84 300TD driving me crazy - PeachParts Mercedes-Benz Forum

#1 10-27-2002, 10:16 PM

I just bought my first MB 300TD, 148kmi, after doing lots of investigating what type of diesel would run best on vegetable oil. Before converting, I want to get the thing running right and am now getting frustrated, I like the car a lot but wondering if I made a bad decision.

Starts good, and seems to run more smoothly when cold than warm. Once warm it runs rough (if it were a gas motor I would suspect a fouled plug). It has a lot of blow by and smoke in the valve cover (is this normal on this car???).....this scares me!!! so I checked compression, seems okay. The car lopes and vibrates a lot, at idle and even when I rev it to about 1500rpm. Also seems like it should have a bit more power, but I haven't driven many of these cars so not sure.
trying to solve the problem I have:
1. pulled injectors and had them tested, they tested okay
2. checked air cleaner (okay)
3. checked compression (hot) and every cylinder was over 300psi, ave. 315 and no more than 10psi dif. between them (it took about 8 seconds to get that high though)
4. adjusted valves
I plan to:
1. check timing chain stretch (just found out how to do that from this page)
2. give up, please help I am at wits end. From what I have read these are supposed to be great diesel motors, but right now I am wondering if I am in over my head......
thanks.
jb

Zoonhollis · #2 10-27-2002, 10:26 PM

Replace both fuel filters and check for gunk along the intake/ALDA system (banjo bolt, pre switchover, post switchover). If the car sat for a long period, it may have algae in the tank.

#3 10-27-2002, 10:30 PM

Algae in the tank?? yuck.
Fuel filters are new, is the internal filter part on the small clear inline filter supposed to look like it is about to sucked apart while the car is running? Can the ALDA really make this thing run so poorly?
thanks

Zoonhollis · #4 10-28-2002, 08:53 PM

On the contrary. The ALDA is designed to make your diesel run better. It functions as an altitude compensator and can be adjusted lean or rich, depending on present elevation. From what I've learned, the turbo wastegate setting and its concomitant ALDA setting are calibrated on the conservative side as your diesel benz leaves the plant in Stuttgart. The turbo delivers a modest 7-9 lbs of boost, and the IP sends an appropriate amount of fuel to be burned.

With some careful tinkering, the wastegate and ALDA can be adjusted to yield more horsepower in the 617 (and other?) engines. I've done this on my '84 300D, and the results were pleasing; I get quicker turbo spin-up and a bit more pep off the line...all without fuel efficiency suffering.

If you attempt something like this, mind two important caveats: monitor the amount of boost from your turbo by tee-ing a gauge into the line that goes to the switchover valve, and be very careful when adjusting fuel enrichment on the ALDA; they can break without warning. Remember to turn CCW for rich adjustments...in 1/8 to 1/4 increments.

If done correctly, you will be amazed at the increased performance.

Peyton300TD · #5 10-28-2002, 09:00 PM

before you change your filters, I would run BG 44K through the system. it is an additive that will clean everything out. it cannot be purchased many places but the dealer is sure to have it. it's amazing though, truly is. $20.

eric

diesel don · #6 10-28-2002, 09:59 PM

It sounds to me that you've done some good work here. I would simply encourage you to try a couple of the easier things first. Sometimes its the simple adjustments that make all the difference:

1. Rack Dampner Pin adjusted inward. This is a simple procedure done while the car is warm and corrects excessive shake at idle. My 84 was running well when cold and shook like crazy when warm. This helped significantly. A new rack pin was the solution.

2. The banjo bolt and ALDA adjustments that Matt [zoonholis] refers to turned my 85TD dog into a respectable performer. In addition to that he had me disconnect the EGR valve.

I have found that there are times when the issues cascade and cause discouragement. I have also found that there are long seasons of uninterrupted driving enjoyment without repair. During such, you are making back serious money and beating the system. Pretty cheap per mile costs.

Don

#7 10-28-2002, 10:11 PM

thanks for all the great advice. I plan to try what you call the "simple things" tommorow although being new to MB diesel makes most things not all that easy....Did check the timing chain, off
about 5-6 degrees, guess it can wait till spring for change. When I do change it is it necessary or advisable to also change the tensioner and I think it is referred to as rails? and how about that funky tool for re-linking the chain, do I need that, seems almost twice the price of the chain itself! I must admit this thing is really not bad to work on compared to almost every other car I have puttered with.
jb

Aaron · #8 10-29-2002, 09:33 AM

5-6 degrees of stretch?? Change the chain ASAP!! Change the chain, the curved guide rail and the tensioner. While you're working around the side of the engine, put a new thermostat bypass hose on there as well. That'll save you a lot of grief later on when it starts leaking.

#9 10-29-2002, 01:15 PM

is changing the chain something the home mechanic can do? looks a bit scary. Have the haynes paper repair manual, it lists the tool needed to crimp the chain on, what can I use for this? the mercedes tool I saw online was almost 200.00. Also how do I change the tensioner and the guide? can all this be done through with just the valve cover off?
thank you

william rogers · #10 10-29-2002, 02:59 PM

Algae can be a real hassle to get rid of the easy way to tell if you have it is that your small pre fuel filter will look very dark instead of white..........
William Rogers.............

#11 10-29-2002, 08:26 PM

Hey I've got that, algae, yeah that's me, the prefilter is dark. Wow, thanks that might be my problem. I did research on algae while doing my masters, but that was in lakes, what do you do with it in a fuel tank? and the timing chain, do I need to change this with 5-6 deg. flex? this job kinda intimidates me how much will it cost to have done?

gerald

#12 10-29-2002, 08:30 PM

Ugh this car has a lot more problems than I bargained for when I bought it. The body is straight, the underside is really clean, but all these little things......when will I get to actually drive it again????

#13 10-29-2002, 09:06 PM

The relatively low mileage of your car means that these regular maintenance issues are worth tackling. To rid your system of algae (formed because of water resting in the tank), clean the filter in the tank (check archives on this forum for procedures) and use the additive described above. Replace the timing chain and tensioner soon. 5 - 6 degrees of stretch could mean an impending chain break - bad news. The improved performance and peace of mind will make it worth while. Clean out the banjo bolt and attached tube, adjust ALDA and disconnect the EGR. The car you will be driving on the other side of these tasks will be a great thing to have. Best of luck and please let us know how it goes.

william rogers · #14 10-29-2002, 10:18 PM

even if you pay to have timing chain done the 300 TD in my opinion is one of the most sot after older model MB's that there is ,and especialy one with that low mileage. Not only are they classic looking enough for a movie star to show up at Pebble Beach in but will offer you years and years and years of driving in comfort and safety that is hard to match...........
William Rogers.......

#15 10-30-2002, 07:41 AM

You need to count your blessings. The compression in your engine is top rate. About anything else can be fixed relatively easily.

Best of luck,