Hi. I've been doing a lot of thread searching around my hot rough idle problem. I don't think I have any air leaks in the lines running in/out of pre-filter (though I intend to eliminate this possibility), and I have a new rack damper that was installed last year when I had my valves adjusted. I'm going to fiddle with the rack damper bolt, but I also wanted to check this spring folks have talked about stretching that is inside of the thing described as a "fuel pressure relief valve." I have an 82 300d.

First question:

Where do I locate this valve? On the injection pump? Next to the spin on filter? Could anybody provide a picture of where I find this?

Second question(s):

I am going to fiddle with my rack damper bolt after I inspect this spring. My idle, measured with a strobe tach at the fan at about 710rpm, so I think I'm within range, unless this is a bad way to measure rpm (my gauge is useless at anything below 1000).
1. If I have a rough idle when hot - should I try turing the rack damper IN or OUT?
2. How many turns are in this thing? Do I try just small, quarter turns at a time, or multiple turns at once if I want to notice any difference?
3. Would I notice any potential change in idle immediately (assuming I was turning while engine was hot and roughly idling?

As always, thanks for wisdom!

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Andrew
Montclair, NJ
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1982 300D Turbo
120k
Petrol Blue Green

The pressure control valve is ahead of the idle set screw on the side of the IP facing the cylinder head. The valve is part of a banjo bolt that holds the fitting for the plastic return line to the big fuel filter.

The rack damper was updated. The updated damper is gold color vs the original silver. You should notice idle get smoother up to a point. Then all you're doing by turning the damper further is limiting full throttle travel. You should notice an improvement with a quarter or half turn if there's an improvement to be had. Back it a full turn to see if idle gets worse for a sense of how to set it.

Sixto
83 300SD can be yours
98 E320s sedan and wagon

I recall reading that 1985 300D engines have the gold rack damper bolt. I moved the one from my failed 1985 engine to the earlier replacement engine, but didn't notice a difference in idle at any adjustment. Took another one off a junkyard 1985 for my 1984 and same "no help" result. Thus, try it but don't expect a miracle.

A good diagnostic would be to measure pressure at the IP inlet. I recall some have drilled & tapped a hole in the banjo fitting to install a tube to a pressure gage. Should be >10 psig to not starve the IP. I think the regulator is a simple spring-loaded relief valve which vents excess fluid into the tank return tubing. In engineering world, such is termed "back-pressure regulator".

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

thanks gents. I see it there.

I've seen cases where people have broken off chunks of the IP housing while trying to fiddle with idle bolt for example. Any precautions I should take when removing this banjo bolt/valve? Just a shot of PB in advance? Do NOT want to inflict any foolish damage to the IP.

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Andrew
Montclair, NJ
--------------
1982 300D Turbo
120k
Petrol Blue Green

The brass(?) banjo bolt shouldn't be on very tight so don't put it back on too tight. If the plastic line is original, it might be brittle. It doesn't have to move much to replace the crush washers but go easy on it or have a replacement ready. Someone on the forum makes stiffer replacement springs available once in a while. Something to consider. There's a smaller washer between valve halves. Have a replacement ready if you plan to take apart the valve. Later valves like on 60x engines (I don't know the actual cutoff) don't come apart.

Sixto
83 300SD can be yours
98 E320s sedan and wagon

ah, thanks. does anyone know the part # for the hard plastic line in case I break it? Would i need just a length of line, or would I need a special part with the banjo fittings integrated?

is it this?

http://www.pelicanparts.com/cgi-bin/ksearch/pel_search_2016.cgi?SUPERCAT_FLAG=Y&make=MBZ&please_wait=N&forumid=&threadid=&command=DWsearch&description=6150705632&I1.x=11&I1.y=8

35 buck for just a piece of plastic tubing? I'm assuming that part is not including any banjo or other "hardware"

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Andrew
Montclair, NJ
--------------
1982 300D Turbo
120k
Petrol Blue Green

I replaced my plastic lines with good quality fuel line and hose clamps. No issues.

Even the later 617s had the new style non-rebuildable ones - mine was that way. It is a '85 Cali version.

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Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

When you adjust the rack dampner bolt look up one of the threads on that. I will give a brief description.

Back the rack dampner bolt out 3 or so turns. Set your idle speed with the normal idle screw somewhere within the range that is on the emission sitcker. I believe on mine 850 rpms is the highest.

Then slowly screw in the rack dampner bolt. The idea is to remove the shaking without effectiong the idle speed. Then turn the lock nut to tighten down the rack dampner bolt.

I believe the rack damper bolt was designed to deal with some excess shaking when the engine was within specs in other areas. If adjusting the rack damper bolt does has little or no effect on the shaking you need to look elsewhere for the problem.

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84 300D, 82 Volvo 244Gl Diesel

That's helpful info. How do you all measure the Rpms when you are making these adjustments? Not with your tach right? My tach is spotty, but gene working it doesn't register anything unless I have my foot slightly on the throttle or I'm rolling

Interesting observation on this rough hot idle subject. I had my car all warmed up and idling when I jacked up the front a bit to do an oil change and replace oil pan. The engine was doing it's normal rough hot idle, but when I raised the front up, to just about where the front wheels lifted, the engine shake nearly stopped altogether.

Do this observation link to any more specific culprit?

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Andrew
Montclair, NJ
--------------
1982 300D Turbo
120k
Petrol Blue Green

What were you lifting to get the car off the ground? It may have just been that the weight shifted on the engine mounts and the shake *SEEMED* to go away.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Can you repeat this at will?

Sixto
98 E320s sedan and wagon