggestions and help.
All the best John.

ps. I did the 1885 straight points replacement.
Thx
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