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Old 08-20-2003, 09:08 PM
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Join Date: Jun 2002
Location: Monrovia, CA
Posts: 496
Engine Pinging on Moderate Acceleration

I'm posting this again because I only got one response and it didn't really apply to my problem, so here goes...

My '86 300E with 120k miles pings noticeably on moderate to hard acceleration. Sounds like somebody's under the hood shaking a coffee can full of rocks! I've never put anything other than premium fuel in it (91 octane So. Cal. gas). I replaced the plugs, rotor, cap and complete ignition wire set recently, and when the plugs were out, they all had a nice medium tan color. None of them appeared to have any significant carbon buildup on them. I looked into a couple of the plug holes with a small penlight and there was just a normal light buildup of carbon on the piston crowns, so I'm at a loss. I do know that the valve guide seals were replaced about 30k mi. ago and currently oil consumption in very low, about 1/2 qt in 3k mi.

Is there any kind of knock sensor in this system that should adjust the timing when it pings?

Is there any manual timing adjustment that needs to be done?

As the cam chain wears, does the distributor timing advance or retard? As far as I know, the cam chain has never been replaced.

Can a worn out O2 sensor cause this? (btw, what triggers the o2 sensor light on the dash? Mine hasn't come on yet, but I'm just curious)

An old trick we used to use to remove carbon deposits involved introducing a fine mist of water into the intake tract. The sudden heating and expansion of the water into steam in the combustion chamber would blow off any excess carbon buildup. Could these carbon particle cause any problem with the catalytic converter?

Thanks for any help


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Old 08-21-2003, 12:11 AM
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Join Date: Mar 2003
Location: Southern California
Posts: 2,148
No knock sensor on your engine. Check the timing and verify that it is equal to what's on the emission label (probably 9 degrees).

The timing cannot be changed by mechanical means. If you search on engine timing and emissions you should find threads that discuss changing the timing by changing a resistor. This resistor changes the rate at which spark advance is added with RPM, but my understanding is that it does not change initial timing.

On my '88 2.6 there is a vacuum line that routes to the EZL module, which alters timing based on engine vacuum. Try disconnecting and plugging this vacuum line and see if it makes any difference. Just a WAG, but the vacuum function in the EZL module may be misbehaving and adding too much timing.

How long has the detonation been an issue and what if any service, maintenance was performed prior to it becomming a problem?

Not sure what triggers your O2 sensor light. On my '88 it's internal diagnostics. On my '84 2.3 it just lite up at 30K miles - no diagnostics. Check to see what your owner's manual says about the O2 sensor. Checking it's function has also been extensively discussed, and a search should get you the test procedure.

Spark timing is triggered off a crank sensor, so timing chaing wear should have no effect.

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Old 08-21-2003, 03:28 AM
Registered User
Join Date: Jun 2002
Location: Monrovia, CA
Posts: 496

Thanks for the info.

I'm not sure when it started getting worse. I usually have the radio and A/C on and the windows closed, so I wouldn't often hear it. My A/C died about a week ago and now I've usually got the windows down. But the other day when I was accelerating on an uphill freeway onramp with a soundwall, the rattling bounced off the wall into my window and really caught my attention.

The EZL module; is that the ignition control unit mounted on the driver's side inside fender well? If so, I did have to have it replaced about a month ago. The original one just up and died with no warning at all. I took the car to a local reputable independent Mercedes shop and they replaced it with one from a salvage yard. The number on the original unit is 004 545 44 32 and on the replacement part it's 006 545 76 32. I was told that they were interchangeable. Can anyone confirm this?


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