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Old 04-17-2000, 10:02 AM
matthew merrill
Posts: n/a
I have been experiencing what I describe as a pre ignition ping in a gas engine in my 78 300d.
This ping noise happens at all different speeds. I am thinking it may be caused by a injector that is dirty and dripping fuel. Does this sound correct? Would a good fuel conditioner / injector cleaner eliminate the problem? Thanks, Matthew Merrill

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Old 04-17-2000, 10:54 AM
Registered User
Join Date: Mar 2000
Location: Southampton, NJ
Posts: 126
I always thought that the "D" in 300D meant that the engine was a diesel and, yeah, you may have a "ping" if you put gas in there. Correct me if I am wrong.
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Old 04-17-2000, 11:32 AM
matthew merrill
Posts: n/a
OK, Zachv,
Yeah D stands for Diesel, and not Dimwit.
I was using the analogy to describe the noise.
I have not put anything but diesel in the car. Any ideas why it would make this noise.

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Old 04-17-2000, 04:17 PM
Registered User
Join Date: Jan 2000
Location: New Bedford, MA USA
Posts: 1,583
You may be hearing a bad injector or fuel distributor noise. with the engine running, see if you can hear the noise, put a fingertip on each injector and see if you can feel any mechanical vibration.

Jeff L
1987 300e
1989 300e
1987 BMW 325
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Old 04-17-2000, 04:46 PM
Registered User
Join Date: Feb 2000
Location: Santa Clarita, CA, USA
Posts: 133
I experienced the same thing in my 84 300SD about a year ago. It definitely sounded like a ping or nailing even over the usual "clack-clack" of the engine. I suspected a dirty injector and put in Red Line Diesel Catalyst. It's a synthetic oil and injector cleaner. After 5 min running with Redline in the tank, the nailing went away. It was probably due to the lubricating properties of the syn. oil. The problem came back on the next tank of fresh diesel. I figured the injector(s) must be really dirty or worn. I pulled the injectors out and tore them down. 4 of the 5 looked clean as a whistle and the pintle (or needle) inside the injector moved freely. 1 though was siezing up and when I managed to pull the pintle out, it was blue. I suspect water in the fuel combined with low sulpher diesel caused the injector to overheat from lack of lubrication. I ended up just buying a set of rebuilt bosch injectors for $45 each. I thought it wasn't that much considering I put on 260,000 miles on the 1st set of injectors.

In you case, I'd try Redline to try to clean/lubricate the injectors. I use Redline on a regular basis for the lubricating properties. One bottle is good for 100 gallons. Hope this helps...

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Old 04-17-2000, 06:51 PM
Posts: n/a
When youtry to locate the exact source of the noise, try using a long socket extension or long screw driver like a stethwscope. Sound travels better and faster through dense objects. Since steel is much denser that air, when one end of the extension is held against the injector and the other end against your ear, youcan zero in on the cylinder. This is also effective for identifyiong the source of bearing whine in the belt driven component train.

87 300TDT
150,000 miles

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Old 04-18-2000, 09:25 AM
matthew merrill
Posts: n/a
Well, I put a can of Red Line conditioner
in the tank yesterday. The "ping" has
decreased significantly. I have another
bottle for the next tank. Maybe this will
solve the problem.

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Old 04-18-2000, 12:41 PM
Posts: n/a

Noone has mentioned anything about timing. I have a similar problem with a 240D engine I'm running temporarily. I plan on checking the timing this weekend. I'll let you know the outcome.

Say hello to my son if you see him around Austin, he's a Junior at UT.

Good luck,

Larry Bible
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

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