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Old 04-01-2022, 11:45 AM
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Join Date: Apr 2022
Location: Soddy Daisy, TN
Posts: 2
1992 300D OM602 feels like it is running rich

I have a 1992 300D that sat untouched in a garage for 10 years. 5 months ago I bought a new battery and it started after a few cranking cycles, but was running rough, as expected. It has 170,000 miles on it and the motor was rebuilt at 125,000 miles. It was my daily driver until I parked it in the garage.

In the past 3 months I have done the following:

New fuel, new fuel filters, Liqui Moly diesel purge, oil & filter change, new Tygon fuel return lines, new Bosch fuel injectors x5, new glow plugs x5.

All of this has resulted in a dramatic improvement in performance overall, but after warming up and coming to an idle @ 750 RPM for about a minute, the smooth idle begins to deteriorate to a shudder and occasional miss, some smoking, and a lot of diesel vapors. I can drive it down the road again with no problems, then stop and idle, and the pattern repeats itself.

To me it seems that it may be running too rich. My question is whether or not I can adjust anything to make it a little leaner, and how I would go about doing that.

Any suggestions or comments would be appreciated.

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Old 04-01-2022, 01:07 PM
engatwork's Avatar
Join Date: May 2000
Location: Soperton, Ga. USA
Posts: 13,376
If it were mine I'd pull the injection pump and get it to an authorized Bosch shop for them to check out.
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Old 04-01-2022, 02:27 PM
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Join Date: Apr 2022
Location: Soddy Daisy, TN
Posts: 2
Thanks Jim.

I will start looking for a shop near me.
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Old 01-12-2023, 10:18 PM
JHZR2's Avatar
Registered User
Join Date: Jan 2002
Location: New Jersey
Posts: 4,964
How long before this starts happening? Does it happen long after the time for afterglow?
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)
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Old 02-08-2023, 11:31 AM
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Join Date: Dec 2021
Posts: 108
It could be air getting into the fuel line somewhere. Does it smooth out after you have driven for a while?
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Old 02-08-2023, 11:52 AM
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Join Date: Mar 2009
Location: San Diego
Posts: 3,456
I would try the simple thing first.

1) change ovp relay. Faulty ovp can cause erratic idle.

2) do a compression test. Could be stuck rings if it drives well at freeway speed.

3) ip, very unlikely.

Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details.

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.
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