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Old 09-27-2003, 09:50 PM
can-do can-do is offline
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Join Date: Jan 2001
Location: Tucson, Arizona
Posts: 758
Checked out spark plugs for fuel

Greetings Paul,

I got off work early today, before sunset anyway, and had a chance to run the Benz to the rough idle situation, or really a missing situation then shut it down. I pulled all the plugs and found nothing out of the ordinary. The first and last plugs were a tad more crystalized with a brown substance than the rest, but all plugs were dry and actually clean looking. I changed out plugs about 11,000 miles ago and after a putting them all to a wire brush they all looked new again. I don't think the problem is in the fuel system as far as a leaking down injector. Let me give you a run down on todays starting and running events on this car.

After sitting over night I started the car about 6 pm the following evening and starting was extremely difficult. I tried to start it using the gas pedal and it would bump off then die. I then tried to start it using no gas pedal and it idled rough for about 15 seconds or so and finally stayed running. I slowly idled it up past 1000 rpm until it stayed running without missing. During this time the antilock light stayed on the entire time and about a minute or so into idling the light went off and the idle went up to about 850 from around 650 and things started to smooth out. I decided to take it out for a drive to reach operating temps and the engine kind of missed as you mashed on the pedal for acceleration, seems like on one cylinder. I drove it out about five miles and returned home and left it in drive as I popped the hood and started checking spark plug wires pulling them one by one to feel the engine difference and all of them seemed to make a difference when disconnected except the number one cylinder than didn't make a huge difference but could feel the miss when it wasn't attached. Seemed like the sixth cylinder was pretty much the same way, so in between cylinders definitely seem to drop out if they aren't operating correctly. After cleaning all the plugs and reinstalling them the car seemed to run a tad bit better but still stumbles a little bit on hard acceleration, think it might be spark plug cables or ends? Only a few seemed weak when pulling them off as far as a spark to ground, the first one is one of them. I noticed the antilock light finally went off and the rpm raised and some of the idle problem subsided so I pulled the OVP after I got home and dismantled the case to find green corrosion on the inner terminals, so I cleaned it all off and painted the circuit board and will try it out in the morning to see if the cleaning made any affect of it's operation. All solder connections in the ovp seemed solid otherwise. I noticed when looking at the dist. cap the other week that there was a heavily carboned terminal and I cleaned it up as best as I could. I did order a new cap and have it in hand and will change it out sometime here shortly, as soon as I order the lower dist. cover as removing the cap basiscally destroyed the lower cover. Do you think this could be the problem as well as the cylinder one not being as hot as the rest? Have you seen the spark plug cables themselves break down in the past, or is just replacing the spark plug connector end going to do the trick? Any thoughts are much appreciated.


"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan
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