'85 300TD No power- need help :-o - PeachParts Mercedes-Benz Forum

pinpoint · #1 06-27-2013, 01:42 PM

Greetings: My '85 300TD has reached the point where it may be unsafe for the highway due to lack of power. This is especially noticeable going up hills, where I actually lose speed even with the pedal pegged. I don't know exactly where to start on troubleshooting, so hoping I can get some input from the forum here.

Here are the symptoms:
very sluggish off the line
harsh and elongated shifts with the (new) a/c compressor running. Shifts smoother w/o air con on
difficult to maintain speed above 60 mph
will not downshift when flooring it from speeds over 40 mph

Here are some other facts that may/may not be related to the problem:
> new alternator
> new a/c compressor, dryer, expansion valve. The center vents do not blow after a/c job, but I cannot see anything disconnected in dash
> in-line fuel filter replaced last year
> spin-on fuel filter replaced 1 yr ago
> fuel usually purchased from same place for last 7 yrs
> not much smoke from exhaust
> I believe turbo has not worked in awhile. I hear no spooling whine, but impeller spins by hand and there is plenty of suction from front intake
> air filter replaced 3 months ago
> door lock has vacuum issue and that line has been disconnected + plugged for some time
> valves adjusted last year (by me). Might I need to re-do/check that again?
> banjo bolt is clean

So, maybe I should start with the turbo? Which lines to I test for vacuum? I am looking for like 10 lb of vac? Assume that I need to drive the car w/vac gauge connected to test this?

I am open to all other troubleshooting suggestions.

Thank you in advance for the help.

BenzDieselTuner · #2 06-27-2013, 01:47 PM

lack of fuel !!!!!!!

you have old fuel filters, and never mentioned cleaning the tank or screen, so heres what to do....

change the fuel filters, blow out all the fuel lines with compressed air and spray some spray down them too to clean them out nice, drain the tank out and remove and clean the tank screen.......put her all back together again, and prime all the air out, and i'm thinking you will be on the way, better than ever before.....

for immediate solution, replace the fuel filters, use 2 pre-filters, instead of one, catches more of the chunks you are surely full of......makes the spin-on filter last a bit longer until you get the tank done.....check the prefilters every day.....if theres gunk in them, especially the first one, dont be afraid to take it off, shake it out a few times with some fuel, and re-use it.....may have to do this daily, but at least you will be on the road !!

kerry · #3 06-27-2013, 02:21 PM

Replace fuel filters and check the turbo overboost protection line to make sure the alda is getting the boost signal.

pinpoint · #4 06-27-2013, 04:32 PM

Quote:

Originally Posted by BenzDieselTuner

lack of fuel !!!!!!!

you have old fuel filters, and never mentioned cleaning the tank or screen, so heres what to do....

change the fuel filters, blow out all the fuel lines with compressed air and spray some spray down them too to clean them out nice, drain the tank out and remove and clean the tank screen.......put her all back together again, and prime all the air out, and i'm thinking you will be on the way, better than ever before.....

for immediate solution, replace the fuel filters, use 2 pre-filters, instead of one, catches more of the chunks you are surely full of......makes the spin-on filter last a bit longer until you get the tank done.....check the prefilters every day.....if theres gunk in them, especially the first one, dont be afraid to take it off, shake it out a few times with some fuel, and re-use it.....may have to do this daily, but at least you will be on the road !!

Thanks Justin. Will give the filters a shot. I have seen some vids re: changing the tank screen. That appears to be a fairly difficult/messy job. I've never drained a tank before :-o

kerry · #5 06-27-2013, 04:42 PM

I wouldn't change the tank screen without determining whether or not it is plugged.

pinpoint · #6 06-27-2013, 04:50 PM

Quote:

Originally Posted by kerry

Replace fuel filters and check the turbo overboost protection line to make sure the alda is getting the boost signal.

Kerry- pardon my apparent ignorance :-o but is the overboost protection line #1 or #2 here? (see pic) and should I be measuring some vacuum there? Thanks.

kerry · #7 06-27-2013, 05:26 PM

That clear line leads back thru the overboost protection switch to the intake manifold. It carries pressure, not vacuum, to the ALDA telling it to give the engine more fuel. If it's not working, you have in affect a non-turbo engine. The hose can get plugged or break.

andrewjtx · #8 06-28-2013, 07:47 AM

That picture clearly shows you have some vacuum problems as well.

You main baby line from the pump to the brake booster is shot and you have at least the locks disconnected.

Once you get your fuel and ala lined cleared, get that vacuum system in order!

DrLou · #9 06-28-2013, 09:05 AM

pinpoint: I'm putting good money on Fuel Starvation as your root problem.

I've just worked through exactly the loss of power problem you describe, and solved it - with help from whunter and others here - with a complete clean-out of the fuel system. Replacing screen (I agree, was probably not necessary), all lines (had a lot of rust) and filters, de-greasing and flushing tank.

Salient Points:

Even though I (ultimately) discovered I had a badly gunked tank screen, the replacement of both fuel filters provided a nearly complete, if temporary, fix. I chalk this up to the engine getting adequate fuel via the roughly 50% of the tank screen not gunked up! Replace filters, see if your performance improvement isn't drastic.

Interestingly, as most of the tank screen's gunk was on the lower half of the screen 'column', this seems to explain why performance got so bad, so quickly, when I allowed the tank to nearly empty...

Similar to your case: I also need a valve adjustment. However, as the car always ran pretty well in all cases other than hill climbs, highway speeds - in short: fuel-stressing situations - I de-selected 'valve adjustment' as the fundamental problem.

In any case, after the cleanout, I did a few days of highway runs. Car accelerates smoothly up to 90-ish mph, climbs nicely, etc. Got a solid 25 mpg, too, even with my crappy, dying AC compressor.

vstech · #10 06-28-2013, 09:21 AM

first thing I'd do is LOOK at the primary filter. if you have a clear one, it's simple to see if gunk is clogging it up. if not, change it, and open it up with a hacksaw and look at the screen. if it's got lots of black fur (I've seen red fur and brown fur also) go to the store and get a large bottle of power service Diesel CLEAR it's in a white bottle with green letters. pull your primary and secondary filters, fill the secondary spin on filter with the diesel clear and put it in place, then put the rest of the bottle in the tank. drive happy.

vstech · #11 06-28-2013, 09:22 AM

if there is not fur or grit on the primary screen, you may indeed just have a plugged overboost line. it connects to the passenger's side of the intake manifold, and goes to a valve on the firewall, then to the alda you pictured. all three fittings can get clogged with gunk from the EGR system, so pull ALL THREE and clean them out.

pinpoint · #12 06-28-2013, 09:45 AM

Looks like I have my weekend work cut out :-o. My daughter (who drives the car most) will be thrilled if I can get this baby running right.

Will report back.

Thanks again all.

pinpoint · #13 06-28-2013, 09:53 AM

Quote:

Originally Posted by andrewjtx

That picture clearly shows you have some vacuum problems as well.

You main baby line from the pump to the brake booster is shot and you have at least the locks disconnected.

Once you get your fuel and ala lined cleared, get that vacuum system in order!

Andrew- I actually do have a brand new main vacuum booster line that I have not installed yet. I have a question on this part. The line has two fittings- one that comes off a check valve. That fitting appears to restrict the air flow, whereas the other does not (via my non-scientific blowing through the tube). This is an aftermarket part, but i am guessing that check valve is designed to do that?

Odd question, but perhaps you know. Thanks.

BenzDieselTuner · #14 06-28-2013, 10:07 AM

Quote:

Originally Posted by pinpoint

Thanks Justin. Will give the filters a shot. I have seen some vids re: changing the tank screen. That appears to be a fairly difficult/messy job. I've never drained a tank before :-o

actually, its not......but u will need the 1 and 13/16 inch socket to unscrew the tank screen from the tank.......drain it by disconnecting the fuel hose down there, simple as removing a hose clamp.......drain as much as comes out, the unscrew the fuel hose (has a fitting) from the tank screen, and then use the big socket to unscrew the screen from the tank....more fuel will come out then, but its nothing that u cant neatly catch in an oil drain pan, and isnt much at this point (unless it was really clogged, but you should have an idea of how much was in the tank and how much u have drained already).....clean it like new, u dont need a new one unless its damaged, wash some of the fuel (without any dirt that was in it) that came out down the tank to "rinse" any further debris a bit, and put it all back together......shouldnt take longer than an hour......u can get a replacement fuel hose with the fitting that screws onto the tank screen fairly cheaply here on pelican parts, or just cut the end off so its "new" and put it back on with its hose clamp......

edit: oh, and the rubber o-ring on the tank screen should usually be replaced, they are cheap, but if u dont have one around, IN PRACTICE (i didnt say it was right, so hold your horses) if the tank screen is being removed for the first time, you can put it back together again, as long as you didnt mess with the old o-ring, and it will not leak a drop......i havent had one leak yet, where i didnt have the o-ring but did the job anyways.....on 3 different cars so far....usually good to have it though, its cheap after all....

BenzDieselTuner · #15 06-28-2013, 10:12 AM

Quote:

Originally Posted by kerry

I wouldn't change the tank screen without determining whether or not it is plugged.

this is true.....if fuel flows easily and it runs nice after changing all the filters, and no or not much further dirt chunks come to the prefilter, u should be allright.....but if its pulling up dirt and clogging the prefilter every 50 miles, its time.......and even if it doesnt, if it has never been done, its an hour of "busy work" that cant hurt.....there will be some dirt and or sand in there, there always is...