1987 300D question power - PeachParts Mercedes-Benz Forum

gsinger86 · #1 10-02-2010, 10:59 AM

I have noticed a marked reduction in power at highway speeds i.e. climbing hills and high speed cruising. The hills I used to climb easily at 95 mph now I can barely climb at 65-70 mph with the pedal floored. I have had the o-rings on the fuel injector pump, alternator, starter, V-belt, and fan clutch (I think) replaced over the 5 years I have owned it. I believe that the engine power weakness was initially related to the fuel pump o-rings failing. I may have damaged the engine by overheating it under heavy driving with fuel injector pump leaking. It got up to 120 C for a short while. Now, from a cold start, it runs rough for about a 30 sec. It starts fine from a warm start. Anyway, I miss the power and speed. What could cause this lack of power? The engine has about 150,000 miles on it.

Wodnek · #2 10-02-2010, 11:09 AM

Turbo, or alda issue. Either boost is not being built, or the fuel is not advancing.
This is about the only thing on a diesel that can bring sudden loss of power.

Wodnek · #3 10-02-2010, 11:11 AM

Open the hood, look at the driver side fender. There are a couple vacuum hoses that lead to the IP area. Make sure they are not off. One fell off on my wagon once, and made it a real dog.

sixto · #4 10-02-2010, 02:04 PM

If coolant temps get that high under load, maybe the oxidation catalyst is getting clogged.

Sixto
87 300D

gsinger86 · #5 10-02-2010, 05:40 PM

After I had the o-rings replaced, the temp stays below 110 under heavy loads. Where is the oxidation catalyst and how do I clean it? I have checked the vacuum lines and all appear to be connected. What is the best way to drain the coolant and put new in? The place that did the o-rings added some green coolant. Given the change in performance, is there any chance that the head gasket is blown? What about the timing chain should that be replaced before 200,000 miles?

Hit Man X · #6 10-02-2010, 06:02 PM

Quote:

Originally Posted by gsinger86

After I had the o-rings replaced, the temp stays below 110 under heavy loads. Where is the oxidation catalyst and how do I clean it? I have checked the vacuum lines and all appear to be connected. What is the best way to drain the coolant and put new in? The place that did the o-rings added some green coolant. Given the change in performance, is there any chance that the head gasket is blown? What about the timing chain should that be replaced before 200,000 miles?

Under the car and you cannot really clean it if the substrate has melted. I would just gut it and get on with life, I did on my SDL.

Do you have disappearing coolant? A pressurized upper radiator hose? White smoke from tailpipe?

Chain depends on stretch, do a search. I would do it if the car had a questionable life before you acquired.

Green coolant? I would flush and go with the MB stuff or Xerex G-05.

BrianCostello · #7 10-02-2010, 07:25 PM

when's the last time you changed your air filter?

oldiesel · #8 10-02-2010, 07:57 PM

Sounds like the first thing i would be looking at would be fuel filters.Simple inexpensive things first! Don

vstech · #9 10-02-2010, 10:40 PM

ditto, fuel filters are first thing I would check.
since you are making it to 65 on a steep hill, I doubt the cat is plugged, but it's possible.
air filter would cause black smoke, and could cause the cat to plug.

jonbobshinigin · #10 10-02-2010, 11:16 PM

As others have said, replace BOTH fuel filters. One is the small clear one which is the primary, the other is the Silver cylinder near the front of the engine on drivers side. Both are easy to replace. Once you replace them, it may take some cranking to get started again. Don't let this concern you but make sure you give your starter a break every 15 seconds of so.

The other thing which is very common is the Overboost protection valve. Although your description does not really indicate this is the problem, it is very common.

Timing chains do not need to be changed before 200k, checking for stretch would be wise at some point perhaps, but not unless you have an issue that points to it. At 150,000 miles, if you are not already on Sythetic oil, get on it!

Feel free to PM me and I can walk you through some basics for the car!

vstech · #11 10-02-2010, 11:46 PM

BEFORE you plan your oil change to synthetic, be sure you have a pair of 6mm orings, for the oil filter shaft. makes a huge difference in the oil pressure readouts, and can prevent dry start wear.

jonbobshinigin · #12 10-03-2010, 12:09 AM

Are said Orings different than the ones that normally come with a filter kit?

Hit Man X · #13 10-03-2010, 12:14 AM

My overboost valve was plugged on my SDL when I brought it home along with loose throttle linkage so the fuel rack barely opened.

I am not a super huge advocate of the syn oil, sure it is better, longer OCI, higher temp protections, etc, etc. But my motors are all running great on that $3/gallon Dino Delvac that was on sale last year.

I picked up nearly 80 gallons

Before that it was 8-10 gallons (I think that is how much it was) Delo that was left in the garage of one of my rentals by some tenants. I put sub 5,000 miles combined on the Diesel vehicles in six months so the syn is really of no use to me for the benefit versus cost.

For the $130 a timing chain costs, it is cheap insurance and brings the cam back in time. I have seen cars driven into the ground by 50,000 miles with maybe a few oil changes. Measure elongation and make your decisive course of action. I did a chain and tensioner on mine.

Hit Man X · #14 10-03-2010, 12:15 AM

Quote:

Originally Posted by jonbobshinigin

Are said Orings different than the ones that normally come with a filter kit?

Yup, look very close next time you do an oil service. At the very tip of the metal rod there are two... chances are yours are as brittle as can be.

Buy or fabricate a magnetic drain plug too, that pulls even more crap out of the crank case.

jonbobshinigin · #15 10-03-2010, 12:51 AM

My oil pressure is fine (usually above 2 even at idle). Interesting though...so there are two 6mm orings AND the two that come with a standard oil filter? Where can these be purchased, are they special?