Power loss at speed 1983 300SD - PeachParts Mercedes-Benz Forum

DrLou · #1 06-03-2013, 02:21 PM

whunter, others(?),

Update: a bit of a 'report' from this weekend...

First: Car generally runs great; I'd even call the pickup great for a 30+ yr-old diesel, which needs a valve adjustment...(!)

However, I occasionally get a nearly complete loss of power - I mean a really crippling, slogging-along-at-20mph kind of power loss.

Had to do some highway driving this weekend, so tested things. Problem only really appears at speed, and especially under load - as in climbing a hill. Issue seems to appear more often after car has been running for a while already.

Also, pulled off the gas cap during all this - no change in behavior - does this remove the fuel return system from the diagnostic mix?

As much as I am planning to do the nozzles and lift pump anyway, I'd still like to get to the bottom of this specific symptom - what could be causing?

whunter · #2 06-03-2013, 03:01 PM

From your description.

My first guess would be a plugged tank strainer, or fuel filters.

.

cirrusman · #3 06-03-2013, 03:49 PM

^ X2. I had the same problem a while ago, and it went away once I replaced both fuel filters.

pgringo · #4 06-03-2013, 04:33 PM

X3

psaboic · #5 06-04-2013, 12:04 AM

Definitely.....replace both fuel filters. I'll be surprised if the issues does not go away after that.

DrLou · #6 06-04-2013, 09:04 AM

whunter - et al, BINGO!

Replacing both fuel filters has made a profound difference. Don't want you to think I don't do my maintenance on this car; I do! Fuel filters are about a year old. But I think - based on the black, cloudy look of the fuel in the old filters - my rubber lines are due for replacement*.

OK, am buying the threaded outflow and return lines to the tank today... How much length of rubber fuel line would I need in total (it's 7.5 mm, I understand?)

Next will be nozzles - I'm thinking the Monarks. Is the Lift Pump rebuild likely to be in order at this point? IE, once the IP is filled adequately, the LP has done its job, no?

And (I'll re-search this forum, but) would someone point me to a posting on the wrench size and other details for emptying/cleaning/dropping(?) the tank?

Many Thanks, All. You guys make this the go-to site.

Lou

*(Have already done hard and soft brake lines to the rear. Slowly working my way around the car!)

Diesel911 · #7 06-04-2013, 02:39 PM

5/16" ID Regular Fuel Hose from the Autoparts Store works fine as it is rated for Diesel Fuel as well as Gasoline.

If you grind or File of the Collar that is one one end of the Fuel Hose under the Fuel Tank you will espose a normal Brass Barb and after that you can use the Autoparts Hose and a Clamp on it.

The Tank Screen takes a 46mm Socket; or a 1-13/16" Socket.
In the pic of the Socket this is one I bought at a cheapie Tool Place. When it comes time to use it on the Fuel Tank I need to grind off most of the tapered part becasue the fuel Tank Screen Nut is kind of thin and due to the taper the way the Socket is it would not grip much of the Nut.
Or when you buy a Socket make sure you get one without very much taper on it.
Another small issue is that these Sockets are more easy to fing in 3/4" drive at a decent price but that means you also need to buy an Adaper for 1/2" drive.

eatont9999 · #8 06-04-2013, 09:44 PM

Get your basics done first and if you find out that you need injector work done, PM me. I pop test injectors for free if you cover the shipping.

Also, make sure your transmission is shifting according to spec. A trans that does not shift at the proper timing, etc can have the same effect as a severely low powered engine.

whunter · #9 06-05-2013, 01:06 AM

Quote:

Originally Posted by DrLou

whunter - et al, BINGO!

Replacing both fuel filters has made a profound difference. Don't want you to think I don't do my maintenance on this car; I do! Fuel filters are about a year old. But I think - based on the black, cloudy look of the fuel in the old filters - my rubber lines are due for replacement*.

OK, am buying the threaded outflow and return lines to the tank today... How much length of rubber fuel line would I need in total (it's 7.5 mm, I understand?)

Next will be nozzles - I'm thinking the Monarks. Is the Lift Pump rebuild likely to be in order at this point? IE, once the IP is filled adequately, the LP has done its job, no?

And (I'll re-search this forum, but) would someone point me to a posting on the wrench size and other details for emptying/cleaning/dropping(?) the tank?

Many Thanks, All. You guys make this the go-to site.

Lou

*(Have already done hard and soft brake lines to the rear. Slowly working my way around the car!)

DrLou · #10 06-05-2013, 12:40 PM

Gents - Many thanks for your feedback here...

OK, based on whunter's admonitions, I'm changing the Project Plan a little bit. Though my injectors are ancient, the car is now running really well with just replacement of both fuel filters... (I've had the injectors apart several times over 20 years, lots of cleaning, etc.)

So, before replacing nozzles, I'm going to start with dropping/cleaning the tank, and replacing all fuel hard lines and hoses. Hopefully this weekend?(!)

Questions (before climbing under there this weekend):
1) what is the approx total length of hard line/rubber fuel line stock in this car? Can someone give me precise stock material dimensions? (Tks, Diesel911, for the 5/16" - I may be able to find metric for all this)
2) Engine Manual indicates that the hard lines have formed fittings on the ends. Is this accurate? Or can I simply cut generally-available steel line to fabricate these?
3) Without using special offset wrench, can the strainer be removed with the tank out?
4) Gonna use a wide adjustable wrench to remove fuel sending unit...
5) Any other special tools/gotchas I'm missing?

Expecting delivery today on the fitted tank outflow and vent lines.

Many thanks again for all the inputs.

eatont999: Transmission is shifting pretty well, though I'm sure I could tweak this a bit. No, this power problem was really profound - power was dropping to near zero, and the trans was downshifting, trying to compensate.

Diesel911 · #11 06-07-2013, 12:29 AM

Quote:

Originally Posted by DrLou

Gents - Many thanks for your feedback here...

OK, based on whunter's admonitions, I'm changing the Project Plan a little bit. Though my injectors are ancient, the car is now running really well with just replacement of both fuel filters... (I've had the injectors apart several times over 20 years, lots of cleaning, etc.)

So, before replacing nozzles, I'm going to start with dropping/cleaning the tank, and replacing all fuel hard lines and hoses. Hopefully this weekend?(!)

Questions (before climbing under there this weekend):
1) what is the approx total length of hard line/rubber fuel line stock in this car? Can someone give me precise stock material dimensions? (Tks, Diesel911, for the 5/16" - I may be able to find metric for all this)
2) Engine Manual indicates that the hard lines have formed fittings on the ends. Is this accurate? Or can I simply cut generally-available steel line to fabricate these?
3) Without using special offset wrench, can the strainer be removed with the tank out?
4) Gonna use a wide adjustable wrench to remove fuel sending unit...
5) Any other special tools/gotchas I'm missing?

Expecting delivery today on the fitted tank outflow and vent lines.

Many thanks again for all the inputs.

eatont999: Transmission is shifting pretty well, though I'm sure I could tweak this a bit. No, this power problem was really profound - power was dropping to near zero, and the trans was downshifting, trying to compensate.

What I call Fuel Injection Lines People on the Various Mercedes Forums call the Fuel Injection Lines "Hard Lines". That means I am not sure which lines you are speaking of?
I don't think you plan to cut the Fuel Injection Hard Lines.

cho · #12 06-07-2013, 06:07 AM

Quote:

Originally Posted by Diesel911

What I call Fuel Injection Lines People on the Various Mercedes Forums call the Fuel Injection Lines "Hard Lines". That means I am not sure which lines you are speaking of?
I don't think you plan to cut the Fuel Injection Hard Lines.

.

I think he refers to hard (supply) lines beneath the car....

edit: if yes,...just blow them with comp.air

.

DrLou · #13 06-07-2013, 03:03 PM

diesel911, cho, Tks for responses...

No, I wasn't referring to the Injector Hard Lines here. Those are surely easy enough to clean - I've done it often. Besides, they're post-filtration...

Rather, I am replacing the long (3+ meters?), under-car fuel and return hard lines. These have clear evidence of rust at various points, most notably under and near their rubber mount grommets. Changing out the threaded in-tank outflow and return lines while at it.

Have settled on 5/16" Aluminum line for this, from Aircraft Spruce, based on inputs from other threads.

My original question was about defining the flare? or shaped fitting? on the end of these long hard lines. The 617 Engine Manual shows some sort of nipple end on these lines... (No, I haven't yet pulled these lines to inspect - thought one of you might have been able to elucidate).

Anyway, update: Seems guys have clamped 5/16 fuel hose onto these lines, unflared, with no leaks. So the original question seems less important.

Open to any corrections, of course!