'73 280SE 4.5 Intermittently running rich - Page 2 - Mercedes-Benz Forum

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post #11 of 35 (permalink) Old 10-17-2008, 10:51 AM
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Thermo-time switch malfunctioning and occasionally firing the CSV? You could test this buy disconnecting the CSV after the engine starts.

Chuck Taylor
Falls Church VA
1998 SL500
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1970 280SL
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post #12 of 35 (permalink) Old 10-18-2008, 03:36 PM Thread Starter
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Thought that too. The cold start valve was disconnected and the car still had the intermittent flooding...

Good thought though.
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post #13 of 35 (permalink) Old 10-26-2008, 01:39 PM Thread Starter
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So, an update. I picked up the car yesterday, and it ran relatively well. It was driven about a mile or so, and promptly started to run like crap. The mechanics stated they found two bad injectors (I had replaced all eight, and two of the new ones were bad), and replaced them both. They further stated another injector went bad.

I'm really frustrated by all this - what on earth would cause all this hate and discontent? I've got until Tuesday to sort everything out before I attempt to drive the car to Colorado for storage (in preps for a duty station transfer), and I need to be able to drive a reliable car ...
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post #14 of 35 (permalink) Old 10-26-2008, 05:06 PM
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I think you need to narrow the possibilities.

Hook a pressure gauge into the rail at the CSV and see if the fuel pressure goes up when this happens.

When it runs rough, let it run for a moment, and pull the plugs to determine if it's happening on all cylinders or one or two or four.

If it's on one, it's probably an injector. Multiples of two, trigger points.

If all cylinders, then something is telling the brain to really increase the pulse width of the injectors. This could be the input from the temp sensors, the throttle switch, the MAP sensor, or the wiring, or the brain itself.

I'm no expert, but I would bet on a fuel pressure spike.

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Falls Church VA
1998 SL500
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1970 280SL
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post #15 of 35 (permalink) Old 10-26-2008, 09:26 PM
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At the rate injectors are going bad (are they?) maybe you are sucking junk from fuel tank. Fuel filter is only as good as its micron rating. Anything smaller will pass through. If it's rust it will damage injector through abrasion. But that takes some time and miles.

I strongly agree with previous poster about monitoring fuel pressure and looking at all plugs after rich running event. Need to catch it in the act. And thank Bosch for ME engine management on newer cars.

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post #16 of 35 (permalink) Old 10-27-2008, 10:53 AM Thread Starter
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Fuel pressure was monitored, but nothing showed up. ALL injectors are new, like literally. Prior to taking it to the mechanic, there was no problem like this. The "Mercedes Brain" guru spent a number of hours on this, and stated all electrial signals into the brain were good. He also stated the brain was good, but I'm having the sucker replaced anyway.

This morning, the temp was a little over 60, and the car wouldn't start. With a little gas added to the intake, it kick right up, leading me to think the cold start circuit doesn't work. Given that it was replaced, as well as the wiring to it, leads me to look at a bad brain again...

I'm headed somewhere hot and sandy soon, and I've got to have this thing fixed for a drive to Colorado. VERY frustrating...
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post #17 of 35 (permalink) Old 10-27-2008, 11:53 AM
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So you are saying that they actually saw normal fuel pressure when the engine was running rich? Or did they just check it with the pump running?

And what's the read on the plugs?

And I assume that the guru tested the resistance in the primary and secondary windings of the MAP sensor?

Chuck Taylor
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post #18 of 35 (permalink) Old 10-27-2008, 02:36 PM Thread Starter
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Fuel pressure was tested, as well as flow rate - all good. The dampeners are about 400 miles and 6 months old. Prior to my taking it to the mechanic, it didn't do this, so I'm ruling out the fuel pressure or spikes in pressure...

The MAP sensor is also new - got that from GermanStar just recently. Hi Ron! Has the new brain been ordered yet??

By plugs, do you mean spark plugs?
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post #19 of 35 (permalink) Old 10-27-2008, 07:10 PM
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Ha! Your guy priced it but did not order. He does seem to be struggling with this a bit...

"If spending money you don't have is the height of stupidity, borrowing money to give it away is the height of insanity." -- anon
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post #20 of 35 (permalink) Old 10-27-2008, 07:55 PM
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Yes. Spark plugs. Ideally, the car would run well for a while, and then start crapping out, and you would shut it off and pull the plugs. If they are all black, then it's a system problem. If it's one or two, it's isolated to individual cylinder(s).

I still have to ask. Normally pressure and flow are checked with just the pump running. Was the test done when the crapping out was happening?

Chuck Taylor
Falls Church VA
1998 SL500
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